mafic replenishment of multiple felsic reservoirs at … · mafic replenishment of multiple felsic...
TRANSCRIPT
Mafic replenishment of multiple felsic reservoirs at the Mono domes and Mono
Lake islands, California
Brandon A. Bray
Department of Earth and Planetary Sciences
McGill University
Montréal, QC, Canada
March 2014
A thesis submitted to McGill University in partial fulfillment of the requirements of the
degree of Master of Science
© Brandon A. Bray 2014
ii
Abstract
The Long Valley Volcanic Field is best known for the paroxysmal 0.76 Ma
Bishop Tuff caldera-forming eruption. Postcaldera volcanic activity initially was focused
within the caldera complex and along its western and southern margins. Starting at ~60
ka, however, intracaldera volcanism ceased and the focus of activity shifted to the north
into the Mono Basin. Frequent eruptions over the past 60,000 years have emplaced the
Mono domes and the Mono Lake lavas. The Mono Lake lavas, as well as enclaves
present in several of the Mono domes, comprise the only material of intermediate
composition (andesite, dacite) erupted in the Mono Basin. Recent unrest in Long Valley,
combined with the youth of the Mono Basin lavas, underlines the importance of better
understanding the petrogenetic processes involved in generating these lavas. To aid in
accomplishing this goal, we have undertaken a study of Mono Basin volcanism
encompassing whole-rock major and trace element, Sr, Nd, Pb, and O isotopic, and
electron microprobe glass, plagioclase, and amphibole analyses. Variations in major and
trace elements suggest that fractional crystallization of feldspar (Sr, K2O), apatite (P2O5),
titanomagnetite (V), zircon (Zr), and a LREE-bearing phase (La, Ce) has influenced the
evolution of the Mono Basin lavas. Field observations, petrography, and chemistry
together demonstrate that injection of more mafic magma is a universal process
throughout the Mono Basin. Mafic enclaves of the Mono domes are stretched and
rounded, with chilled margins between enclave and host rhyolite. Thin sections cut along
the enclave-host border show millimeter-scale inclusions of rhyolite in the enclaves and
vice versa. Paoha Island dacite has glass with 67-72 wt.% SiO2 and contains microscopic
clots of more mafic glasses, with SiO2 contents as low as 64 wt.%. Isotopically, recently
iii
erupted regional basalts (e.g., Black Point) and the Mono dome enclaves represent the
least radiogenic material in the Long Valley Volcanic Field, with 87
Sr/86
Sri <0.7056 and
143Nd/
144Nd >0.5126. The silicic Mono Lake lavas and Mono dome rhyolites display
increasingly crustal signatures, with 87
Sr/86
Sri >0.7058 and 143
Nd/144
Nd <0.5127,
comparable to the Bishop Tuff. Oxygen and Pb isotopes throughout the sample suite also
have crustal signatures, with 206
Pb/204
Pb >19 and δ18
O >+6.5‰. The Mono Lake lavas
generally are both younger and less evolved than the Mono domes, with lower
143Nd/
144Nd, higher
206Pb/
204Pb, and enrichment in trace elements
including Ba and Sr.
This implies that the Mono domes and the Mono Lake lavas are derived from different
batches of magma, if not from separate magma chambers. The lack of any systematic
relationship between the degree of chemical evolution and the age of a lava implies that
several magma batches have been involved in the development of the Mono domes.
Pronounced differences in trace element composition (Nb, Y) and isotopic values
between the Negit Island and Paoha Island lavas indicate that they, too, are produced by
the evolution of at least two different batches of intermediate-composition magma.
Continued unrest in the south moat of Long Valley caldera hints at the potential for future
volcanic activity there. Given the recent history of volcanism north of the caldera and the
clear evidence presented here for continued mafic recharge beneath the Mono Basin,
Mono Lake and the Mono domes are likely candidates for future eruptions.
iv
Résumé
Le champ volcanique de Long Valley est surtout connu pour l’éruption
paroxysmale du Bishop Tuff, qui a excavé la caldeira il y a 0.76 Ma. L’activité
postcaldeira fut concentrée initialement au sein du complexe de la caldeira et le long de
ses frontières occidentales et méridionales. À partir de 60 ka, cependant, le volcanisme
intracaldeira a cessé et le centre de l’activité s’est dirigé vers le nord, dans le bassin de
Mono. Au cours des 60 000 années suivantes, les éruptions fréquentes ont produit les
dômes de Mono et les laves du lac Mono. Les laves du lac Mono et les enclaves qui sont
présentes dans plusieurs des dômes de Mono constituent le seul matériau de composition
intermédiaire (andésitique, dacitique) qui a été éclaté dans le bassin de Mono. L’activité
récente à Long Valley, combinée avec la jeunesse des laves du bassin de Mono, met
l’accent sur l’importance de mieux comprendre les processus pétrogénétiques qui ont
mené à la génération de ces roches. Afin d’atteindre cet objectif, nous avons entrepris une
étude du volcanisme du bassin de Mono qui inclut des analyses des éléments majeurs et
traces dans les roches, des analyses isotopiques de Sr, Nd, Pb, et O, et des analyses par
microsonde électronique de verres volcaniques, de plagioclases et d’amphiboles. Les
variations en éléments majeurs et traces suggèrent que la cristallisation fractionnée de
feldspaths (Sr, K2O), d’apatites (P2O5), de titanomagnétites (V), de zircons (Zr), et d’une
phase qui affecte les éléments de terres rares légères (La, Ce) a influencé l’évolution des
laves du bassin de Mono. Les observations de terrain, la pétrographie, et la chimie
démontrent ainsi que l’injection de magma mafique est un processus important dans tout
le bassin de Mono. Les enclaves mafiques des dômes de Mono sont de formes étirées et
arrondies, avec des marges figées entre les enclaves et la rhyolite hôte. Les lames minces
v
de roches qui proviennent du long de la marge entre les enclaves et la rhyolite révèlent
des inclusions de rhyolite de taille de l’ordre de quelques millimétres, et vice versa. La
dacite de l’île de Paoha contient du verre ayant une composition en silice de 67-72% par
masse. Elle contient aussi des gouttes microscopiques de verre plus mafique, avec un
contenu en SiO2 aussi bas que 64 pourcent poids. Les basaltes régionaux récentes (e.g., le
Point Noir) et les enclaves des dômes de Mono possèdent les valeurs isotopiques les
moins radiogéniques de tout le champ volcanique de Long Valley, avec 87
Sr/86
Sri
<0.7056 et 143
Nd/144
Nd >0.5126. Les laves siliciques du lac Mono et les rhyolites des
dômes de Mono ont des signatures plus influencées par la croûte terrestre, avec 87
Sr/86
Sri
>0.7058 et 143
Nd/144
Nd <0.5127. Ces valeurs sont comparables à celles du Bishop Tuff.
Les isotopes d’oxygène et de plomb dans la suite possèdent également des signatures
crustales, avec 206
Pb/204
Pb >19 et δ18
O > +6.5 ‰. Les laves du lac Mono sont
généralement plus jeunes et moins évoluées que celles des dômes de Mono, avec des
valeurs de 143
Nd/144
Nd inférieures et de 206
Pb/204
Pb supérieures à celles des dômes. Elles
démontrent aussi un enrichissement en éléments traces comme le Ba et le Sr. Ces
observations impliquent que les dômes de Mono et les laves du lac Mono sont issus de
lots de magmas différents, sinon de chambres magmatiques distinctes. L’absence de
relation systématique entre le niveau d’évolution chimique et l’âge des laves suggère que
plusieurs lots de magmas sont impliqués dans le développement des dômes de Mono. Les
différences prononcées dans la composition en éléments traces (Nb, Y) et en valeurs
isotopiques entre les laves de l’île de Negit et de l'île de Paoha indiquent que celles-ci
sont aussi les produits d’une évolution d'au moins deux lots différents de magma de
compositions intermédiaires. L’activité volcanique actuelle dans la région sud de la
vi
caldeira de Long Valley n’écarte pas la possibilité d'activité volcanique future. De plus, le
volcanisme récent dans le nord de la caldeira, combiné avec la thèse de la recharge
mafique sous le bassin de Mono, suggère que le bassin et les dômes de Mono pourraient
connaitre de nouvelles éruptions futures.
vii
Preface
The following thesis presents original research conducted by the author at the
McGill University Department of Earth and Planetary Sciences in the 2011-2013
academic years. This research is ultimately intended to form a manuscript to be submitted
to a peer-reviewed journal.
Fieldwork, sample cutting for geochemical analysis and for thin sections,
microprobe analysis, radiogenic isotope analysis, and preparation for oxygen isotope
analysis were performed by the author. The author was responsible for writing and
formatting the following thesis, and all new scientific data are the responsibility of the
author. Data acquisition, analysis, and interpretation were supervised by Professor John
Stix.
viii
Acknowledgements
Above all others, I must thank Professor John Stix for his tireless and seemingly
effortless supervision. His energy and insight are unparalleled and never fail to remind
me of the reasons I chose to study geochemistry and volcanology in the first place.
Dr. Wes Hildreth of the U.S. Geological Survey served as the external reader and
evaluator of the first draft of this thesis. His feedback has been invaluable.
Mono Lake can be rather inaccessible, and our research would not have been
successful without the help of a number of people. Dave Marquart of the Mono Lake
Tufa State Natural Reserve and Tamara Sasaki of California State Parks were
instrumental in ensuring that we received the proper permits needed to explore Negit and
Paoha. Dan Dawson, Kim Rose, and the rest of the staff of the Sierra Nevada Aquatic
Research Lab provided us with housing and lab space during the 2012 field season, and
this work was supported, in part, by a grant from the University of California Valentine
Eastern Sierra Reserve. Bartshe Miller and the determined volunteers of the Mono Lake
Committee, in addition to ensuring that Mono Lake remains a natural wonder for
generations to come, were kind enough to let us rent their boat on several occasions.
Kristie Nelson, our fearless captain on those unpredictable and often stormy waters, is a
keen observer and a faithful companion in the field, whether she is preparing chili inside
of a decades-old movie set in the middle of Mono Lake or single-handedly guiding our
boat into frigid, brackish water at 6 A.M. in mid-October.
Paul Alexandre, Kristen Feige, and the rest of the Queen’s Facility for Isotope
Research staff were kind enough to let me come play with their rather scary toys for a
week, and for that experience I am most grateful. Rhea Mitchell and Brian Cousens at the
ix
Carleton Isotope Geochemistry and Geochronology Research Centre were unflagging in
their efforts to make sure that we obtained the best data, even when that involved coming
back to work after midnight when the TIMS started misbehaving.
This thesis would never have come together without the support of all of my
wonderful friends in the McGill Department of Earth and Planetary Sciences. Special
thanks go to Marc-Antoine Fortin for his assistance in translating the abstract. The
members of the volcanology research group have helped to make the past several years a
blur. Gregor Lucic was instrumental in the success of the 2012 field season, and I could
not ask for a better friend. Patrick Beaudry was a delight to have as a field assistant, and
braved storms on Mono Lake like no other. Jason Coumans has made many a late night
in the office far more fun than it should be, and is always available to talk geochemistry.
And, of course, Melissa Maisonneuve, my twin, without whom I would have lost both my
sanity and my drive long ago.
Angela DiNinno, Anne Kosowski, Nancy Secondo, and Kristy Thornton are the
gears that the keep the wheels turning in EPS. I am ever thankful to be able to lean on
them for guidance through the bureaucratic mazes of graduate school, or for a good chat.
The tutelage and friendship of Karen Harpp are the only reason I ever stepped into
a geochemistry lab in the first place. Thank you, Karen, for the inspiring example you set.
May we climb many more volcanoes together! Finally, I must thank my parents, who
push me to keep inching forward, no matter how unmotivated I may get, and who
encourage all of my pursuits, academic and otherwise. Who else would be willing to
humor my attempts at explaining mafic rejuvenation of a felsic system in terms of
ketchup and peanut butter? Thank you.
x
Table of contents
Abstract .............................................................................................................................. ii
Résumé .............................................................................................................................. iv
Preface ............................................................................................................................. vii
Acknowledgements ........................................................................................................ viii
Table of contents ................................................................................................................ x
List of figures ................................................................................................................... xii
List of tables ................................................................................................................... xiii
Section 1: General statement .......................................................................................... 1
1.1 Previous work .................................................................................................. 2
Section 2: Introduction .................................................................................................... 8
Section 3: Geologic setting ............................................................................................. 10
3.1 Volcanic history ............................................................................................ 11
3.1.1 Postcaldera volcanism .................................................................... 11
3.1.2 Magmatism in the Mono Basin ....................................................... 14
Section 4: Methodology ................................................................................................. 17
4.1 Fieldwork ....................................................................................................... 17
4.2 Petrography ................................................................................................... 18
4.3 Whole-rock geochemistry ............................................................................. 18
4.3.1 Major and trace element analysis ................................................... 18
4.3.2 Isotope geochemistry ...................................................................... 19
xi
4.4 Electron microprobe analysis ....................................................................... 20
Section 5: Results ........................................................................................................... 21
5.1 Field observations ......................................................................................... 21
5.2 Petrographic analysis .................................................................................... 25
5.3 Whole-rock major and trace element geochemistry .................................... 29
5.4 Radiogenic isotopes ....................................................................................... 36
5.5 Stable oxygen isotopes .................................................................................. 37
5.6 Glass chemistry ............................................................................................. 37
5.7 Plagioclase chemistry .................................................................................... 39
5.8 Amphibole chemistry ..................................................................................... 43
Section 6: Discussion ...................................................................................................... 43
6.1 Fractional crystallization of the Mono lavas ............................................... 43
6.2 Basalt-rhyolite and magma-crust interactions in the Mono Basin ............. 44
6.3 Separate sources of the Mono domes and Mono Lake magmas ................. 47
6.4 Regional context ............................................................................................ 49
Section 7: Conclusions ................................................................................................... 51
Section 8: Major conclusions and suggestions for future work ................................. 52
References ....................................................................................................................... 54
xii
List of figures
Figure 1a: Map of the Mono and Inyo domes .................................................................. 12
Figure 1b: Map of Mono Lake ......................................................................................... 13
Figure 2: Field photographs of the Mono dome enclaves ................................................ 22
Figure 3: Field photographs of dacite lava textures in Mono Lake ................................. 23
Figure 4: Photomicrograph of mafic material observed in the Mono Lake lavas ........... 26
Figure 5: Photomicrographs of plagioclase crystals with disequilibrium textures .......... 28
Figure 6: Photomicrographs of rhyolitic glass inclusions in the Mono dome enclaves .. 30
Figure 7: Silica variation and fractional crystallization in the Mono Basin lavas – K2O
(wt.%) v. SiO2 (wt.%); Rb (ppm) v. SiO2 (wt.%) ................................................ 32
Figure 8: Fractional crystallization in the Mono Basin lavas – K2O (wt.%) v. Rb (ppm);
P2O5 (wt.%) v. Rb (ppm); V (ppm) v. Rb (ppm); Zr (ppm) v. Rb (ppm) ............ 33
Figure 9: Trace element variations in the Mono Basin lavas – Y(ppm) v. Rb (ppm); Nb
(ppm) v. Rb (ppm); La (ppm) v. Rb (ppm); Ce (ppm) v. Rb (ppm) .................... 34
Figure 10: Trace element enrichment in the Mono domes – Sr (ppm) v. Rb (ppm); Ba
(ppm) v. Rb (ppm) ............................................................................................... 35
Figure 11: Isotope variations in the Mono Basin lavas and the Long Valley Volcanic
Field – 143
Nd/144
Nd v. 87
Sr/86
Sri; 87
Sr/86
Sri v. 206
Pb/204
Pb; δ18
O (‰) v. 87
Sr/86
Sri;
δ18
O (‰) v. 143
Nd/144
Nd ....................................................................................... 38
Figure 12: Glass chemistry of the Mono domes, the Mono dome enclaves, and the Mono
Lake lavas – CaO (wt.%) v. SiO2 (wt.%); K2O (wt.%) v. SiO2 (wt.%) ............... 40
Figure 13: Plagioclase chemistry and distribution in the Mono Basin lavas ................... 41
Figure 14: Amphibole chemistry of the Mono domes – Mg/(Mg+Fe) v. Si (au) ............ 42
xiii
List of tables
Table 1: Mono Basin samples from the 2011 and 2012 field seasons ............................. 62
Table 2a: Comparison of XRF measured values with UTR-2 glass standard ................. 67
Table 2b: Comparison of acid-washed and unwashed samples from Mono Lake and the
Mono domes ......................................................................................................... 69
Table 2c: Comparison of electron microprobe measured values with M3N, PCD glass
standards .............................................................................................................. 70
Table 2d: Comparison of electron microprobe measured values with Amelia albite
standard ................................................................................................................ 71
Table 3: Major and trace element compositions of the Mono Basin lavas ...................... 72
Table 4: Isotopic compositions of the Mono Basin lavas ................................................ 81
Table 5a: Electron microprobe analysis of Mono Basin glass ......................................... 82
Table 5b: Electron microprobe analysis of Mono Basin amphiboles .............................. 89
Table 5c: Electron microprobe analysis of Mono Basin plagioclases ............................. 96
Table 6: Compilation of isotopic compositions of the Long Valley Volcanic Field ..... 109
1
Section 1: General statement
Volcanism in the Long Valley Volcanic Field of eastern California commenced at
roughly 4 Ma and has continued well into the Holocene. Initial activity involved the
extrusion of large volumes of basaltic lava. Over the following nearly 2.5 million years,
lavas evolved to more silicic compositions. This trend culminated when the Long Valley
caldera was excavated at approximately 0.76 Ma during the Bishop Tuff eruption.
Following caldera formation, basaltic and rhyolitic volcanism was renewed in the caldera
complex and outside of its margins, especially to the west and to the north. For the past
60,000 years, little if any magmatic activity has taken place in Long Valley caldera itself,
although regional unrest has been occurring since the late twentieth century. Recent
magmatism has been concentrated in the Mono Basin, directly to the north of Long
Valley caldera. Several dozen explosive eruptions of felsic pyroclastic material and lava
domes, referred to as the Mono domes, have occurred, in addition to several basalt flows.
Most recently, volcanic activity has uplifted several islands in the center of Mono Lake,
at the northern end of the Mono Basin.
Within the Mono Basin suite of lavas are several units with divergent
compositions and unknown petrogenetic origins. The oldest of these units, and indeed the
oldest of the Mono domes, is a porphyritic dacite bearing mafic magmatic enclaves,
which was dated by Wood (1983) to 40 ka but may be significantly older according to
Hildreth (personal communication 2014). A number of younger domes also contain
basaltic and andesitic enclaves. At the northern end of the Mono Basin, Mono Lake is the
home to the youngest lavas in the Long Valley Volcanic Field, the dacitic and low-silica
2
rhyolitic lavas of Negit Island and Paoha Island. Collectively, these lavas are the only
intermediate-composition lavas produced by Mono Basin magmatism.
With increased unrest in Long Valley, concern over an impending eruption has
swelled. It is improbable that the Long Valley magma chamber will generate a Bishop
Tuff-type catastrophe, although volcanic activity along the caldera’s southern moat,
where recent unrest has been focused, is a possibility (Bailey et al. 1976; Bailey 1983;
Bailey and Hill 1990). Considering the youth of the Mono domes and the Mono Lake
lavas and the recent dearth of volcanic activity within Long Valley caldera, an improved
understanding of the igneous processes operating in the Mono Basin is imperative, and
can provide a useful perspective on the present state of magmatic activity in the Long
Valley Volcanic Field. This study aims to determine the provenance of the Mono dome
enclaves and the Mono Lake lavas, and through this analysis to assess the nature of
interactions that exist between the Mono Lake, Mono dome, and Long Valley magmatic
systems.
1.1 Previous work
A significant body of literature on Long Valley exists and has been growing
rapidly. In the 1960s, development of the Casa Diablo Hot Springs area began, leading to
geothermal exploration of the caldera (Muffler and Williams 1976; Ewert and Harpel
2000). Renewed seismic and geodetic unrest in Long Valley caldera beginning in May
1980 sparked a renaissance of scientific interest in the region. Monitoring of the caldera
by the U.S. Geological Survey was increased, and a thorough reexamination of the
tectonic setting in which Long Valley caldera is situated and its eruptive history was
begun.
3
Long Valley occupies a unique tectonic position at the intersection of the Sierra
Nevada and Basin and Range provinces. It is the northernmost of the three volcanic fields
in the Owens Valley Rift, which also includes the Coso and Big Pine lavas (Manley et al.
2000; Bailey 2004). These volcanic fields are all associated with the eruption of large
volumes of silicic magma through Jurassic to Cretaceous granites and metasediments of
the Sierra Nevada batholith (Stern et al. 1981; Hill et al. 1985b; Ducea and Saleeby
1998a; Bailey 2004). The presence of these highly evolved magma systems in such a
geographically confined area is facilitated by the profound crustal weakness of the
region, which is in turn related to the interaction of north-northwest trending faults of the
Sierra Nevada and north- and northeast- trending faults of the Basin and Range (Pakiser
1970; Bailey 2004). The weakened crust has likely stimulated high levels of melting of
the underlying asthenosphere, has provided shallow storage space for the resultant
magmas, and allows efficient transport of magma along local zones of weakness and
faulting. It is hypothesized that this tectonic regime also led to lithospheric delamination
between 4 and 3 Ma, which would further incite the production of substantial volumes of
magma (Ducea and Saleeby 1998b; Manley et al. 2000; Farmer et al. 2002).
Precaldera volcanism started at approximately 4 Ma with the extrusion of large
volumes of basaltic lava. It is likely that these mafic melts were generated by the
decompression of the asthenosphere underlying present-day Long Valley as delamination
of the Sierra Nevada crust was initiated (Ducea and Saleeby 1998b; Manley et al. 2000).
Magmatism was exclusively mafic in nature for nearly 1.5 million years and largely
concentrated within, northeast, and west of what would eventually become Long Valley
caldera (Gilbert et al. 1968; Bailey 1989; Lange et al. 1993; Bailey 2004). It is possible
4
that this geographic variation in the volume of precaldera lava produced was influenced
by the dominant tectonic regime through which magma was rising (Bailey 2004). The
thick Sierra Nevada basement to the west of Long Valley may have impeded magma
ascent, whereas the thin Basin and Range lithosphere to the east could facilitate magma
transfer.
At around 2.5 Ma, basaltic volcanism waned as more evolved magmas began to
govern regional activity. The Glass Mountain complex contains at least 15 km3 of high-
silica precaldera lavas and pyroclastics, and was formed between 2.5 and 0.8 Ma, as
established by Metz and Mahood (1985, 1991), Metz and Bailey (1993), and Christensen
and DePaolo (1993). Precaldera volcanism climaxed at 0.76 Ma with the paroxysmal
Bishop Tuff eruption, which led to the formation of Long Valley caldera after nearly 700
km3 of rhyolitic magma was transported from the Long Valley magma chamber to the
surface via a series of vents located along ring faults (Hildreth 1979; Wilson and Hildreth
1997; Holohan et al. 2008).
Postcaldera volcanism started with silicic volcanism around 0.7 Ma. From 0.7 to
0.1 Ma, intracaldera basalts were erupted in the western half of the caldera and
extracaldera basalts to the south in the Devils Postpile area (Bailey 1989; Cousens 1996;
Bailey 2004). Simultaneously, the Long Valley resurgent dome formed, as well as the
Early and Moat rhyolites (Bailey et al. 1976; Bailey 1989). From 115 to 50 ka, the
Mammoth Mountain complex of intermediate and felsic pyroclastic rocks and lavas was
erupted in the southwestern quadrant of the caldera (Bailey et al. 1976; Bailey 2004;
Hildreth 2004; Hildreth et al. 2013). Successive volcanism has been focused to the north
5
of the caldera in the Mono Basin, with activity within and near the caldera fading since
60 ka (Hill et al. 1985a).
Explosive volcanic activity and lava dome extrusion in the Mono Basin began at
>40 ka with the eruption of a dacitic Mono dome (Wood 1983; Kelleher 1986; Kelleher
and Cameron 1990; Bailey 2004). Wood (1983) established the approximate ages of this
and other Mono domes using hydration rind ages. Bursik and Sieh (1989) and Kelleher
and Cameron (1990) confirmed the accuracy of these ages through field relationships.
After the eruption of the dacitic Mono dome, several series of high-silica rhyolites were
erupted. Biotite-bearing, porphyritic rhyolite was extruded at 13 ka; andesitic enclave-
and orthopyroxene-bearing, porphyritic rhyolite and fayalite-bearing, porphyritic rhyolite
from 13 to 7 ka; sparsely porphyritic rhyolites from 7 to 1.2 ka; and aphyric rhyolites
since 1.2 ka, with major pulses at 1.2 and 0.7 ka (Wood 1983; Kelleher and Cameron
1990).
The latter phase of Mono domes volcanism has inspired particular interest due to
its temporal association with the Inyo domes. The Inyo domes are a sequence of rhyolite
domes erupted along and near the margin of the caldera at ~0.7 ka. Many researchers,
including Miller (1985), Sieh and Bursik (1986), Sampson and Cameron (1987), Varga et
al. (1990), Bursik et al. (2003), and Hildreth (2004) have considered the question of
whether the youngest Mono domes and the Inyo domes are related, due to the fact that
they were likely erupted mere years apart, over two periods of several days, during what
are commonly referred to as the North Mono and Inyo eruptions, respectively. Several
different lava compositions are apparent in the Inyo domes, and it has been hypothesized
6
that they represent the interaction of Long Valley magma, Mono domes magma, and
basaltic magma (Sieh and Bursik 1986; Varga et al. 1990; Hildreth 2004).
Roughly contemporaneous with the Mono dome aphyric rhyolites are the oldest
porphyritic dacites of Mono Lake (Stine 1987; Bailey 2004). At approximately 1.7 ka,
volcanic activity began at the site of present-day Negit Island, with the eruption of
several dacitic lava flows from 1.7 to 0.4 ka (Stine 1987). Soon afterward, Paoha Island
was formed by updoming of lake sediment caused by magma intrusion and the eruption
of dacite and low-silica rhyolite at some point from 0.3 to 0.1 ka (Sinte 1987; Kelleher
and Cameron 1990; Bailey 2004). The Mono Lake eruptions denote the most recent
volcanic activity in the Long Valley Volcanic Field.
The use of geochemical techniques including major and trace element, radiogenic
and stable isotope, and mineral chemistry analyses is an established and important tool in
determining the sources and petrogenetic processes affecting magmas. Geochemical
studies of the Long Valley region have been numerous, and the precaldera lavas, the
Bishop Tuff, and postcaldera lavas from before 60 ka are well understood (e.g., Van
Kooten 1981; Wood 1983; Halliday et al. 1984; Chaudet 1986; Sampson and Cameron
1987; Ormerod 1988; Kelleher and Cameron 1990; Varga et al. 1990; Christensen and
DePaolo 1993; Cousens 1996; Heumann and Davies 1997; Davies and Halliday 1998;
Bailey 2004). Only Wood (1983) and Kelleher and Cameron (1990) have examined the
Mono dome enclaves and the Mono Lake islands, however, and little explanation is
provided as to the petrogenesis of either group of lavas.
This thesis hence addresses the major gap in our understanding of recent activity
in the Long Valley Volcanic Field that is represented by the lavas of the Mono Basin.
7
Samples of the Mono Lake lavas, the Mono dome enclaves, the Mono domes, recent
basalt, and the Inyo domes were collected during field work in 2011 and 2012. Whole-
rock major and trace element analyses of these samples were conducted, as well as
isotopic analyses of Sr, Nd, Pb, and O. Due to the usefulness of regional isotopic data in
contextualizing the Mono Basin lavas, a compilation of isotope data for the Long Valley
Volcanic Field is presented in this study that includes precaldera mafic and felsic
volcanic rocks, the Bishop Tuff, postcaldera mafic and felsic eruptive material, the Inyo
domes, and the Sierra Nevada crust. Electron microprobe analyses of glasses, as well as
plagioclase and amphibole populations, also have been conducted to assess the nature of
interactions occurring among the various Mono Basin lavas.
8
Section 2: Introduction
The longevity of large silicic volcanic systems commonly associated with
calderas is an issue of global concern. At their most extreme, these systems can generate
volumes on the order of 100 to >1000 km3 of magma in extremely explosive eruptions. It
is thus imperative that, in systems known to be capable of producing these catastrophic
eruptions, an accurate assessment of the state of the magmatic system and the
petrogenetic mechanisms presently at work be available. One such system is the Long
Valley Volcanic Field in eastern California.
Concern over the possibility of emergent volcanic activity in the Long Valley
Volcanic Field began after seismic and magmatic unrest in the region started in 1980
(Hill et al. 1985a). The volcanic and tectonic history of the region has since been well
established, in order to better assess the potential for future eruptions within and near
Long Valley caldera, and the hazards that would be posed by those eruptions.
Long Valley caldera was formed during the catastrophic Bishop Tuff eruption of
0.76 Ma. Since then, volcanism has occurred both within the caldera complex and around
its periphery. Postcaldera activity has been largely bimodal, generally alternating between
basaltic and rhyolitic compositions. In the past 60,000 years, the focus of magmatic
instability has shifted to the north of the caldera, in the Mono Basin, where an extensive
series of high-silica pyroclastic rocks and lava domes and several basalt flows have been
erupted.
Among these units are several of abnormal composition and ambiguous origin
that have important implications for the future of the entire system. The oldest of the
Mono domes, a porphyritic dacite profuse with basaltic enclaves, predates all other
9
domes by nearly 20,000 years (Wood 1983). Several other, younger domes contain
abundant enclaves of basalt and andesite. The lavas of Mono Lake are mostly dacitic in
composition, representing the only significant volume of intermediate-composition
magma generated in the Long Valley region in the past 60,000 years. These are also the
youngest eruptions in the region.
A future eruption of the magnitude of the Bishop Tuff eruption is considered
highly unlikely. Indeed, the Long Valley magma chamber is widely considered to be on
the decline, with very little actual melt remaining in spite of the mafic intrusions assumed
to have initiated unrest in the late twentieth century (Bailey et al. 1976; Bailey 1983;
Bailey and Hill 1990). The most likely locations of any imminent volcanic activity are
the Mono Basin, where activity has been occurring periodically for 60,000 years, and the
southern moat of the caldera, where volcanism related to the Mammoth Mountain
complex occurred as recently as 65 ka and the greatest geophysical activity and unrest
has been observed since 1980.
Despite the enigmatic compositions of many of the Mono Basin rhyolites and
dacites, there is a general paucity of conclusions regarding their petrogenetic origin and
their relation to the Long Valley system as a whole. This is somewhat surprising
considering their youth compared to other eruptive products of the Long Valley Volcanic
Field. An improved understanding of the igneous processes responsible for the
emplacement of the Mono domes and the Mono Lake islands is therefore essential,
particularly considering the region’s recent history of unrest. This study aims to better
integrate Mono volcanism into the broader volcanic history of Long Valley, and to use
10
the chemistry of these rocks as a lens through which to examine the igneous processes
currently occurring beneath the Mono Basin.
Section 3: Geologic setting
The Long Valley Volcanic Field, encompassing Glass Mountain, Long Valley
caldera, Mammoth Mountain, the Mono and Inyo domes, the Mono Lake islands, and
several Quaternary basalt flows, lies along the eastern margin of the Sierra Nevada and
the western margin of the Basin and Range province. Long Valley is situated at the
northern end of the Owens Valley Rift, which also includes the Coso and Big Pine
Volcanic Fields (Manley et al. 2000; Bailey 2004). Lavas associated with the Owens
Valley Rift are erupted through the basement rocks of the Sierra Nevada batholith, which
comprises a series of granitic plutons and metasedimentary rocks varying in age from
~210 to 88 Ma (Stern et al. 1981; Hill et al. 1985b; Bailey 2004).
The regional structure is defined by the north-northwest trending faults of the
eastern Sierra Nevada and the north- and northeast-trending Basin and Range-related
faults that fringe the Mono Basin (Pakiser 1970). Bailey (2004) hypothesized that the
coexistence of these two major tectonic regimes is responsible for weakening the crust in
the area, facilitating the generation of large volumes of magma and providing space for
its storage at shallow crustal levels. Furthermore, it is likely that this crustal weakness
promoted delamination of the Sierra Nevada crustal root between 4 and 3 Ma, which in
turn stimulated decompression melting on a substantial scale (Ducea and Saleeby 1998b;
Manley et al. 2000; Farmer et al. 2002).
11
3.1 Volcanic history
Regional volcanism commenced at roughly 4 Ma, coincident with the onset of
delamination, and has continued into the Holocene, with the most recent volcanic activity
being the 0.3-0.2 ka dacite and rhyolite eruptions on Paoha Island, near the center of
Mono Lake (Fig. 1; Stine 1987; Smith 1993; Bailey 2004). Two distinct periods of
frequent, dominantly bimodal activity can be discerned: precaldera volcanism, which was
initiated at 4 Ma, culminating with the paroxysmal 0.76 Ma caldera-forming Bishop Tuff
eruption; and postcaldera activity, which followed caldera formation almost immediately
with intracaldera volcanism, followed by a shift in activity to the west and north of Long
Valley caldera (Wood 1983; Bailey 2004). Since ~60 ka, postcaldera volcanic activity
has been limited to the emplacement of an extensive series of pyroclastics, lava domes,
and lava flows in the Mono Basin, directly to the north of Long Valley caldera.
3.1.1 Postcaldera volcanism
Following caldera formation, rhyolite eruptions resumed almost immediately both
within and around the margin of the new caldera. Between 0.7 and 0.1 Ma, the rhyolite
sequences known as the Early and Moat rhyolites were erupted, and the bulk of the
contemporary Long Valley resurgent dome was formed (Bailey et al. 1976; Bailey 1989).
Starting around 0.2 Ma, several basalt flows were erupted primarily in the western half of
the caldera, but also to the south in the Devils Postpile area, simultaneous with some later
postcaldera rhyolites (Bailey 1989; Cousens 1996).
Compositionally unique among the postcaldera intracaldera lavas is the Mammoth
Mountain complex, an extensive series of dacitic and rhyolitic pyroclastics and lavas
erupted from 115 to 50 ka (Bailey 2004; Mahood et al. 2010; Hildreth et al. 2013). Since
12
Fig. 1a: Map of the Mono domes, adapted from Bailey (1989) and Kelleher and
Cameron (1990). Domes are numbered using the scheme of Wood (1983).
13
Fig. 1b: Map of Mono Lake, adapted from Bailey (1989).
14
60 ka, volcanism proximal to Long Valley caldera has waned, leading Hill et al. (1985a)
to theorize that, in spite of recent unrest, future eruptions fueled by the moribund Long
Valley magma chamber are unlikely, especially near Mammoth Mountain.
3.1.2 Magmatism in the Mono Basin
As with the previous pulses of Long Valley volcanism, activity in the Mono Basin
has been for the most part bimodal. Starting at ~60 ka, a series of high-silica rhyolites,
with one exceptional dacite, erupted explosively, each eruption culminating with the
emplacement of a lava dome (Fig. 1a; Kelleher 1986; Kelleher and Cameron 1990;
Bailey 2004; Vazquez and Lidzbarski 2012). Collectively, this suite is referred to as the
Mono domes. Several local basalt flows are interspersed chronologically among these
domes. Achauer et al. (1986) hypothesized that a substantial, partially molten magma
chamber exists beneath the Mono Basin and is the likely source of these recent lavas as
magma production has shifted to the north of Long Valley caldera.
It has been well established through field relationships and several studies looking
at the hydration rind ages of the Mono domes that, in general, the mineralogy and
geochemistry of the Mono domes correspond chronologically with the typical
progression that would be expected from a system undergoing fractional crystallization
(Wood 1983; Bursik and Sieh 1989; Kelleher and Cameron 1990). Using the dome
numbering system of Wood (1983) and the classification scheme of Kelleher and
Cameron (1990), as will be done throughout this study, dome 12 is the oldest dome,
estimated to be >40 ka, and is of dacitic composition. Dome 12 is replete with basaltic
enclaves. The next eruptions in the region involved biotite-rich, porphyritic rhyolites
(domes 11, 19, and 24), established by hydration rind dates to have been emplaced
15
around 13 ka (Wood 1983). Between 13 and 7 ka, a pair of andesitic enclave- and
orthopyroxene-bearing, porphyritic rhyolite domes (domes 14 and 18) were first erupted,
followed by a more extensive series of porphyritic, fayalite-bearing rhyolite domes
(domes 6, 15, 17, 20, 25, and 27-30). From roughly 7 until 1.2 ka, volcanism in the Mono
Basin was dominated by the eruption of sparsely porphyritic, high-silica rhyolite in the
form of dome 8 (often referred to as the Northwest Coulée) and domes 10, 16, 21, 23, and
26. In the past 1200 years, two voluminous pulses of aphyric, high-silica rhyolite
volcanism have occurred. The first pulse was at ~1.2 ka, emplacing dome 22 (the South
Coulée), and the second pulse occurred at ~0.7-0.6 ka, emplacing dome 3 (Panum Crater)
and domes 4, 5, 7, 9, and 13 (the North Coulée). The later event is commonly referred to
as the North Mono eruption (Sieh and Bursik 1986; Hildreth 2004). Tephra produced
during the explosive phases of these eruptions blankets most of the older domes.
Coeval with dome emplacement are the June Lake, Black Point, and Red Cones
basalt flows. Between 30 and 25 ka, the June Lake basalt flowed from a cinder cone near
June Lake, located in the southwestern Mono Basin (Bursik and Gillespie 1993; Bailey
2004). While the biotite-bearing Mono domes were being emplaced, at roughly 13 ka, the
Black Point basalt was erupted subaqueously into Pleistocene Mono Lake, taking the
form of a flat-topped cinder cone (Lajoie 1968; White 2000; Bailey 2004). The Red
Cones basalt flow was erupted to the south of Mammoth Mountain at 8 ka, at the height
of sparsely porphyritic rhyolite volcanism in the Mono domes (Cousens 1996; Bailey
2004).
Concurrent with the eruption of aphyric rhyolite in the Mono Basin was the
commencement of sparsely porphyritic dacitic volcanism in Mono Lake, a 15 km x 21
16
km lake located north of the Mono domes (Stine 1987; Tierney 2000; Bailey 2004). The
initial locus of Mono Lake volcanism was Negit Island, which is dominated by a dacitic
cinder cone and several dacitic lava flows originating therein; it is estimated to have been
active from 1.7 to 0.4 ka according to Stine (1987). Further outcrops of these dacite flows
are seen to the north of Negit Island on a series of small islands referred to here as the
Negit islets. Closely following the last eruption on Negit Island, an intrusion beneath the
central part of Mono Lake caused updoming of a significant volume of lake sediment and
the eruption of a small volume of dacite, including several cinder cones and lava flows,
forming present-day Paoha Island (Stine 1987; Kelleher and Cameron 1990). Between
300 and 150 years ago, several low-silica rhyolite flows were erupted in the northwestern
quadrant of Paoha Island; these appear to be the most recent eruptions in the Long Valley
Volcanic Field. The exact timing of these events is not well constrained and is due largely
to anecdotal evidence. Several expeditions in the Mono Basin in the mid-nineteenth
century noted the continued presence of large, meter-scale pumice rafts on the surface of
Mono Lake, leading modern observers to conclude that the eruption or eruptions
generating the pumices likely occurred in the preceding decades, that is, sometime
between ~1750 and 1865 (Twain 1872; Smith 1993).
Bridging the gap between intracaldera and extracaldera volcanism are the Inyo
domes, a series of rhyolite domes straddling the northwestern margin of Long Valley
caldera erupted between 0.7 and 0.6 ka, nearly contemporaneous with the North Mono
eruption (Fig. 1a; Miller 1985; Sampson and Cameron 1987). The magmatic source of
the Inyo sequence is uncertain, although it has been argued that they are a mixture of
relict Long Valley rhyolite, Mammoth Mountain dacite, Mono Basin rhyolite, and Long
17
Valley chamber-rejuvenating basalt (Sieh and Bursik 1986; Varga et al. 1990; Hildreth
2004). Situated between Glass Creek Dome and South Deadman Creek Dome, just within
the northern caldera margin, is North Deadman Creek Dome, an enclave-bearing,
sparsely porphyritic dome estimated by Wood (1983) and Miller (1985) to be
approximately 6000 years old (Fig. 1a). North of Obsidian Dome lies Wilson Butte, a
1300 year old enclave-bearing, sparsely porphyritic rhyolite dome (Miller 1985). Lajoie
(1968) and Bailey (1989) classified both North Deadman Creek Dome and Wilson Butte
as members of the Mono domes suite. The geochemical data presented below support this
classification.
Section 4: Methodology
4.1 Fieldwork
Two field seasons were conducted for this study. The first, in October 2011,
involved focused sampling of the Mono Lake islands and the enclave-bearing Mono
domes, as well as several other Mono domes, the June Lake and Black Point basalts, and
South Deadman Creek Dome, the southernmost of the Inyo domes. A second field
campaign was conducted in July-August 2012, which more broadly sampled the Mono
domes, associated mafic enclaves, and the Mono Lake islands. In total, twenty-four Mono
domes were sampled (Table 1). The Mono Lake islands and the mafic enclave
populations of the Mono domes were sampled extensively. Where possible,
representative samples of 1-2 kg were selected, based upon the overall freshness of the
rock. Interesting textures and field relationships were examined, documented, and
photographed for later reference. Precise coordinates of each outcrop sampled were
recorded on a GPS using the WGS 84 datum (Table 1).
18
4.2 Petrography
Thin section billets were cut from fresh surfaces of the sampled rocks. In total,
sixty-eight billets were cut, ensuring that complete geographic coverage was attained in
order to document any variations in enclave populations or local textures. A further
subset of nineteen thin sections was polished for electron microprobe analysis. Billets
were polished at Spectrum Petrographic, Inc., in Vancouver, WA, USA.
4.3 Whole-rock geochemistry
An extensive series of geochemical analyses was conducted on a subset of
sampled rocks. Rock chips from fifty-four samples, covering the Mono Lake islands, the
Mono domes, all mafic enclave populations, and local basalts, were analyzed for major
and trace elements by X-ray fluorescence (XRF) at the Washington State University
GeoAnalytical Lab, in Pullman, WA, USA. Rock powders of sixteen representative
samples were then selected for Rb-Sr, Sm-Nd, and Pb-Pb isotopic analyses at the
Carleton University Isotope Geochemistry and Geochronology Research Centre
(IGGRC), in Ottawa, ON, Canada. This same subset of samples, in addition to the June
Lake and Black Point basalts, were analyzed for 18
O/16
O stable oxygen isotopes at the
Queen’s University Facility for Isotope Research (QFIR), in Kingston, ON, Canada.
4.3.1 Major and trace element analysis
Major- and trace element analysis by XRF was conducted at Washington State
University using the methods of Johnson et al. (1999). Spec pure dilithium tetraborate
flux powder and freshly ground rock powder were mixed in a 2:1 ratio, fused, and
polished (Johnson et al. 1999). The polished beads were then analyzed by a ThermoARL
Advant’XP+XRF spectrometer. For major elements, reported analytical precision is
19
within <1 wt. %; trace element analyses are precise to within 2 parts per million (ppm)
(Johnson et al. 1999). Several powders of the UTR-2 standard were included in each
batch of XRF samples to further gauge the accuracy and precision of the analyses (Table
2). As most rocks from Mono Lake were at one point submerged, rock chips from the
2011 field season were carefully cleaned using acetic acid and deionized water. Repeat
analyses comparing cleaned samples to uncleaned splits of the same samples show that
the cleaning method had a negligible effect (Table 2). This implies that the waters of
Mono Lake have had little, if any, effect on the trace element composition of the Mono
Lake lavas, so the samples collected in the 2012 field season were simply rinsed with
deionized water.
4.3.2 Isotope geochemistry
Thermal ionization mass spectrometer (TIMS) analyses for Rb-Sr, Sm-Nd, and
Pb-Pb isotopes were conducted on a ThermoFinnigan Triton TI TIMS at Carleton
University. Samples of 0.1-0.2 g were dissolved, passed through chromatographic
columns to elute Pb, Sr, and Nd, and analyzed using the standard methods of the IGGRC
(http://www.carleton.ca/iggrc/). The maximum instrumental uncertainty for 87
Sr/86
Sr is
0.000014; 0.000012 for 143
Nd/144
Nd; 0.005 for 206
Pb/204
Pb; 0.0002 for 207
Pb/204
Pb; and
0.00005 for 206
Pb/204
Pb, according to calculated 2σ values.
Oxygen isotopes were analyzed at Queen’s University on a Finnigan MAT 252
Isotope Ratio Mass Spectrometer (IRMS). Gas for 18
O/16
O analysis was extracted from 5
mg samples of rock powder using the BrF5 reaction method of Clayton and Mayeda
(1963) on the QFIR silicate extraction line. Reproducibility of δ 18
O values is ±0.3 ‰.
20
4.4 Electron microprobe analysis
Electron microprobe analyses of selected minerals in polished thin sections were
conducted at McGill University in Montreal, QC, Canada using a JEOL 8900 electron
microprobe. Based on their importance to petrographic observations, amphibole,
plagioclase, and glass populations from throughout the sample suite were analyzed.
Glass analyses were conducted using a 15 kV accelerating voltage, an 8 mA beam
current, and a 20 μm beam diameter, to prevent Na2O loss. Glass standards BMAK and
KE-12 were used to calibrate Mg, Fe, Ca, and Ti; and Na, Al, Si, and K, respectively.
Manganese and phosphorous were calibrated using synthetic standards. The PCD and
M3N standards were analyzed after each sample to gauge instrumental accuracy (Table
2). Since PCD has very low H2O and M3N has relatively high H2O, these two standards
were used to accurately assess variations in the H2O content of different glasses.
Amphibole analyses used an accelerating voltage of 15 kV, a beam current of 20
mA, and a 10 μm beam diameter. All elements were standardized to a mixture of
synthetic standards; results are compared to the HBLD standard to gauge instrumental
precision and accuracy.
Plagioclase analyses used an accelerating voltage of 15 kV, a beam current of 20
mA, and a 5 μm beam diameter. Calibration involved a number of synthetic standards,
and the Amelia albite standard was analyzed periodically to gauge instrumental precision
and accuracy (Table 2d).
21
Section 5: Results
5.1 Field observations
The Mono domes rise abruptly above the relatively flat terrain of the Mono Basin,
~5 km to the east of US Highway 395. Most of the domes are comprised of light gray,
finely vesicular rhyolite of varying mineralogy covered with tephra from the 0.7 ka North
Mono eruption (Bailey 2004; Hildreth 2004). The most salient observations from field
relationships are those for the centimeter-scale mafic enclaves hosted within Mono
domes 12, 14, and 18. The enclaves in domes 14 and 18 range from black to red in color,
with populations of each hue present in each dome. They are finely vesicular, stretched
and rounded, and commonly have glassy, chilled margins coupled with melting rims in
their felsic hosts (Fig. 2). These three observations imply that, when the mafic material
was in contact with the felsic material, it was at least partially molten. Kelleher and
Cameron (1990) noted similar enclave textures. The uniformly red enclaves of dome 12
are much more thoroughly integrated into the host rock, and on a much finer scale. Rare
andesitic enclaves are also present in Wilson Butte and North Deadman Creek Dome.
Intimate sediment-dacite interaction is apparent on Paoha Island. This is
especially apparent on the east side of the island, where fumarolic activity is ongoing.
Outcrops of peperite are common in this area, with glassy black dacite, more vesicular
gray dacite, and tan sediment occurring in centimeter-scale layers (Fig. 3c). The northern
edge of this fumarolic area also has a sizable outcrop of extremely vitreous, black dacitic
obsidian.
The northeastern corner of Paoha Island has several nested dacitic cinder cones.
Black, vesicular dacite outcrops are found on the inner slopes of these cones. A
22
Fig. 2: Field photographs of mafic enclaves. (a) Elongate enclave in flow-banded
rhyolite, sample BB-2011-05, Mono dome 14. (b) Small, rounded enclave in sparsely
porphyritic rhyolite, sample BB-2011-14, North Deadman Creek Dome. (c) Reddish,
rounded enclave in porphyritic rhyolite, sample BB-2011-05, Mono dome 14. (d)
Numerous elongate enclaves in porphyritic rhyolite, sample BB-2012-05, Mono dome
18; photo courtesy Patrick Beaudry.
23
Fig. 3: Field photographs of dacite lava textures in Mono Lake. (a) Decimeter-scale
columnar jointing in the Tahiti dacite, sample BB-2011-02. (b) Brecciated Tahiti
dacite cemented by Mono Lake tufa, sample BB-2011-02. (c) Finely layered dacite
and sediment of peperite on Paoha Island, sample BB-2011-11c. (d) Welded ledges at
the summit of the Negit Island dacitic cinder cone, reminiscent of Strombolian-style
deposits, sample BB-2011-19; photo courtesy Patrick Beaudry.
24
voluminous dacite lava stemming from the center of this cone complex flows to the west,
ending at the northern tip of Paoha Island, locally referred to as Lunacy Point.
Centimeter-scale columnar jointing hints at the subaqueous history of this flow. Going
south from Lunacy Point along the western coast of Paoha Island are several outcrops of
rhyolitic obsidian with a pumiceous carapace.
Negit Island is dominated by a black and red dacitic cinder cone. The summit of
this cinder cone, rather than having a large, well-defined crater, consists of a series of
reddish ledges and hills of welded scoria and bombs (Fig. 3d). These ledges are
reminiscent of Strombolian-style deposits, as they appear to be comprised of scoria clasts
that have agglutinated in rapid succession. Several lavas originate from the base of this
cinder cone, flowing primarily to the north and west. The lavas are uniformly black
dacite, with sparse, millimeter-scale vesicles and crystals.
The Negit islets are a series of small outcrops to the northeast of Negit Island. The
easternmost of these islands, locally referred to as Norway, consists of a reddish-black
vent area surrounded by associated dark gray, flow-banded, finely vesicular low-silica
rhyolitic lava. The island is in turn surrounded by white, pumiceous material and is
possibly the source of the young pumices described by Smith (1993) and Twain (1872).
Much of the lava is coated in Mono Lake tufa, owing to fluctuating lake levels that often
leave Norway and the other Negit islets partially submerged. Directly southwest of
Norway are two vents collectively referred to as Tahiti. The vents were once located on a
single, continuous island, but at present they are separated due to the rise in lake level.
The Tahiti dacite is noticeably darker in hue than the Norway rhyolite. The subaqueous
nature of the Tahiti eruptions is obvious; in some areas, centimeter-scale columnar
25
jointing is visible. Some outcrops on both islands are brecciated, with Mono Lake tufa
cementing together lava clasts (Fig. 3a-b).
5.2 Petrographic analysis
As previously shown by Kelleher and Cameron (1990), several distinct groupings
can be made among the high-silica rhyolites of the Mono domes based upon their
respective mineralogies. The porphyritic rhyolites all contain mineral assemblages
dominated by plagioclase, with sanidine and quartz appearing rarely. Accessory phases
throughout the Mono domes include titanomagnetite, apatite, zircon, and a light rare-
earth element (LREE)-bearing phase, likely allanite (Kelleher and Cameron 1990). These
lavas can be further distinguished by the presence of phenocrysts of biotite (domes 11,
19, and 24), orthopyroxene (domes 14 and 18), and fayalite (6, 15, 17, 20, 25, and 27-30).
Domes 8, 10, 16, 21, 23, and 26, while porphyritic, do not contain any unique,
discriminatory ferromagnesian minerals. The youngest of the Mono domes are the
aphyric rhyolites of the South Coulée and North Mono eruptions (domes 3, 4, 5, 7, 9, 13,
and 22).
The dacites and rhyolites of Mono Lake exhibit similar mineralogies. The Mono
Lake lavas are sparsely porphyritic to nearly aphyric. Plagioclase is by far the dominant
mineral in the porphyritic lavas. Rarely, hornblende and biotite appear in the Negit
Island, Paoha Island, and Negit islet lavas. Unique to the Paoha Island lavas are
microscopic clots of foreign, possibly more mafic material, in the form of round pockets
of glass, plagioclase, and biotite that stand out from the groundmass of the lava (Fig. 4).
Regardless of the location, whether a sample is from the Mono domes, Mono
26
1 cm
glass
plagioclase
biotite
Fig. 4: Mafic clot containing glass, biotite, and plagioclase in sample BB-2011-10,
Paoha Island dacite.
27
Lake, or a mafic enclave, most plagioclase phenocrysts exhibit pronounced dissolution
textures (Fig. 5). For example, otherwise euhedral plagioclase crystals appear to be
dissolving into the host rhyolite along their rims. Phenocrysts commonly have spectacular
sieve textures, with almost the entire crystal pockmarked (Fig. 5a-b). Many of the voids
have been filled subsequently with glass and microlites, although most appear to be
actual voids in the crystal structure. These sieve textures imply that either reheating or
depressurization of the felsic magma occurred. The sieve texture is commonly coupled
with distinct regrowth rims, suggesting that recrystallization of the felsic magmas
occurred. This ubiquitous sieve texture implies that a similar petrogenetic process is
occurring at depth throughout the Mono Basin.
The dome 12 dacite contains abundant centimeter-scale plagioclase and
millimeter-scale hornblende and clinopyroxene crystals. Enclaves of basalt and basaltic
andesite within the dacite are vesicular, contain plagioclase, olivine, and clinopyroxene
phenocrysts, and range from microscopic to upwards of 5 centimeters in scale. Owing to
the intimate commingling of the enclaves and the host dacite, geochemical analyses of
the host rock proved impossible. Kelleher and Cameron (1990) do however present a
geochemical analysis of the dome 12 dacite, which is used here.
The mafic and intermediate enclaves of domes 14 and 18 are broadly similar.
Millimeter-scale olivine, plagioclase, and orthopyroxene phenocrysts are present in all
enclaves. It is common to see microscopic inclusions of rhyolitic magma within the
28
Fig. 5: Plagioclase crystals with pronounced disequilibrium textures are present in all
crystal-bearing lavas of the Mono Basin. (a) Plagioclase with sieved center and calcic
regrowth rim, sample BB-2011-05, Mono dome 14. (b) Partially dissolved, finely sieved
plagioclase, sample BB-2011-10, Paoha Island dacite. (c) Finely sieved plagioclase
pierced by biotite, sample BB-2011-18, Negit Island. (d) Coarsely sieved, zoned
plagioclase, sample BB-2012-17, Mono dome 29.
29
enclaves, and vice versa, along the host-enclave margin, reinforcing the idea that both
magmas were at least partially molten upon initial contact, although it appears that this
condition did not last sufficiently long for wholesale mixing to occur (Fig. 6).
5.3 Whole-rock major and trace element geochemistry
Several important trends are apparent in the major and trace element data (Table
3). Silica shows strong positive correlations with K2O and Rb (Fig. 7). As it is the most
incompatible element analyzed, Rb is used as an index of differentiation in all other
geochemical plots (Figs. 8-10). Throughout the sample suite, pronounced fractionation
trends are present in elements such as P, K, Sr, V, and Zr (Fig. 8). These trends underpin
the important role played by the crystallization of plagioclase, as well as accessory
mineral phases such as zircon, apatite, titanomagnetite, and LREE-bearing minerals.
In major element space, the Mono domes lie within a very narrow compositional
range. The variation in SiO2 concentration is only from 75 to 77 wt.% on an anhydrous
basis; all other major elements are similarly uniform (Table 3). The minor increase in
SiO2 content in the Mono domes corresponds to the temporal evolution from biotite-
bearing lavas to orthopyroxene-bearing lavas, fayalite-bearing lavas, porphyritic lavas
lacking any notable ferromagnesian mineral phases, and, finally, aphyric lavas.
The Mono Lake islands, on the other hand, are quite varied in major element
composition and are more primitive than the Mono domes, in spite of their comparative
youth. On Paoha Island, SiO2 varies from 63 to 72 wt.%, while Negit Island and the Negit
islets display a range from 64 to 70 wt.% SiO2. In general K2O increases with SiO2,
except in the Mono domes, which are depleted in K2O relative to the most evolved Paoha
Island rhyolites, while all other major element concentrations decrease (Fig. 7a).
30
Fig. 6: Intimate commingling of enclaves and host lava. (a) Rhyolitic inclusion within
an andesitic enclave, sample BB-2011-05b-2, Mono dome 14 enclave. (b) Vesicles
filled with felsic glass at the enclave-host border, sample BB-2011-05b-2, Mono dome
14 enclave.
31
Trace elements are more useful in differentiating among the different groups of
Mono domes. Domes 14 and 18, the orthopyroxene- and enclave-bearing porphyritic
rhyolites, are the most depleted in Rb, with 156 and 164 ppm, respectively. They are also
depleted in Nb and Y compared to the rest of the Mono domes (Fig. 9) and enriched in
Zr, La, and Ce (Figs. 8d, 9c-d). At first glance, the considerable range in La (18 to 38
ppm) and Ce (42 to 69 ppm) concentrations within the remaining domes would appear to
further distinguish them; careful examination, however, reveals that the variations in La
and Ce do not correspond to geography, mineralogy, or major element composition.
Rather, they are likely reflective of either minor heterogeneities in the source or small
variations in accessory mineral crystallization trends.
As with major elements, the Mono Lake lavas display significant trace element
variations and are overall less evolved than the Mono domes. The lavas of Mono Lake
have extremely high and variable Ba concentrations when compared to all other
postcaldera lavas, ranging from 1000 to 1600 ppm, and Sr concentrations from 95 to 530
ppm (Fig. 10; Table 3). Similarly, they are conspicuously depleted in Rb relative to the
Mono domes, with concentrations ranging from 100 to 130 ppm. For comparison, within
the Mono domes, Sr ranges from 1 to 25 ppm, Ba from 10 to 40 ppm, and Rb from 130 to
180 ppm (Fig. 10).
While broadly similar, the Negit and Paoha lavas exhibit some marked
differences. Among the high field strength elements (HFSE), particularly Y and Nb, the
Negit and Paoha lavas define discrete fields with no overlap, suggesting that the islands
can be separated chemically (Fig. 9). The older Negit lavas have Y and Nb concentrations
reflective of a less evolved magma (18 to 20 ppm and 12 to 14 ppm, respectively), while
32
Fig. 7: (a) K2O and SiO2 show a positive correlation, except at high SiO2 values, where
K2O declines in the Mono domes. (b) Rb and SiO2 are positively correlated throughout the
entire sample suite. The analyses presented in Figs. 7-11 of Mono dome 12 and of several
mafic enclaves come from Kelleher and Cameron (1990). An Inyo enclave sample from
Glass Creek comes from Varga et al. (1990).
33
Fig. 8: (a) K2O and Rb show a positive correlation, except at high Rb values, where K2O
declines in the Mono domes. (b) P2O5 and Rb are negatively correlated except for the
most mafic lavas. (c) V decreases with increasing Rb content throughout the entire system
and is completely depleted in the Mono domes. (d) Zr concentrations increase with Rb
concentration in the mafic and intermediate lavas, then decline abruptly in the more
evolved lavas of the Paoha Island rhyolite, the Inyo domes, and the Mono domes.
34
Fig. 9: (a-b) Y and Nb concentrations are notably different between Paoha Island and
Negit Island. They are broadly consistent within individual enclave populations. (c-d)
LREE concentrations are depleted in the Mono domes compared to the less silicic
lavas. The Mono domes form clusters at different LREE contents.
35
Fig. 10: The Mono Lake lavas have noticeable differences in trace element content
compared to the more mafic and more felsic lavas. (a) Sr concentrations in Mono Lake
show some overlap with more mafic enclaves and lavas and are enriched relative to the
Mono domes. (b) The Mono Lake lavas are extremely enriched in Ba compared to all
other samples.
36
the more youthful Paoha lavas are comparatively enriched in Y and Nb (19 to 27 ppm
and 15 to 19 ppm, respectively).
Integrating the new geochemical data presented here with those of Kelleher and
Cameron (1990) shows that the basaltic enclaves from dome 12 vary little from one
another, with an SiO2 range of 50 to 54 wt.%, notably lower than that of the dome 14 and
18 enclaves, and with no systematic variation in the other elements analyzed (Table 3).
The dome 14 and 18 enclaves define two distinct populations chemically, as they do
petrographically (Figs. 7-10). In each dome, one set of enclaves has 55 to 56 wt.% SiO2,
while another set has 59 to 61 wt.% SiO2, with correlative variations in the other major
and trace elements. The two enclave populations form distinct clusters in most major and
trace element diagrams. A fractionation trend between the two populations is often
apparent, particularly in trace elements such as Rb and Sr (Fig. 10a). The enclaves of the
Inyo domes and North Deadman Creek dome, on the other hand, have compositions
much more similar to the Mono dacites than to the other Mono enclaves, with SiO2 from
60 to 62 wt.% and Rb and Ba concentrations that are enriched compared to the enclaves
of domes 12, 14, and 18 (Table 3).
5.4 Radiogenic isotopes
Strontium and Nd isotopic values are consistent with what would be expected for
rocks whose isotopic signatures are dominated by a mantle component (mafic lavas) or
by a crustal component (intermediate-felsic lavas). Within the Mono domes, 87
Sr/86
Sri
presents a range from 0.70596-0.70690, and 143
Nd/144
Nd from 0.51260 to 0.51262. The
Mono Lake lavas are similar, with 87
Sr/86
Sri from 0.70587-0.70642, and 143
Nd/144
Nd from
0.51252 to 0.51259. The mafic enclaves present within the Mono domes display an
37
87Sr/
86Sri range of 0.70442-0.70486, significantly lower than the silicic Mono lavas, and
143Nd/
144Nd from 0.51274-0.51278, well above other values for silicic rocks in the Mono
Basin. The exceptions are the enclaves of the Inyo domes, which have radiogenic isotopic
ratios resembling the Mono domes (87
Sr/86
Sri 0.70622, 143
Nd/144
Nd 0.51252), and the
enclaves of North Deadman Creek Dome (87
Sr/86
Sri 0.70564, 143
Nd/144
Nd 0.51264). The
entire sample suite has a very tight range of Pb isotopic values, all reflecting a crustal or
sedimentary signature; 208
Pb/204
Pb ranges from 38.86-39.04, 207
Pb/204
Pb from 15.66-
15.71, and 206
Pb/204
Pb from 19.09-19.24 (Fig. 11; Table 4).
5.5 Stable oxygen isotopes
Similar to Pb, δ18
O values are quite consistent throughout the entire sample suite,
and all signify the influence of a crustal component throughout the system. The range in
our δ 18
O values is +6.5 to +9.5‰, ignoring two outliers: a peperite sample from Paoha
Island with δ 18
O of +11.6‰, which is likely due to the profound integration of sediment
into the dacites in the locality at which this sample was taken; and a dome 18 enclave
with δ 18
O of +12.7‰ (Table 4). Although the overall δ 18
O range is characteristic of
crustal compositions, reported by Bindeman (2008) as +5 to +18‰, there are notable
variations within. The Mono domes, rather than defining a tight cluster as they do for
other chemical components, range from +6.9 to +9.0‰; similarly, the Paoha Island lavas
vary from +7.6 to +9.4‰, ignoring the abnormally elevated sample from the Paoha
peperite.
5.6 Glass chemistry
Microprobe analyses of glasses from throughout the Mono Basin confirm many of
the inferences offered by petrography alone. The enclave-bearing Mono dome lavas, such
38
Fig. 11: (a-b) The mafic lavas of the Mono Basin have the least radiogenic Sr and Nd
values of the Long Valley Volcanic Field. The Negit Island lavas tend toward more
crustal values than the Paoha Island lavas, and the lavas of both islands are more
radiogenic than the Mono dome rhyolites. (c-d) Crustal signatures dominate O isotope
values throughout the Mono Basin. This is the case even in the otherwise mantle-like
mafic magmas. Regional isotopic data used in plotting fields come from Van Kooten
(1981); Halliday et al. (1984); Chaudet (1986); Kelleher (1986); Ormerod (1986);
Sampson and Cameron (1987); Christensen and DePaolo (1993); Cousens (1996);
Heumann and Davies (1997); Davies and Halliday (1998); and Bailey (2004) (Table 6).
39
as dome 14, have millimeter-scale inclusions of glass that are more mafic than the host
rhyolite, with SiO2 contents of 49 to 55 wt.%, CaO contents in excess of 8 wt.%, and K2O
contents less than 2 wt.% (Fig. 12c-d; Table 5). On Paoha Island, where the host glass
compositions are dominantly felsic, with SiO2 of 67 to 72 wt.%, CaO less than 2 wt.%,
and K2O greater than 4 wt.%, microscopic clots of more mafic glass have SiO2
concentrations as low as 64 wt.%, CaO up to 3.3 wt.%, and K2O as low as 3.5 wt.%
(Figs. 4, 12a-b; Table 5). These mafic clots contain glass, plagioclase, and biotite, and
appear to be unique to Paoha Island (Fig. 4).
5.7 Plagioclase chemistry
Plagioclase is by far the most common mineral in all Mono lavas. Except for the
few aphyric Mono domes, plagioclase is present in every lava analyzed. The Mono dome
plagioclases analyzed are sodic, with An14-16. Distinct compositional populations in
plagioclase are present within the other groups of lavas. The Paoha and Negit Island
dacites have one plagioclase population with An20-28 and a second population with An37-53
(Fig. 13; Table 5). Plagioclase crystals in each population commonly are normally zoned.
In general, the plagioclase populations in the Mono dome enclaves are much more
calcic than those of the host Mono domes and the Mono Lake lavas. In dome 14, enclave
plagioclase compositions define a nearly continuous array from An49 to An72. The dome
18 enclave andesite also has a large plagioclase population with An46-75; however, some
crystals have anorthite contents as low as An25 (Fig. 13; Table 5). It is likely that this is a
xenocrystic population, incorporated into the mafic material from the more evolved host
rhyolite during magma mingling.
40
Fig. 12: Lavas throughout the Mono Basin exhibit multiple glass populations. (a-b)
Paoha Island has clots of material that is more mafic (higher CaO, lower K2O) than
the host dacite. (c-d) Inclusions of glass in the Mono domes are basaltic in
composition; rhyolitic inclusions in the Mono dome andesitic enclaves have glass
that is more felsic (lower CaO, higher K2O) than the andesite.
41
Fig. 13: (a) Mono Basin plagioclase crystals are low in K2O, and vary between
more sodic and more calcic populations, often within the same lava. Bimodal
plagioclase populations are apparent in (b) the Mono dome enclaves and (c) the
Mono Lake lavas.
42
Fig. 14: Two distinct populations of amphiboles exist between the Mono Lake
lavas and the Inyo domes. The Mono Lake population has noticeably lower Si
and Fe compared to the Inyo population.
43
5.8 Amphibole chemistry
While vanishingly rare in the Mono domes, amphiboles found in the Mono Lake
lavas are fairly uniform in composition. Throughout the entire sample suite, SiO2 varies
from 41.2 to 42.5 wt.%, FeOT from 12.6 to 17.4 wt.%, and MgO from 10.8 to 13.9 wt.%
(Fig. 14; Table 5). All Mono Lake amphiboles plot as tschermakite, reflecting their
relatively low Fe contents (Fig. 14). In comparison, amphiboles from the Inyo domes plot
as magnesio-hornblende and are more enriched in Fe. No systematic variation is apparent
between rims and cores of hornblende crystals.
Section 6: Discussion
The data presented above offer several implications as to the petrogenetic
processes involved in the generation of the Mono Basin lavas, and their context for the
Long Valley Volcanic Field as a whole. These processes include fractional crystallization
as well as interaction with both mafic intrusions and the felsic Sierra Nevada crust. We
now discuss these aspects in detail.
6.1 Fractional crystallization of the Mono lavas
Chemical trends throughout our sample suite indicate that fractional
crystallization is an important petrogenetic process. Trace elements are generally
positively correlated with SiO2 and Rb in the June Lake and Black Point basalts and the
Mono dome enclaves, with the notable exceptions of V and Sr (Figs. 7, 8c, 10a). It is thus
likely that crystallization of minerals such as titanomagnetite and plagioclase has some
control upon the evolution of the mafic lavas. For magmas of more silicic, dacitic
compositions, plagioclase crystallization continues to play a dominant role, and Sr in turn
continues to decrease (Fig. 10a). Likewise, V contents decrease continually as Rb
44
increases, indicating titanomagnetite crystallization (Fig. 8c). Apatite becomes saturated
in the magmas at around 64 wt.% SiO2 and ~70 ppm Rb, at which point it too begins to
crystallize, as shown by the strong decline in P2O5 concentrations at higher Rb contents
(Fig. 8b). A sharp downturn in Zr contents occurs around 72 wt.% SiO2 and 130 ppm Rb,
so the Paoha Island low-silica rhyolite also appears to have crystallized zircon (Fig. 8d).
The conspicuous depletion of the Mono dome lavas in many major and trace
elements indicates that the system is controlled by the introduction of several important
new mineral phases at high silica contents. Plagioclase is the most prominent mineral in
all but the aphyric domes. Chemically, this is supported by the domes’ strong depletion in
Sr (Fig. 10a). Furthermore, the downturn in K2O concentrations at 71 wt.% SiO2 and
~155 ppm Rb implies that K-feldspar begins crystallizing in the system at this point (Figs.
7a, 8a). Indeed, sanidine is occasionally present in the Mono domes. Similar to the less
silicic lavas of the Mono Basin, the strong P2O5 and V depletions demonstrate apatite and
titanomagnetite crystallization, respectively (Fig. 8b-c). The depletion of Zr content in the
Mono domes implies continued zircon crystallization (Fig. 8d). Zircon may have some
control on LREE concentrations, although as noted by Kelleher and Cameron (1990), it
seems much more likely that allanite crystallization is responsible for the notable
fractionation trends of La and Ce seen in the Mono domes (Fig. 9c-d).
6.2 Basalt-rhyolite and magma-crust interactions in the Mono Basin
The Mono dome enclaves display clear evidence of having been at least partially
molten upon intrusion. They are vesicular, rounded, and have chilled margins (Fig. 2).
Field and petrographic observations of the Mono domes suggest that mingling between
the mafic enclaves and their felsic hosts has occurred. Microscopic inclusions along the
45
enclave-host margin reveal clots of each magma contained within the other (Fig. 6). For
example, while the groundmass glass of the dome 14 andesitic enclaves has 60 wt.%
SiO2, 6 wt.% CaO, and less than 2 wt.% K2O, millimeter-scale globules of rhyolite found
within the enclaves have nearly 77 wt.% SiO2, less than 1 wt.% CaO, and nearly 6 wt.%
K2O (Fig. 12c-d; Table 5).
The presence of basaltic enclaves in the Mono dome rhyolites is a direct line of
evidence of mafic magma interacting with the silicic magma. Some of the enclaves are
intermediate in composition between the host rhyolite and the mafic material; hence this
material likely represents mixing between the Mono dome rhyolites and intruding basalt,
in addition to the magma mingling described above (Fig. 12c-d).
In contrast to the Mono domes, there is no direct evidence of basaltic magma
input beneath Mono Lake. The clots in the Paoha Island lavas are only slightly less silicic
than their host lavas, compared to the Mono dome enclaves (Fig. 12a-b). It may be the
case that Mono Lake magmas are being replenished by intermediate magma, or
alternatively that small volumes of intruding basalt are being mixed efficiently with
larger volumes of Mono Lake dacite.
The pervasive disequilibrium textures visible in plagioclase phenocrysts further
demonstrate that mafic rejuvenation is a common process beneath the Mono Basin. Even
in lavas with no other physical evidence of basaltic recharge, plagioclase phenocrysts
have sieve textures and regrowth rims (Fig. 5). The dissolution of crystals, and their
subsequent regrowth, implies the reheating of the felsic host rock, which in turn implies
intrusion of a hotter, mafic magma. Compositional variation throughout individual
plagioclase crystals and within single lava units supports the hypothesis that
46
disequilibrium is caused by temperature variation rather than pressure changes.
Plagioclase phenocrysts in the Mono Lake lavas exhibit reverse zoning, with more calcic
compositions along their rims and more sodic compositions in their cores; in the Mono
dome enclaves and Mono Lake we also observe bimodal plagioclase populations (Fig.
13b-c). Within enclaves from the Mono domes, the presence of more sodic and sieved
plagioclase xenocrysts and more calcic, less sieved plagioclase phenocrysts provides
further evidence of physical interaction between felsic hosts and mafic intrusions,
including transfer of crystals.
Isotopic data indicate that magma-crust interaction is also an important process in
the evolution of the Mono Basin magmas. While 87
Sr/86
Sr and 143
Nd/144
Nd ratios preserve
mantle signatures in the basalts and mafic enclaves, the silicic rocks of the Mono domes
and Mono Lake have significantly more crustal signatures (Fig. 11a; Table 4). The
mantle signatures of the mafic enclaves suggest that limited chemical exchange occurred
between mafic magmas and host rocks, while the lithospheric signatures of the silicic
rocks suggest that substantial crustal input has occurred throughout the system. This is
reinforced by our Pb and O isotopic data, which have strong crustal signatures (Fig. 11).
Mafic recharge of a felsic magma reservoir is the most likely explanation for the
textures, mineral chemistries, and crustal signatures observed throughout the Mono
domes and Mono Lake. Mafic parental magmas partially melt Sierra Nevada basement
material, which then lies dormant in shallow reservoirs, evolving until intruded by hot
mafic magma. This intrusive magma mixes and mingles with the preexisting, crustal
felsic magma and facilitates its eruption, a process that has been well established in large,
silicic igneous systems (e.g., Sparks et al. 1977; Bailey 2004). The influx of hot magma
47
encourages further partial melting of basement rock, promoting the evolution of silicic
magmas with crustal isotopic signatures. The remaining magmas continue crystallizing
and interacting until the next intrusion of mantle melt, when the process repeats.
6.3 Separate sources of the Mono domes and Mono Lake magmas
While the Mono Lake lavas are generally younger than the Mono domes, they are
also significantly less evolved. In addition to the obvious differences in SiO2 content and
other major elements, the lavas of Paoha and Negit are markedly enriched in trace
elements such as Ba and Sr compared to the Mono domes (Figs. 9-10). With the
exception of one sample from Paoha Island, Mono Lake lavas have lower 143
Nd/144
Nd
and slightly higher 206
Pb/204
Pb than the Mono dome rhyolites (Fig. 11; Table 4).
The eruption of dacites and low-silica rhyolites in Mono Lake is a reversal of the
chemical trend that dominated the Mono Basin for the preceding 60,000 years, in which
successive eruptions were generally more silicic and more evolved than preceding
eruptions. The implication is that even if the deeper, mantle source of the Mono dome
and Mono Lake magmas is the same, each suite represents a different batch of magma
that has been variably affected by basaltic rejuvenation, fractional crystallization, and
crustal contamination, if not storage in entirely separate magma chambers.
Bailey (2004) theorized that the postcaldera dacites erupted within and proximal
to Long Valley caldera, including the Mammoth Mountain dacite and the Mono dacites,
have likely formed from a number of discrete magma batches in separate subsurface
chambers. This is consistent with the chemical and physical diversity noted here between
the Mono dome dacite (dome 12) and the Mono Lake dacites, and the theorized presence
of a magma chamber beneath the Mono Basin separate from the Long Valley caldera
48
chamber (Achauer et al. 1986). The older lavas of each suite (dome 12 for the Mono
domes; Negit Island for Mono Lake) reflect two separate batches of dacitic magma that
were likely formed by fractional crystallization of mantle-sourced basalt and partial
melting of the Sierra Nevada basement.
Furthermore, Negit Island and Paoha Island are themselves potentially the
products of discrete magma batches. All of the Negit lavas have slightly higher 87
Sr/86
Sri
and 206
Pb/204
Pb ratios than the Paoha lavas (Fig. 11b; Table 4). Negit Island also has
pronouncedly lower Nb and Y concentrations (Fig. 9a-b; Table 3). The trace element and
radiogenic isotope signatures together indicate that the Negit flows, arguably the older of
the lavas, were produced from a different felsic magma than the Paoha flows.
The idea that several distinct magma batches were produced and erupted is not
unique to Mono Lake. Indeed, it appears likely to have occurred in the Mono domes as
well, as is supported by chemical evidence. For almost all elements, three individual
clusters of rhyolitic domes can be seen, with notable compositional gaps between each
cluster (Figs. 7-10). These dome clusters do not correspond temporally, meaning that
they cannot reflect the evolution of a single batch of magma. There is no systematic
relationship between the age of a dome cluster and its degree of chemical evolution. The
majority of Mono dome lavas, including the biotite- and fayalite-bearing, sparsely
porphyritic, and aphyric domes, define a continuous array that does not suggest temporal
or spatial patterns. The orthopyroxene- and enclave- bearing domes 14 and 18 are
consistently less evolved than this large array, but are intermediate in age between the
biotite-bearing domes and the other high-silica rhyolites. The least evolved rhyolitic
Mono dome is North Deadman Creek dome, notably the southernmost dome of the chain.
49
Sampson and Cameron (1987) and Bailey (1989) estimated the age of North Deadman
Creek dome to be as old as 6000 years, chronologically between the other two, more
evolved dome clusters. Given the lack of chronological correlation present among the
three Mono dome clusters, they were likely produced by several magma batches
undergoing similar petrogenetic processes.
6.4 Regional context
Wark et al. (2007) provide compelling evidence from quartz cathodoluminescence
and thermometry that the Bishop Tuff eruption was stimulated by mafic recharge of the
Long Valley magma chamber. Early postcaldera silicic lavas, erupted on the floor of
Long Valley caldera from ~0.7 to 0.5 Ma, contain mafic magmatic enclaves similar to
those present in the Mono domes (Bailey 2004). Vesicular, rounded mafic enclaves with
chilled margins also have been reported in the Moat rhyolites (Bailey 2004). The textures
of these enclaves are comparable to those observed for the Mono dome enclaves, and as
such, indicate that mafic rejuvenation of the Long Valley magma system has been an
important process since at least the time of caldera formation. Seismic activity beneath
Long Valley caldera starting in 1980 has also been interpreted as basaltic recharge of the
current Long Valley magma chamber (Hill et al. 1985a; Battaglia et al. 1999; Bailey
2004). The present study indicates that the same process continues beneath the Mono
Basin.
The mafic lavas of the Mono Basin, including the Mono dome enclaves and the
June Lake, Black Point, and Red Cones basalts, exhibit the least radiogenic 87
Sr/86
Sri and
143Nd/
144Nd values of the entire Long Valley Volcanic Field (Fig. 11a). By contrast, Sr
and Nd isotopic signatures in both precaldera and postcaldera mafic lavas resemble the
50
Sierra Nevada crust (Fig. 11; Table 6; Van Kooten 1981; Cousens 1996). There is a
striking difference in 206
Pb/204
Pb between precaldera and postcaldera mafic lavas, with
postcaldera basalts and andesites tending towards higher values, hence more pronounced
levels of crustal contamination (Fig. 11b). The marked difference between mafic material
erupted in and around Long Valley and mafic material in the Mono Basin may indicate
that extracaldera mantle melts are being brought to the surface more efficiently than in
Long Valley, and that their crustal residence time is shorter. In comparison, the silicic
Mono Basin lavas exhibit 87
Sr/86
Sri and 143
Nd/144
Nd values comparable to Glass
Mountain and the Bishop Tuff (Fig. 11a; Tables 4, 6; Cousens 1996). This similarity
suggests that the processes affecting the Mono Basin dacites and rhyolites are similar to
those that affected the high-silica precaldera and caldera-forming magmas.
It remains uncertain whether a distinct magma chamber underlies Mono Lake, as
has been suggested by Achauer et al. (1986). However, it is evident that the Mono domes
and Mono Lake lavas are derived from disparate and discrete magma batches, as
proposed by Hildreth (2004). The full extent of interaction between the Long Valley and
Mono Basin systems is unclear. There is little evidence of Long Valley magma having
migrated north to beneath the Mono Basin. The occurrence of Mono domes as far south
as Wilson Butte and North Deadman Creek Dome, however, supports the theory of Sieh
and Bursik (1986) and Varga et al. (1990) that Mono-type magma is one component of
the most recent Inyo eruptions, in addition to Mammoth Mountain magma and what little
mobile material remains in the Long Valley magma chamber.
51
Section 7: Conclusions
Our field and petrographic observations made throughout the study area are
consistent with mafic recharge playing an important role in the genesis and evolution of
silicic magmas in the Mono Basin. In the case of the Mono domes, the felsic reservoir
may be the Mono Basin magma chamber first proposed by Achauer et al. (1986). In the
case of the Mono Lake lavas, the felsic reservoir must have been either a separate batch
of less evolved magma within the Mono Basin chamber or, more likely, dacite stored in
an as-yet unmapped chamber (or chambers) beneath Mono Lake. Variable amounts of
partial melting of the Sierra Nevada crust, fractional crystallization, and magma mixing
and mingling have generated the chemical variations observed for the silicic rocks of the
Mono Basin.
In terms of future magmatic unrest at the Long Valley Volcanic Field, current
seismic and geodetic unrest suggests that mafic recharge in the south moat of the caldera
has the potential, however unlikely, to cause an eruption (Hill et al. 1985a; Bailey 2004).
A more probable scenario is that future activity will occur in the Mono Basin, the site of
all Long Valley-related volcanic activity for the past 60,000 years and the location of
periodic yet continued input of mafic magma. This region has a lengthy history of
explosive and effusive volcanism involving high-silica magmas. Moreover, Mono Lake
increasingly has been the focus of Mono Basin volcanism, adding a likely
phreatomagmatic component to future volcanic activity.
52
Section 8: Major conclusions and suggestions for future work
The most salient findings of our research are as follows:
1. It is likely that magma genesis and eruption throughout the Mono Basin is
influenced by repeated intrusion of mafic mantle melts. In the Mono domes, clear
evidence of basaltic input into the system is provided by the presence of mafic
glasses and mafic enclaves. Evidence of mafic rejuvenation is more obscure in the
Mono Lake lavas, but the occurrence of clots of material that is less silicic than
the host dacites and rhyolites, as well as reversely zoned and sieved plagioclase
crystals, indicate either magma chamber recharge by an intermediate magma or
efficient mixing of Mono Lake dacite with small volumes of intruding basalt.
2. Differences in major element, trace element, and isotopic geochemistry of the
Mono Basin lavas signify either residence of parental magmas in separate magma
chambers and/or the production of several different batches of magma in a single
chamber.
3. Chemical differences within the Mono domes and between Negit Island and
Paoha Island suggest that, in addition to being sourced by disparate magmas, each
suite is in turn composed of the products of multiple magma batches that have
been influenced by varied amounts of fractional crystallization and interaction
with mafic magma intrusions and the Sierra Nevada crust.
4. The mafic lavas and enclaves of the Mono Basin represent the least radiogenic
magmas in the entire Long Valley Volcanic Field. Mantle melts are thus either
transported more efficiently or more quickly to the surface outside the caldera.
53
Much remains to be learned about the processes currently affecting the Long
Valley Volcanic Field. Our examination of the Mono Lake lavas and the mafic enclave
populations in the Mono domes is the most thorough study to date of these youthful
lavas. Similarly textured enclaves have been noted in the Early and Moat rhyolites by
Bailey (2004), but no analysis of these enclaves has been made. Considering the uniquely
mantle-like isotopic signatures of the Mono dome enclaves, the enclaves hosted in
intracaldera rhyolites could yield significant insight for our understanding of the past and
present state of Long Valley caldera.
The compilation of isotope analyses of Long Valley volcanic rocks presented here
underscores the need to examine multiple isotope systems. Given the lens that isotopes
provide into petrogenetic processes, a systematic approach to geochemical studies of
Long Valley caldera and the Mono Basin should yield beneficial insights into the future
of magmatic and volcanic activity in the Long Valley Volcanic Field.
The study of Achauer et al. (1986) was an important first step in assessing
whether a magma chamber exists beneath the Mono Basin. The results of the teleseismic
survey discussed therein have yet to be replicated by other researchers. The extensive
suite of geochemical data presented in this study provides compositional evidence
supporting the existence of this hypothesized magma chamber, and a better understanding
of its physical parameters would greatly augment our ability to assess the hazards and
risks posed by volcanism in the Mono Basin. Similar work in Mono Lake is necessary to
confirm whether the Mono Lake lavas are the products of a discrete magma system, as
has been suggested here.
54
References
Achauer, U., Greene, L., Evans, J.R., and Iyer, H.M. (1986). Nature of the magma
chamber underlying the Mono Craters area, eastern California, as determined
from teleseismic travel time residuals. Journal of Geophysical Research 91,
13873-13891.
Bailey, R.A. (1983). Mammoth Lakes earthquakes and ground uplift: precursors to
possible volcanic activity? Eathquake Information Bulletin 15, 88-101.
Bailey, R.A. (1989). Geologic map of Long Valley caldera, Mono-Inyo Craters volcanic
chain, and vicinity, eastern California. U.S. Geological Survey Miscellaneous
Investigations Series Map I-1933, 11 pp., scale 1:62,500, 2 sheets.
Bailey, R.A. (2004). Eruptive history and chemical evolution of the precaldera and
postcaldera basalt-dacite sequences, Long Valley, California: implications for
magma sources, current seismic unrest, and future volcanism. U.S. Geological
Survey Professional Paper 1692, 76 pp.
Bailey, R.A., Dalrymple, G.B., and Lanphere, M.A. (1976). Volcanism, structure, and
geochronology of Long Valley caldera, Mono County, California. Journal of
Geophysical Research 81, 725-744.
Bailey, R.A. and Hill, D.P. (1990). Magmatic unrest at Long Valley caldera, California,
1980-1990. Geoscience Canada 17, 175-179.
Battaglia, M., Roberts, C., and Segall, P. (1999). Magma intrusion beneath Long Valley
caldera confirmed by temporal changes in gravity. Science 285, 2119-2122.
Bindeman, I. (2008). Oxygen isotopes in mantle and crustal magmas as revealed by
single crystal analysis. Reviews in Mineralogy and Geochemistry 69, 445-478.
55
Bursik, M. and Sieh, K.E. (1989). Range front faulting and volcanism in the Mono Basin,
eastern California. Journal of Geophysical Research 94, 15587-15609.
Bursik, M.I. and Gillespie, A.R. (1993). Late Pleistocene glaciation of Mono Basin,
California. Quaternary Research 39, 24-35.
Bursik, M., Renshaw, C., McCalpin, J., and Berry, M. (2003). A volcanotectonic cascade:
activation of range front faulting and eruptions by dike intrusion, Mono Basin-
Long Valley caldera, California. Journal of Geophysical Research 108, 2393.
doi: 10.1029/2002JB002032.
Chaudet, R.E. (1986). The petrology and geochemistry of precaldera magmas, Long
Valley caldera, eastern California. Blacksburg, Virginia Polytechnic Institute,
M.Sc. thesis, 34 pp.
Christensen, J.N. and DePaolo, D.J. (1993). Time scales of large volume silicic magma
systems: Sr isotopic systematics of phenocrysts and glass from the Bishop Tuff,
Long Valley, California. Contributions to Mineralogy and Petrology 113, 100-
114.
Clayton, R.N. and Mayeda, T.K. (1963). The use of bromine pentafluoride in the
extraction of oxygen from oxides and silicates for isotopic analysis. Geochimica
et Cosmochimica Acta 27, 43-52.
Cousens, B.L. (1996). Magmatic evolution of Quaternary mafic magmas at Long Valley
caldera and the Devils Postpile, California: effects of crustal contamination on the
lithospheric mantle-derived magmas. Journal of Geophysical Research 101,
27673-27689.
Davies, G.R. and Halliday, A.N. (1998). Development of the Long Valley rhyolitic
56
magma system: strontium and neodymium isotope evidence from glasses and
individual phenocrysts. Geochimica et Cosmochimica Acta 62, 3561-3574.
Devine, J.D., Gardner, J.E., Brack, H.P., Layne, G.D., and Rutherford, M.J. (1995).
Comparison of microanalytical methods for estimating H2O contents of silicic
volcanic glasses. American Mineralogist 80, 319-328.
Ducea, M. and Saleeby, J. (1998a). Crustal recycling beneath continental arcs: silica-rich
glass inclusions in ultramafic xenoliths from the Sierra Nevada, California. Earth
and Planetary Science Letters 156, 101-116.
Ducea, M. and Saleeby, J. (1998b). A case for delamination of the deep batholithic crust
beneath the Sierra Nevada, California. International Geology Review 40, 78-93.
Ewert, J.W. and Harpel, C.J. (2000). Bibliography of literature pertaining to Long Valley
caldera and associated volcanic fields. U.S. Geological Survey Open File Report
00-221, 156 pp.
Farmer, G.L., Glazner, A.F., and Manley, C.R. (2002). Did lithospheric delamination
trigger late Cenozoic potassic volcanism in the southern Sierra Nevada,
California? Geological Society of America Bulletin 114, 754-768.
Gilbert, C.M., Christensen, M.N., Al-Rawi, Y., and Lajoie, K.R. (1968). Structural and
volcanic history of Mono Basin, California-Nevada. In Coats, R.R., ed., Studies in
volcanology: a memoir in honor of Howel Williams. Geological Society of
America Memoir 116, 275-329.
Halliday, A.N., Fallick, A.E., Hutchinson, J., and Hildreth, W. (1984). A Nd, Sr and O
isotopic investigation into the causes of chemical and isotopic zonation in the
Bishop Tuff, California. Earth and Planetary Sciences Letters 68, 379-391.
57
Heumann, A. and Davies, G.R. (1997). Isotopic and chemical evolution of the post-
caldera rhyolitic system at Long Valley, California. Journal of Petrology 38,
1661-1678.
Hildreth, W. (1979). The Bishop Tuff: evidence for the origin of compositional zoning in
silicic magma chambers. In Chapin, C.E. and Elston, W.E., eds., Ash-flow tuffs.
Geological Society of America Special Paper 180, 43-72.
Hildreth, W. (2004). Volcanological perspectives on Long Valley, Mammoth Mountain,
and Mono Craters: several contiguous but discrete systems. Journal of
Volcanology and Geothermal Research 136, 169-198.
Hildreth, W., Fierstein, J., Calvert, A.T., and Champion, D.E. (2013). Eruptive history of
Mammoth Mountain and its mafic periphery, Abstract V11D-06: 2013 Fall
Meeting, AGU, San Francisco, CA, 9-13 Dec, 2013.
Hill, D.P., Bailey, R.A., and Ryall, A.S. (1985a). Active tectonic and magmatic processes
beneath Long Valley caldera, eastern California: an overview. Journal of
Geophysical Research 90, 11111-11120.
Hill, D.P., Wallace, R.E., and Cockerham, R.S. (1985b). Review of evidence on the
potential for major earthquakes and volcanism in the Long Valley-Mono Craters-
White Mountains region of eastern California. Earthquake Prediction Research 3,
571-594.
Holohan, E.P., Troll, V.R., van Wyk de Vries, B., Walsh, J.J., and Walter, T.R. (2008).
Unzipping Long Valley: an explanation for vent migration patterns during an
elliptical ring fracture eruption. Geology 36, 323-326.
Johnson, D.M., Hooper, P.R., and Conrey, R.M. (1999). XRF analysis of rocks and
58
minerals for major and trace elements on a single low dilution Li-tetraborate fused
bead. JCPDS – International Centre for Diffraction Data.
Kelleher, P.C. (1986). The Mono Craters-Mono Lake islands volcanic complex, eastern
California: evidence for several magma types, magma mixing, and a
heterogeneous source region. Santa Cruz, University of California, M.Sc. thesis,
110 pp.
Kelleher, P.C. and Cameron, K.L. (1990). The geochemistry of the Mono Craters-Mono
Lake volcanic complex, eastern California. Journal of Geophysical Research 95,
17643-17659.
Lajoie, K.R. (1968). Late Quaternary stratigraphy and geologic history of Mono Basin,
eastern California. Berkeley, University of California, Ph.D. thesis, 271 pp.
Lange, R.B., Carmichael, I.S.E., and Renne, P.R. (1993). Potassic volcanism near Mono
Basin, California: evidence for high water and oxygen fugacities inherited from
subduction. Geology 21, 949-952.
Mahood, G.A., Ring, J.H., Manganelli, S., and McWilliams, M.O. (2010). New 40
Ar/39
Ar
ages reveal contemporaneous mafic and silicic eruptions during the past 160,000
years at Mammoth Mountain and Long Valley caldera, California. Geological
Society of America Bulletin 122, 396-407.
Manley, C.R., Glazner, A.F., and Farmer, G.L. (2000). Timing of volcanism in the Sierra
Nevada of California: evidence for Pliocene delamination of the batholithic root?
Geology 28, 811-814.
Metz, J.M. and Bailey, R.A. (1993). Geologic map of Glass Mountain, Mono County,
California. U.S. Geological Survey Miscellaneous Investigations Series Map I-
59
1995, scale 1:24,000.
Metz, J.M. and Mahood, G.A. (1985). Precursors of the Bishop Tuff eruption: Glass
Mountain, Long Valley caldera, California. Journal of Geophysical Research 90,
11121-11126.
Metz, J.M. and Mahood, G.A. (1991). Development of the Long Valley, California,
magma chamber recorded in precaldera rhyolite lavas of Glass Mountain.
Contribution to Mineralogy and Petrology 106, 379-397.
Miller, C.D. (1985). Holocene eruptions of the Inyo Volcanic Chain, California:
implications for possible eruptions in Long Valley caldera. Geology 13, 14-17.
Muffler, L.J.P. and Williams, D.L. (1976). Geothermal investigations of the U.S.
Geological Survey in Long Valley, Calfornia. Journal of Geophysical Research
81, 721-724.
Ormerod, D.S. (1988). Late- to post-subduction magmatic transitions in the western
Great Basin, U.S.A. Milton Keynes, The Open University, Ph.D. thesis, 331 pp.
Pakiser, L.C. (1970). Structure of Mono Basin, California. Journal of Geophysical
Research 75, 4077-4080.
Sampson, D.E. and Cameron, K.L. (1987). The geochemistry of the Inyo volcanic chain:
multiple magma systems in the Long Valley region, eastern California. Journal of
Geophysical Research 92, 10403-10421.
Sieh, K.E. and Bursik, M.I. (1986). Most recent eruption of the Mono Craters, eastern
Central California. Journal of Geophysical Research 91, 12539-12571.
Smith, G. (1993). Mammoth Lakes Sierra: handbook for road and trailside. Mammoth
Lakes, Genny Smith Books, 220 pp.
60
Sparks, R.J.S., Sigurdsson, H., and Wilson, L. (1977). Magma mixing: a mechanism for
triggering acid explosive eruptions. Nature 267, 315-318.
“Sr-Nd-Pb-U-Th isotope procedures.” Isotope Geochemistry and Geochronology
Research Centre. 2012. <http://www.carleton.ca/iggrc/>.
Stern, T.W., Bateman, P.C., Morgan, B.A., Newell, M.F., and Peck, D.L. (1981). Isotopic
U-Pb ages of zircon from the granitoids of the central Sierra Nevada, California.
U.S. Geological Survey Professional Paper 1185, 22 pp.
Stine, S. (1987). Mono Lake: the past 4000 years. Berkeley, University of California,
Ph.D. thesis, 615 pp.
Stix, J., Gauthier, G., and Ludden, J.N. (1995). A critical look at quantitative laser-
ablation ICP-MS analysis of natural and synthetic glasses. The Canadian
Mineralogist 33, 435-444.
Tierney, T. (2000). Geology of the Mono Basin. Lee Vining, Kutsavi Press, Mono Lake
Committee, 73 pp.
Twain, M. (1872). Roughing It. Hartford American Publishing Company, 607 pp.
Van Kooten, G.K. (1981). Pb and Sr systematics of ultrapotassic and basaltic rocks from
the central Sierra Nevada, California. Contributions to Mineralogy and Petrology
76, 378-385.
Varga, R.J., Bailey, R.A., and Suemnicht, G.A. (1990). Evidence for 600 year-old basalt
and magma mixing at Inyo Craters volcanic chain, Long Valley caldera,
California. Journal of Geophysical Research 95, 21441-21450.
Vazquez, J.A. and Lidzbarski, M.I. (2012). High-resolution tephrochronology of the
Wilson Creek Formation (Mono Lake, California) and Laschamp event using
61
238
U-230
Th SIMS dating of accessory mineral rims. Earth and Planetary Science
Letters 357-358, 54-67.
Wark, D.A., Hildreth, W., Spear, F.S., Cherniak, D.J., and Watson, E.B. (2007). Pre-
eruption recharge of the Bishop magma system. Geology 35, 235-238.
White, J.D.L. (2000). Subaqueous eruption-fed density currents and their deposits.
Precambrian Research 101, 87-109.
Wilson, C.J.N. and Hildreth, W. (1997). The Bishop Tuff: new insights from eruptive
stratigraphy. Journal of Geology 105, 407-439.
Wood, S.H. (1983). Chronology of late Pleistocene and Holocene volcanics, Long Valley
and Mono Basin geothermal areas, eastern California. U.S. Geological Survey
Open-File Report 83-747, 84 pp.
62
Table 1: Mono Basin samples from the 2011
and 2012 field seasons. Sample
Number
Magma
group
UTM Coordinates
(WGS ’84 datum) Locality Rock type
BB-2011-01 Negit Island
11S
0321345/4211192 Norway Island
sparsely porphyritic
rhyolite
BB-2011-02 Negit Island
11S
0320829/4211181 Tahiti Island
sparsely porphyritic, flow
banded dacite
BB-2011-03 Negit Island
11S
0320985/4211108 Tahiti Island
sparsely porphyritic, flow
banded dacite
BB-2011-04 Mono domes
11S
0322636/4195314
Mono dome 13
(North Coulée) aphyric rhyolite
BB-2011-
04b Mono domes
11S
0322377/4195303
Mono dome 13
(North Coulée) breccia
BB-2011-05 Mono domes
11S
0322199/4195444 Mono dome 14
orthopyroxene- and
enclave-bearing rhyolite
BB-2011-
05b
Dome 14
enclaves
11S
0322199/4195444 Mono dome 14 mafic enclaves
BB-2011-06 Mono domes
11S
0321305/4196207 Mono dome 12 enclave-bearing dacite
BB-2011-07 Mono domes
11S
0320836/4198805 Mono dome 6 fayalite-bearing rhyolite
BB-2011-08 Mono domes
11S
0321078/4198661 Mono dome 7 aphyric rhyolite
BB-2011-09 Paoha Island
11S
0322513/4207227
Paoha Island (east
dacite flow) peperite
BB-2011-10 Paoha Island
11S
0322569/4207300
Paoha Island (east
dacite flow)
sparsely porphyritic
dacite
BB-2011-11 Paoha Island
11S
0322287/4207052
Paoha Island (east
dacite flow) grey dacite in peperite
BB-2011-
11b Paoha Island
11S
0322287/4207052
Paoha Island (east
dacite flow) black dacite in peperite
BB-2011-
11c Paoha Island
11S
0322287/4207052
Paoha Island (east
dacite flow) peperite
BB-2011-12 Paoha Island
11S
0322458/4208935
Paoha Island
(northeast cinder
cones)
sparsely porphyritic
dacite
BB-2011-
12b Paoha Island
11S
0322458/4208935
Paoha Island
(northeast cinder
cones) dacitic scoria
BB-2011-13 Paoha Island
11S
0322273/4209031
Paoha Island
(northeast cinder
cones) dacitic bomb
63
Table 1 (continued)
Sample
Number Magma group
UTM Coordinates
(WGS ’84 datum) Locality Rock type
BB-2011-14 Mono domes 11S 0321591/4176223
North Deadman
Creek Dome
enclave-bearing
rhyolite
BB-2011-14b
N. Deadman
Creek enclaves 11S 0321591/4176223
North Deadman
Creek Dome mafic enclaves
BB-2011-15 Inyo domes 11S 0322210/4176138
South Deadman
Creek Dome
coarse-grained
rhyolite
BB-2011-15b Inyo domes 11S 0322210/4176138
South Deadman
Creek Dome
fine-grained
rhyolite
BB-2011-15c Inyo enclaves 11S 0322210/4176138
South Deadman
Creek Dome mafic enclaves
BB-2011-16 Paoha Island 11S 0321501/4209348
Paoha Island
(Lunacy Point)
sparsely
porphyritic dacite
BB-2011-17 Paoha Island 11S 0320844/4208752
Paoha Island (west
rhyolite flow)
sparsely
porphyritic
rhyolite
BB-2011-18 Negit Island 11S 0320116/4209814
Negit Island (east
dacite flow)
sparsely
porphyritic dacite
BB-2011-19 Negit Island 11S 0319934/4209903
Negit Island (cinder
cone) dacitic scoria
BB-2011-20 Mono domes 11S 0321937/4183577 Wilson Butte
sparsely
porphyritic
rhyolite
BB-2011-20b - 11S 0321937/4183577 Wilson Butte xenoliths
BB-2011-21 Basalt 11S 0318272/4185971
June Lake cinder
cone
oxidized vent
breccia
BB-2011-22 Basalt 11S 0318310/4188377 June Lake basalt basalt
BB-2011-23 Negit Island 11S 0314795/4205740
Mono Lake
shoreline pumice
BB-2011-24 Basalt 11S 0315244/4210530 Black Point degassed basalt
BB-2011-24b - 11S 0315244/4210530 Black Point vesicular basalt
64
Table 1 (continued)
Sample
Number Magma group
UTM Coordinates
(WGS ’84 datum) Locality Rock type
BB-2011-24c - 11S 0315244/4210530 Black Point pumices
BB-2011-24d - 11S 0315244/4210530 Black Point sedimentary matrix
BB-2011-24e - 11S 0315244/4210530 Black Point fine, sandy layer
BB-2012-01 - 11S 0345948/4180113 Glass Mountain rhyolite
BB-2012-01b - 11S 0345948/4180113 Glass Mountain xenoliths
BB-2012-02 Mono domes 11S 0322262/4195540 Mono dome 14
orthopyroxene- and
enclave-bearing rhyolite
BB-2012-02b
Dome 14
enclaves 11S 0322262/4195540 Mono dome 14 mafic enclaves
BB-2012-03 Mono domes 11S 0321340/4196196 Mono dome 12 enclave-bearing dacite
BB-2012-03b
Dome 12
enclaves 11S 0321340/4196196 Mono dome 12 mafic enclaves
BB-2012-04 Mono domes 11S 0321865/4176572
North Deadman
Creek Dome enclave-bearing rhyolite
BB-2012-04b
N. Deadman
Creek enclaves 11S 0321865/4176572
North Deadman
Creek Dome mafic enclaves
BB-2012-05 Mono domes - Mono dome 18
orthopyroxene- and
enclave-bearing rhyolite
BB-2012-05b
Dome 18
enclaves - Mono dome 18 mafic enclaves
BB-2012-06 Mono domes 11S 0320260/4199922 Mono dome 3 aphyric rhyolite
BB-2012-06b Mono domes 11S 0320260/4199922 Mono dome 3 breadcrust bomb
BB-2012-06c Mono domes 11S 0320260/4199922 Mono dome 3 obsidian
65
Table 1 (continued)
Sample
Number
Magma
group
UTM Coordinates
(WGS ’84 datum) Locality Rock type
BB-2012-07
Mono
domes 11S 0320485/4199437 Mono dome 4 aphyric rhyolite
BB-2012-08
Mono
domes 11S 0321801/4183976 Wilson Butte
sparsely porphyritic
rhyolite
BB-2012-08b - 11S 0321801/4183976 Wilson Butte xenoliths
BB-2012-09 - 11S 0342840/4179773
Intracaldera dacite
dome porphyritic dacite
BB-2012-09b - 11S 0342840/4179773
Intracaldera dacite
dome columnar dacite
BB-2012-10
Mono
domes 11S 0321639/4199224 Mono dome 5 aphyric rhyolite
BB-2012-11
Mono
domes 11S 0323738/4190283
Mono dome 22
(South Coulée) aphyric rhyolite
BB-2012-11b
Mono
domes 11S 0323738/4190283
Mono dome 22
(South Coulée) obsidian
BB-2012-11c
Mono
domes 11S 0323738/4190283
Mono dome 22
(South Coulée) pumice
BB-2012-12
Paoha
Island 11S 0322289/4207031
Paoha Island (east
dacite flow) peperite sediment layer
BB-2012-12b
Paoha
Island 11S 0322289/4207031
Paoha Island (east
dacite flow)
peperite dacite inclusions
in sediment layer
BB-2012-12c
Paoha
Island 11S 0322289/4207031
Paoha Island (east
dacite flow) peperite dacite layer
BB-2012-13
Paoha
Island 11S 0322311/4207325
Paoha Island
(eastern shoreline) Paoha Island sediment
BB-2012-14
Negit
Island 11S 0320302/4210218
Negit Island (north
dacite flow) sparsely porphyritic dacite
BB-2012-14b
Negit
Island 11S 0320302/4210218
Negit Island (north
dacite flow) sparsely porphyritic dacite
BB-2012-15
Negit
Island 11S 0320043/4209970
Negit Island (cinder
cone) sparsely porphyritic dacite
66
Table 1 (continued)
Sample Number
Magma
group
UTM Coordinates (WGS
’84 datum) Locality Rock type
BB-2012-15b
Negit
Island 11S 0320043/4209970
Negit Island
(cinder cone) dacitic bombs
BB-2012-16
Mono
domes 11S 0321147/4187050 Mono dome 30
fayalite-
bearingrhyolite
BB-2012-17
Mono
domes 11S 0321604/4187195 Mono dome 29
fayalite-
bearingrhyolite
BB-2012-18
Mono
domes 11S 0321796/4187441 Mono dome 28
fayalite-bearing
rhyolite
BB-2012-18b - 11S 0321796/4187441 Mono dome 28 xenoliths
BB-2012-19
Mono
domes 11S 0322473/4187760 Mono dome 27
fayalite-bearing
rhyolite
BB-2012-20
Mono
domes 11S 0322947/4189213 Mono dome 25
fayalite-bearing
rhyolite
BB-2012-21
Mono
domes 11S 0322681/4189219 Mono dome 26
sparsely porphyritic
rhyolite
BB-2012-21b - 11S 0322681/4189219 Mono dome 26 xenoliths
BB-2012-22
Mono
domes 11S 0323162/4189746 Mono dome 23
sparsely porphyritic
rhyolite
BB-2012-23
Mono
domes 11S 0322531/4198256 Mono dome 9
sparsely porphyritic
rhyolite
BB-2012-24
Mono
domes 11S 0322299/4198350 Mono dome 8 aphyric rhyolite
BB-2012-25
Mono
domes 11S 0323560/4192222 Mono dome 20
fayalite-bearing
rhyolite
BB-2012-26
Mono
domes 11S 0322608/4193567 Mono dome 19
biotite-bearing
rhyolite
BB-2012-27
Mono
domes 11S 0323467/4193790 Mono dome 17
fayalite-bearing
rhyolite
BB-2012-27b - 11S 0323467/4193790 Mono dome 17 xenoliths
67
Table 2a: Comparison of XRF measured values with accepted UTR-2 values of Stix et
al. (1995).
Sample UTR-2011-1 UTR-2011-2 UTR-2011-3 UTR-2011 average UTRAccepted % diff.
SiO2 74.18 73.58 73.74 73.83 74.16 0.44
TiO2 0.22 0.22 0.22 0.22 0.24 7.66
Al2O3 10.26 10.17 10.21 10.22 10.44 2.15
FeOT 4.09 4.09 4.06 4.08 4.43 7.88
MnO 0.09 0.09 0.09 0.09 0.09 -0.57
MgO 0.00 0.00 0.00 0.00 0.05 100.00
CaO 0.18 0.18 0.18 0.18 0.18 1.07
Na2O 5.54 5.47 5.51 5.51 5.52 0.26
K2O 4.35 4.32 4.33 4.33 4.39 1.30
P2O5 0.01 0.01 0.01 0.01 0.01 15.13
Total 98.89 98.11 98.35 98.45 99.51 1.06
Ba 13 11 12 12
Ce 175 174 170 173 179 3
Cr 41 44 43 43
Cu 3 2 3 3 5 47
Ga 33 34 34 33
La 78 80 80 79 79 0
Nb 79 79 81 79 91 13
Nd 80 79 78 79 81 2
Ni 4 3 4 4 3 -22
Pb 25 27 25 26 25 -3
Rb 131 131 131 131 137 4
Sc 1 0 1 1 0 -333
Sr 1 1 2 1 1 0
Th 17 16 17 17 17 2
U 5 4 5 5 4 -8
V 1 3 2 2
Y 121 121 121 121 126 4
Zn 218 215 214 216 200 -8
Zr 1018 1013 1017 1016 1174 13
68
Table 2a (continued)
Sample UTR-2012-1 UTR-2012-2 UTR-2012-3 UTR-2012 average UTRAccepted % diff.
SiO2 74.15 74.25 74.47 74.29 74.16 -0.17
TiO2 0.23 0.22 0.22 0.23 0.24 5.72
Al2O3 10.32 10.32 10.34 10.32 10.44 1.11
FeOT 4.21 4.20 4.12 4.18 4.43 5.72
MnO 0.09 0.09 0.09 0.09 0.09 -1.21
MgO 0.13 0.00 0.00 0.04 0.05 10.73
CaO 0.23 0.18 0.18 0.20 0.18 -9.58
Na2O 5.48 5.52 5.55 5.52 5.52 0.06
K2O 4.34 4.36 4.39 4.36 4.39 0.61
P2O5 0.01 0.01 0.01 0.01 0.01 11.36
Total 99.20 99.13 99.36 99.23 99.51 0.28
Ba 11 12 13 12
Ce 168 175 172 172 179 4
Cr 52 44 42 46
Cu 5 5 5 5 5 2
Ga 33 33 33 33
La 79 82 83 81 79 -3
Nb 79 79 79 79 91 13
Nd 79 80 80 80 81 2
Ni 10 3 2 5 3 -59
Pb 25 25 25 25 25 -1
Rb 131 132 132 132 137 4
Sc 1 0 0 0 0.2 -68
Sr 3 1 1 2 1.4 -17
Th 17 17 17 17 17 0
U 4 5 4 4 4.4 0
V 5 2 0 2
Y 120 121 122 121 126 4
Zn 215 213 216 215 200 -7
Zr 1014 1016 1020 1016 1174 13
69
Table 2b: Comparison of acid-washed and unwashed samples from Mono Lake and the
Mono domes.
Sample BB-2011-02cleaned BB-2011-02
%
diff. BB-2011-15cleaned BB-2011-15
%
diff.
SiO2 68.81 68.56 -0.37
70.73 70.06 -0.95
TiO2 0.43 0.41 -4.47
0.42 0.42 -1.75
Al2O3 15.80 15.66 -0.95
14.56 14.27 -2.01
FeOT 2.83 2.76 -2.52
2.30 2.21 -4.40
MnO 0.07 0.07 -0.43
0.06 0.06 -3.13
MgO 0.56 0.54 -4.13
0.68 0.64 -6.26
CaO 1.95 1.90 -2.60
1.85 1.76 -5.39
Na2O 4.71 4.68 -0.68
4.32 4.27 -1.20
K2O 4.39 4.43 0.89
4.14 4.19 1.21
P2O5 0.13 0.13 -3.68
0.12 0.12 -0.26
Total 99.68 99.13 -0.56
99.19 97.99 -1.22
Ba 1218 1195 -2
708 793 11
Ce 84 83 -1
66 74 11
Cr 3 1 -143
5 6 14
Cu 3 4 25
3 7 63
Ga 19 19 -3
18 18 -1
La 46 47 2
38 46 17
Nb 14 15 6
17 16 -4
Nd 31 30 -5
23 24 2
Ni 3 2 -13
5 4 -12
Pb 23 24 5
26 25 -2
Rb 102 103 1
114 112 -2
Sc 5 4 -25
4 4 -5
Sr 303 291 -4
273 265 -3
Th 10 11 10
13 13 -2
U 3 2 -27
4 4 0
V 14 13 -7
28 26 -9
Y 19 20 5
17 16 -9
Zn 62 61 -2
50 45 -10
Zr 312 314 1 224 216 -4
70
Table 2c: Comparison of measured values for M3N, PCD glass stds. relative to values of Devine et al. (1995).
Sample M3N1 M3N2 M3N3 M3N4 M3N5 M3N6 M3N7 M3N8 M3N9 M3N10 M3N11 M3N avg. M3NAccepted % diff.
SiO2 70.42 70.99 71.20 70.70 70.14 70.56 70.48 71.07 70.62 70.82 70.93 70.72 71.38 0.93
TiO2 0.28 0.24 0.28 0.24 0.27 0.29 0.24 0.30 0.20 0.36 0.29 0.27 0.26 -4.69
Al2O3 13.05 12.95 12.96 12.99 13.06 12.92 13.04 13.24 13.20 13.03 13.05 13.04 13.05 0.04
FeOT 1.65 1.54 1.52 1.56 1.53 1.61 1.68 1.68 1.57 1.67 1.62 1.60 1.56 -2.63
MnO 0.29 0.25 0.28 0.27 0.27 0.26 0.23 0.27 0.27 0.26 0.24 0.26 0.29 9.72
MgO 1.18 1.18 1.15 1.33 1.25 1.20 1.18 1.16 1.22 1.13 1.23 1.20 1.19 -0.86
K2O 3.96 4.06 3.94 3.95 4.10 3.81 4.03 4.23 4.12 4.06 4.02 4.03 4.06 0.85
Na2O 4.20 4.10 4.35 4.31 4.10 4.14 4.22 4.21 4.29 4.14 4.15 4.20 4.11 -2.21
CaO 0.06 0.05 0.01 0.04 0.03 0.03 0.00 0.05 0.05 0.04 0.04 0.04 0.02 -76.36
P2O5 0.00 0.05 0.02 0.03 0.00 0.04 0.05 0.06 0.06 0.04 0.01 0.03
Total 95.07 95.41 95.70 95.40 94.74 94.84 95.15 96.27 95.60 95.56 95.57 95.39 95.92 0.55
Sample PCD1 PCD3 PCD4 PCD5 PCD6 PCD7 PCD8 PCD9 PCD10 PCD11 PCD avg. PCDAccepted % diff.
SiO2 76.44 76.99 76.46 75.27 75.62 74.87 76.08 75.95 75.77 75.75 75.92 76.40 0.63
TiO2 0.08 0.09 0.06 0.02 0.06 0.08 0.03 0.03 0.04 0.08 0.06 0.07 20.57
Al2O3 12.46 12.28 12.40 12.56 12.46 12.39 12.72 12.53 12.55 12.59 12.49 12.44 -0.44
FeOT 0.98 1.05 0.93 0.85 0.96 0.97 1.01 1.02 0.97 0.99 0.97 1.02 4.73
MnO 0.05 0.04 0.02 0.05 0.01 0.02 0.01 0.02 0.03 0.04 0.03 0.02 -39.50
MgO 0.54 0.51 0.54 0.53 0.55 0.52 0.55 0.56 0.56 0.49 0.53 0.53 -0.81
K2O 4.07 4.04 4.05 4.14 3.96 3.91 4.22 4.10 4.11 4.16 4.08 4.21 3.19
Na2O 4.77 4.74 4.66 4.69 4.59 4.65 4.76 4.67 4.78 4.61 4.69 4.68 -0.22
CaO 0.02 0.04 0.01 0.05 0.07 0.04 0.05 0.04 0.07 0.06 0.04 0.03 -45.67
P2O5 0.00 0.00 0.03 0.00 0.03 0.05 0.00 0.00 0.00 0.00 0.01
Total 99.41 99.75 99.16 98.15 98.31 97.51 99.42 98.91 98.87 98.75 98.82 99.40 0.58
71
Table 2d: Comparison of measured values for Amelia albite plagioclase standard values reported by C.M. Taylor Company (2013).
Sample ameliaalbite1 ameliaalbite2 ameliaalbite3 ameliaalbite4 ameliaalbite5 ameliaalbite avg. Amelia albite accepted % diff.
SiO2 67.82 68.30 68.33 68.90 67.76 68.22 68.14 -0.12
Al2O3 19.80 19.97 19.32 19.46 19.62 19.63 19.76 0.64
FeOT 0.00 0.01 0.02 0.00 0.00 0.01
MgO 0.00 0.00 0.00 0.00 0.00 0.00
CaO 0.36 0.32 0.01 0.02 0.36 0.21 0.40 46.90
Na2O 11.41 11.44 11.48 11.44 11.36 11.43 11.46 0.29
K2O 0.14 0.11 0.14 0.16 0.12 0.13 0.20 32.80
Total 99.53 100.15 99.30 99.97 99.22 99.63 99.96 0.33
72
Table 3: Major and trace element compositions of the Mono Basin lavas. Major
elements reported in wt.%. Trace elements reported in ppm.
Sample BB-2011-04 BB-2011-05 BB-2011-07 BB-2011-08 BB-2011-14 BB-2011-20
BB-2012-
05
Magma group Mono domes Mono domes Mono domes Mono domes Mono domes Mono domes
Mono
domes
UTM coordinates
(WGS ’84 datum)
11S
0322636/
4195314
11S
0322199/
4195444
11S
0320836/
4198805
11S
0321078/
4198661
11S
0321591/
4176223
11S
0321937/
4183577
SiO2 75.83 74.49 74.33 76.06 73.10 75.80 73.48
TiO2 0.06 0.07 0.06 0.06 0.11 0.06 0.07
Al2O3 12.46 12.57 12.21 12.48 13.13 12.43 12.43
FeOT 1.04 1.13 0.98 1.02 1.27 1.02 1.13
MnO 0.04 0.05 0.04 0.04 0.05 0.04 0.05
MgO 0.01 0.02 0.00 0.00 0.05 0.00 0.06
CaO 0.54 0.57 0.51 0.54 0.64 0.53 0.69
Na2O 3.97 3.93 3.81 3.96 3.91 3.96 3.81
K2O 4.65 4.78 4.58 4.64 5.12 4.63 4.73
P2O5 0.01 0.01 0.01 0.01 0.02 0.01 0.04
Total 98.62 97.61 96.54 98.80 97.39 98.49 96.49
Ba 28 41 20 23 137 22 37
Ce 47 69 43 48 108 48 65
Cr 3 2 3 3 4 4 3
Cu 1 2 2 2 1 1 4
Ga 17 18 17 17 16 17 17
La 24 34 21 20 58 22 35
Nb 21 20 21 21 18 21 19
Nd 19 26 20 20 38 20 25
Ni 3 3 2 4 3 2 0
Pb 28 28 29 29 28 29 27
Rb 178 168 175 177 156 180 164
Sc 2 2 2 3 2 2 3
Sr 6 9 6 7 25 6 12
Th 20 21 20 21 21 19 20
U 6 6 6 5 5 7 6
V 0 0 2 1 1 2 4
Y 28 27 27 29 23 28 27
Zn 40 43 41 41 41 41 42
Zr 111 132 107 107 175 109 126
73
Table 3 (continued)
Sample
BB-2012-06c BB-2012-07 BB-2012-10
BB-2012-11b BB-2012-16 BB-2012-17 BB-2012-18
Magma group
Mono
domes
Mono
domes
Mono
domes
Mono
domes
Mono
domes
Mono
domes
Mono
domes
UTM coordinates
(WGS ’84 datum)
11S 0320260/
4199922
11S 0320485/
4199437
11S 0321639/
4199224
11S 0323738/
4190283
11S 0321147/
4187050
11S 0321604/
4187195
11S 0321796/
4187441
SiO2 76.11 75.89 75.62 76.08 75.36 74.76 75.15
TiO2 0.06 0.06 0.06 0.06 0.06 0.06 0.06
Al2O3 12.54 12.48 12.46 12.56 12.47 12.43 12.54
FeOT 1.03 1.03 1.02 1.02 1.01 0.97 1.02
MnO 0.05 0.05 0.04 0.05 0.05 0.04 0.05
MgO 0.01 0.00 0.00 0.00 0.01 0.01 0.00
CaO 0.53 0.54 0.54 0.54 0.53 0.54 0.54
Na2O 3.98 3.98 3.94 3.98 3.92 3.86 3.92
K2O 4.68 4.64 4.64 4.66 4.62 4.64 4.71
P2O5 0.01 0.01 0.01 0.01 0.01 0.01 0.01
Total 99.00 98.68 98.34 98.95 98.05 97.32 97.99
Ba 22 23 24 22 20 18 20
Ce 50 51 48 48 48 42 46
Cr 3 4 4 4 3 2 4
Cu 1 6 3 1 3 3 6
Ga 16 18 18 17 19 17 17
La 22 22 25 21 23 21 26
Nb 20 21 20 21 20 21 21
Nd 22 21 22 20 19 17 20
Ni 1 1 0 0 1 0 1
Pb 29 28 28 28 30 28 29
Rb 179 177 178 178 177 176 177
Sc 3 3 3 3 2 2 2
Sr 6 6 6 6 5 6 7
Th 21 20 21 21 21 20 21
U 6 7 7 6 6 5 6
V 0 1 0 2 1 1 1
Y 28 28 27 27 28 27 28
Zn 41 40 39 40 41 41 40
Zr 108 107 108 107 110 107 109
74
Table 3 (continued)
Sample BB-2012-19 BB-2012-20 BB-2012-21 BB-2012-22 BB-2012-23 BB-2012-24 BB-2012-25
Magma group
Mono domes
Mono domes
Mono domes
Mono domes
Mono domes
Mono domes
Mono domes
UTM coordinates
(WGS ’84 datum)
11S
0322473/ 4187760
11S
0322947/ 4189213
11S
0322681/ 4189219
11S
0323162/ 4189746
11S
0322531/ 4198256
11S
0322299/ 4198350
11S
0323560/ 4192222
SiO2 74.93 76.05 76.08 75.73 76.35 75.18 75.71
TiO2 0.06 0.06 0.06 0.06 0.06 0.06 0.06
Al2O3 12.38 12.59 12.50 12.46 12.57 12.45 12.53
FeOT 1.02 1.07 1.04 1.03 1.04 1.03 1.04
MnO 0.05 0.05 0.05 0.05 0.05 0.04 0.05
MgO 0.00 0.07 0.02 0.01 0.01 0.01 0.01
CaO 0.54 0.60 0.54 0.53 0.54 0.53 0.53
Na2O 3.88 3.94 3.97 3.92 4.00 3.88 3.94
K2O 4.68 4.65 4.68 4.68 4.69 4.67 4.65
P2O5 0.01 0.01 0.01 0.01 0.01 0.01 0.01
Total 97.54 99.07 98.93 98.47 99.30 97.88 98.53
Ba 19 17 20 21 23 26 19
Ce 49 43 47 48 54 49 47
Cr 4 4 2 4 4 4 3
Cu 4 4 3 3 2 3 3
Ga 17 18 18 18 18 17 18
La 23 18 22 24 22 23 20
Nb 20 21 20 20 20 21 21
Nd 22 19 21 22 25 20 22
Ni 1 3 1 1 1 1 1
Pb 29 28 29 29 29 28 29
Rb 178 178 180 178 179 177 179
Sc 3 2 2 3 3 2 3
Sr 6 5 5 6 5 6 5
Th 20 20 21 21 20 21 20
U 5 7 7 6 7 7 7
V 2 2 3 0 0 2 2
Y 28 27 27 27 28 27 27
Zn 42 39 41 42 40 40 42
Zr 110 110 106 106 107 108 109
75
Table 3 (continued)
Sample BB-2012-26 BB-2012-27 M12-1A2 BB-2011-15
BB-2011-15b BB-2011-22 BB-2011-24
Magma group Mono domes Mono domes
Mono
domes Inyo domes Inyo domes Basalt Basalt
UTM coordinates
(WGS ’84 datum)
11S 0322608/
4193567
11S 0323467/
4193790
11S 0322210/
4176138
11S 0322210/
4176138
11S 0318310/
4188377
11S 0315244/
4210530
SiO2 74.57 75.82 66.67 70.73 71.22 54.00 50.54
TiO2 0.06 0.06 0.84 0.42 0.21 1.48 1.50
Al2O3 12.31 12.52 14.86 14.56 14.55 17.71 18.77
FeOT 0.97 1.05 4.59 2.30 1.91 7.44 8.56
MnO 0.05 0.05
0.06 0.06 0.12 0.14
MgO 0.00 0.00 1.99 0.68 0.18 3.94 6.23
CaO 0.57 0.54 3.52 1.85 0.96 8.23 8.62
Na2O 3.73 3.98 3.68 4.32 4.51 3.59 3.95
K2O 4.63 4.66 3.54 4.14 5.12 1.71 1.14
P2O5 0.01 0.01 0.15 0.12 0.04 0.43 0.31
Total 96.91 98.68 99.84 99.19 98.75 98.65 99.76
Ba 29 15 297 708 835 829 559
Ce 42 51 47 66 118 52 43
Cr 3 3 14 5 4 28 21
Cu 3 3
3 2 24 25
Ga 17 17
18 18 20 19
La 23 24 20 38 65 25 18
Nb 19 21 22 17 17 11 11
Nd 17 21 18 23 39 25 21
Ni 2 3 15 5 4 17 62
Pb 29 28
26 25 10 5
Rb 180 181 124 114 137 28 15
Sc 2 1 9 4 4 20 20
Sr 10 5 277 273 103 961 816
Th 21 21
13 17 3 3
U 6 7
4 5 1 1
V 0 1 82 28 4 194 180
Y 27 28 27 17 24 19 20
Zn 38 42
50 54 80 83
Zr 96 113 126 224 310 157 144
76
Table 3 (continued)
Sample BB-2011-09 BB-2011-10 BB-2011-11 BB-2011-12 BB-2011-13 BB-2011-16 BB-2011-17
Magma group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
UTM coordinates
(WGS ’84 datum)
11S
0322513/ 4207227
11S
0322569/ 4207300
11S
0322287/ 4207052
11S
0322458/ 4208935
11S
0322273/ 4209031
11S
0321501/ 4209348
11S
0320844/ 4208752
SiO2 66.22 67.27 69.56 64.56 63.26 64.52 68.99
TiO2 0.54 0.53 0.17 0.93 1.05 0.90 0.29
Al2O3 15.76 15.90 14.38 16.53 16.63 16.47 15.24
FeOT 2.95 2.90 1.88 4.39 4.88 4.25 2.36
MnO 0.07 0.07 0.06 0.09 0.10 0.09 0.07
MgO 0.65 0.62 0.15 1.28 1.52 1.22 0.31
CaO 1.87 1.82 0.90 3.14 3.51 3.05 1.40
Na2O 4.86 5.04 4.05 4.93 4.79 4.93 4.64
K2O 4.41 4.50 5.14 3.80 3.60 3.83 4.81
P2O5 0.15 0.15 0.04 0.33 0.40 0.32 0.08
Total 97.51 98.79 96.34 99.98 99.74 99.60 98.18
Ba 1498 1560 917 1362 1315 1358 1094
Ce 88 84 105 83 79 85 92
Cr 3 3 4 2 3 2 3
Cu 1 1 1 2 14 1 2
Ga 21 21 17 22 21 21 20
La 46 45 57 44 41 46 52
Nb 19 19 17 18 18 19 15
Nd 36 34 38 38 37 36 31
Ni 3 3 3 3 4 3 3
Pb 22 23 25 19 19 19 25
Rb 110 111 130 96 91 96 110
Sc 6 6 3 9 10 8 4
Sr 305 296 97 488 528 479 198
Th 11 12 14 11 9 9 11
U 3 3 5 6 2 3 3
V 9 7 2 36 50 29 3
Y 25 26 22 26 25 27 19
Zn 68 69 56 79 82 78 59
Zr 392 413 311 309 287 313 350
77
Table 3 (continued)
Sample BB-2011-01 BB-2011-02 BB-2011-03 BB-2011-18 BB-2011-23 BB-2012-14 BB-2012-15
Magma group Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island
UTM coordinates
(WGS ’84 datum)
11S
0321345/ 4211192
11S
0320829/ 4211181
11S
0320985/ 4211108
11S
0320116/ 4209814
11S
0314795/ 4205740
11S
0320302/ 4210218
11S
0320043/ 4209970
SiO2 68.06 68.81 68.71 63.45 66.62 65.38 64.68
TiO2 0.43 0.43 0.43 0.94 0.21 0.77 0.80
Al2O3 15.68 15.80 15.73 16.46 13.73 16.50 16.34
FeOT 2.83 2.83 2.82 4.68 2.04 4.05 4.22
MnO 0.07 0.07 0.07 0.09 0.06 0.08 0.08
MgO 0.56 0.56 0.56 1.47 3.43 1.15 1.22
CaO 1.95 1.95 1.95 3.71 1.11 3.19 3.22
Na2O 4.68 4.71 4.69 4.67 4.00 4.71 4.66
K2O 4.35 4.39 4.38 3.34 4.31 3.56 3.63
P2O5 0.13 0.13 0.13 0.34 0.06 0.28 0.28
Total 98.76 99.68 99.45 99.14 95.58 99.67 99.14
Ba 1250 1218 1228 1327 898 1402 1303
Ce 81 84 83 61 86 68 70
Cr 4 3 2 2 3 1 2
Cu 1 3 3 7 14 6 8
Ga 18 19 20 20 16 21 20
La 44 46 48 34 49 34 36
Nb 14 14 14 13 14 12 13
Nd 29 31 30 29 28 26 30
Ni 3 3 3 3 4 2 2
Pb 22 23 22 17 23 18 19
Rb 100 102 101 75 98 80 81
Sc 5 5 4 8 3 8 8
Sr 306 303 302 521 142 480 459
Th 10 10 11 7 11 6 7
U 2 3 2 3 1 4 2
V 12 14 11 68 4 46 52
Y 18 19 20 20 18 19 20
Zn 61 62 62 76 51 71 71
Zr 312 312 311 261 325 263 274
78
Table 3 (continued)
Sample
83083-1 1
BB-2011-15c-1
BB-2011-15c-2
LV87-1 1 VGC-1 1
BB-2011-05b-1
BB-2011-05b-2
Magma group
Inyo
enclaves Inyo enclaves Inyo enclaves
Inyo
enclaves
Inyo
enclaves
Dome 14
enclaves
Dome 14
enclaves
UTM coordinates
(WGS ’84 datum)
11S 0322210/ 4176138
11S 0322210/ 4176138
11S 0322199/ 4195444
11S 0322199/ 4195444
SiO2 58.50 59.65 59.90 59.70 57.30 56.17 54.86
TiO2 0.91 0.76 1.33 0.98 0.92 1.93 1.75
Al2O3 15.40 17.26 16.27 16.30 17.00 15.73 16.28
FeOT 5.80 4.67 5.82 6.03 5.66 8.62 8.34
MnO 0.18 0.11 0.15 0.17 0.11 0.15 0.15
MgO 3.13 3.06 2.16 3.3.8 2.74 3.92 4.63
CaO 4.99 5.81 4.32 5.31 5.33 6.53 6.71
Na2O 4.65 4.17 4.77 4.50 4.11 3.98 4.02
K2O 2.46 2.54 2.93 2.61 2.90 2.24 2.10
P2O5 0.30 0.18 0.41 0.23 0.35 0.44 0.39
Total 96.32 98.21 98.07 95.83 96.42 99.71 99.22
Ba 464 676 650 477 937 413 378
Ce
49 84
64 61
Cr 12 15 3 49 6 37 41
Cu 15 8 16 10 9 23 30
Ga
18 20
21 20
La
23 30
32 29
Nb 27 8 19 29 26 19 19
Nd
21 41
32 26
Ni 22 25 4 31 14 28 46
Pb
15 18
10 9
Rb 77 72 75 80 89 60 52
Sc
12 12
20 20
Sr 492 583 371 483 873 446 452
Th
5 8
8 6
U
2 2
3 3
V
93 145
179 154
Y 11 16 29 14 10 31 30
Zn 110 65 102 100 83 92 96
Zr 187 150 241 182 167 217 230
79
Table 3 (continued)
Sample
BB-2012-02b-1
BB-2012-02b-2 M14-1B 2
BB-2012-03b-1
BB-2012-03b-2 M12-1B 2 M12-2B 2
Magma group
Dome 14
enclaves
Dome 14
enclaves
Dome 14
enclaves
Dome 12
enclaves
Dome 12
enclaves
Dome 12
enclaves
Dome 12
enclaves
UTM coordinates
(WGS ’84 datum)
11S 0322262/
4195540
11S 0322262/
4195540
11S 0321340/
4196196
11S 0321340/
4196196
SiO2 59.68 59.29 57.85 50.06 52.68 54.59 52.60
TiO2 1.40 1.43 1.49 2.38 2.09 0.94 2.08
Al2O3 15.51 15.92 15.87 17.26 17.12 17.46 17.48
FeOT 6.99 6.96 8.02 11.02 9.59 9.23 10.15
MnO 0.13 0.13
0.19 0.16
MgO 3.58 3.66 4.04 5.09 5.00 4.47 4.25
CaO 5.36 5.64 5.84 8.49 7.84 7.76 7.64
Na2O 4.04 4.01 3.84 3.73 3.65 3.38 3.79
K2O 2.66 2.62 2.55 1.25 1.48 1.66 1.58
P2O5 0.32 0.33 0.37 0.43 0.39 0.39 0.31
Total 99.68 100.00 99.87 99.90 100.00 99.88 99.88
Ba 283 311 303 429 383 358 444
Ce 62 62 59 52 44 45 47
Cr 32 32 39 29 25 19 10
Cu 21 21
34 31
Ga 21 20
22 22
La 31 29 27 24 18 20 21
Nb 19 20 22 18 18 18 19
Nd 30 28 29 30 26 22 27
Ni 35 35 35 36 34 27 21
Pb 13 13
4 9
Rb 82 78 71 33 35 45 35
Sc 17 15 15 26 23 19 18
Sr 348 374 374 643 588 592 643
Th 9 9
3 4
U 3 3
2 4
V 131 127 136 249 212 197 196
Y 30 30 32 33 27 25 26
Zn 81 80
112 99
Zr 207 209 212 188 168 159 171
80
Table 3 (continued)
Sample
BB-2012-05b-1
BB-2012-05b-2
BB-2012-05b-3 M18-1B 2 BB-2012-04b
Magma
group
Dome 18
enclaves
Dome 18
enclaves
Dome 18
enclaves
Dome 18
enclaves
N. Deadman
enclaves
UTM
coordinates
(WGS ’84
datum)
11S 0321865/
4176572
SiO2 55.01 56.46 60.44 61.73 61.63
TiO2 1.81 1.64 1.32 1.20 1.03
Al2O3 16.57 16.18 15.38 15.31 16.31
FeOT 8.60 8.02 6.49 6.63 5.51
MnO 0.15 0.14 0.12
0.10
MgO 4.73 4.48 3.53 3.01 2.11
CaO 6.96 6.58 5.28 4.82 4.15
Na2O 4.04 3.96 3.90 3.99 4.38
K2O 2.04 2.22 2.81 2.96 3.38
P2O5 0.42 0.47 0.29 0.27 0.24
Total 100.34 100.15 99.57 99.92 98.83
Ba 379 315 255 298 961
Ce 70 62 61 62 63
Cr 39 52 40 26 5
Cu 23 20 18
9
Ga 21 20 20
21
La 31 28 28 31 33
Nb 19 20 19 21 14
Nd 31 31 27 29 27
Ni 43 43 34 30 6
Pb 9 10 15
16
Rb 52 59 85 87 81
Sc 21 18 16 12 11
Sr 465 419 331 308 405
Th 6 7 10
9
U 4 4 3
2
V 168 153 123 111 103
Y 31 31 30 30 22
Zn 92 89 134
73
Zr 231 211 195 198 290
1 Data from Varga et al. (1990).
2 Data from Kelleher and Cameron (1990).
81
Table 4: Isotopic compositions of the Mono Basin lavas.
Sample Magma group 87
Sr/86
Sri 143
Nd/144
Nd εNd 206
Pb/204
Pb 207
Pb/204
Pb 208
Pb/204
Pb δ18
O
BB-2011-22 Basalt 0.706160 1 0.512580
1
19.250 1 15.670
1 38.890
1 7.42
BB-2011-24 Basalt 0.705380 1 0.512670
1
19.220 1 15.660
1 38.830
1 7.95
BB-2012-03b-1 Dome 12 enclaves 0.704869 0.512758 2.34 19.137 15.672 38.869 7.79
BB-2011-05b-2 Dome 14 enclaves 0.704535 0.512785 2.87 19.094 15.665 38.864 6.82
BB-2012-02b-2 Dome 14 enclaves 0.704520 0.512749 2.17 19.122 15.668 38.886 6.89
BB-2012-05b-1 Dome 18 enclaves 0.704421 0.512779 2.75 19.105 15.674 38.895 12.68
BB-2012-05b-3 Dome 18 enclaves 0.704516 0.512754 2.26 19.114 15.661 38.865 7.15
BB-2011-14 Mono domes 0.706024 0.512602 -0.70 19.127 15.666 38.902 9.02
BB-2011-20 Mono domes 0.705960 0.512614 -0.47 19.138 15.677 38.939 6.91
BB-2012-05 Mono domes 0.706905 0.512618 -0.39 19.173 15.697 39.008 7.73
BB-2012-04b N. Deadman enclaves 0.705640 0.512646 0.16 19.174 15.673 38.920 7.97
BB-2011-01 Negit Island 0.706239 0.512537 -1.97 19.209 15.696 38.992 7.73
BB-2011-23 Negit Island 0.706209 0.512581 -1.11 19.186 15.690 38.978 8.82
BB-2012-14 Negit Island 0.706429 0.512527 -2.16 19.240 15.709 39.036 8.11
BB-2011-10 Paoha Island 0.705998 0.512571 -1.31 19.176 15.707 39.033 9.44
BB-2011-11 Paoha Island 0.706094 0.512594 -0.86 19.172 15.686 38.968 11.55
BB-2011-16 Paoha Island 0.705873 0.512563 -1.46 19.153 15.689 38.970 7.58
BB-2011-15c-2 Inyo enclaves 0.706225 0.512520 -2.30 19.202 15.694 38.977 6.89
1 Sr, Nd, and Pb data for the Black Point and June Lake basalts from Cousens (1996)
82
Table 5a: Electron microprobe analyses of Mono Basin glasses. Major
elements reported in wt.%.
Sample
09112013_BB-2012-
17_Glass_1
09112013_BB-2012-
17_Glass_3
09112013_BB-2012-
17_Glass_4
09112013_BB-2012-
17_Glass_5
BB-2011-
05_Glass_2
BB-2011-
05_Glass_3
BB-2011-
05_Glass_4
Magma
group Mono domes Mono domes Mono domes Mono domes Mono domes Mono domes Mono domes
SiO2 74.41 75.87 76.52 76.10 54.94 48.49 50.92
TiO2 0.07 0.00 0.06 0.06 1.80 3.13 3.47
Al2O3 11.97 12.42 12.49 13.56 15.03 16.31 16.73
FeOT 0.67 0.82 0.79 0.74 8.61 11.07 8.62
MnO 0.03 0.00 0.05 0.01 0.22 0.18 0.18
MgO 0.00 0.00 0.01 0.00 3.40 4.20 4.00
CaO 0.45 0.45 0.46 0.61 8.89 8.74 9.21
Na2O 3.89 3.89 3.90 4.53 4.52 4.12 4.18
K2O 4.64 4.58 4.68 4.43 1.72 1.52 1.34
P2O5 0.00 0.00 0.04 0.01 0.57 0.65 0.63
Total 96.13 98.03 99.00 100.05 99.70 98.40 99.27
83
Table 5a (continued)
Sample BB-2011-05_Glass_5 BB-2011-05_Glass_6
BB-2012-
11b_Glass_1
BB-2012-
11b_Glass_2
BB-2012-
11b_Glass_3
BB-2012-
11b_Glass_4
BB-2012-
11b_Glass_5
Magma group Mono domes Mono domes Mono domes Mono domes Mono domes Mono domes Mono domes
SiO2 52.17 76.20 75.05 76.23 76.42 75.89 75.73
TiO2 2.49 0.10 0.06 0.05 0.12 0.03 0.00
Al2O3 15.73 12.45 11.85 12.46 12.48 12.43 12.52
FeOT 9.73 0.87 0.74 0.85 0.93 0.94 0.82
MnO 0.34 0.06 0.06 0.05 0.02 0.04 0.06
MgO 3.85 0.02 0.01 0.02 0.01 0.03 0.00
CaO 9.58 0.46 0.51 0.55 0.52 0.53 0.46
Na2O 4.10 4.02 3.78 4.08 4.00 4.03 4.08
K2O 1.32 4.91 4.62 4.58 4.84 4.67 4.66
P2O5 0.50 0.00 0.00 0.02 0.01 0.00 0.00
Total 99.79 99.08 96.68 98.87 99.34 98.57 98.32
84
Table 5a (continued)
Sample
BB-2012-
11b_Glass_6
BB-2012-
16_Glass_1
BB-2012-
16_Glass_2
BB-2012-
16_Glass_3
BB-2012-
16_Glass_6
09112013_BB-2011-
10_Glass_1
09112013_BB-2011-
10_Glass_10
Magma
group Mono domes Mono domes Mono domes Mono domes Mono domes Paoha Island Paoha Island
SiO2 76.43 75.79 75.51 74.78 74.19 67.23 70.20
TiO2 0.09 0.02 0.00 0.02 0.05 0.42 0.44
Al2O3 12.55 12.46 12.44 12.13 11.99 18.07 15.92
FeOT 0.86 0.70 0.84 0.69 0.82 1.19 1.65
MnO 0.04 0.07 0.03 0.05 0.04 0.06 0.06
MgO 0.01 0.01 0.01 0.00 0.00 0.09 0.15
CaO 0.55 0.52 0.54 0.46 0.53 2.25 1.12
Na2O 4.20 4.12 4.06 3.96 3.93 6.24 5.30
K2O 4.72 4.63 4.45 4.58 4.45 3.83 5.14
P2O5 0.05 0.00 0.00 0.00 0.00 0.13 0.12
Total 99.48 98.31 97.88 96.66 96.03 99.50 100.09
85
Table 5a (continued)
Sample
09112013_BB-2011-
10_Glass_11
09112013_BB-2011-
10_Glass_2
09112013_BB-2011-
10_Glass_3
09112013_BB-2011-
10_Glass_4
09112013_BB-2011-
10_Glass_5
09112013_BB-2011-
10_Glass_6
09112013_BB-2011-
10_Glass_7
Magma
group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 69.29 68.38 66.51 69.15 69.52 69.04 64.06
TiO2 0.32 0.53 0.52 0.55 0.66 0.47 0.70
Al2O3 17.15 16.58 17.77 16.64 14.57 14.55 16.54
FeOT 1.20 1.50 2.10 1.32 2.83 3.00 4.40
MnO 0.04 0.02 0.02 0.00 0.08 0.17 0.13
MgO 0.07 0.25 0.30 0.13 0.61 1.01 1.27
CaO 1.88 1.76 2.56 1.60 0.86 1.11 3.32
Na2O 5.80 5.74 6.44 5.70 4.49 4.54 5.41
K2O 4.36 4.46 3.46 4.78 5.86 5.26 3.70
P2O5 0.13 0.16 0.13 0.18 0.17 0.16 0.89
Total 100.23 99.38 99.81 100.05 99.65 99.31 100.41
86
Table 5a (continued)
Sample
09112013_BB-2011-
10_Glass_8
09112013_BB-2011-
10_Glass_9
BB-2011-
10_Glass_3
BB-2011-
10_Glass_4
BB-2011-
10_Glass_5
BB-2011-
10_Glass_7
BB-2011-
10_Glass_8
Magma
group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 69.81 68.87 67.25 69.23 70.71 68.77 71.06
TiO2 0.44 0.77 0.33 0.73 0.40 0.37 0.40
Al2O3 15.34 13.95 16.34 14.35 14.23 15.44 15.06
FeOT 1.67 5.53 2.03 2.08 1.89 2.57 1.48
MnO 0.05 0.09 0.05 0.05 0.07 0.10 0.04
MgO 0.23 0.15 0.54 0.12 0.28 0.68 0.13
CaO 1.21 0.56 2.12 1.06 0.75 1.64 1.10
Na2O 5.03 4.37 5.62 4.50 4.63 5.11 4.86
K2O 5.27 5.72 4.11 5.46 5.49 4.70 5.17
P2O5 0.04 0.09 0.23 0.26 0.10 0.08 0.06
Total 99.10 100.10 98.63 97.83 98.54 99.47 99.37
87
Table 5a (continued)
Sample BB-2011-17_Glass_2 BB-2011-17_Glass_3 BB-2011-17_Glass_5 BB-2011-18_Glass_2 BB-2011-18_Glass_3 BB-2011-18_Glass_4 BB-2011-18_Glass_5
Magma group Paoha Island Paoha Island Paoha Island Negit Island Negit Island Negit Island Negit Island
SiO2 70.94 71.26 70.81 65.84 66.18 69.82 64.85
TiO2 0.16 0.19 0.14 0.71 0.68 0.81 0.90
Al2O3 14.57 14.84 14.69 16.80 17.07 14.99 15.99
FeOT 1.75 2.03 1.95 2.78 2.45 2.03 4.05
MnO 0.06 0.05 0.08 0.05 0.07 0.04 0.07
MgO 0.16 0.13 0.15 0.50 0.58 0.17 1.48
CaO 1.04 1.08 1.05 3.05 3.28 1.66 3.28
Na2O 4.48 4.61 4.53 5.04 5.24 4.62 4.66
K2O 5.19 5.11 5.14 3.56 3.72 4.86 3.61
P2O5 0.07 0.00 0.06 0.22 0.31 0.21 0.37
Total 98.43 99.29 98.59 98.55 99.58 99.20 99.24
88
Table 5a (continued)
Sample BB-2011-05b-2_Glass_3 BB-2011-05b-2_Glass_6 BB-2011-05b-2_Glass_8
Magma group Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves
SiO2 76.44 64.73 59.90
TiO2 0.03 0.84 0.56
Al2O3 12.95 16.11 15.13
FeOT 0.72 3.58 5.69
MnO 0.04 0.04 0.13
MgO 0.04 0.90 3.73
CaO 0.31 1.35 6.15
Na2O 3.11 4.62 5.81
K2O 5.92 5.78 1.59
P2O5 0.00 0.15 0.76
Total 99.56 98.11 99.44
89
Table 5b: Electron microprobe analyses of Mono Basin amphiboles. Major elements reported in
wt.%.
Sample BB201110-C1-1 BB201110-C1-2 BB201110-C5-1 BB201110-C6-1 BB201110-C7-1
BB-2011-
12_amph_1
BB-2011-
12_amph_2
Magma group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 42.14 42.83 42.87 41.69 42.36 42.19 42.14
TiO2 3.869 3.422 3.428 3.769 3.750 3.832 3.955
Al2O3 10.61 10.37 10.32 10.47 10.70 10.88 11.14
FeOT 12.65 12.78 13.60 12.82 12.96 13.06 13.48
MnO 0.259 0.247 0.281 0.246 0.225 0.226 0.237
MgO 13.42 13.67 13.39 13.27 13.13 13.68 13.25
CaO 10.88 10.89 10.47 11.17 10.84 10.93 10.91
Na2O 2.475 2.495 2.423 2.519 2.568 2.562 2.509
K2O 0.913 0.960 0.921 0.869 0.943 0.977 0.957
Cr2O3 0.000 0.000 0.007 0.000 0.000 0.000 0.000
Cl 0.016 0.004 0.019 0.000 0.004 0.007 0.002
F 0.252 0.319 0.306 0.307 0.294 0.173 0.390
Total 97.37 97.85 97.90 96.99 97.64 98.45 98.81
90
Table 5b (continued)
Sample
BB-2011-
12_amph_3
BB-2011-
12_amph_4
BB-2011-
12_amph_5
BB-2011-
17_amph_1
BB-2011-
17_amph_3
BB-2011-
17_amph_4
BB-2011-
17_amph_5
Magma
group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 41.67 41.92 42.32 42.40 42.61 42.44 42.44
TiO2 3.992 4.031 3.795 3.359 3.249 2.961 3.197
Al2O3 10.98 10.93 10.90 10.82 10.90 10.66 10.89
FeOT 13.04 13.08 13.18 14.36 14.46 15.66 15.64
MnO 0.225 0.215 0.246 0.222 0.274 0.260 0.259
MgO 12.78 13.34 13.48 12.43 11.64 12.09 11.91
CaO 10.96 11.04 10.95 10.79 10.77 10.61 10.56
Na2O 2.509 2.548 2.545 2.363 2.443 2.356 2.351
K2O 1.012 0.989 0.953 0.851 0.906 0.920 0.912
Cr2O3 0.000 0.016 0.000 0.000 0.000 0.000 0.010
Cl 0.013 0.004 0.029 0.019 0.025 0.012 0.033
F 0.405 0.585 0.280 0.229 0.004 0.220 0.224
Total 97.41 98.46 98.56 97.75 97.26 98.10 98.31
91
Table 5b (continued)
Sample
BB-2011-
17_amph_6
BB-2011-
15_amph_1
BB-2011-
15_amph_2
BB-2011-
15_amph_3
BB-2011-
15_amph_4
BB-2011-
15_amph_5
BB-2011-
15_amph_6
Magma
group Paoha Island Inyo domes Inyo domes Inyo domes Inyo domes Inyo domes Inyo domes
SiO2 42.56 47.20 44.00 42.95 47.98 46.82 45.65
TiO2 3.324 1.202 2.468 2.869 1.163 1.276 1.670
Al2O3 10.91 6.267 8.786 9.429 5.654 6.709 7.313
FeOT 13.69 16.52 17.45 17.18 15.72 16.24 17.19
MnO 0.218 0.657 0.609 0.639 0.634 0.651 0.664
MgO 11.99 12.44 10.97 10.85 13.59 12.93 11.85
CaO 11.15 11.45 11.22 11.17 11.33 11.50 11.22
Na2O 2.379 1.444 1.973 2.091 1.315 1.553 1.682
K2O 0.896 0.685 0.853 0.794 0.565 0.782 0.835
Cr2O3 0.006 0.000 0.000 0.027 0.000 0.000 0.000
Cl 0.017 0.043 0.046 0.037 0.042 0.061 0.068
F 0.285 0.077 0.128 0.167 0.233 0.193 0.187
Total 97.30 97.94 98.44 98.13 98.11 98.63 98.24
92
Table 5b (continued)
Sample
BB-2011-
15_amph_7
BB-2011-
15_amph_8
BB-2011-
15_amph_9
BB-2011-
15_amph_10
BB-2011-
15_amph_11
BB-2011-
15_amph_12
BB-2011-
15_amph_13
Magma
group Inyo domes Inyo domes Inyo domes Inyo domes Inyo domes Inyo domes Inyo domes
SiO2 46.56 46.45 46.27 45.72 45.55 45.58 45.54
TiO2 1.366 1.394 1.483 1.462 1.519 1.652 1.650
Al2O3 6.985 6.854 7.347 7.439 7.405 7.500 7.370
FeOT 17.00 16.60 16.59 17.31 17.28 16.44 16.41
MnO 0.674 0.672 0.599 0.643 0.592 0.605 0.579
MgO 12.31 12.24 12.54 11.95 11.53 12.66 12.57
CaO 11.31 11.25 11.35 11.32 11.22 11.25 11.15
Na2O 1.668 1.574 1.682 1.702 1.643 1.683 1.686
K2O 0.792 0.736 0.838 0.899 0.880 0.903 0.852
Cr2O3 0.019 0.000 0.000 0.000 0.000 0.000 0.000
Cl 0.042 0.053 0.040 0.048 0.062 0.068 0.067
F 0.197 0.274 0.055 0.249 0.320 0.400 0.254
Total 98.82 97.97 98.76 98.62 97.84 98.56 97.99
93
Table 5b (continued)
Sample
BB-2011-
15_amph_14
BB-2011-
15_amph_15
BB-2011-
15_amph_16
BB-2011-15c-
1_amph_1
BB-2011-15c-
1_amph_2
BB-2011-15c-
1_amph_3
BB-2011-15c-
1_amph_4
Magma
group Inyo domes Inyo domes Inyo domes Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves
SiO2 46.58 45.03 45.60 47.44 45.29 45.39 45.74
TiO2 1.512 1.639 1.646 1.278 1.575 1.599 1.405
Al2O3 7.436 7.720 7.430 5.742 6.898 7.201 6.850
FeOT 15.98 16.58 16.43 15.21 16.98 16.81 16.58
MnO 0.577 0.563 0.561 0.435 0.693 0.630 0.652
MgO 12.19 12.64 12.87 13.93 12.61 12.25 12.32
CaO 11.03 11.17 11.19 11.20 10.86 11.01 11.26
Na2O 1.747 1.768 1.715 1.425 1.558 1.693 1.550
K2O 1.063 0.925 0.840 0.648 0.757 0.805 0.766
Cr2O3 0.000 0.000 0.000 0.000 0.005 0.000 0.021
Cl 0.059 0.037 0.046 0.028 0.057 0.064 0.071
F 0.236 0.395 0.153 0.092 0.239 0.282 0.249
Total 98.28 98.29 98.41 97.38 97.41 97.60 97.33
94
Table 5b (continued)
Sample
BB-2011-15c-
1_amph_5
BB-2011-15c-
1_amph_6
BB-2011-15c-
1_amph_7
BB-2011-15c-
1_amph_8
BB-2011-15c-
1_amph_9
BB-2011-15c-
1_amph_10
BB-2011-
18_amph_1
Magma
group Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves Negit Island
SiO2 46.78 43.17 43.96 46.30 43.86 43.62 41.21
TiO2 1.283 2.503 1.771 1.272 1.866 2.197 4.073
Al2O3 6.451 10.42 9.222 5.512 9.273 9.822 11.35
FeOT 16.00 13.99 14.59 17.23 15.48 15.35 12.84
MnO 0.606 0.290 0.367 0.660 0.460 0.464 0.159
MgO 12.74 12.38 13.11 13.24 12.65 11.75 13.23
CaO 11.24 11.42 11.35 10.69 11.17 11.17 11.08
Na2O 1.526 2.263 2.013 1.425 2.030 2.182 2.346
K2O 0.701 0.846 0.798 0.605 0.809 0.782 0.790
Cr2O3 0.019 0.000 0.000 0.029 0.000 0.000 0.000
Cl 0.049 0.033 0.028 0.063 0.035 0.048 0.008
F 0.175 0.244 0.227 0.344 0.206 0.111 0.025
Total 97.49 97.45 97.33 97.21 97.74 97.44 97.10
95
Table 5b (continued)
Sample
BB-2012-
15_amph_1
BB-2012-
15_amph_2
Magma
group Negit Island Negit Island
SiO2 41.99 42.00
TiO2 3.681 3.578
Al2O3 10.98 10.67
FeOT 12.89 13.19
MnO 0.213 0.214
MgO 13.90 13.86
CaO 11.17 11.02
Na2O 2.443 2.450
K2O 0.761 0.764
Cr2O3 0.000 0.020
Cl 0.016 0.013
F 0.000 0.212
Total 98.04 97.90
96
Table 5c: Electron microprobe analyses of Mono Basin plagioclases. Major elements reported in
wt.%.
Sample
BB-2012-
17_fsp_5
BB-2012-
17_fsp_6
BB-2012-
17_fsp_7
BB-2011-
10_fsp_1
BB-2011-
10_fsp_2
BB-2011-
10_fsp_3
BB-2011-
10_fsp_10
Magma
group Mono domes Mono domes Mono domes Negit Island Negit Island Negit Island Negit Island
SiO2 64.883 64.903 64.241 57.622 57.168 58.000 62.467
Al2O3 21.602 21.810 22.156 26.172 26.390 25.662 22.999
FeOT 0.122 0.132 0.086 0.396 0.362 0.462 0.196
MgO 0.000 0.015 0.000 0.014 0.044 0.013 0.013
CaO 2.799 2.937 3.414 8.431 8.709 8.238 4.790
Na2O 8.816 8.858 8.767 6.135 6.002 5.793 7.450
K2O 1.447 1.397 1.203 0.650 0.572 0.674 1.315
Total 99.669 100.052 99.867 99.420 99.247 98.842 99.230
An (mol. %) 14 14 16 42 43 42 24
97
Table 5c (continued)
Sample
BB-2011-
10_fsp_11
BB-2011-
10_fsp_14
BB-2011-
10_fsp_17
BB-2011-
10_fsp_18
BB-2011-
10_fsp_19
BB-2011-
10_fsp_21
BB-2011-
10_fsp_22
Magma
group Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island
SiO2 62.250 62.402 58.155 58.569 58.946 61.295 61.466
Al2O3 22.508 22.808 25.442 25.229 23.852 23.452 23.346
FeOT 0.147 0.191 0.347 0.320 1.000 0.227 0.166
MgO 0.000 0.000 0.021 0.017 0.184 0.026 0.000
CaO 4.253 4.159 7.592 7.402 7.250 5.185 5.038
Na2O 7.647 7.583 6.231 6.342 5.506 7.329 7.434
K2O 1.506 1.611 0.771 0.819 1.558 1.204 1.336
Total 98.311 98.754 98.559 98.698 98.296 98.718 98.786
An (mol. %) 21 21 38 37 38 26 25
98
Table 5c (continued)
Sample
BB-2011-
10_fsp_23
BB-2011-
10_fsp_24
BB-2011-
10_fsp_25
BB-2011-
10_fsp_26
BB-2011-
10_fsp_27
BB-2011-
10_fsp_28
BB-2011-
10_fsp_31
Magma
group Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island Negit Island
SiO2 61.221 61.598 61.864 60.740 62.058 63.581 61.907
Al2O3 23.109 23.127 23.033 23.714 23.023 20.485 23.087
FeOT 0.163 0.220 0.123 0.262 0.184 0.960 0.210
MgO 0.000 0.000 0.000 0.006 0.000 0.071 0.000
CaO 5.158 5.019 4.814 5.711 4.915 4.196 5.045
Na2O 7.466 7.474 7.582 7.246 7.398 6.202 7.663
K2O 1.235 1.272 1.393 1.056 1.288 2.763 1.346
Total 98.352 98.710 98.809 98.735 98.866 98.258 99.258
An (mol. %) 26 25 24 28 25 22 25
99
Table 5c (continued)
Sample BB-2011-10_fsp_32
BB-2011-
16_fsp_1
BB-2011-
16_fsp_2
BB-2011-
16_fsp_3
BB-2011-
16_fsp_4
BB-2011-
16_fsp_5
BB-2011-
16_fsp_8
Magma
group Negit Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 62.940 56.442 56.776 57.535 54.940 59.304 56.021
Al2O3 22.394 26.823 26.558 25.566 27.876 24.208 27.074
FeOT 0.157 0.446 0.376 0.788 0.464 0.923 0.454
MgO 0.000 0.044 0.060 0.075 0.051 0.032 0.044
CaO 4.081 9.455 9.210 9.503 10.558 7.907 9.678
Na2O 7.937 5.623 5.818 5.366 5.007 5.155 5.447
K2O 1.623 0.528 0.552 1.095 0.443 1.617 0.488
Total 99.132 99.361 99.350 99.928 99.339 99.146 99.206
An (mol. %) 20 47 45 46 52 41 48
100
Table 5c (continued)
Sample
BB-2011-
16_fsp_9
BB-2011-
16_fsp_10
BB-2011-
16_fsp_13
BB-2011-
16_fsp_14
BB-2011-
16_fsp_15
BB-2011-
16_fsp_18
BB-2011-
16_fsp_19
Magma
group Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island Paoha Island
SiO2 57.122 54.907 55.744 57.769 56.460 63.565 62.047
Al2O3 26.329 27.966 27.552 26.006 26.861 22.040 23.115
FeOT 0.430 0.503 0.480 0.390 0.436 0.452 0.195
MgO 0.004 0.045 0.045 0.024 0.011 0.035 0.000
CaO 9.034 10.768 10.100 8.433 9.866 4.520 4.946
Na2O 5.914 5.014 5.351 6.155 5.633 6.762 7.766
K2O 0.598 0.417 0.453 0.699 0.504 2.254 1.316
Total 99.431 99.620 99.725 99.476 99.771 99.628 99.385
An (mol. %) 44 53 50 41 48 23 24
101
Table 5c (continued)
Sample
BB-2011-
16_fsp_20
BB-2011-05b-
2_fsp_1
BB-2011-05b-
2_fsp_3
BB-2011-05b-
2_fsp_4
BB-2011-05b-
2_fsp_7
BB-2011-05b-
2_fsp_8
BB-2011-05b-
2_fsp_9
Magma
group Paoha Island Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves
SiO2 62.214 50.556 50.248 51.431 53.276 53.224 53.554
Al2O3 23.163 30.871 31.485 30.806 28.941 29.134 28.794
FeOT 0.183 0.423 0.423 0.395 0.509 0.490 0.491
MgO 0.016 0.143 0.095 0.129 0.072 0.070 0.058
CaO 4.966 14.476 14.058 13.510 12.242 12.241 12.009
Na2O 7.688 3.108 2.995 3.428 4.118 4.269 4.302
K2O 1.306 0.131 0.137 0.147 0.298 0.268 0.288
Total 99.536 99.708 99.441 99.846 99.456 99.696 99.496
An (mol.
%) 24 71 72 68 61 60 60
102
Table 5c (continued)
Sample
BB-2011-05b-
2_fsp_11
BB-2011-05b-
2_fsp_12
BB-2011-05b-
2_fsp_13
BB-2011-05b-
2_fsp_14
BB-2011-05b-
2_fsp_15
BB-2011-05b-
2_fsp_16
BB-2011-05b-
2_fsp_17
Magma
group Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves
SiO2 54.723 56.142 55.656 55.978 53.027 54.008 53.149
Al2O3 28.014 27.126 27.520 27.347 29.302 28.816 29.015
FeOT 0.531 0.494 0.482 0.503 0.473 0.498 0.584
MgO 0.079 0.056 0.040 0.051 0.086 0.072 0.066
CaO 10.676 9.699 10.228 10.047 12.583 11.723 12.096
Na2O 4.885 5.429 5.118 5.261 4.005 4.349 4.256
K2O 0.349 0.397 0.359 0.375 0.239 0.291 0.284
Total 99.257 99.343 99.403 99.562 99.715 99.757 99.450
An (mol.
%) 54 49 51 50 63 59 60
103
Table 5c (continued)
Sample
BB-2011-05b-
2_fsp_18
BB-2011-05b-
2_fsp_19
BB-2011-05b-
2_fsp_20
BB-2012-03b-
1_fsp_1
BB-2012-03b-
1_fsp_2
BB-2012-03b-
1_fsp_3
BB-2012-03b-
1_fsp_4
Magma
group Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves
Dome 14
enclaves
Dome 14
enclaves
Dome 14
enclaves
Dome 14
enclaves
SiO2 53.187 53.728 53.375 53.930 51.637 52.010 53.342
Al2O3 29.030 28.634 28.938 28.664 30.094 30.014 28.829
FeOT 0.495 0.484 0.473 0.508 0.351 0.327 0.514
MgO 0.070 0.062 0.067 0.067 0.100 0.095 0.087
CaO 11.850 11.966 11.984 11.942 13.123 13.116 12.204
Na2O 4.283 4.403 4.240 4.515 3.884 3.905 4.329
K2O 0.293 0.299 0.317 0.301 0.231 0.241 0.287
Total 99.208 99.576 99.394 99.927 99.420 99.708 99.592
An (mol.
%) 59 59 60 58 64 64 60
104
Table 5c (continued)
Sample
BB-2012-03b-
1_fsp_5
BB-2012-03b-
1_fsp_6
BB-2012-03b-
1_fsp_7
BB-2012-03b-
1_fsp_10
BB-2012-03b-
1_fsp_11
BB-2012-03b-
1_fsp_12
BB-2012-05b-
1_fsp_1
Magma
group
Dome 14
enclaves
Dome 14
enclaves
Dome 14
enclaves Dome 14 enclaves Dome 14 enclaves Dome 14 enclaves
Dome 18
enclaves
SiO2 53.196 53.293 52.529 51.986 52.246 52.259 55.672
Al2O3 28.809 28.759 29.211 29.554 29.867 29.246 23.548
FeOT 0.526 0.587 0.543 0.529 0.351 0.381 3.594
MgO 0.085 0.082 0.080 0.106 0.075 0.096 1.864
CaO 12.066 12.325 12.640 12.958 12.946 12.885 8.116
Na2O 4.494 4.369 4.069 3.877 3.975 4.159 4.337
K2O 0.297 0.265 0.314 0.287 0.251 0.261 1.510
Total 99.473 99.680 99.386 99.297 99.711 99.287 98.641
An (mol.
%) 59 60 62 64 63 62 46
105
Table 5c (continued)
Sample
BB-2012-05b-
1_fsp_2
BB-2012-05b-
1_fsp_3
BB-2012-05b-
1_fsp_4
BB-2012-05b-
1_fsp_8
BB-2012-05b-
1_fsp_9
BB-2012-05b-
1_fsp_10
BB-2012-05b-
1_fsp_11
Magma
group
Dome 18
enclaves
Dome 18
enclaves
Dome 18
enclaves
Dome 18
enclaves
Dome 18
enclaves Dome 18 enclaves Dome 18 enclaves
SiO2 59.151 60.140 60.241 62.473 53.105 55.190 50.520
Al2O3 22.681 24.084 24.405 22.989 28.915 27.834 30.681
FeOT 1.814 0.377 0.371 0.179 0.494 0.419 0.389
MgO 0.634 0.001 0.028 0.000 0.112 0.106 0.115
CaO 7.632 7.347 7.254 4.969 12.291 10.842 14.084
Na2O 5.498 6.322 6.165 7.541 4.203 4.987 3.285
K2O 1.296 0.892 0.893 1.286 0.328 0.365 0.151
Total 98.706 99.163 99.357 99.437 99.448 99.743 99.225
An (mol.
%) 40 37 37 25 61 53 70
106
Table 5c (continued)
Sample
BB-2012-05b-
1_fsp_12
BB-2012-05b-
1_fsp_13
BB-2012-05b-
1_fsp_15
BB-2012-05b-
1_fsp_16
BB-2012-05b-
1_fsp_17
BB-2012-05b-
1_fsp_18
BB-2012-05b-
1_fsp_20
Magma
group Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves
SiO2 53.340 52.383 53.612 53.335 50.550 50.973 49.553
Al2O3 28.987 29.612 28.801 28.792 30.882 30.814 31.271
FeOT 0.469 0.462 0.493 0.475 0.320 0.300 0.371
MgO 0.083 0.079 0.067 0.068 0.120 0.135 0.136
CaO 12.546 12.660 12.007 12.118 14.496 13.976 14.942
Na2O 4.125 4.071 4.443 4.528 3.185 3.236 2.884
K2O 0.275 0.270 0.305 0.297 0.140 0.142 0.150
Total 99.825 99.537 99.728 99.613 99.693 99.576 99.307
An (mol.
%) 62 62 59 59 71 70 73
107
Table 5c (continued)
Sample
BB-2012-05b-
1_fsp_21
BB-2012-05b-
1_fsp_22
BB-2012-05b-
1_fsp_23
BB-2011-15c-
1_fsp_1
BB-2011-15c-
1_fsp_2
BB-2011-15c-
1_fsp_4
BB-2011-15c-
1_fsp_8
Magma
group Dome 18 enclaves Dome 18 enclaves Dome 18 enclaves Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves
SiO2 50.317 49.794 49.513 54.878 54.435 54.419 57.648
Al2O3 30.910 31.345 31.831 27.604 28.190 28.321 26.437
FeOT 0.304 0.390 0.443 0.634 0.506 0.521 0.232
MgO 0.135 0.151 0.126 0.018 0.051 0.038 0.000
CaO 14.346 14.800 15.009 10.996 11.371 11.270 8.239
Na2O 3.162 2.982 2.714 4.928 4.655 4.663 6.364
K2O 0.147 0.134 0.134 0.308 0.283 0.344 0.437
Total 99.321 99.596 99.770 99.366 99.491 99.576 99.357
An (mol.
%) 71 73 75 54 56 56 41
108
Table 5c (continued)
Sample
BB-2011-15c-
1_fsp_9
BB-2011-15c-
1_fsp_10
BB-2011-15c-
1_fsp_14
BB-2011-15c-
1_fsp_15
BB-2011-15c-
1_fsp_16
BB-2011-15c-
1_fsp_17
Magma
group Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves Inyo enclaves
SiO2 54.072 53.784 62.968 63.146 59.214 57.847
Al2O3 28.447 28.323 22.699 22.038 24.856 26.273
FeOT 0.553 0.571 0.175 0.177 0.157 0.169
MgO 0.006 0.043 0.000 0.000 0.000 0.000
CaO 11.386 11.575 4.505 4.069 7.677 8.490
Na2O 4.648 4.543 8.228 8.488 6.843 6.181
K2O 0.273 0.294 1.060 1.205 0.514 0.451
Total 99.385 99.133 99.635 99.123 99.261 99.411
An (mol. %) 57 57 22 20 37 42
109
Table 6: Compilation of isotopic data for the Long Valley Volcanic Field.
Sample Reference Magma group 87
Sr/86
Sri 143
Nd/144
Nd εNd 206
Pb/204
Pb 207
Pb/204
Pb 208
Pb/204
Pb δ18
O
IC-48f 1 Mono domes 0.706073 0.512592 -0.90 19.115 15.685 38.911
M14-1A 2 Mono domes
0.512680 0.90
Pao3 2 Paoha Island 0.706330 0.512650 0.20
Neg-
RD2 2 Negit Island 0.706310 0.512530 -2.00
M14-1B 2 Dome 14 enclave 0.705260 0.512780 2.90
D85-56 3 Basalt 0.705160 0.512760
19.190 15.690 38.940
RCQyb-
1 4 Basalt 0.705210 0.512770
19.220 15.680 38.910
RCQyb-
2 4 Basalt 0.705310 0.512770
19.220 15.680 38.910
2011-24 4 Basalt 0.705380 0.512670
19.220 15.660 38.830
2011-22 4 Basalt 0.706160 0.512580
19.250 15.670 38.890
IC-47v 1 Inyo domes 0.706050 0.512551 -1.70 19.142 15.683 38.902
IC-52f 1 Inyo domes 0.706077 0.512614 -0.51 19.120 15.677 38.892
IC-50f 1 Inyo domes 0.706192 0.512564 -1.44 19.162 15.679 38.887
I-5-23 5 Inyo domes 0.706200 0.512595
8.30
I-3-2 5 Inyo domes 0.706320 0.512565
7.90
I-2-2 5 Inyo domes
0.512666
8.10
I-3-20 5 Inyo domes
8.10
I-3-26 5 Inyo domes
8.40
LV-9 5 Inyo domes
8.00
IC-46f 1 Inyo domes 0.706063
19.136 15.674 38.867
IC-49f 1 Inyo domes 0.706195
19.154 15.667 38.846
IC-51v 1 Inyo domes 0.706034
19.123 15.678 38.882
IC-53v 1 Inyo domes 0.706090
19.125 15.673 38.895
WCTba 4 precaldera mafic 0.706030 0.512470
GSTba 4 precaldera mafic 0.706080 0.512490
18.900 15.630 38.800
D85-55 3 precaldera mafic 0.706090 0.512400
MSTba 4 precaldera mafic 0.706130 0.512450
18.930 15.660 38.870
D85-235 3 precaldera mafic 0.706230 0.512500
8 6 precaldera mafic 0.707440
18.704 15.663 38.921
4 6 precaldera mafic 0.706750
18.891 15.649 38.890
12 6 precaldera mafic 0.704310
19.117 15.626 38.847
7 6 precaldera mafic 0.706280
18.889 15.640 38.877
6 6 precaldera mafic 0.706440
18.896 15.655 38.890
5 6 precaldera mafic 0.705980 18.862 15.640 38.833
110
Table 6 (continued)
Sample Reference Magma group 87
Sr/86
Sri 143
Nd/144
Nd εNd 206
Pb/204
Pb 207
Pb/204
Pb 208
Pb/204
Pb δ18
O
11 6 precaldera mafic 0.706530
19.018 15.648 38.897
3 6 precaldera mafic 0.706070
18.914 15.672 38.937
10 6 precaldera mafic 0.706480
19.002 15.660 38.889
9 6 precaldera mafic 0.705990
19.002 15.681 38.949
1 6 precaldera mafic 0.706310
18.873 15.663 38.913
2 6 precaldera mafic 0.706350
18.916 15.686 38.950
cDP83-85 7 precaldera mafic 0.706220
cDP83-90 7 precaldera mafic 0.706290
cDP83-100 7 precaldera mafic 0.706180
cDP83-94 7 precaldera mafic 0.706700
cDP83-68 7 precaldera mafic 0.707020
DP78-34 7 precaldera mafic 0.707390
cDP83-81 7 precaldera mafic 0.707320
CT72-1 8 precaldera mafic 0.706010
OAB-1 9 precaldera mafic 0.706130
M72-19 8 precaldera mafic 0.706330
CT74-2 8 precaldera mafic 0.705960
D85-191 3 precaldera mafic 0.705950
D85-204 3 precaldera mafic 0.705940
YG WR 10 precaldera felsic 0.706270 0.512580 -1.20
YE WR 10 precaldera felsic 0.706540 0.512600 -0.80
YO WR 10 precaldera felsic 0.706580 0.512580 -1.20
YA WR 10 precaldera felsic 0.707180 0.512590 -1.00
YK WR 10 precaldera felsic 0.707240 0.512590 -1.00
DP78-33 7 precaldera felsic 0.707240
DP78-35 7 precaldera felsic 0.709490
B69 11 Bishop Tuff 0.706000 0.512584
6.82
B77 11 Bishop Tuff 0.706670 0.512574
8.09
B143 11 Bishop Tuff 0.706820 0.512590
7.41
B107 11 Bishop Tuff 0.706830 0.512567
8.49
B94 11 Bishop Tuff 0.707280 0.512574
5.88
HCQpb 4 postcaldera mafic 0.705910 0.512550
19.190 15.640 38.790
SSQab 4 postcaldera mafic 0.705960 0.512560 19.260 15.710 38.990
111
Table 6 (continued)
Sample Reference Magma group 87
Sr/86
Sri 143
Nd/144
Nd εNd 206
Pb/204
Pb 207
Pb/204
Pb 208
Pb/204
Pb δ18
O
2123.5 4 postcaldera mafic 0.705960 0.512590
19.170 15.670 38.860
2159.1 4 postcaldera mafic 0.705970 0.512590
19.190 15.670 38.880
2209 4 postcaldera mafic 0.705970 0.512590
19.230 15.720 39.000
2130.4 4 postcaldera mafic 0.705980 0.512570
19.230 15.740 39.070
L82-107 3 postcaldera mafic 0.706030 0.512520
DPQpb 4 postcaldera mafic 0.706130 0.512290
19.170 15.680 38.890
686.6 4 postcaldera mafic 0.706170 0.512530
19.190 15.680 38.900
883.3 4 postcaldera mafic 0.706180 0.512510
LMQa-1 4 postcaldera mafic 0.706200 0.512430
19.250 15.710 39.000
MLQab 4 postcaldera mafic 0.706200 0.512500
19.270 15.700 38.980
527 4 postcaldera mafic 0.706200 0.512520
19.160 15.740 39.030
LMQa-3 4 postcaldera mafic 0.706200 0.512530
19.230 15.700 38.950
503.4 4 postcaldera mafic 0.706210 0.512520
19.200 15.730 39.060
540.4 4 postcaldera mafic 0.706220 0.512470
19.180 15.720 39.030
DCQgb-1 4 postcaldera mafic 0.706230 0.512530
19.180 15.690 38.920
405.8 4 postcaldera mafic 0.706260 0.512480
19.160 15.680 38.880
DCQab 4 postcaldera mafic 0.706280 0.512470
19.200 15.680 38.920
PBQa-1 4 postcaldera mafic 0.706280 0.512530
19.170 15.670 38.880
PBQa-3 4 postcaldera mafic 0.706290 0.512510
MMQpb 4 postcaldera mafic 0.706290 0.512550
19.240 15.710 39.010
PBQa-2 4 postcaldera mafic 0.706300 0.512520
19.180 15.680 38.890
127.8 4 postcaldera mafic 0.706310 0.512520
19.170 15.680 38.870
BSQpb 4 postcaldera mafic 0.706330 0.512520
19.240 15.690 38.970
RMQa 4 postcaldera mafic 0.706330 0.512530
19.240 15.710 38.990
LVQpb 4 postcaldera mafic 0.706340 0.512470
19.220 15.660 38.880
73.8 4 postcaldera mafic 0.706380 0.512510
19.190 15.700 38.940
TBQob-2 4 postcaldera mafic 0.706400 0.512390
18.900 15.600 38.710
TBQob-1 4 postcaldera mafic 0.706460 0.512420
18.920 15.640 38.830
TFQpb 4 postcaldera mafic 0.706670 0.512480
19.210 15.710 38.980
HLQpb 4 postcaldera mafic 0.706700 0.512470
19.180 15.670 38.890
DP73-1 8 postcaldera mafic 0.706320
D85-59 3 postcaldera mafic 0.705990
LV-10 9 postcaldera mafic 0.706250
19.240 15.700 38.990
DPQaq 4 postcaldera felsic 0.706360 0.512560 19.220 15.700 38.990
112
Table 6 (continued)
Sample Reference Magma group 87
Sr/86
Sri 143
Nd/144
Nd εNd 206
Pb/204
Pb 207
Pb/204
Pb 208
Pb/204
Pb δ18
O
M72-92 8 postcaldera felsic 0.706290
DP73-140 8 postcaldera felsic 0.706300
IC-10v 1 postcaldera felsic 0.706733 0.512516 -2.38 19.250 15.663 38.908
IC-37o 1 postcaldera felsic 0.706647
19.271 15.678 38.964
IC-22o 1 postcaldera felsic 0.706563 0.512541 -1.89 19.236 15.666 38.877
IC-06v 1 postcaldera felsic 0.706686 0.512523 -2.24 19.298 15.699 39.028
IC-08v 1 postcaldera felsic 0.706589
19.264 15.673 38.927
IC-09v 1 postcaldera felsic 0.706545 0.512529 -2.16 19.254 15.672 38.928
IC-12o 1 postcaldera felsic 0.706621
19.237 15.660 38.872
IC-15v 1 postcaldera felsic 0.706631
19.260 15.672 38.905
IC-16v 1 postcaldera felsic 0.706554
19.242 15.661 38.881
IC-25o 1 postcaldera felsic 0.706547
19.228 15.664 38.879
IC-32v 1 postcaldera felsic 0.706636 0.512546 -1.79 19.213 15.670 38.873
IC-35v 1 postcaldera felsic 0.706626 0.512520 -2.30 19.279 15.695 39.016
IC-18v 1 postcaldera felsic 0.706640
19.241 15.678 38.930
IC-20v 1 postcaldera felsic 0.706568 0.512542 -1.87 19.265 15.684 38.970
IC-31f 1 postcaldera felsic 0.706401 0.512561 -1.50 19.232 15.691 38.954
IC-30f 1 postcaldera felsic 0.706389 0.512580 -1.13 19.252 15.703 39.002
IC-29f 1 postcaldera felsic 0.706415 0.512539 -1.93 19.277 15.682 38.927
IC-02f 1 postcaldera felsic 0.706292 0.512571 -1.31 19.206 15.671 38.875
IC-42f 1 postcaldera felsic 0.706299 0.512548 -1.76 19.191 15.696 38.959
IC-24f 1 postcaldera felsic 0.706135 0.512572 -1.29 19.175 15.682 38.921
IC-38f 1 postcaldera felsic 0.706120 0.512564 -1.44 19.159 15.678 38.896
IC-05f 1 postcaldera felsic 0.706422 0.512578 -1.17 19.216 15.686 38.922
IC-03f 1 postcaldera felsic 0.706454 0.512600 -0.74 19.245 15.728 39.048
IC-04f 1 postcaldera felsic 0.706486 0.512589 -0.96 19.245 15.717 39.027
IC-01v 1 postcaldera felsic 0.706390 0.512582 -1.09 19.212 15.687 38.930
IC-41f 1 postcaldera felsic 0.706317 0.512565 -1.42 19.182 15.687 38.930
IC-40f 1 postcaldera felsic 0.706331 0.512563 -1.46 19.178 15.689 38.928
IC-39f 1 postcaldera felsic 0.706315 0.512542 -1.87 19.178 15.690 38.932
BSJg 4 Sierran granitoid 0.706660 0.512610
19.290 15.660 38.980
DPKg 4 Sierran granitoid 0.707510 0.512230
18.930 15.650 38.850
RCKg 4 Sierran granitoid 0.707790 0.512280 18.960 15.640 38.840
[Sources: 1. Heumann and Davies (1997); 2. Kelleher (1986); 3. Ormerod (1986); 4. Cousens (1996); 5.
Sampson and Cameron (1987); 6. Van Kooten (1981); 7. Chaudet (1986); 8. Bailey (2004); 9. Christensen
and DePaolo (1993); 10. Davies and Halliday (1998); 11. Halliday et al. (1984)]