adakites mex

www.elsevier.com/locate/jvolgeores

Journal of Volcanology and Geotherm

Sr, Nd and Pb isotope and geochemical data from the Quaternary

Nevado de Toluca volcano, a source of recent adakitic magmatism,

and the Tenango Volcanic Field, Mexico

Raymundo G. Martınez-Serranoa,*, Peter Schaaf a, Gabriela Solıs-Pichardob,

Ma. del Sol Hernandez-Bernalb, Teodoro Hernandez-Trevinoa,

Juan Julio Morales-Contrerasa, Jose Luis Macıasa

aUniversidad Nacional Autonoma de Mexico, Instituto de Geofısica, Laboratorio Universitario de Geoquımica Isotopica (LUGIS),

Ciudad Universitaria, Mexico D.F. 04510, MexicobUniversidad Nacional Autonoma de Mexico, Instituto de Geologıa, Laboratorio Universitario de Geoquımica Isotopica (LUGIS),

Ciudad Universitaria, Mexico D.F. 04510, Mexico

Received 24 November 2003; accepted 22 June 2004

Abstract

Volcanic activity at Nevado de Toluca (NT) volcano began 2.6 Ma ago with the emission of andesitic lavas, but over the past

40 ka, eruptions have produced mainly lava flows and pyroclastic deposits of predominantly orthopyroxene–hornblende dacitic

composition. In the nearby Tenango Volcanic Field (TVF) pyroclastic products and lava flows ranging in composition from

basaltic andesite to andesite were erupted at most of 40 monogenetic volcanic centers and were coeval with the last stages of

NT. All volcanic rocks in the study area are characterized by a calc-alkaline affinity that is consistent with a subduction setting.

Relatively high concentrations of Sr (N460 ppm) coupled with low Y (b21 ppm), along with relatively low HREE contents and

Pb isotopic values similar to MORB-EPR, suggest a possible geochemical adakitic signature for the majority of the volcanic

rocks of NT. The HFS- and LIL-element patterns for most rocks of the TVF suggest a depleted source in the subcontinental

lithosphere modified by subduction fluids, similar to most rocks from the Trans-Mexican Volcanic Belt (TMVB). The isotopic

compositions are similar for volcanic rocks of NT and TVF regions (87Sr/86Sr: 0.703853–0.704226 and 0.703713–0.704481;

qNd: +4.23–+5.34 and +2.24–+6.85; 206Pb/204Pb: 18.55–18.68 and 18.58–18.69; 207Pb/204Pb: 15.54–15.62 and 15.56–15.61;208Pb/204Pb: 38.19–38.47 and 38.28–38.50, respectively), suggesting a MORB-like source with low crustal contamination.

Metamorphic xenoliths from deeper continental crust beneath NT volcano show isotopic patterns similar to those of Grenvillian

rocks of north-central Mexico (87Sr/86Sr: 0.715653–0.721984, qNd: –3.8 to –7.2, 206Pb/204Pb: 18.98–19.10, 207Pb/204Pb: 15.68–15.69, 208Pb/204Pb: 39.16–39.26 and Nd model age (TDM) of 1.2–1.3 Ga). In spite of a thick continental crust (N45 km) that

underlies the volcanoes of the study area, the geochemical and isotopic patterns of these rocks indicate low interaction with this

crust. NT volcano was constructed at the intersection of three fault systems, and it seems that the Plio–Quaternary E–W system

0377-0273/$ - s

doi:10.1016/j.jv

* Correspon

E-mail addr

al Research 138 (2004) 77–110

ee front matter D 2004 Elsevier B.V. All rights reserved.

olgeores.2004.06.007

ding author. Tel.: +52 55 56 22 40 28; fax: +52 55 55 50 24 86.

ess: [email protected] (R.G. Martınez-Serrano).

R.G. Martınez-Serrano et al. / Journal of Volcanology and Geothermal Research 138 (2004) 77–11078

played an important role in the ascent and storage of magmas during the recent volcanic activity in the two regions. Chemical

and textural features of orthopyroxene, amphibole and Fe–Ti oxides from NT suggest that crystallization of magmas occurred at

polybaric conditions, confirming the rapid upwelling of magmas.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Geochemistry; isotopes; volcanic rocks; Adakites; Nevado de Toluca; Mexico

1. Introduction

Nevado de Toluca (NT) volcano and the Tenango

Volcanic Field (TVF) belong to the Trans-Mexican

Volcanic Belt (TMVB) in central Mexico (Fig. 1).

This is one of the best-studied volcanic zones

because of its accessibility and position next to the

cities of Mexico and Toluca. The TMVB is

considered to be a continental magmatic arc that

transects central Mexico with an almost E–W

orientation, from the Pacific Ocean to the Gulf of

Mexico. Activity in this volcanic arc apparently

started at about 16 Ma (Ferrari et al., 1994) and

continues until today. The TMVB is 1200 km long,

and can be divided into three regions on the basis of

petrological, tectonic and volcanological character-

istics (Pasquare et al., 1988 and references therein).

The western region consists of alkaline and calc-

alkaline volcanic rocks at the Colima–Chapala–Tepic

junction. The central region is composed of extensive

monogenetic volcanism and by higher stratovolca-

noes with predominantly calc-alkaline compositions.

The eastern region is characterized by the presence

of some dacitic-rhyolitic stratovolcanoes and mono-

genetic volcanic fields with alkaline–calc-alkaline

composition. Volcanism in the TMVB has been

associated with the subduction of the Cocos and

Rivera plates beneath the North America plate (Fig.

1) (Robin, 1976, 1982; Demant, 1978, 1981; Pal et

al., 1978; Nixon, 1982; Negendank et al., 1985;

Besch et al., 1987; Nixon et al., 1987; Verma and

Nelson, 1989; Ferrari et al., 1999; Wallace and

Carmichael, 1999 and others). However, Mooser

(1972), Cebull and Shurbet (1987), Marquez et al.

(1999) and Verma (1984, 1987, 1999, 2000) pro-

posed that the TMVB is the result of a combination

of several tectonic processes including crustal frac-

turing, a continental rifting scenario associated with

an upwelling mantle, and production of ocean island

basalts (OIB) by a propagating rift opening from

west to east that is related to the effects of a mantle

plume.

Many geological, geochemical, geophysical and

volcanological studies have been carried out on the

TMVB during the past 35 years. In spite of these

studies, little attention has been focussed on the

geochemical and isotopic variations existing in the

rock sequences of stratovolcanoes or monogenetic

volcanic products. Many geochemical and isotopic

(Sr, Nd and Pb) data exist in all regions along the

TMVB. However, most active volcanoes lack detailed

geochemical and isotopic characterization of their

main magmatic events.

In the present study, geochemical and isotopic

characterization of the main products of Nevado de

Toluca and the Tenango Volcanic Field was carried

out in order to improve the understanding of the

chemical evolution of these volcanic structures.

Geochemical data for the Nevado de Toluca and

Tenango Volcanic Field products are then used to

test models accounting for compositional variations

in the source region, contamination and mixing of

magmas. These results can be used to further study

volumetric discharges, cyclicity of eruptions and

tectonic models.

2. Geological setting

NT is the fourth highest peak in Mexico (4680 m

asl) and a thick sequence of several hundreds meters

of Mesozoic and Tertiary metamorphic, carbonate

and volcanic sequences from the Guerrero Block

(Johnson and Harrison, 1990) underlies the volcanic

structures in the study area. Stratigraphic and

petrographic descriptions of these older sequences

are summarized by Garcıa-Palomo et al. (2000,

2002). In these papers and references therein, the

authors propose that NT volcano was constructed at

the intersection of three complex fault systems of

Fig. 1. Location of the TMVB in central Mexico (RFZ=Rivera Fracture Zone, EPR=East Pacific Rise, MAT=Middle America Trench,

CP=Cocos Plate, C=Ceboruco, Co=Colima, P=Paricutın, NT=Nevado de Toluca, Po=Popocatepetl, Pi=Pico de Orizaba, SM=San Martın Tuxtla,

C=Chichon and T=Tacana volcanoes) and the study area. The Tenango Volcanic Field is in the westermost part of the Sierra Chichinautzin. This

was characterized by Bloomfield (1975), Martin del Pozzo (1989), Marquez et al. (1999) and others. Stratovolcanoes are indicated as triangles

and important volcanic cones are shown by white squares. T=Tenango, TC=Tres Cruces, TX=Texontepec, X=Xitle, TA=Tabaquillo,

CH=Chichinautzin, P=Pelado, D=Dos, Iz=Iztaccıhuatl and Po=Popocatepetl.

R.G. Martınez-Serrano et al. / Journal of Volcanology and Geothermal Research 138 (2004) 77–110 79

different ages, orientations and kinematics. These

fault systems are Taxco-Queretaro with a NNW–

SSE orientation, San Antonio with a NE–SW

orientation and Tenango with an E–W direction

(Fig. 2). This last fault system controls the position

of monogenetic volcanoes in the TVF. The fault

systems have coexisted since the late Miocene

(Garcıa-Palomo et al., 2000). Fig. 2 shows a

generalized geologic map and locations of samples

included in this study.

Fig. 2. Schematic geologic map of Nevado de Toluca and the Tenango Volcanic Field with location of samples (modified from Macıas et al.,

1997). Inset shows distribution of the main fault systems (H=horst and G=graben).



2.1. Nevado de Toluca volcano

Cantagrel et al. (1981) proposed that volcanic

activity at NT started some 1.5 Ma with the emplace-

ment of andesitic lava flows that constructed the

primitive volcano (bPaleo-NevadoQ). However,

recently published K–Ar ages from some andesitic

lavas suggest that the volcanic activity started at 2.6

Ma (Garcıa-Palomo et al., 2002). The volcanic

activity at NT between 1.5 Ma and 100 ka was

volcaniclastic, according to Cantagrel et al. (1981). A

thick volcaniclastic sequence of debris avalanches,

lahars and fluvial deposits on the southern flanks of

the volcano give evidence that bPaleo-NevadoQ was

Fig. 3. Composite stratigraphic sequences of NT and, in italics, the TVF. A

Macıas et al. (1997), 2. Bloomfield (1974), 3. Bloomfield and Valastro (197

et al. (2003) and 7. Caballero et al. (2001).

destroyed at least twice by failure of the volcanic

structure (Capra and Macıas, 2000). Macıas et al.

(1997) and Garcıa-Palomo et al. (2002) presented a

detailed stratigraphic description of the main units

emplaced during late Pleistocene and Holocene time

at NT (Fig. 3):

– A debris-avalanche deposit (DAD1), up to 15 m

thick, composed of blocks showing jigsaw-fit

structures, embedded in an indurated coarse sandy

matrix, overlies a paleosoil and a thick sequence

of epiclastic deposits from bPaleo-NevadoQ.Blocks of porphyritic gray juvenile dacite and

red altered dacite from the volcanic structure are

lso indicated are the samples analyzed in this study. Ages from: 1.

7), 4. Cantagrel et al. (1981), 5. Garcıa-Palomo et al. (2002), 6. Arce


present. DAD1 spreads south to a distance of 55

km from the volcano.

– The Pilcaya and Mogote debris flow deposits (PDF

and MDF, Capra and Macıas, 2000) were

emplaced on a pale brown paleosoil. The PDF

deposit shows blocks of gray porphyritic dacite,

red altered dacite, green altered andesite, basalt and

schist from the local basement, all embedded in a

coarse sandy matrix. A block-and-ash flow deposit

that covers the PDF and MDF deposits yielded a14C age of 37 ka (Macıas et al., 1997). Thus, the

age of these debris flow deposits must be N37 ka.

– A thick, pink pumice-rich pyroclastic flow deposit

(PPF) with at least four units was emplaced

around NT. A radiocarbon age obtained by Macıas

et al. (1997) from a tree trunk within the deposit

indicated 42 ka. Outcrops of this unit are scarce

and no samples for geochemical studies were

available.

– The first pumice-fall deposit, dated between 36

and 39 ka, was emplaced on the northern slope of

NT (5 km from the summit, Garcıa-Palomo et al.,

2002). It consists of an alternating sequence of

pumice-fall, pyroclastic-surge and pyroclastic-

flow deposits (3.5 m thick).

– Two violent eruptions at NT produced large

magmatic explosions that destroyed old dacitic

central domes and excavated the present-day

crater. The explosions produced two block-and-

ash flow (BAF in Fig. 3) deposits at 37 and 28 ka,

with a similar maximum thickness of 35 m

(Macıas et al., 1997). Garcıa-Palomo et al.

(2002) identified four BAF deposits that consist

almost entirely of gray porphyritic juvenile dacitic

clasts with minor amounts of pumice, glassy

dacitic lithic clasts and red oxidized dacitic clasts

from the volcanic structure set in ash matrix.

– A fallout deposit with inverse grading, denomi-

nated Lower Toluca Pumice (LTP), covers the

BAF deposits. The LTP is clast-supported with

62% pumice, 27% lithic clasts and 11% crystals

for the entire deposit (Bloomfield et al., 1977). In

the present study, we observed abundant ochre

dacitic pumice fragments with hornblende and

orthopyroxene, lesser amounts of gray dense

juvenile dacite, altered dacitic clasts and meta-

morphic fragments (xenoliths) such as gneiss,

schists and phyllites from the local basement.

Isolated crystals of euhedral amphibole, pyroxene

and feldspar are disseminated in this deposit. A

thin ash-flow deposit and a dark-brown paleosoil

dated at 24.3 ka (Bloomfield and Valastro, 1977)

overlie the LTP.

– A younger gray BAF overlies the LTP. It differs

strikingly from the older BAF because it has a

more radial distribution around the volcano. This

unit consists of a gray cross-bedded pyroclastic-

surge deposit overlain by two massive gray block-

and-ash flow units made of block-sized lithic

fragments in a coarse ash matrix with a total

thickness of 10 m (Garcıa-Palomo et al., 2002).

The age of this deposit is uncertain, although

Caballero et al. (2001) assumed an age N14 ka.

– The Middle Toluca Pumice (MTP; Cervantes et

al., 2004) consists of a complex sequence of three

fallout layers, two pyroclastic-surge deposits, and

two massive pumice-rich pyroclastic-flow depos-

its (7 m thick), the reason for which it was first

dubbed as the White Pumice Flow (WPF). The

age of the MTP was defined through 14C dates of

charcoal found inside the pyroclastic-flow depos-

its at 12.1 ka (Garcıa-Palomo et al., 2002).

– Pumice-fall deposits, a pyroclastic-flow, and

pyroclastic-surge beds, with a minimum age of

11 ka (14C, Bloomfield and Valastro, 1974, 1977)

(Fig. 3) were referred to by these authors as the

Upper Toluca Pumice (UTP). Macıas et al. (1997)

and Arce et al. (2003) refined the stratigraphy of

this deposit, that in some places reaches a total

thickness of about 30 m. These authors recognized

four pumice-fall layers that contain abundant pink

pumice, banded pumice, gray juvenile dacite

clasts and altered andesitic lithics, within an ash

matrix. Pyroclastic-surge deposits with cross-

stratification, dunes and antidunes are intercalated

in the sequence. The volcanic products of the UTP

cover an area of 2000 km2 with a minimum

estimated volume of 8 km3 with an age of 10.5 ka

(14C) (Arce, 2003). The UTP event ended with the

emplacement of a dacitic dome in the Nevado de

Toluca crater.

– Gray cross-stratified pyroclastic-surge deposits

and pyroclastic-flow deposits dated by Macıas et

al. (1997) at 3.3 ka (14C) represent the most recent

volcanic event at NT, and indicate that activity has

continued into Holocene time.


2.2. Tenango Volcanic Field

The TVF represents the westernmost part of the

Sierra Chichinautzin (Fig. 1) described by Bloomfield

(1975), Martin del Pozzo (1989), Marquez et al.

(1999, 2001) and others. The Sierra Chichinautzin

consists of nearly 220 Quaternary monogenetic

volcanic cones with an E–W general structural

orientation. This volcanic province is bracketed by

NT to the west, Popocatepetl volcano to the east and

by the Mexico Basin in the north (Fig. 1). The TVF

(Fig. 2) is composed of more than 40 volcanic

monogenetic cones and associated lava flows with

ages from 8 to N38.5 ka BP (Bloomfield, 1975).

Cinder cones, lava cones and effusive fissural lava

flows with andesite and basaltic-andesite composi-

tions dominate in the TVF. The cone density in the

TVF is 0.5/km2 but locally reaches 1/km2; the mean

cone height is 650 m.

The cinder cones consist of dark gray to brick-red

scoria and ash fragments with diameters of 0.5–7 cm,

in layers 3–15 cm thick and dips from 208 to 268.Well-sorted scoria and a small proportion of bombs

are the main ejecta products of the cinder cones. Thin

lenses of lava are present in some cone sequences.

Bloomfield (1975) described the presence of at least

220 separate beds of black ash in some cinder cones

that indicate repeated short eruptive pulses.

The lava cones are made up of angular to

subangular lava blocks with sizes of 1–30 cm, that

form dip layers of 258. Although scoria fragments are

rare in these volcanoes, thin lenses (35 cm thick) are

occasionally observed in lavas. The effusive fissure-

fed lava flows are the most recent volcanic events

(b8.5 ka, Bloomfield, 1975) in the TVF. These lava

flows have the greatest length (~8 km long) and

volume of those in the area. The fissure-fed lava flows

are mainly aa-type and in minor proportion appear as

pahoehoe and lava blocks. A complex set of faults and

fractures with a similar E–W orientation to that

observed in the Sierra Chichinautzin seems to control

the distribution of volcanic cones in the TVF as well

(Fig. 2). Mooser and Maldonado-Koerdell (1961) and

Bloomfield (1974) have presented the relationships

between these structures and the monogenetic activity,

and Garcıa-Palomo et al. (2000) proposed that this

fault system is a continuation of the older Chapala-

Tula Fault Zone that has been reactivated during

Pleistocene–Holocene times. Fig. 3 shows the relative

ages of volcanic events for the TVF on the basis of

radiocarbon age data and morphologic characteriza-

tion of cones developed by Bloomfield (1975). We

used the nomenclature proposed by Bloomfield

(1975) to describe the volcanic cone ages: PLV1c40

ka, PLV2c30 ka, PLV3 from 18.6 to 21.9 ka and

HVb8.5 ka (Fig. 3). These data suggest that volcanic

events in the TVF have occurred simultaneously with

the emplacement of some pyroclastic deposits at NT.

3. Analytical methods

A representative suite of volcanic products (N100

samples) was obtained on the flanks of NT and

around the TVF (Figs. 2 and 3). Pumice, lava and

scoria fragments were sampled considering their

stratigraphic position. Thin sections were studied to

assess the mineralogy and petrography of the rocks

and fresh samples were selected for bulk chemical

analyses and Sr, Nd and Pb isotopic determinations.

Metamorphic xenolith fragments from the LTP were

handpicked for geochemical and isotopic studies.

Major-elements and Sc abundances were determined

by inductively coupled plasma-emission spectro-

scopy, and all other trace elements by inductively

coupled plasma mass spectrometry (ICP-MS) at the

analytical laboratories of the Centre de Recherches

Petrographiques et Geochimiques, Nancy, France

(SARM, 2003). Sr, Sm, Nd and Pb isotopic ratios

of whole rock samples were measured using a

Finnigan MAT 262 thermal ion mass spectrometer

at LUGIS (Laboratorio Universitario de Geoquimica

Isotopica), UNAM. The spectrometer is equipped

with a variable multicollector system (eight Faraday

cups) and all measurements were done in static

mode. Rb isotope ratios were measured with an NBS

type single collector mass spectrometer (Teledyne

Model SS-1290). Rb, Sr, Sm and Nd samples were

loaded as chlorides on double rhenium filaments and

measured as metallic ions. Lead samples were loaded

with a mixture of silica gel+phosphoric acid. Sixty

isotopic ratios were determined for Rb, Sr, Sm and

Nd, and 100 for Pb on each sample. Elements were

separated using standard ion-exchange methods.

Total procedure blanks during analyses of these

samples were less than: 1 ng Rb, 10 ng Sr, 1 ng


Sm, 20 ng Nd and 300 pg Pb. More than 350

analyses of pyroxene, amphibole, olivine, Fe–Ti

oxides and feldspar from lava samples and juvenile

fragments from pyroclastic deposits were carried on

an automated CAMECA SX100 electron microprobe

(University of Barcelona, Spain). An acceleration

voltage of 15 kV was used. The excitation current

varied from 8 to 10 nA and the counting time was 10

s. The maximum analytical error in major oxides is

estimated to be less than 3%.

4. Results

4.1. Mineral studies and petrographic characteristics

Sixty samples from NT and the TVF were studied

petrographically, and a subset of them were analyzed

by electron microprobe. Table 1 shows modal

Table 1

Modal mineral assemblages (vol.%) of selected NT and TVF lava and py

Sample Phenocrysts Groundmass

Plag

(An32–54)

Horn Opx Cpx Oliv Qtz Plag

(Ab32–54)

B

Nevado de Toluca

NT9 4 3 2 0 0 0 1 0

NT12 7 4 2 0 0 0 1 0

NT13 7 5 2 0 0 0 1 0

NT6 21 5 3 0 0 0 20 1

NT8 4 2 2 0 0 0 2 0

NT33 7 4 2 0 0 0 2 0

NT14 7 6 1 0 0 0 0 1

NT10 11 5 3 0 0 0 5 0

NT11 20 7 4 0 0 0 40 1

NT15 24 5 3 1 0 1 25 2

NT17 20 3 3 1 0 1 15 1

NT22 20 4 2 0 0 1 15 1

NT24 25 7 4 3 0 1 50 0

NT29 30 3 2 4 0 0 41 0

NT30 27 3 3 5 0 0 50 0

Tenango Volcanic Field

TEO1 2 0 3 5 1 5 56 0

TEP1 0 0 0 7 2 0 50 0

RMS7 0 0 2 6 1 0 67 0

RMS8 0 0 2 5 2 0 75 0

RMS9 0 0 2 5 2 0 73 0

JAJ1 20 0 2 2 0 1 66 T

Plag=Plagioclase, Horn=hornblende, Opx=orthopyroxene (hypersthene),

Biot.=biotite, Oxides=Fe–Ti oxides, Zr=zircon, Ap=apatite, C. mins=clay

mineralogical analyses and petrography of the major-

ity of the samples. Lava, pumice and other pyroclastic

samples from NT display porphyritic textures, with a

predominantly dacitic composition. However, ande-

sites have been observed in the earliest volcanic

events of bPaleo-NevadoQ and also in some pyroclas-

tic materials such as the LTP. Lava and pyroclastic

products show different proportions of crystals, 50

and 10 vol.%, respectively. Phenocrysts of plagio-

clase, amphibole, orthopyroxene (hypersthene) and

rare biotite appear in two sizes in all samples, as

macrophenocrysts (1–2.5 mm) and phenocrysts (b1

mm), although plagioclase and some pyroxene appear

also as microlites in the glassy groundmass. Macro-

phenocrysts of hornblende, plagioclase, and biotite

from dacitic lavas commonly show reaction rims. The

petrography of most NT rocks is very similar. Phase

abundances, without considering vesicular porosity,

range as follow: plagioclase (oligoclase–andesine)

roclastic samples

iot Oxides Other phases Glass Total Petrography

1 0 89 100 Dacitic pumice


1 Zr, Ap=T 83 100 Dacitic pumice

2 0 48 100 Andesitic tuff

2 0 88 100 Andesitic pumice



1 C. mins=T 75 100 Dacite

1 0 27 100 Dacite

1 Zr, Ap=T 38 100 Dacite

11 Zr, Ap=T 45 100 Dacite

7 0 50 100 Dacite

4 0 7 100 Andesite

5 Xen=8 7 100 Andesite

5 0 7 100 Andesite

5 0 25 100 Andesite

2 0 39 100 Basaltic-andesite

2 0 22 100 Andesite



2 0 7 100 Andesite

Cpx=clinopyroxene (augite-diopside), Oliv=olivine, Qtz=quartz,

minerals, T=traces, Xen=xenoliths.


between 4 and 50 vol.%, hypersthene between 2 and 5

vol.%, hornblende between 2 and 7 vol.%, Fe–Ti

oxides b2 vol.% and biotite appears in traces (b1

vol.%). The glassy matrix is very abundant (N30

vol.%). A typical characteristic of most pumices and

dacitic lavas from NT is the presence of orthopyrox-

ene (hypersthene) and the absence of clinopyroxene,

although some dacitic flows display rare phenocrysts

of augite. This petrographic characteristic is rarely

observed in rocks of the TMVB.

Rocks from the TVF show a predominantly

andesitic composition, although basaltic andesites have

also been observed. All samples from this field show

aphanitic textures with rare disseminated phenocrysts

(~1 mm) of plagioclase, pyroxene and olivine (Table

1). Phase abundances are: plagioclase in microlites ~55

vol.%, andesitic glass between 10 and 40 vol.%, ortho-

and clinopyroxene ~7 vol.%, Fe–Ti oxides ~3 vol.%

and olivine ~1%. Some TVF samples exhibit xenoliths

of dioritic composition. Minor amounts of quartz (b1

vol.%) exist in some TVF samples and in some NT

andesites. Olivine and xenocrystic quartz coexist in

some TVF samples with textural evidence of disequi-

librium. This is a common characteristic observed in

some Chichinautzin samples. Marquez and De Ignacio

(2002) considered these assemblages as the result of

magma mixing, whereas Siebe et al. (2004) proposed

that similar mineralogy and textures are consistent with

normal fractional crystallization processes and the

assimilation of some wall rock material in the Sierra

Chichinautzin volcanic field.

Plagioclase phenocrysts and microlites in NT

samples show normal and reverse zoning, twinning

and sieve textures. Some phenocrysts show clear

evidence of multiple periods of dissolution and

growth. In the TVF, plagioclase appears mostly as

microlites, but rare phenocrysts with reaction rims are

also observed. Phenocrysts and microlites show

similar compositions (An32–54) in NT samples,

although reverse zoning leads to more An-rich rims

(An55–58) in some dacitic rocks. Plagioclase in some

TVF andesites displays a more rich An (An54–60)

content than in NT rocks. For comparison, plagio-

clases from two important pumice events of Popoca-

tepetl volcano show values more rich in An than those

from our study area (An60–80, Siebe et al., 1999).

Olivine is commonly present in TVF basaltic

andesites as disseminated phenocrysts or as rare

glomerophenocrysts associated with clinopyroxene

and minor plagioclase. The crystals vary from

subhedral to anhedral in shape and skeletal forms

are also observed. Analyses of olivine show homoge-

neous compositions (Fo84–86). Some crystals display

evidence of disequilibrium conditions such as coronas

of reaction rims of clinopyroxene. Iddingsite as

secondary alteration of the olivine is observed in

some rocks.

In some dacitic NT samples, clinopyroxene is

present as rare subhedral phenocrysts (~1 mm) with

reaction rims of orthopyroxene and amphibole, and

the composition ranges from salite to diopside-augite

with minor proportions of endiopside (Wo41–47,

En41–50, Fs5–14). Clinopyroxene is absent in most

NT pumices and other pyroclasts. In TVF rocks

clinopyroxene appears as subhedral to anhedral

phenocrysts (~1 mm), commonly small isolated

crystals in the groundmass or in minor proportions

as corona reaction rims on quartz. Twinning and

zoning are rarely observed, and disequilibrium

conditions of crystallization can been inferred from

the presence of reaction borders in some samples.

Most analyses are augite to diopside, although nearly

30% of the analyses fall within the endiopside field.

Clinopyroxene found in quartz corona reaction rims

shows compositions of Wo38–45, En45–51, Fs8–14 and

very low Al2O3 concentrations (0.29–0.77 wt.%),

whereas isolated crystals disseminated in the same

rock sample display similar compositions (Wo35–45,

En46–53, Fs7–11) but different Al2O3 concentrations

(1.44–4.0 wt.%). Clinopyroxene compositions of NT

and TVF are very similar to values observed in rocks

of Popocatepetl volcano (Siebe et al., 1999).

Orthopyroxene is very common in NT pumice and

lava samples, and a minor phase in TVF rocks. At NT,

it is subhedral to euhedral with several indications of

reaction with the groundmass and sometimes it is

associated with amphibole. Important pumice-fall

deposits such as the UTP and LTP, with wide aerial

distributions in central Mexico contain only orthopyr-

oxene as a ferromagnesian mineral. Macrocrysts and

phenocrysts of hypersthene display zoned borders,

and compositional ranges of En70–78 for cores and

En55–76 for rims. Orthopyroxene shows relatively

variable compositions in dacitic NT lavas, ranging

from En84–90 to En60–67. In TVF rocks, orthopyroxene

is present in microcrystals (b0.4 mm) disseminated in

Table 2

Major oxide and trace element abundances of selected rocks from Nevado de Toluca (A=andesite, B-A=basaltic andesite, D=dacite, D-P=dacitic pumice,

A-P=andesitic pumice, T=tuff)

Sample NT4 NT11 NT15 NT17 NT22G NT22R NT24 NT25 NT29 NT30 NT6

Rock D D D D D D D D A A A-P

Long. W 99847.41V 99839.77V 99845.37V 99845.9V 99846.49V 99846.49V 99846.49V 99846.49V 99847.99V 99848.09V 99847.41VLat. N 19813.36V 19811.12V 1986.37V 1986.95V 18851.29 18851.29 18851.29 18851.29 1988.28V 1988.59V 19813.16V

(wt.%)

SiO2 64.88 65.98 64.87 64.25 63.83 64.05 63.41 63.13 57.41 61.93 59.95

TiO2 0.65 0.64 0.62 0.63 0.70 0.69 0.62 0.70 0.90 0.75 0.70

Al2O3 16.76 16.44 16.57 16.51 16.76 16.66 15.75 16.05 18.47 17.08 18.56

Fe2O3 4.32 4.29 4.31 4.50 4.72 4.66 4.85 4.97 6.77 5.46 4.77

MnO 0.06 0.05 0.05 0.05 0.06 0.06 0.08 0.06 0.09 0.08 0.07

MgO 1.75 1.72 1.79 2.67 1.99 1.98 4.00 3.29 3.23 2.65 2.01

CaO 4.20 4.10 4.15 4.71 4.51 4.43 4.56 5.06 6.26 5.03 4.64

Na2O 4.35 4.41 4.37 4.26 4.27 4.19 4.05 4.25 3.92 4.36 4.28

K2O 1.94 2.01 1.94 1.98 2.02 2.05 2.16 2.02 1.76 1.87 1.28

P2O5 0.17 0.17 0.18 0.20 0.18 0.18 0.17 0.25 0.23 0.18 0.18

LOI 0.80 0.04 1.02 0.13 0.82 0.91 0.75 0.15 0.86 0.47 3.44

Total 99.88 99.85 99.87 99.89 99.86 99.86 100.40 99.93 99.90 99.86 99.88

Trace elements (ppm)

V 71 70 62 77 84 81 71 84 145 113 83

Cr 23 23 29 83 21 22 161 125 20 45 29

Co. 7.56 7.52 8.81 11.33 10.18 9.90 18.21 14.47 17.83 14.74 9.25

Ni 6 b5 21 40 11 10 104 69 8 16 6

Cu 8 7 10 19 13 15 23 19 13 15 8

Zn 71 70 75 76 81 76 70 74 84 78 78

Rb 36.14 37.25 40.70 35.39 37.55 37.87 38.09 32.87 35.22 39.72 19.68

Sr 543 541 527 694 548 560 629 843 678 514 597

Y 14.74 14.73 13.61 14.35 15.42 15.69 14.22 14.36 21.15 22.69 15.72

Zr 149 142 160 160 140 138 135 149 152 163 150

Nb 4.23 4.19 4.97 4.30 4.19 4.12 4.03 4.60 4.24 4.07 4.29

Ba 481 464 513 511 430 413 521 578 397 409 410

La 14.41 14.63 16.64 17.53 13.33 13.11 17.06 22.66 18.30 19.35 13.62

Ce 30.51 30.77 35.10 38.81 28.78 27.18 35.23 47.65 37.61 38.24 31.18

Pr 3.84 3.93 4.47 4.99 3.91 3.69 4.63 6.51 5.40 5.16 4.02

Nd 15.55 15.49 18.45 19.33 15.62 14.89 18.07 24.69 22.69 20.95 15.82

Sm 3.33 3.50 3.86 4.03 3.42 3.33 3.64 5.22 5.29 4.66 3.61

Eu 1.08 1.09 1.17 1.25 1.12 0.96 1.10 1.41 1.49 1.20 1.18

Gd 2.78 3.06 3.22 3.13 3.11 2.89 2.96 3.64 4.38 4.14 3.21

Tb 0.44 0.43 0.43 0.48 0.44 0.42 0.43 0.51 0.64 0.63 0.49

Dy 2.57 2.64 2.50 2.57 2.54 2.53 2.19 2.71 3.73 3.65 2.77

Ho 0.51 0.53 0.48 0.49 0.53 0.50 0.45 0.50 0.73 0.77 0.56

Er 1.34 1.33 1.26 1.32 1.39 1.33 1.26 1.35 1.96 2.05 1.52

Tm 0.22 0.20 0.19 0.20 0.21 0.20 0.18 0.18 0.28 0.30 0.21

Yb 1.33 1.34 1.20 1.23 1.39 1.37 1.25 1.21 1.87 2.10 1.59

Lu 0.22 0.21 0.20 0.19 0.21 0.22 0.19 0.19 0.30 0.32 0.26

Hf 3.77 3.72 4.31 3.99 3.48 3.47 3.37 3.99 3.93 4.48 4.17

Ta 0.38 0.38 0.44 0.37 0.34 0.34 0.37 0.39 0.38 0.37 0.42

Th 3.74 3.82 4.02 3.70 3.35 3.04 4.23 4.15 4.18 4.78 4.29

U 1.47 1.47 1.51 1.34 1.52 1.43 1.71 1.60 1.42 1.59 1.48

Ta/Yb 0.28 0.28 0.37 0.30 0.25 0.25 0.30 0.32 0.20 0.18 0.26

Hf/U 2.57 2.53 2.84 2.98 2.29 2.42 1.97 2.49 2.78 2.81 2.81

Zr/U 101 96 106 120 92 96 79 93 107 102 101

U/Ta 0.39 0.38 0.38 0.36 0.45 0.47 0.40 0.39 0.34 0.33 0.35

Th/Hf 0.99 1.03 0.93 0.93 0.96 0.88 1.26 1.04 1.06 1.07 1.03

Ba/Zr 3.24 3.28 3.20 3.18 3.07 3.00 3.87 3.87 2.61 2.52 2.73

Ba/La 33.35 31.73 30.85 29.12 32.27 31.49 30.50 25.50 21.68 21.15 30.06

La/Nb 3.41 3.49 3.35 4.07 3.18 3.19 4.24 4.92 4.32 4.76 3.18

Th/Ta 9.95 10.01 9.12 9.92 9.75 8.89 11.38 10.69 11.08 12.94 10.32


Sample NT7 NT9 NT14 NT13 NT8 NT10 NT12 NT31 NT32 NT33

Rock D D-P D-P D-P A-P D D-P D D D

Long. W 99839.77V 99839.77V 99839.05V 99841.37V 99839.77V 99839.77V 99841.37V 99845.9V 99845.35V 99845.66VLat. N 19811.12V 19811.16V 1982.76V 1986.33V 19811.12V 19811.12" 1986.33V 1986.95V 1987.17V 19813.37V

(wt.%)

SiO2 63.26 62.35 63.30 63.76 55.59 64.69 63.46 64.90 66.48 62.02

TiO2 0.58 0.65 0.58 0.62 0.68 0.64 0.61 0.61 0.64 0.64

Al2O3 17.39 17.03 16.52 16.54 18.61 16.66 16.53 15.96 16.25 16.93

Fe2O3 4.10 4.34 4.16 4.13 4.82 4.32 4.21 4.16 3.95 4.01

MnO 0.05 0.05 0.06 0.05 0.05 0.05 0.05 0.07 0.07 0.06

MgO 1.78 1.79 1.83 1.69 2.08 1.79 1.75 2.44 1.65 1.70

CaO 4.28 4.28 4.19 4.18 4.44 4.32 4.22 4.41 4.12 4.05

Na2O 4.29 4.21 3.96 4.35 3.31 4.29 4.32 4.31 4.47 4.14

K2O 1.69 1.75 1.89 1.90 1.28 2.06 1.87 2.00 1.98 1.78

P2O5 0.21 0.18 0.16 0.17 0.21 0.15 0.19 0.17 0.15 0.20

LOI 2.25 3.24 3.22 2.46 8.79 0.89 2.65 0.62 �0.04 4.21

Total 99.88 99.87 99.87 99.85 99.86 99.86 99.86 99.65 99.72 99.74


V 66 63 70 62 89 78 64 68 64 55

Cr 32 29 31 28 37 27 28 162 72 69

Co. 7.80 8.21 8.19 7.98 9.29 8.38 8.50 9.49 6.79 7.33

Ni 7 9 13 10 12 6 10 38

Cu 9 10 6 6 14 6 7 21 13 32

Zn 72 79 69 76 75 75 84 78 64 75

Rb 30.15 37.78 39.44 39.60 25.23 37.54 39.43 39.26 41.09 36.86

Sr 569 557 553 547 553 559 541 608 482 470

Y 15.18 14.31 14.83 13.47 16.30 14.67 13.42 15.12 15.25 14.80

Zr 167 163 123 159 173 138 160 143 125 150

Nb 4.99 5.08 4.14 4.91 4.93 3.89 4.89 4.21 4.06 4.80

Ba 528 524 444 528 381 433 505 543 457 531

La 17.70 16.57 12.90 16.62 15.19 12.50 16.18 16.93 12.41 16.42

Ce 32.69 37.56 28.61 35.25 29.36 27.77 33.93 36.16 26.12 31.43

Pr 5.01 4.61 3.86 4.47 4.65 3.58 4.31 4.29 3.13 4.11

Nd 19.77 18.58 15.27 18.92 19.14 14.77 17.38 18.85 13.58 17.51

Sm 3.99 3.86 3.36 3.91 4.42 3.31 3.84 3.87 3.09 3.75

Eu 1.27 1.28 1.01 1.23 1.24 1.02 1.17 1.20 1.01 1.17

Gd 3.52 3.25 3.23 3.21 3.51 2.71 3.02 3.59 3.12 3.64

Tb 0.52 0.52 0.47 0.46 0.57 0.44 0.46 0.51 0.48 0.51

Dy 2.79 2.54 2.45 2.30 3.02 2.43 2.43 2.74 2.69 2.77

Ho 0.51 0.46 0.50 0.46 0.54 0.46 0.45 0.50 0.51 0.49

Er 1.36 1.26 1.41 1.21 1.52 1.31 1.09 1.46 1.52 1.35

Tm 0.21 0.19 0.21 0.16 0.21 0.21 0.17 0.21 0.22 0.19

Yb 1.46 1.31 1.40 1.19 1.49 1.35 1.10 1.38 1.44 1.25

Lu 0.22 0.19 0.22 0.17 0.24 0.21 0.18 0.20 0.22 0.18

Hf 4.34 4.34 3.58 4.27 4.21 3.43 3.83 3.35 3.02 3.50

Ta 0.48 0.46 0.39 0.45 0.42 0.35 0.42 0.30 0.30 0.40

Th 4.76 4.05 3.46 4.02 4.03 3.55 3.88 4.20 3.76 4.19

U 1.69 1.49 1.60 1.65 1.35 1.42 1.49 1.38 1.43 1.42

Ta/Yb 0.33 0.35 0.28 0.38 0.28 0.30 0.38 0.21 0.21 0.29

Hf/U 2.57 2.91 2.24 2.58 3.11 2.40 2.57 2.43 2.11 2.47

Zr/U 99 109 77 96 128 97 107 104 87 105

U/Ta 0.35 0.37 0.46 0.41 0.34 0.40 0.38 0.33 0.38 0.34

Th/Hf 1.10 0.93 0.97 0.94 0.96 1.03 1.01 1.25 1.25 1.19

Ba/Zr 3.16 3.23 3.61 3.33 2.20 3.14 3.16 3.79 3.67 3.55

Ba/La 29.81 31.65 34.40 31.79 25.06 34.61 31.20 32.09 36.87 32.32

La/Nb 3.55 3.26 3.12 3.39 3.08 3.21 3.31 4.02 3.05 3.42

Th/Ta 9.92 8.86 8.81 8.98 9.67 10.10 9.25 14.42 12.43 11.57

(continued on next page)


Major oxide and trace element abundances of selected rocks from Tenango Volcanic Field (A=andesite, B-A=basaltic andesite, D=dacite)

Sample JAJ1 TEO1 STA1 ESP1 TEP1 RMS2 RMS3 RMS4 RMS5 RMS7

Rock A A A A A B-A B-A B-A A A

Long. W 99833.47V 99836V 99826.97V 99826.06V 99826.29V 99823.88V 99824.26V 99825.26V 99829.57V 99831.11VLat. N 1986.91V 1985.76V 1989.80V 1984.23V 1983.5V 19813.35V 19811.78V 1988.91V 1987.95V 1987.04V

(wt.%)

SiO2 59.52 59.78 60.46 60.60 58.74 52.71 54.76 54.62 59.42 59.47

TiO2 0.79 0.72 1.01 0.75 0.78 0.89 1.32 1.20 0.91 0.75

Al2O3 15.99 16.42 16.55 16.41 16.58 15.21 16.02 16.33 16.21 15.66

Fe2O3 6.08 5.77 6.42 5.73 6.06 7.24 7.81 7.69 6.01 6.05

MnO 0.09 0.07 0.10 0.08 0.09 0.11 0.11 0.11 0.08 0.09

MgO 4.42 4.50 3.93 4.38 4.92 8.21 5.80 6.24 4.36 5.24

CaO 6.06 6.06 5.51 5.90 6.41 8.15 6.97 7.05 5.73 6.12

Na2O 3.73 3.91 4.14 4.12 4.05 3.59 4.34 3.96 4.39 4.06

K2O 2.03 1.71 1.90 1.67 1.58 2.17 1.63 1.22 1.71 1.62

P2O5 0.25 0.19 0.31 0.25 0.26 0.62 0.49 0.41 0.31 0.27

LOI 0.95 0.76 �0.02 0.02 0.46 0.60 0.43 0.90 0.60 0.40

Total 99.91 99.89 100.31 99.91 99.93 99.50 99.68 99.73 99.73 99.73


V 124 123 109 107 118 147 131 134 100 117

Cr 170 119 120 198 230 353 197 262 144 254

Co. 33.22 33.85 43.45 37.92 36.07 28.20 25.30 24.60 17.30 19.90

Ni 50 55 52 90 105 198 117 81 81 113

Cu 11 17 19 24 27 34 23 19 21 23

Zn 87 82 95 82 90 81 78 81 72 74

Rb 33.21 27.53 44.02 36.50 34.04 29.80 28.40 21.60 32.60 39.10

Sr 611 649 448 588 623 1310 761 646 583 591

Y 20.15 15.42 23.33 16.94 17.96 26.50 25.50 21.70 17.90 18.10

Zr 150 139 247 181 185 192 208 176 174 150

Nb 4.94 3.83 9.15 5.23 5.11 4.27 14.40 10.20 8.14 4.85

Ba 532 379 538 497 527 1246 563 405 493 562

La 21.73 12.88 25.06 22.71 23.77 59.51 31.80 22.27 21.82 22.94

Ce 49.62 30.54 55.55 51.60 54.15 133.80 67.95 49.05 44.29 47.46

Pr 6.51 3.88 6.85 6.43 6.62 17.70 8.79 6.40 5.71 6.17

Nd 27.47 15.96 26.74 24.70 27.27 77.97 38.14 27.94 24.22 26.88

Sm 5.77 3.43 5.35 4.84 5.17 14.24 7.62 5.86 4.83 5.43


Eu 1.55 1.09 1.45 1.40 1.59 3.81 2.18 1.71 1.49 1.54

Gd 4.21 2.84 4.31 3.84 4.32 10.11 6.18 4.80 4.17 4.23

Tb 0.62 0.44 0.67 0.53 0.59 1.24 0.88 0.72 0.59 0.62

Dy 3.44 2.58 3.89 3.13 3.27 5.72 4.66 4.18 3.36 3.39

Ho 0.65 0.48 0.77 0.53 0.61 1.01 0.98 0.87 0.71 0.74

Er 1.70 1.21 1.92 1.44 1.66 2.35 2.31 2.03 1.73 1.76

Tm 0.25 0.22 0.31 0.21 0.24 0.32 0.35 0.33 0.25 0.25

Yb 1.72 1.32 2.00 1.33 1.47 2.12 2.38 2.05 1.75 1.67

Lu 0.30 0.20 0.31 0.23 0.25 0.31 0.35 0.30 0.24 0.25

Hf 3.55 3.27 5.39 4.04 4.28

Ta 0.51 0.39 0.91 0.55 0.50

Th 4.15 2.85 4.67 4.37 4.42

U 1.57 0.95 1.30 1.34 1.30

Ta/Yb 0.30 0.29 0.45 0.41 0.34

Hf/U 2.27 3.43 4.15 3.01 3.30

Zr/U 96 145 190 135 142

U/Ta 0.38 0.34 0.28 0.31 0.29

Th/Hf 1.17 0.87 0.87 1.08 1.03

Ba/Zr 3.54 2.73 2.18 2.74 2.85 2.71 2.30 2.83 3.75

Ba/La 24.95 29.41 21.47 21.88 22.20 20.94 17.70 18.19 22.59 24.50

La/Nb 4.40 3.36 2.74 4.35 4.65 2.21 2.18 2.68 4.73

Th/Ta 8.14 7.39 5.14 8.02 8.78

Table 2 (continued)


Sample RMS8 RMS9 RMS10 MX84 MX33 MX47 MX49 MX46 MX85 MX45

Rock B-A B-A B-A A A A A A A A

99827.09V 99823.56V 99823V 99827.19V 99826.69V 99828.66V 99831.46V 99825.91 99836.7V 99826.04VLat. N 19810.31V 1989.3V 1989.78V 1980.96V 19813.42V 1987.76V 1986.51V 1984.5V 1983.70V 1986.05V

(wt.%)

SiO2 54.77 53.97 53.92 56.70 61.04 61.25 61.63 60.67 60.12 63.93

TiO2 1.22 1.29 1.30 0.82 0.75 0.80 0.80 0.77 0.72 0.69

Al2O3 16.34 16.30 16.30 16.07 15.92 15.97 16.01 16.12 16.22 16.08

Fe2O3 7.88 7.96 8.12 6.54 5.59 5.43 5.58 5.72 5.59 4.52

MnO 0.11 0.12 0.12 0.10 0.09 0.09 0.09 0.09 0.09 0.07

MgO 5.92 6.14 6.50 6.07 4.91 4.37 4.00 4.69 4.33 2.41

CaO 7.42 7.58 7.50 6.90 5.62 6.02 5.69 6.08 5.78 4.65

Na2O 4.02 4.13 4.14 3.99 4.38 4.25 4.39 4.24 4.10 4.51

K2O 1.23 1.36 1.35 1.41 1.56 1.70 1.86 1.62 1.78 2.03

P2O5 0.38 0.47 0.47 0.24 0.19 0.26 0.26 0.24 0.17 0.22

LOI 0.46 0.36 �0.03 0.12 �0.01 �0.01 �0.01 �0.01 0.63 0.02

Total 99.75 99.68 99.69 98.96 100.04 100.13 100.30 100.23 99.53 99.13


V 138 144 148 119 101 99 105 102 115 79

Cr 220 221 250 262 193 167 145 200 92 58

Co. 24.60 24.80 26.10 43.90 48.40 51.50 56.70 54.90 43.20 70.60

Ni 63 77 89 126 106 76 67 87 18

Cu 25 25 27 35 21 21 19 22 11

Zn 84 84 82 69 63 67 71 66 62

Rb 22.30 24.30 23.70 34.00 26.00 51.00 44.00 35.00 20.00 54.00

Sr 692 679 685 545 465 661 571 573 633 477

Y 23.70 24.80 24.70 18.00 17.00 18.00 18.00 17.00 15.00 16.00

Zr 173 195 194 149 137 176 174 169 124 185

Nb 9.73 12.30 12.50

Ba 431 491 494 495 389 587 528 529 398 604

La 23.93 26.89 27.30 21.60 14.90 28.10 25.10 24.60 14.20 24.80

Ce 51.99 58.26 59.25 50.00 37.00 61.00 60.00 58.00 30.00 51.00

Pr 6.86 7.78 7.85

Nd 30.04 33.64 33.38 24.00 18.00 31.00 27.00 28.00 14.00 25.00

Sm 6.34 7.20 7.34 4.69 3.85 5.66 5.14 4.88 3.55 4.39


Eu 1.95 2.17 2.14 1.53 1.21 1.49 1.65 1.57 1.20 1.32

Gd 5.18 5.45 5.63

Tb 0.77 0.81 0.84 0.60 0.60 0.60 0.60 0.60 0.50 0.60

Dy 4.40 4.47 4.62

Ho 0.93 0.94 0.96

Er 2.26 2.12 2.26

Tm 0.33 0.30 0.32

Yb 2.23 2.20 2.30 1.83 1.74 1.76 1.98 1.82 1.48 1.64

Lu 0.33 0.36 0.36 0.23 0.26 0.26 0.28 0.27 0.22 0.25

Hf

Ta 0.40 0.50 1.20 0.60 0.90 0.60

Th 3.30 2.70 4.30 4.00 3.60 4.90

U 1.10 1.10 1.20 1.70 1.40 1.40

Ta/Yb 0.22 0.29 0.68 0.30 0.49 0.37

Hf/U 3.64 3.09 4.33 2.59 3.00 3.64

Zr/U 135 125 147 102 121

U/Ta 0.33 0.41 0.28 0.43 0.39 0.29

Th/Hf 0.83 0.79 0.83 0.91 0.86 0.96

Ba/Zr 2.49 2.52 2.55 3.32 2.84 3.34 3.03 3.13 3.21 3.26

Ba/La 18.01 18.26 18.10 22.92 26.11 20.89 21.04 21.50 28.03 24.35

La/Nb 2.46 2.19 2.18

Th/Ta 8.25 5.40 3.58 6.67 4.00 8.17


Fig. 4. (a) Total alkalis (Na2O+K2O) vs. SiO2 diagram for volcanic rocks of NT and the TVF (after Le Maitre et al., 1989). Division between

alkaline and subalkaline fields from Irvine and Baragar (1971). (b) Analyzed samples displaying a typical calc-alkaline trend in the AFM

diagram, A=Na2O+K2O, B=Fe2O3T and C=MgO.


the groundmass, with compositions of En70–88, similar

to that observed in orthopyroxene from Popocatepetl

pumices.

Amphibole is relatively abundant in NT rocks as

subhedral to euhedral macrocrysts and phenocrysts,

and in some samples this phase becomes resorbed by

the magma. Amphiboles in dacitic NT rocks are

pargasitic (nomenclature of Leake, 1978), whereas in

UTP and LTP amphiboles fall within the fields of

pargasitic–hornblende and edenitic–hornblende. For

comparison, some amphiboles from Popocatepetl

volcano show compositions that fall in the fields of

pargasite and ferroan–pargasite. In the case of

Popocatepetl and NT volcanoes, hornblende may be

used to identify the volcanic source of regional

pumice deposits.

Quartz abundance is less than 1 vol.% in some

andesitic and dacitic lavas from NT and the TVF. It is

observed as rare phenocrysts with corona reactions of

radiating augite–diopside, indicating disequilibrium.

Fe–Ti oxides are present in all NT and TVF

rocks as rare phenocrysts and as a groundmass

phase. In TVF samples, opaque microlites (1–6

vol.%) of titanomagnetite and ilmenite occur in the

matrix as euhedral–subhedral crystals, b0.7 mm in

size and randomly distributed. In NT rocks, titanif-

erous magnetite is present as sub- to anhedral

phenocrysts (0.1–0.5 mm) and as a groundmass

phase. Magnetite comprises from 1 to 2 vol.% of

lavas and ilmenite is much less abundant. Some-

times, opaque oxides are present as inclusions or as

reaction borders on amphibole.

Glass is in most cases the most voluminous

groundmass phase in NT rocks. This phase displays

a dominant rhyolitic composition, regardless of bulk

lava composition (Arce, 2003). In TVF samples, glass

is also abundant in the matrix with an andesitic

predominant composition.

The LTP is a clast-supported pumice-fall

deposit with 20% of metamorphic and igneous

lithics derived from the local basement. Metamor-

phic xenoliths show diameters varying from 0.5 to

1.5 cm. Handpicking of these metamorphic frag-

ments under a polarizing binocular microscope

Fig. 5. Variation diagrams for (a) SiO2 (wt.%), (b) Al2O3 (wt.%), (c) CaO (wt.%), (d) TiO2 (wt.%), (e) K2O (wt.%) and (f) Cr (ppm) as a

function of MgO (wt.%). Samples NT24 and NT25 represent blocks from an avalanche deposit of NT (see text for discussion). Black circles

represent compositions of lavas from three volcanoes oriented E–W in the TVF.


Fig. 6. Trace-element diagrams for (a) NT and (b) TVF rocks. Primitive mantle normalized using the values of Sun and McDonough (1989).


allowed us to group them into two types: (1)

green low-grade metaigneous schists with chlorite,

epidote and plagioclase along with some phyllite

fragments; (2) high-grade gneiss and some meta-

sedimentary schists.

4.2. Major and trace element results

Table 2 shows major and trace element concen-

trations of NT and TVF rocks analyzed in this work.

Previous chemical data for these areas have been


obtained by Bloomfield (1974, 1975), Macıas et al.

(1997) and Verma (1999), and in some parts of this

paper are cited for comparison. Chemical classifica-

tion of rocks is given in the alkalis vs. SiO2 diagram

in Fig. 4a (Le Maitre et al., 1989). The early

products of NT are andesites (SiO2 from 58 to 62.31

wt.%), whereas the later ones are mainly dacites

(SiO2 from 63 to 67 wt.%) with minor andesites (e.g.

LTP). The TVF rocks have compositions ranging

from basaltic andesites to andesites (53–61 wt.%

SiO2) with rare dacites and basaltic trachy-andesites.

All volcanic rocks in the study area belong to the

subalkaline series as defined by Irvine and Baragar

(1971) (Fig. 4a). They lack iron enrichment, dis-

Fig. 7. Variation diagrams for (a) Th vs. Th/Hf, (b) U/Ta vs. Z

playing a typical calc-alkaline trend in the AFM

diagram of Fig. 4b. This is equivalent to the low- to

medium-Fe suite proposed by Arculus (2003). These

features are consistent with their subduction setting.

Chemical data from Macıas et al. (1997) and Verma

(1999) show patterns similar to our data for rocks of

NT and the western Sierra Chichinautzin. Bloom-

field’s (1975) chemical data show important dis-

persion in values of major elements for the TVF

rocks (Fig. 4a).

NT rocks show a decrease in SiO2 from 67 to

57 wt.% with increasing MgO contents (1.5–4

wt.%). TVF rocks display a similar trend, but with

lower SiO2 concentrations (61–54 wt.%) and higher

r/U and (c) Th/Hf vs. U/Ta of the NT and TVF rocks.

Fig. 8. Chondrite-normalized rare earth element data for (a) NT and (b) TVF rocks, using the values of Nakamura (1974).


MgO (4–7 wt.%) (Fig. 5a). Al2O3 contents are also

characteristic in each volcanic zone. NT rocks

display values from 16.2 to 20.5 wt.% with very

little variation in MgO, whereas the TVF rocks

have a narrow range of Al2O3 (15.8–16.7, Fig. 5b).

CaO and TiO2 concentrations in most NT and TVF


samples are in the range of island volcanic arcs and

correlate positively with MgO (Fig. 5c,d), whereas

K2O correlates negatively with MgO (Fig. 5e). Data

from Macıas et al. (1997) and Verma (1999) show

similar patterns for these elements. However, TiO2

Table 3

Sr, Nd and Pb present-day isotopic compositions for NT and TVF rocks

Sample Agea Rock type 87Sr/86Sr

F1j 143Nd/144Nd

F

Nevado de Toluca volcano

NT15 3300 dacite 0.704150 46 0.512907 1

NT17 3300 dacite 0.703868 43 0.512912 2

NT31 3300 dacite 0.703912 46 0.512887 1

NT6 10,500 andes. pumice 0.703958 36 0.512899 2

NT9 10,500 daci. pumice 0.704226 56 0.512884 2

NT13 10,500 daci. pumice 0.704205 52 0.512886 2

NT12 10,500 daci. Pumice 0.704208 44 0.512876 2

NT14 12,040 daci. pumice 0.703853 48 0.512893 1

NT8 24,000 andes. pumice 0.704039 40 0.512896 1

NT33 24,260 andes. pumice 0.704211 46 0.512855 2

NT4 28,000 dacite 0.703952 40 0.512870 2

NT7 28,000 dacite 0.704019 40 0.512872 2

NT11 37,000 dacite 0.703940 43 0.512901 2

NT10 37,000 dacite 0.703965 55 0.512903 2

NT22G 43,000 dacite 0.703887 44 0.512888 1

NT22R 43,000 dacite 0.703899 43 0.512890 1

NT24 dacite block 0.703702 31 0.512980 2

NT25 dacite block 0.703776 43 0.512945 2

NT29 1,500,000 andesite 0.703923 45 0.512862 3

NT30 1,500,000 andesite 0.703959 38 0.512876 2

NT32 dacite 0.704030 40 0.512832 2

Tenango Volcanic Field

TEO1 8500 andesite 0.703728 48 0.512878 1

TEP1 8500 andesite 0.704165 46 0.512906 1

RMS7 8500 andesite 0.704320 46 0.512948 1

MX84 8500 andesite 0.704141 38 0.512946 1

MX33 8500 andesite 0.703994 45 0.512937 1

MX85 8500 andesite 0.703713 41 0.512831 2

ESP1 19,530 andesite 0.704065 41 0.512901 1

RMS8 19,530 basal. andesite 0.703877 54 0.512989 2

RMS10 19,530 basal. andesite 0.704040 43 0.512957 2

CUATL1 19,530 andesite 0.704005 45 0.512938 2

SIL1 19,530 andesite 0.704167 39 0.512954 1

STA1 30,000 andesite 0.704481 52 0.512753 1

JAJ1 30,000 andesite 0.704028 50 0.512972 1

RMS2 40,000 andesite 0.704338 40 0.512981 2

Isotopic composition for La Jolla Nd standard are 143Nd/144Nd=0.511880F(1j, n=220), for NBS981 standard 206Pb/204Pb=16.89F0.04%, 207Pb/20

standard deviation correspond to the last two digits.a Relative age (years) proposed after data of Bloomfield (1974), Blo

(1997), Garcıa-Palomo et al. (2002) and Arce et al. (2003). daci.=dacitic,

concentrations in some TVF samples (RMS3,

RMS4, RMS8, RMS9 and RMS10; Table 2) are

unusually high (1.2–1.32 wt.% TiO2) for subduc-

tion-zone magmas and more typical of intraplate-

type mafic alkalic rocks. Similar concentrations

1j qNd 206Pb/204Pb

1 S.D.

(%)

207Pb/204Pb

1 S.D.

(%)

208Pb/204Pb

1 S.D.

(%)

7 +5.25 18.573 0.016 15.544 0.017 38.225 0.018

5 +5.34 18.576 0.014 15.556 0.015 38.256 0.015

6 +4.86 18.590 0.019 15.570 0.023 38.310 0.028

8 +5.09 18.577 0.020 15.572 0.020 38.298 0.022

3 +4.80 18.610 0.048 15.587 0.065 38.374 0.087

2 +4.84 18.603 0.017 15.579 0.018 38.342 0.021

1 +4.64 18.607 0.018 15.583 0.021 38.358 0.025

8 +4.97 18.593 0.020 15.585 0.021 38.354 0.023

9 +5.03 18.598 0.027 15.569 0.027 38.314 0.030

2 +4.23 18.635 0.034 15.617 0.035 38.475 0.038

4 +4.53 18.557 0.020 15.548 0.025 38.217 0.026

9 +4.56 18.612 0.018 15.581 0.018 38.359 0.020

0 +5.13 18.554 0.012 15.545 0.013 38.206 0.012

9 +5.17 18.580 0.018 15.576 0.017 38.312 0.018

7 +4.88 18.553 0.017 15.567 0.017 38.192 0.017

8 +4.92 18.555 0.015 15.546 0.016 38.200 0.016

1 +6.67 18.587 0.016 15.570 0.017 38.295 0.016

2 +5.99 18.596 0.019 15.578 0.021 38.332 0.020

8 +4.37 18.677 0.024 15.594 0.027 38.431 0.032

1 +4.64 18.611 0.080 15.568 0.019 38.315 0.018

4 +3.78 18.576 0.020 15.570 0.023 38.294 0.027

7 +4.68 18.581 0.020 15.562 0.025 38.275 0.028

7 +5.23 18.671 0.024 15.595 0.023 38.454 0.023

9 +6.05 18.635 0.020 15.578 0.022 38.369 0.025

9 +6.01

8 +5.83

9 +3.76

9 +5.13 18.679 0.034 15.607 0.039 38.496 0.051

1 +6.85 18.659 0.021 15.595 0.020 38.433 0.020

4 +6.22 18.667 0.025 15.575 0.025 38.386 0.026

1 +5.85 18.689 0.021 15.599 0.019 38.472 0.021

5 +6.16

9 +2.24

5 +6.52 18.616 0.027 15.575 0.028 38.346 0.031

3 +6.69

22 (1j, n=116), for the SRM987 standard 87Sr/86Sr=0.710234F184Pb=15.42F0.06% and 208Pb/204Pb=36.50F0.09%. Values for 1j

omfield and Valastro (1977), Cantagrel et al. (1981), Macıas et al.

andes.=andesitic, basal.=basaltic.


have been determined in other lava samples from

the Sierra Chichinautzin volcanic field (Marquez et

al., 1999; Siebe et al., 2004).

Samples NT24 and NT25 (black squares in Figs.

5 and 7) show a slightly different chemical compo-

sition in comparison to most NT rocks. These

samples are blocks of the debris avalanche deposit

DAD1 south of NT (Fig. 3). Therefore, it is very

likely that the source of these blocks is not NT. On

the other hand, although sample NT29 shows an

andesitic composition, the presence of small xen-

oliths (b8 vol.%) in its matrix seems to affect its

chemical patterns, shifting them away from the

average trend of NT rocks (Figs. 4, 5 and 7).

Samples RMS4, RMS8, RMS9 and RMS10 were

obtained from lava flows produced by three E–W

aligned TVF monogenetic cones with similar ages

(~21 ka) (Fig. 2). Major and trace element concen-

trations for these samples are very similar (black

Table 4

Sr, Nd and Pb present-day isotopic compositions for xenoliths found in th

found in the La Goleta Tertiary volcanic field by Elıas-Herrera et al. (199

Sample NT35PB NT35PV NT35EC NT3

Rock type White phyllite Green phyllite Chlorite schist Gne87Rb/86Sr 5.92 2.94 0.46 6.87Sr/86Sr 0.721098 0.716177 0.705731 0.

F1j 38 39 38 38147Sm/144Nd 0.109 0.127 0.144 0.143Nd/144Nd 0.512281 0.512351 0.512693 0.

F1j 17 18 18 20

qNd �6.96 �5.60 +1.07 �7.

F1j 0.33 0.35 0.35 0.

Rb (ppm)b 111.71 115.72 31.88 89.

Sr (ppm)b 54.70 113.90 199.50 40.

Sm (ppm)b 4.57 3.28 3.04 3.

Nd (ppm)b 25.24 15.64 12.76 18.

TDM (Ga)c 1.27 1.42 1.02 1.206Pb/204Pb 18.984 19.021 18.864 19.

1 S.D. (%) 1.035 0.048 0.131 0.207Pb/204Pb 15.631 15.690 15.632 15.

1 S.D. (%) 1.031 0.052 0.131 0.208Pb/204Pb 39.114 39.162 38.713 39.

1 S.D. (%) 1.039 0.067 0.131 0.

a Data from Elıas-Herrera et al. (1998).b Concentrations obtained by isotope dilution.c Depleted mantle model ages calculated using 147Sm/144Sm=0.2

uncertainties (1j) of 87Rb/86Sr=F2.0% and of 147Sm/144Nd=F2.5%. Relati

laboratory are F4.5%, F1.8%, F3.2% and F2.7%, respectively.

circles in Fig. 5), suggesting that the same magmatic

source fed these vents.

Relatively high contents of compatible elements

are observed in rocks of the TVF, such as Cr 92–353

ppm, Ni 50–198 ppm and Co 17–56 ppm. These

relatively high values, coupled with Mg#

(MgO�100/(MgO+Fe2O3)) between 34 and 53, and

SiO2 compositions indicate that magmas of this

region were produced by fairly primitive melts. In

contrast, dacitic pumice and lava flows of NT

volcano show lower concentrations of these trace

elements (Cr 20–83 ppm, Ni 0–20 ppm and Co 6–11

ppm) and Mg# 28–37. The TVF rocks exhibit a

positive correlation between Cr (Fig. 5f), Ni and

MgO, but no similar correlation is observed in rocks

of NT (Fig. 5f). These results indicate the importance

of crystal fractionation processes in melts from the

TVF. However, element ratios such as Th/Hf vs. Th

(Fig. 7a) indicate that partial melting processes have

e Lower Toluca Pumice of NT volcano and for high-grade xenoliths

8)

5EM NT35EN NT35PN PEP2a PEP3a

iss Schist Phyllite Gneiss Gneiss

34 6.25 4.02 – –

721887 0.717112 0.715653 – –

37 32 – –

111 0.109 0.114 0.130 0.138

512268 0.512442 0.512279 0.512296 0.512263

18 20 – –

22 �3.82 �7.00 �6.67 �7.32

39 0.35 0.39 – –

66 124.88 125.28 – –

95 57.89 90.17 – –

47 4.53 5.73 4.99 4.63

90 25.18 30.42 23.17 20.17

32 1.04 1.34 1.54 1.79

036 19.100 19.025 – –

022 0.062 0.075 – –

694 15.679 15.675 – –

136 0.074 0.076 – –

256 39.224 39.223 – –

154 0.099 0.075 – –

14 and 143Nd/144Nd=0.51316 (Goldstein et al., 1984). Relative

vely reproducibility (1j) for Rb, Sr, Sm and Nd concentrations at the

Fig. 9. Sr vs. qNd present-day isotopic ratios for NT and TVF rocks. Inset shows isotopic composition of metamorphic xenoliths found in the

LTP and data of the Guerrero terrane from Talavera-Mendoza et al. (1995). Data of Colima volcano from Verma and Luhr (1993), data of

Popocatepetl from Schaaf et al. (2002, submitted for publication), and average isotopic data of DSDP 487 and 488 Cocos plate sediments,

Mexico from Verma (2000).


also played an important role in the composition of

magmas from the study area.

Variation diagrams for trace elements are shown

in Fig. 6a,b. Trace-element patterns of NT and

TVF samples are very similar, with enrichment in

the large-ion lithophile elements (LILE) relative to

the high-field-strength element (HFSE). This

enrichment is typical of calc-alkaline volcanic arcs.

All rocks show negative Nb anomalies as well as

several other negative anomalies (P, Ta and Ti) that

are also characteristic of subduction-related magma-

tism (e.g. Gill, 1981; Pearce, 1983; Walker et al.,

2001). The patterns of the immobile elements (Nb,

Zr, Hf, Ti, Y and Yb) on the variation diagrams

and the enrichment in LILE suggest a depleted

mantle source in the subcontinental lithospheric

mantle modified by subduction fluids, which have

added the more mobile elements (Rb, Ba, K and

maybe Pb) (Pearce, 1983; Wilson, 1989). NT rocks

display little chemical variation for the major and

trace elements such as Y (11–17 ppm), Hf (3.4–4.5

ppm), Zr (123–180 ppm) and Nb (3.9–5.0 ppm). In

contrast, TVF rocks show a wide variation Y (15–

25 ppm), Hf (3.3–5.4 ppm), Zr (124–219 ppm) and

Nb (3.8–14.4 ppm) (Table 2). These HFSE data,

along with some ratios of incompatible elements

such as Zr/U vs. U/Ta and U/Ta vs. Th/Hf (Fig.

7b,c), may suggest that NT products were produced

by a relatively homogeneous magmatic source,

whereas the volcanic rocks from the TVF were

Fig. 10. Plot of 207Pb/204Pb–206Pb/204Pb for whole-rock samples of NT and the TVF. Reference lines are the two-stage terrestrial lead evolution

curve (Stacey and Kramers, 1975), graduated at 250 Ma intervals (SK), and the Northern Hemisphere Reference Line (NHRL) (Hart, 1984). Pb

isotopic data for the Paleozoic Acatlan complex are from Martiny et al. (2000). Data for the Oaxaca Complex field from Solari et al. (1998).

MORB-EPR data are from PETDB (2002), Pacific Ocean Sediments (POS) from Church and Tatsumoto (1975) and Hemming and McLennan

(2001). Pb isotopic data of DSDP 487 and 488 Cocos plate sediments, Mexico from Verma (2000).


probably derived from a more heterogeneous

source.

The rare earth element (REE) abundances in the

NT and TVF samples show similar trends. Chondrite-

normalized REE patterns display light rare earth

element enrichment (LREE, La–Sm) and relatively

bflatQ patterns for the heavy rare earth elements

(HREE, Tb–Lu). However, NT rocks show the lowest

concentrations of HREE in comparison to Popocate-

petl, Sierra Chichinautzin (e.g. Siebe et al., 2004), and

the TVF rocks. No Eu anomalies are observed (Fig.

8a,b) in rocks of the study area, indicating that

plagioclase fractionation was not significant. This is

consistent with Na2O and Al2O3 concentrations that

slightly increase with SiO2 concentrations, indicating

that plagioclase crystallized late and was not substan-

tially removed during ascent to the surface. Dacites of

NT show slightly lower REE concentrations in

comparison to andesites and basaltic andesites of the

TVF. La/Lucn ratios range from 7 to 12 in NT dacites,

from 7 to 13 in NT and TVF andesites, and from 12 to

14 in TVF basaltic andesites. In addition, NT and TVF

rocks show a general decrease in incompatible

elements as SiO2 increases. Verma (1999, 2000),

Marquez et al. (1999), and Marquez and De Ignacio

(2002) noticed that the suite of rocks from the Sierra

Chichinautzin and other sites of the TMVB display a

trend opposite of that most frequently observed at

many volcanoes in continental arcs, in which abun-

dances of incompatible trace elements (HFSE and

REE) typically increase with increasing SiO2. They

proposed that mixing between OIB magma types and

a lower-crustal component of dacitic composition

produced lavas of the Sierra Chichinautzin. However,


Siebe et al. (2004) suggested that the trace element

patterns in the Sierra Chichinautzin could be

explained by polybaric assimilation and fractional

crystallization (AFC; DePaolo, 1981) processes. In

our case, petrographical and chemical data of NT and

TVF rocks suggest that the presence of some mineral

phases such as hornblende, Fe–Ti oxides, and minor

clinopyroxene can explain the fractionation of these

trace elements as an AFC process.

4.3. Isotopic results

Isotopic analyses of Sr, Nd and Pb are given in

Table 3 for volcanic samples of NT and the TVF

and in Table 4 for the metamorphic xenoliths found

in the LTP. Despite the contrast in the petrographic

and chemical compositions between NT and TVF

rocks, they show similar isotopic values. Present-day87Sr/86Sr ratios range from 0.70385 to 0.70423 for

NT rocks and from 0.70371 to 0.70448 for TVF

rocks. qNd values generally range from +3.8 to +5.3

for NT rocks and from +2.2 to +6.8 for the

monogenetic field (Table 3 and Fig. 9). The narrow

range of isotopic data, with generally low 87Sr/86Sr

ratios and qNd values mostly above that of bulk

Earth that are within the mantle array, suggest

relatively low crustal contamination of the magmas.

In contrast, metamorphic xenoliths representing the

basement under NT show variable isotopic ratios

(Table 4 and Fig. 9) and can be grouped in two

lithologic types. The first type includes gneiss,

mica-schist, and some phyllites with 87Sr/86Sr

present-day values from 0.71565 to 0.72189 and

qNd from �3.8 to �7.2. The second type, formed

by green schists, is less radiogenic (87Sr/86Sr=

0.70573 and qNd=+1.1). Sr and Nd isotopic ratios,

obtained by Schaaf et al. (2002, submitted for

publication), for pumices and lavas from Popocate-

petl show more variation than the volcanic rocks

analyzed in the present study (Fig. 9), indicating a

larger interaction of these magmas with the crust.

Pb isotopic data of lava and pumice from the study

area display a relatively narrow range, suggesting a

similar source for these rocks. In Fig. 10, the ratios of

volcanic rocks of NT and TVF overlap and plot below

the average crust model curve of Stacey and Kramers

(1975). Pb isotopic ratios for NT rocks vary as follows:206Pb/204Pb=18.55–18.68, 207Pb/204Pb=15.54–15.62

and 208Pb/204Pb=38.19–38.47, whereas for the TVF

the range of isotopic ratios is 206Pb/204Pb=18.58–

18.69, 207Pb/204Pb=15.56–15.61 and 208Pb/204

Pb=38.28–38.50. Volcanic rocks from the study area

appear to define a steep mixing trend between a mantle

component such as the MORB of the Pacific Ocean

(PETDB, 2002) and a 207Pb-rich reservoir. This 207Pb-

rich component might correspond to the influence of

fluids derived from the subduction zone in the mantle

wedge or perhaps it is represented by addition of

continental crust. Pb isotopic data for the metamorphic

xenoliths from the basement also show two different

groups (Fig. 10). Most gneiss, mica-schist and phyllite

samples exhibit radiogenic values (206Pb/204Pb=

18.98–19.10, 207Pb/204Pb=15.68–15.69 and 208Pb/204Pb=39.16–39.26), whereas the green schists display

less radiogenic values (206Pb/204Pb=18.86, 207Pb/204Pb=15.63 and 208Pb/204Pb=38.71). These isotopic

data lie above and to the right of the average

Pb crustal evolution curve of Stacey and Kramers

(1975).

5. Discussion

5.1. Petrographic patterns

Stratigraphic studies in the area are difficult

because several lava flows and pyroclastic products

with similar petrographic compositions were erupted

and distributed over wide areas in a short period of

time (between ~40 and 3 ka). Considering these

complications, we used petrographic, mineralogical

and geochemical data for rocks, and also 14C and K–

Ar age determinations (age data of Bloomfield,

1975; Cantagrel et al., 1981; Macıas et al., 1997;

Garcıa-Palomo et al., 2002) to understand the

magmatic evolution of the NT and TVF regions.

The mineral association of NT products changed

from phenocrysts of plagioclase–clinopyroxene–

orthopyroxene–hornblende in an andesitic glassy

matrix for the events of bPaleo-NevadoQ, to dacitic

pumices, lavas and domes with phenocrysts of

plagioclase–hornblende–orthopyroxene. The presence

of lavas with only orthopyroxene as phenocrysts is

relatively uncommon in TMVB rocks. Volcanoes

such as Popocatepetl, Pico de Orizaba and Iztaccı-

huatl and most monogenetic volcanoes from TMVB

Fig. 11. Chemical and isotopic variations over time for rocks of NT and the TVF. Measured isotopic error is indicated for each sample. Data ages

are taken from Fig. 3.


show the presence of two pyroxene types (clino- and

orthopyroxene) in andesitic–dacitic rocks and pumi-

ces. The distribution of most pumice and lava

erupted by NT could be evaluated by identifying

the pyroxene types present in the volcanic products

of central Mexico.


Paricutın volcano (McBirney et al., 1987) and

some of the other volcanoes in the TMVB show

similar pyroxene characteristics. Activity at Paricutın

began with the eruption of an olivine-bearing basaltic

andesite (55 wt.% SiO2) and ended with a hypersthene

andesite when 85% of the magma volume had been

discharged (McBirney et al., 1987). These authors

suggest that the absence of Ca-rich pyroxene on their

liquidus could be attributed to a loss of water after

differentiation by fractional crystallization and crustal

contamination of the magma had taken place.

The chemical compositions of Fe–Ti oxides from

some UTP samples were determinated by Arce (2003)

and in the present study. These chemical data were

used to calculate preliminary temperatures of magma

crystallization. Based on the ilmenite–titanomagnetite

geothermometer of Anderson and Lindsley (1998) and

the mineral reformulation model of Stormer (1983),

crystallization temperatures of 815–852 8C for the

magma of UTP were calculated. Only titanomagnetite

crystals in equilibrium conditions with the matrix

were considered for the temperature calculations.

Fig. 12. Sr isotopic variations vs. differentiation index (SiO2) for

volcanic rocks of NT and the TVF. Isotopic data from Popocatepetl

and Pico de Orizaba from Schaaf et al. (2002, submitted for

publication).

Hydrothermal experiments using a UTP sample

were conducted by Arce (2003). This author con-

structed P–T stability fields for the main mineral

phases with water pressures going from 150 to 200

MPa, equivalent to depths around 4–6 km below the

volcano. Most NT samples show petrographic and

chemical characteristics similar to those of the dacitic

rocks described by Blundy and Cashman (2001) for

the Mount St. Helens volcano. Based on the composi-

tional variations in natural and experimental glasses

from this volcano, these authors proposed a model for

magmatic crystallization of plagioclase, amphibole,

orthopyroxene and Fe–Ti oxides at pressures between

300–400 MPa (6–8 km depth) and 11 MPa (550 m

depth). Crystallization of magma at NT could follow a

polybaric process over 4 km depth as was suggested

by Blundy and Cashman (2001) for the Mount St.

Helens volcano.

Petrographic characteristics of the TVF rocks are

very similar to sample descriptions reported by

Marquez et al. (2001), Marquez and De Ignacio

(2002) and Siebe et al. (2004) for the Sierra

Chichinautzin rocks. The most common rocks in

this region are andesites, basaltic andesites, some

basalts and minor dacites with a predominant calc-

alkaline character. Nonetheless, some mafic rocks in

the Sierra Chichinautzin bear resemblances to OIBs,

as noticed by Marquez et al. (1999), Wallace and

Carmichael (1999) and Verma (2000). In the TVF,

some lavas are characterized by the coexistence of

olivine and xenocrystic quartz with evidence of

disequilibrium, as mentioned above. The presence

of these xenocrysts has been interpreted as some

type of magma mixing (Marquez et al., 2001;

Marquez and De Ignacio, 2002). However, as was

mentioned by Blatter and Carmichael (1998) in

andesites from Zitacuaro, in the central part of the

TMVB, there is no evidence in the TVF of

contemporaneous silicic magmas that contain quartz

phenocrysts that could explain the presence of

xenocrysts in andesites. In addition, no petrographic

evidences of magma mixing such as reverse zoning,

dissolution structures and mottled groundmass,

observed at the neighbouring Iztaccıhuatl (Nixon,

1988), were identified in NT and TVF lavas. The

occurrence of partially digested sandstone and

granodiorite fragments provides evidence of the

assimilation of some crustal material in the TVF.


5.2. Geochemical patterns

The most evident difference between NT and TVF

rocks is the degree of differentiation. Volcanic rocks at

NT are more silicic than in the TVF (57–67 and 54–61

wt.% SiO2, respectively). In addition, geochemical

patterns of some trace elements (Fig. 7) and isotopic

data (Table 3) suggest that volcanic rocks of the two

regions were produced by magmas derived from

similar sources. Nonetheless, Sr and Nd isotopic data

are relatively more variable in rocks of the TVF than

at NT, suggesting a slightly different magmatic source

or crustal contamination.

Fig. 11 displays SiO2, V and Y concentrations, and

Sr and Nd isotopic variations over time for NT and the

TVF. The time scale was constructed according to the

stratigraphic column of Fig. 3. The most noticeable

aspects of this figure are the sharp decreases of SiO2

and the corresponding increases of V, Y, MgO and

Fe2O3t (data not shown for the oxides) for rocks of

NT during at least four periods of activity. The first

one occurs at 2.6 Ma (andesites and dacites were

reported by Bellotti et al., 2003, but no chemical data

are available), the second one at 1.5 Ma, the third one

at 25 ka and the last one at 10.5 ka. These sharp

chemical variations could be related to the input of

new less silicic magma into the NT magma reservoir.

TVF rocks only show a slight increase in SiO2 and

corresponding decreases in the other elements with

time (e.g. V and Y). Sr isotopic values for most rocks

of NT are homogeneous; although two peaks are

observed at 25 and 10.5 ka. These variations could

represent mafic replenishments of the magmatic

system that also led to greater crustal interactions.

TVF rocks display a scattered distribution of Sr

isotopes with time, indicating different amounts of

magma interaction with the crust during each mag-

matic event. Nd isotopic values for rocks of NT seem

to be less sensitive to variations over time, because all

rocks show values between 0.51283 and 0.51291.

TVF rocks show a slight decrease in 143Nd/144Nd over

time, interpreted as progressively stronger interaction

of magmas with the crust.

A diagram of Sr isotope ratios vs. SiO2 differ-

entiation index (Fig. 12) is used to characterize AFC

processes. For NT rocks SiO2 concentrations are

nearly similar (57–64 wt.%) with a range of Sr

isotopic values from 0.70385 to 0.704230, suggesting

a slight positive correlation for them. The correlation

of the data confirms the existence of assimilation and

crystal fractionation processes in NT lavas. TVF rocks

do not show any correlation between SiO2 wt.% and

Sr isotopic compositions. A rather scattered distribu-

tion of the Sr isotopic values is observed for rocks of

the monogenetic field (Fig. 12). However, assimila-

tion and crystal fractionation can also be inferred for

these rocks.

The nature of continental crust in the study area is

not known because a thick volcanic pile of the TMVB

covers the older rocks. However, it is assumed that

rocks from the Upper Cretaceous Guerrero terrane

(Campa and Coney, 1983) underlie the region. This

terrane is considered a major tectonic accretion of an

Upper Jurassic–Lower Cretaceous intraoceanic vol-

canic arc complex, essentially devoid of an old sialic

basement, onto the continental framework of Mexico.

Geochemical and isotopic data for typical sedimentary

and volcanic sequences from this terrane suggest that

these rocks were formed in a complex fossil island

arc-trench system similar to the present-day western

Pacific island arc system (Mendoza and Suastegui,

2000). Present-day Sr and Nd isotopic values range

from 0.70403 to 0.70473 and 0.51267 to 0.51282,

respectively, for volcanic rocks of this Mesozoic

terrane (Talavera-Mendoza et al., 1995). Nevertheless,

some geological and geochemical data (Elıas-Herrera

et al., 1998; Elıas-Herrera and Ortega-Gutierrez,

2000) suggest involvement of an old continental crust

in the Pre-Cretaceous magmatic evolution of the

Guerrero terrane. Gneiss xenoliths found by these

authors in a Tertiary volcanic field (La Goleta), 50 km

SW of the study area are characterized by an orogenic

low-pressure granulite facies metamorphism. These

xenoliths have present-day 143Nd/144Nd values of

0.51230 and 0.51226 (qNd=�6.7 and �7.3) and Nd

model ages (TDM) of 1.54 and 1.79 Ga (Elıas-Herrera

et al., 1998). These data are similar to values of

Grenvillian rocks in Mexico; therefore, it is very

likely that in the vicinity of the study area an old

continental crust covered by the Mesozoic Guerrero

terrane could exist.

The petrographic characteristics of gneiss and

some schist xenoliths found in the LTP are similar

to those described by Elıas-Herrera et al. (1998).

However, green schist xenoliths show characteristics

similar to the metamorphic volcanic andesitic sequen-


ces described by Talavera-Mendoza et al. (1995) for

the Guerrero terrane. This type of xenolith is relatively

abundant in the LTP. Sr and Nd isotopic data obtained

in the present work for representative xenoliths are

listed in Table 4 and displayed in Fig. 9. Isotopic data

are relatively variable but are mainly similar to values

obtained by Elıas-Herrera et al. (1998) for their

granulitic xenoliths. Green schist xenoliths (sample

NT35EC, Table 4) display values similar to those of

the volcanic rocks of the Guerrero terrane (Talavera-

Mendoza et al., 1995). Therefore, it is very probable

that the metamorphic xenoliths present in the Lower

Toluca Pumice were scavenged from different crustal

depths. The high Rb/Sr ratios of the gneiss, phyllites

and some schists might indicate a highly evolved

sedimentary crust. In addition, present-day qNd values(between �3.8 and �7.2) and Nd model ages (TDM

between 1.04 and 1.42 Ga) for most of the analyzed

xenoliths also show typical values of Grenvillian

rocks in Mexico, supporting the existence of a

recycled older continental crust. Therefore, isotopic

characteristics of xenoliths from the NT deposits

appear to confirm the presence of a Pre-Mesozoic

sialic basement under the southern border of the

TMVB.

Considering the possible effect of crustal contam-

ination on the magmas of the study area along with

the geochemical and isotopic data of the continental

crust, represented by the metamorphic xenoliths

analyzed here, it seems plausible that any degree of

assimilation would have resulted in a greater dis-

persion of the isotopic and trace element data in

volcanic rocks. However, Sr, Nd and Pb isotopic

compositions of the volcanic rocks of the Toluca area

plot in a restricted range (Figs. 9 and 10), excluding

an important role for crustal contamination in the

generation of the chemical and isotopic compositions

observed in the volcanic rocks. Therefore, fractional

crystallization could represent the most important

process of magma differentiation in the Toluca

volcanic rocks. Coherent linear trends with little

scattering of samples in the variation diagrams of

major and trace elements vs. SiO2 or MgO could,

thus, be explained by fractional crystallization. This

does not preclude that continental crust could slightly

influence the compositions of the volcanic rocks.

Volcanic rocks from other volcanoes of the central-

eastern TMVB, such as Pico de Orizaba and

Popocatepetl, show more variable isotopic composi-

tions (e.g. qNd ranges from �2 to +2 and from +3 to

+5, respectively, Schaaf et al., submitted for publica-

tion). These isotopic data suggest a more significant

interaction of magmas with the continental crust than

observed for NT and the TVF. The thickness (50 km

average) of the crust under the central-eastern part of

the TMVB is similar to that suspected beneath NT and

the TVF (Urrutia-Fucugauchi and Flores-Ruiz, 1996).

However, the weak interaction of magmas with

continental crust beneath the study area could be

explained by the presence of important fault systems

(Garcıa-Palomo et al., 2000) that facilitate magma

ascent through the crust. Three complex fault systems,

of different ages, orientations and kinematics, inter-

sect at NT volcano (Fig. 2). These authors propose

that at least three main deformation events affected

central Mexico since the late Miocene. During the

early Miocene, an extensional phase with a Basin and

Range deformation style occurred in northern Mexico

and produced NW–SE and NNW–SSE horsts and

grabens south of NT. In the middle Miocene, a

transcurrent event generated NE–SW faults with two

movements: (a) left-lateral strike-slip displacement

and (b) normal faulting. The latest deformation event

started during the late Pliocene and involved oblique

extension accommodated by E–W right-lateral fault-

ing that changed to normal faults. It is clear that

during the last tectonic event, the majority of the

volcanic eruptions in the study area and also in other

areas of the central TMVB were produced, indicating

a narrow relationship between E–W extensional

faulting and magma ascent. Recent laboratory experi-

ments (Hall and Kincaid, 2001) have indicated that

the interaction between buoyantly upwelling diapirs

and subduction-induced flow in the mantle creates a

network of low-density, low-viscosity conduits

through which buoyant flow is rapid (b30 ka).

5.3. Relationship between tectonics and magmatism

(magma source)

The petrologic origin and evolution of the TMVB

has been intensely debated recently. Two composi-

tionally contrasting suites of rocks have been recog-

nized in this volcanic region on the basis of

geochemical data: (1) calc-alkaline rocks with high

LILE/HFSE ratios that have been associated with a

Fig. 13. Sr/Y vs. Y discrimination diagram between adakites and typical arc calc-alkaline compositions (after Drummond and Defant, 1990).


subduction environment; and (2) alkaline or transi-

tional rocks with low LILE/HFSE ratios and compo-

sitions similar to OIB. The simultaneous existence of

these two suites of rocks in the volcanic arc has been

explained by means of two main divergent hypoth-

eses. Some authors (e.g. Wallace and Carmichael,

1999; Luhr, 1997; and others) considered that the

predominantly calc-alkaline character of rocks and the

production of the OIB magma-types could be

explained by the generation of magmas in a sub-

duction setting along the Middle America Trench.

However, Verma (1999, 2000), Sheth et al. (2000),

Marquez et al. (1999) and Marquez and De Ignacio

(2002) regard the rocks of the central part of the

TMVB as produced by magma mixing between the

OIBs and a lower-crustal component of dacitic

composition. They deny a direct relationship between

subduction processes and the genesis of the TMVB.

Because these two divergent points of view have been

widely discussed in several recent works such as

Verma (2000), Ferrari et al. (2001), Marquez and De

Ignacio (2002) and Siebe et al. (2004), it is not our

aim to extend here its discussion. On the basis of our

petrographic, geochemical and isotopic data of NT

and the TVF, along with the present-day geodynamic

facts between the North America and Cocos plates

(summarized by Siebe et al., 2004), we propose that

magma generation in the study area is related to a

subduction environment.

Geochemical and isotopic data for NT and TVF

rocks, particularly LILE/HFSE ratios, suggest that

these rocks were produced in a typical subduction

environment where a depleted-mantle source

(MORB-type) was modified by different proportions

of fluids or melts from the subducted lithosphere.

Rocks of NT and the TVF show narrow ranges in Pb

isotopic values, suggesting similar sources. Most

rocks of NT and some from the TVF fall in the DM

(depleted mantle) field (206Pb/204Pb from 18.58 to

18.69 and 207Pb/204Pb from 15.54 to 15.61), repre-

sented by the EPR-MORB (Fig. 10), evoking partial

fusion of the oceanic slab. Pb isotopic data from NT,

the TVF, and some rocks from the Sierra Chichinaut-

zin (Verma, 1999) define a steep mixing line with a


narrow range (Fig. 10), where the possible end

members could be the MORB-EPR and the fluids of

the Pacific Ocean Sediment type (Church and

Tatsumoto, 1975; Plank and Langmuir, 1998; Hem-

ming and McLennan, 2001; Verma, 2000). Indeed, the

positive anomalies of Ba and Pb and also the high

values of some element ratios (e.g. Ba/Zr and K/Nb)

shown by the volcanic rocks (NT and the TVF)

confirm that fluids and/or melts from the subducted

slab contributed to magma genesis.

Melting of subducted hydrous basaltic crust

(MORB) is argued to produce magmas with a

distinctive chemical signature known as adakites

(Kay, 1978; Defant and Drummond, 1990; Martin,

1999; Garrison and Davidson, 2003). The major and

trace element characteristics used to classify rocks as

adakites are SiO2 contents between 63 and 70 wt.%,

high Sr concentrations (N400 ppm) coupled with low

Y (b19 ppm) and Sr/Y ratios N20. Typical adakites are

phenocryst-bearing volcanic rocks with compositions

of hornblende andesite to dacite, and basalts are

systematically lacking. Adakites commonly show a

low HREE content that is interpreted as reflecting the

presence of garnetFhornblende in the residual source

after partial melting. Most rocks of NT and two

Fig. 14. Ba/Zr vs. 87Sr/86Sr diagram showing the results of a mixing mod

(Hemming and McLennan, 2001).

samples (TEO1 and MX85, Fig. 2) from the western-

most part of the TVF display relatively high Sr and

low Y concentrations (460–694 and 14–21 ppm,

respectively) (Fig. 13). These rocks also show other

characteristics such as relatively low HREE contents

and Pb isotopic values similar to MORB-EPR,

suggesting a possible adakitic signature for them.

Typical models for the generation of adakites require

the subduction of a young (b5 Ma) and warm oceanic

lithosphere, where temperatures in the slab rise above

the solidus of wet basalts at high pressures, producing

melts (Defant and Drummond, 1990). However, some

authors such as Gutscher et al. (2000) have suggested

that most of the known Pliocene–Quaternary adakites

are paradoxically related to subduction of N10 Ma

lithosphere. They proposed an unusual mode of

subduction known as flat subduction, occurring in

~10% of the world’s convergent margins, that can

produce the temperature and pressure conditions

necessary for the fusion of moderately old oceanic

crust (e.g. Chile, Ecuador and Costa Rica subduction

regions). In central Mexico, it was generally believed

that the Cocos plate was subducting at a constant dip

angle N258. However, seismic data show that the

subducted Cocos slab is subhorizontal beneath south-

el between EPR-DM (White et al., 1987) and bulk Pacific sediment


central Mexico (Suarez et al., 1990; Singh and Pardo,

1993; Pardo and Suarez, 1995). A similar geometry

has been observed in regions of central Peru and Chile

where it was designated as a bflat-slabQ. Pardo and

Suarez (1995) inferred that the 80–100 km depth

contours of the subducted slab lie beneath the

volcanic front of the TMVB in central Mexico.

However, the position of the subducted slab can not

be confirmed due to the paucity of earthquake

hypocenters along the volcanic front.

In southwestern Japan, Morris (1995) described the

existence of adakitic magma in at least two Quater-

nary volcanoes, Daisen and Sambe, that are associated

with the volcanic arc. In this area, no intermediate-

and deep-focus earthquakes have been identified,

similar to the central part of the TMVB. However,

this author proposes that melting of the Philippine Sea

plate beneath southwestern Japan can explain the

presence of the adakitic magmas. In addition, he

argued that slab melting can account for the aseis-

micity in the area, because the plate behaves as a

plastic body rather than a solid. In central Mexico the

behavior of the subducted plate could be similar.

Although adakitic signatures can be identified in

rocks of NT and in some rocks from the TVF,

suggesting a melting process of the subducted

oceanic crust, some authors (Garrison and Davidson,

2003) proposed that similar geochemical patterns can

be obtained by melting another basaltic source such

as the lower continental crust. Distinction between

these two sources of magma is nontrivial, and

requires integrated investigations of regional geo-

chemistry along with tectonic and geophysical data.

On the basis of geochemical and isotopic data, we

propose that melts of the subducted oceanic crust

contributed to the magmas erupted at NT and the

western part of the TVF. Melting of the lower

continental crust under NT could produce magmas

with higher isotopic variations, similar to values

observed in metamorphic xenoliths analyzed here.

However, the geochemical data attest to minor

interaction of magmas with the continental crust,

but interaction of adakitic magma with the mantle

during its passage to the surface could produce

fractionation of some elements (Y and Sr/Y ratios).

This is the first time that Quaternary adakitic

magmas have been identified in the central part of

the TMVB. Recently, adakitic signatures have also

been determined on the eastern section of the TMVB

but in Miocene volcanic rocks (Gomez-Tuena et al.,

2003).

The Valle de Bravo Volcanic field (VBVF) is also

located in the central part of the arc front of the

TMVB. It is bracketed by NT to the east and the

Zitacuaro Volcanic Complex to the west. Lava ages

from this volcanic field range from 300 to b10 ka

(Blatter et al., 2001) and the main rock compositions

are andesite and dacite. In addition we have noticed

an adakitic signature for some of the samples of the

VBVF based on rock compositions and Sr and Y

concentrations reported by Blatter and Carmichael

(2001). In fact, this adakitic composition was also

suggested by Aguirre-Diaz et al. (2003) for rocks

from the same region. Therefore, it is very likely that

the presence of adakites at NT is not a local

phenomenon but a regional characteristic of the

volcanic arc in central Mexico. However, more

detailed geochemical and isotopic studies are neces-

sary in the VBVF to further evaluate this hypothesis.

On the basis of some trace element ratios and

isotopic data of the studied rocks indicating partic-

ipation of slab components and mantle melts, a two-

component mixing model is proposed to explain the

genesis of NT and TVF rocks. This model is

characterized by the presence of a depleted mantle

(DM) source and a subduction component with

different fluid/melt ratios. The mixing calculation

assumes that the subducted component and the DM,

represented by the composition of a MORB-like

composition (White et al., 1987), are the two end

members of the model. The results of modeling

isotopic values and trace element ratios are displayed

in Fig. 14. The volcanic rocks plot above the mixing

line between the DM source and the subduction

component. With variable fluid/melt proportions the

mixing line shifts upward. The amount of subduction

component involved in the genesis of NT volcanic

rocks is estimated to be around 15–20%.

6. Concluding remarks

Understanding magma genesis and petrological

processes in the TMVB might be a relatively

difficult task because neighboring volcanic centers,

such as NT and the TVF, present particular geo-


chemical and isotopic patterns that can not be

generalized for the whole volcanic province.

Detailed geochemical and isotopic studies allowed

us to determine two slightly different magmatic

sources for the two areas. Most rocks of NT and

some from the TVF can be related to an adakite

magma source that was slightly modified by its

passage into the mantle wedge. It is feasible that

Quaternary adakitic magmas in the central part of

the TMVB are a common phenomenon associated

with melting of subducting slab. On the other hand,

most TVF magmas show typical calc-alkaline

patterns, where the mantle wedge was modified by

different fluid/melt proportions derived from the

subducted slab. Melting of the Cocos plate beneath

south-central Mexico could explain the distinctive

chemistry of NT volcano and the aseismic nature of

this region.

Although a thick continental crust (~50 km) has

been inferred by geophysical data in the study area,

there is no strong evidence for partial melting of the

lower continental crust having produced the magmas.

Isotopic compositions (Sr, Nd and Pb) suggest a

MORB-slab melting source for the rocks. In addition,

metamorphic xenoliths in the area suggest the

presence of an older continental crust (Nd model

age N1.0 Ga).

Mechanisms of melt generation at subduction

zones and transfer to the surface still remain uncertain.

However, laboratory experiments have indicated that

rapid ascent (b30 ka) of magmas is possible. It is

important to remember that during the Late Pleisto-

cene (~40 ka) a distensive tectonic event produced the

E–W normal fault system in the study area. Most

volcanic eruptions of NT and the TVF were produced

during the last 40 ka and probably were controlled by

this last fault system. Therefore, this last tectonic

event favored the rapid ascent of magmas to the

surface and it can explain the low crustal contami-

nation observed and the presence of typical mineral

associations indicating the ascent and crystallization

of magmas following polybaric processes.

Acknowledgements

Financial support by the National Council of

Science and Technology (CONACYT) (project

32330-T) in Mexico is gratefully acknowledged. The

authors wish to thank Jose Luis Arce for assistance in

the field, and Giovanni Sosa and Benjamin Domı-

nguez for assistance in the field, mechanical prepara-

tion of rock samples and in the analytical aspects of the

isotopic determinations. We are also grateful to

Barbara Martiny for revision and comments on the

English. Editorial handling by Margaret Mangan and

reviews by Jim Luhr and Alvaro Marquez were very

helpful and are greatly appreciated.

References

Aguirre-Diaz, G., Jaimes Viera, M.C., Nieto Obregon, J., Lozano

Santacruz, R., 2003. El campo volcanico monogenetico de Valle

de Bravo, Edo. de Mexico. Geologıa y Geoquımica. Geos 23,

202. Puerto Vallarta, Mexico.

Anderson, D.J., Lindsley, D.H., 1998. Internally consistent solution

models for Fe–Mg–Mn–Ti oxides: Fe–Ti oxides. Am. Mineral.

73, 714–726.

Arce, J.L., 2003. Condiciones pre-eruptivas y evolucion de la

erupcion Pliniana Pomez Toluca Superior, Volcan Nevado de

Toluca. PhD thesis, Posgrado en Ciencias de la Tierra, UNAM.

Mexico, 136 pp.

Arce, J.L., Macıas, J.L., Vazquez-Selem, L., 2003. The 10.5 Ka

Plinian eruption of Nevado de Toluca volcano, Mexico:

stratigraphy and hazard implications. Geol. Soc. Amer. Bull.

115, 230–248.

Arculus, R.J., 2003. Use and abuse of the terms calcalkaline and

calcalkalic. J. Petrol. 44, 929–935.

Bellotti, F., Capra, L., Casartelli, M., D’Antonio, M., De Beni, E.,

Gigliuto, A., Groppelli, G., Lunghi, R., Merlini, A. y Norini,

G. 2003. Geologıa y geoquımica de los edificios volcanicos

pre-Nevado de Toluca (2.6–1.3): Resultados Preliminares. XIII

Congreso de Geoquımica, INAGEQ, CD abstr.

Besch, Th., Grauert, B., Tobschall, H.J., Negendank, J.F.W., 1987.

Evidence of assimilation during the genesis of subduction

related volcanics in the eastern Trans Mexican Volcanic Belt.

Terra Cogn. 7, 274–275.

Blatter, D.L., Carmichael, I.S.E., 1998. Plagioclase-free andesites

from Zitacuaro (Michoacan), Mexico: petrology and experi-

mental constraints. Contrib. Mineral. Petrol. 132, 121–138.

Blatter, D.L., Carmichael, I.S.E., 2001. Hydrous phase equilibria of

a Mexican high-silica andesite: a candidate for a mantle origin?

Geochim. Cosmochim. Acta 65, 4043–4065.

Blatter, D.L., Carmichael, I.S.E., Deino, A.L., Renne, P., 2001.

Neogene volcanism at the front of the central Mexican

Volcanic Belt: basaltic andesites to dacites, with contempora-

neous shoshonites and high-TiO2 lavas. Geol. Soc. Am. Bull.

113, 10.

Bloomfield, K., 1974. The age and significance of the Tenango

Basalt Central Mexico. Bull. Volcanol. 37, 585–595.

Bloomfield, K., 1975. A late-Quaternary monogenetic volcano field

in central Mexico. Geol. Rundsch. 64, 476–497.


Bloomfield, K., Valastro, S., 1974. Late Pleistocene eruptive history

of Nevado de Toluca volcano, central Mexico. Bull. Volcanol.

85, 901–906.

Bloomfield, K., Valastro, S., 1977. Late quaternary tephrochronol-

ogy of Nevado de Toluca volcano, central Mexico. Overs. Geol.

Miner. Resur. 46, 1–15.

Bloomfield, K., Sanchez-Rubio, G., Wilson, L., 1977. Plinian

eruptions of Nevado de Toluca volcano Mexico. Geol. Rundsch.

66, 120–146.

Blundy, J.D., Cashman, K.V., 2001. Ascent-driven crystallisation of

dacite magmas at Mount St. Helens, 1980–1986. Contrib.

Mineral. Petrol. 140, 631–650.

Caballero, M., Macıas, J.L., Urrutia-Fucugauchi, J., Lozano-

Garcıa, S., Castaneda, R., 2001. Volcanic stratigraphy and

palaeolimnology of the Upper Lerma Basin during the late

Pleistocene and Holocene: sedimentology special volume.

Lacustrine Volcaniclastic-Sedimentation. 30, 57–71.

Campa, M.F., Coney, P.J., 1983. Tectonostratigraphic terranes and

mineral resource distribution in Mexico. Can. J. Earth Sci. 20,

1040–1051.

Cantagrel, J.M., Robin, C., Vincent, P., 1981. Les grandes etapes

d’evolution d’un volcan andesitique composite: example du

Nevado de Toluca. Bull. Volcanol. 44, 177–188.

Capra, L., Macıas, J.L., 2000. Pleistocene cohesive debris flow at

Nevado de Toluca volcano central Mexico. J. Volcanol. Geo-

therm. Res. 102, 149–168.

Cebull, S.E., Shurbet, D.H., 1987. Mexican volcanic belt: an

intraplate transform. Geofıs. Int. 26, 1–13.

Cervantes, K.E., Arce, J.L., Macıas, J.L., Mora, J.C., 2004. The

12.1 ka Middle Toluca Pumice: a dacitic small Plinian eruption

of Nevado de Toluca in central Mexico. J. Volcanol. Geotherm.

Res. under revision.

Church, S.E., Tatsumoto, M., 1975. Lead isotope relations in

oceanic ridge basalts from the Juan de Fuca-Gorda

Ridge area N.E. Pacific Ocean. Contrib. Mineral. Petrol.

53, 253–279.

Defant, M.J., Drummond, M.S., 1990. Derivation of some modern

arc magmas by melting of young subducted lithosphere. Nature

347, 662–665.

Demant, A., 1978. Caracterısticas del Eje Neovolcanico Trans-

mexicano y sus problemas de interpretacion. Rev.-Inst. Geol.,

UNAM 2, 172–187.

Demant, A., 1981. L’axe neovolcanique transmexicain: etude

volcanologique et petrographique, signification geodynamique.

PhD thesis, Univ. De Droit, d’Economie et de Sciences d’Aix-

Marseille, France. 259

DePaolo, D.J., 1981. Trace element and isotopic effects of

combined wall-rock assimilation and fractional crystallization.

Earth Planet. Sci. Lett. 53, 189–202.

Drummond, M.S., Defant, M.J., 1990. A model for trondhje-

mite–tonalite–dacite genesis and crustal growth via slab

melting: Archean to modern comparisons. J. Geophys. Res.

95, 21503–21521.

Elıas-Herrera, M., Ortega-Gutierrez, F., 2000. Petrology of high-

grade metapelitic xenoliths in an Oligocene rhyodacite plug-

Precambrian crust beneath the southern Guerrero Terrain

Mexico? Rev. Mex. Cienc. Geol. 14-1, 101–109.

Elıas-Herrera, M., Ortega-Gutierrez, F., Lozano-Santa Cruz, R.,

1998. Evidence for pre-Mesozoic sialic crust in the southern

Guerrero Terrane: geochemistry of the Pepechuca high-grade

gneiss xenoliths. Actas INAGEQ-Mexico 4, 169–181.

Ferrari, L., Garduno, V.H., Pasquare, G., Tibaldi, A., 1994. Volcanic

and tectonic evolution of central Mexico: Oligocene to present.

Geofıs. Int. 33, 91–105.

Ferrari, L., Lopez-Martınez, M., Aguirre-Dıaz, G., Carrasco-Nunez,

G., 1999. Space–time patterns of Cenozoic arc volcanism in

Central Mexico: from the Sierra Madre Occidental to the

Mexican volcanic belt. Geology 27-4, 303–306.

Ferrari, L., Petrone, C., Francalanci, L., 2001. Generation

of oceanic-island basalt-type volcanism in the western

Trans-Mexican Volcanic Belt by slab rollback, astheno-

sphere infiltration, and variable flux melting. Geology 20,

507–510.

Garcıa-Palomo, A., Macıas, J.L., Garduno, V.H., 2000. Miocene to

Recent structural evolution of the Nevado de Toluca volcano

region central Mexico. Tectonophysics 318, 281–302.

Garcıa-Palomo, A., Macıas, J.L., Arce, J.L., Capra, L., Garduno,

V.H., Espindola, J.M., 2002. Geology of Nevado de Toluca

Volcano and surrounding areas, central Mexico. Geol. Soc. Am.

Map and Chart Series MCH089, pp. 1–48.

Garrison, J.M., Davidson, J.P., 2003. Dubious case for slab

melting in the northern volcanic zone of the Andes. Geology

31, 565–568.

Gill, J.B., 1981. Orogenic Andesites and Plate Tectonics. Springer,

Berlin. 390 pp.

Goldstein, S.L., O’Nions, R.K., Hamilton, P.J., 1984. A Sm–Nd

isotopic study of atmospheric dusts and particulates from major

river systems. Earth Planet. Sci. Lett. 70, 221–236.

Gomez-Tuena, A., LaGatta, A., Langmuir, C., Goldstein, S.,

Ortega-Gutierrez, F., Carrasco-Nunez, G., 2003. Temporal

control of subduction magmatism in the eastern Trans-Mexican

Volcanic Belt: mantle sources, slab contributions and crustal

contamination. Geochem. Geophys. Geosyst. 4, doi:10.1029/

2003GC000524.

Gutscher, M.A., Maury, R., Eissen, J.P., Bourdon, E., 2000.

Can slab melting be caused by flat subduction? Geology 28,

535–538.

Hall, P.S., Kincaid, C., 2001. Diapiric flow at subduction zones: a

recipe for rapid transport. Science 292, 2472–2475.

Hart, S.R., 1984. A large-scale isotope anomaly in the Southern

Hemisphere mantle. Nature 309, 753–757.

Hemming, S.R., McLennan, S.M., 2001. Pb isotope compositions

of modern deep sea turbidites. Earth Planet. Sci. Lett. 184,

489–503.

Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical

classification of the common volcanic rocks. Can. J. Earth Sci.

8, 523–548.

Johnson, C.A., Harrison, C.G.A., 1990. Neotectonics in central

Mexico. Phys. Earth Planet. Inter. 64, 187–210.

Kay, R.W., 1978. Aleutian magnesian andesites: melts from

subducted Pacific Ocean crust. J. Volcanol. Geotherm. Res. 4,

117–132.

Leake, B.E., 1978. Nomenclature of amphiboles. Am. Mineral. 63,

1023–1052.

http://dx.doi.org/doi:10.1029/2003GC000524


Le Maitre, R.W., Bateman, P., Dudek, A., Keller, J., Lameyre Le

Bas, M.J., Sabine, P.A., Schmid, R., Sorensen, H., Streck-

eisen, A., Woolley, A.R., Zanettin, B., 1989. A Classification

of Igneous Rocks and Glossary of Terms. Blackwell, Oxford,

193 pp.

Luhr, J., 1997. Extensional tectonics and the diverse primitive

volcanic rocks in the western Mexican volcanic belt. Can. Miner

35, 473–500.

Macıas, J.L., Garcıa-Palomo, A., Arce, J.L., Siebe, C., Espındola,

J.M., Komorowski, J.C., Scott, K.M., 1997. Late Pleistocene–

Holocene cataclysmic eruptions at Nevado de Toluca and

Jocotitlan volcanoes, central Mexico. In: Kowallis, B.J. (Ed.),

Proterozoic to Recent stratigraphy, tectonic and volcanology,

Utah, Nevada, Southern Idaho and Central Mexico. Buffalo Y U

Geology Studies, pp. 493–528.

Marquez, A., De Ignacio, C., 2002. Mineralogical and geo-

chemical constraints for the origin and evolution of magmas

in Sierra Chichinautzin Central Mexican volcanic belt. Lithos

62, 3562.

Marquez, A., Oyarzum, R., Doblas, M., Verma, S.P., 1999.

Alkalic (ocean island type) and calc-alkalic volcanism in the

Mexican volcanic belt: a case for plume-related magmatism

and propagating rifting at an active margin? Geology 27,

51–54.

Marquez, A., Oyarzun, R., De Ignacio, C., Doblas, M., 2001.

Southward migration of volcanic activity in the central Mexican

volcanic belt: asymmetric extension within a two-layer crustal

stretching model. J. Volcanol. Geotherm. Res. 112, 175–187.

Martin, H., 1999. Adakitic magmas: modern analogues of Archaean

granitoids. Lithos 46, 411–429.

Martin del Pozzo, A.L., 1989. Geoquımica y paleomagnetismo de la

Sierra Chichinautzin. PhD thesis, UNAM, Mexico, 148 pp.

Martiny, B., Martınez-Serrano, R.G., Moran-Zenteno, D.J.,

Macıas-Romo, C., Ayuso, R.A., 2000. Stratigraphy, geo-

chemistry and tectonic significance of the Oligocene mag-

matic rocks of western Oaxaca Southern Mexico.

Tectonophysics 318, 71–98.

McBirney, A.R., Taylor, H.P., Armstrong, R.L., 1987. Paricutin re-

examined: a classic example of crustal assimilation in calc-

alkaline magma. Contrib. Mineral. Petrol. 95, 4–20.

Mendoza, O.T., Suastegui, M.G., 2000. Geochemistry and isotopic

composition of the Guerrero terrane (western Mexico): impli-

cations for the tectono-magmatic evolution of southwestern

North America during the late Mesozoic. J. South Am. Earth

Sci. 13, 297–324.

Mooser, F., 1972. The Mexican volcanic belt: structure and

tectonics. Geofıs. Int. 12-2, 55–70.

Mooser, F., Maldonado-Koerdell, M., 1961. Mexican national report

on volcanology. An. Inst. Geofıs., UNAM VII, 46–53.

Morris, P.A., 1995. Slab melting as an explanation of quaternary

volcanism and aseismicity in southwest Japan. Geology 23,

395–398.

Nakamura, N., 1974. Determinations of REE, Ba, Fe, Mg, Na and K

in carbonaceous and ordinary chondrites. Geochim. Cosmo-

chim. Acta. 38, 757–775.

Negendank, J.F.W., Emmermann, R., Krawczyk, R., Mooser, F.,

Tobschall, H., Werle, D., 1985. Geological and geochemical

investigations on the eastern Trans-Mexican Volcanic Belt.

Geofıs. Int. 24-4, 477–575.

Nixon, G.T., 1982. The relationship between quaternary volcanism

in central Mexico and the seismicity and structure of subducted

ocean lithosphere. Geol. Soc. Am. Bull. 93, 514–523.

Nixon, G.T., 1988. Petrology of the younger andesites and dacites

of Iztaccıhuatl volcano: 2. Chemical stratigraphy magma

mixing, and the composition of basaltic magma influx. J. Petrol.

29, 265–303.

Nixon, G.T., Demant, A., Armstrong, R.L., Harakal, J.E., 1987. K–

Ar and geologic data bearing on the age and evolution of the

Trans-Mexican Volcanic Belt. Geofıs. Int. 26-1, 109–158.

Pal, S., Lopez, M.M., Perez, J.R., Terrel, D.J., 1978. Magma

characterization of the Mexican volcanic belt (Mexico). Bull.

Volcanol. 41, 379–389.

Pardo, M., Suarez, G., 1995. Shape of the subducted Rivera and

Cocos plates in southern Mexico: seismic and tectonic

implications. J. Geophys. Res. 100, 12357–12373.

Pasquare, G., Garduno, V.H., Tibaldi, A., Ferrari, M., 1988. Stress

pattern evolution in the central sector of the Mexican volcanic

belt. Tectonophysics 146, 353–364.

Pearce, J.A., 1983. Role of the sub-continental lithosphere in

magma genesis at active continental margins. In: Hawkesworth,

C.J., Norry, M.J. (Eds.), Continental Basalts and Mantle

Xenoliths. Shiva, Nantwich, pp. 230–249.

PETDB Database 2002. Geochemical database of the Ocean Floor.

http://petdb.Ideo.columbia.edu.

Plank, T., Langmuir, C.H., 1998. The chemical composition of

subducting sediments and its consequences for the crust and

mantle. Chem. Geol. 145, 325–394.

Robin, C., 1976. Presence simultanee de magmatismes et signi-

fications tectoniques opposees dans l’est du Mexique. Bull. Soc.

Geol. Fr. 7 (XVII), 1637–1645.

Robin, C., 1982. Relations volcanologie–magmatologie–geodyna-

miques: applications au passage entre volcanismes alcalins et

andesitiques dans le sud Mexicain (Axe Trans-mexicain et

Province alcaline Orientale). Ann. Sci. Univ. Clermont, Biol.

Anim. 30, 503 pp.

SARM. 2003. Service d’analyse de roches et mineraux du CNRS.

http:www.crpg.cnrs-nancy.fr/SARM/index.html.

Schaaf, P., Martınez-Serrano, R., Solıs-Pichardo, G., Hernandez-

Trevino, T., Morales-Contreras, J.J., Hernandez-Bernal, M.S.,

Valdez-Moreno, G., Castro-Govea, R., Siebe, C., Carrasco-

Nunez, G., 2002. Reconocimiento de la corteza continental bajo

los grandes estratovolcanes de la Faja Neovolcanica Mexicana:

evidencias isotopicas. 3 Reunion Nacional de Ciencias de la

Tierra, Geos vol. 22, pp. 152.

Schaaf, P., Stimac, J., Siebe, C., Macıas, J.L., 2003. Magmatic

processes at Popocatepetl volcano, Mexico: petrology, geo-

chemistry and Sr–Nd–Pb isotopes. Geol. Soc. Am. Bull.

submitted for publication, 20 pp.

Sheth, H.C., Torres-Alvarado, I.S., Verma, S.P., 2000. Beyond

subduction and plumes: a unified tectonic–petrogenetic

model for the Mexican volcanic belt. Int. Geol. Rev. 42,

1116–1132.

Siebe, C., Schaaf, P., Urrutia-Fucugauchi, J., 1999. Mammoth bones

embedded in a late Pleistocene lahar from Popocatepetl volcano,

http://www.petdb.Ideo.columbia.edu

http://www.crpg.cnrs-nancy.fr/SARM/index.html


near Tocuila, central Mexico. Geol. Soc. Am. Bull. 111-10,

1550–1562.

Siebe, C., Rodrıguez-Lara, V., Schaaf, P., Abrams, M., 2004.

Geochemistry, Sr–Nd isotope composition, and tectonic setting

of Holocene Pelado, Guespalapa and Chichinautzin scoria

cones, south of Mexico city. J. Volcanol. Geotherm. Res. 130,

197–226.

Singh, S.K., Pardo, M., 1993. Geometry of the Benioff zone and

state of stress in the overriding plate in central Mexico.

Geophys. Res. Lett. 20, 1483–1486.

Solari, L.A., Lopez, R., Cameron, K.L., Ortega-Gutierrez, F.,

Keppie, J.D., 1998. Reconnaissance U/Pb geochronology and

common Pb isotopes from the northern portion of the 1Ga

Oaxacan Complex Southern Mexico. EOS Trans. AGU. 79,

F931. Abstract.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead

isotope evolution by a two-stage model. Earth Planet. Sci. Lett.

26, 207–221.

Stormer, J.C., 1983. The effects of recalculation on estimates of

temperature and oxygen fugacity from analysis of multi-

component iron–titanium oxides. Am. Mineral. 68, 586–594.

Suarez, G., Monfret, T., Wittlinger, G., David, C., 1990. Geometry

of subduction and depth of the seismogenic zone in the Guerrero

gap Mexico. Nature 345, 336–338.

Sun, S., McDonough, W., 1989. Chemical and isotopic system-

atics of oceanic basalts: implications for mantle compositions

and processes. In: Saunders, A., Norry, M. (Eds.), Magmatism

in the Ocean Basins, vol. 42. Geol. Soc. London Spec. Publ.,

pp. 313–345.

Talavera-Mendoza, O., Ramırez-Espinoza, J., Guerrero-Suastegui,

M., 1995. Petrology and geochemistry of the Teloloapan

subterrane: a lower cretaceous evolved intra-oceanic island arc.

Geofıs. Int. 34, 3–22.

Urrutia-Fucugauchi, J., Flores-Ruiz, H., 1996. Bouger gravity

anomalies and regional structure in central Mexico. Int. Geol.

Rev. 38, 176–194.

Verma, S.P., 1984. Alkali and alkaline earth element geochemistry

of Los Humeros caldera, Puebla, Mexico. J. Volcanol. Geo-

therm. Res. 20, 21–40.

Verma, S.P., 1987. Mexican volcanic belt: present stage of knowl-

edge and unsolved problems. Geofıs. Int. 26, 309–340.

Verma, S.P., 1999. Geochemistry of evolved magmas and their

relationship to subduction-unrelated mafic volcanism at the

volcanic front of the central Mexican volcanic belt. J. Volcanol.

Geotherm. Res. 93, 151–171.

Verma, S.P., 2000. Geochemistry of subducting Cocos plate and the

origin of subduction-unrelated mafic volcanism and the volcanic

front of Central Mexican volcanic belt. Spec. Pap. Geol. Soc.

Am. 334, 195–222.

Verma, S.P., Luhr, J.F., 1993. Sr–Nd–Pb isotope and trace element

geochemistry of calc-alkaline andesites from Volcan Colima

Mexico. Geofıs. Int. 32-4, 616–631.

Verma, S.P., Nelson, S.A., 1989. Isotopic and trace element

constraints on the origin and evolution of alkaline and calc-

alkaline magmas in the northwestern Mexican volcanic belt. J.

Geophys. Res. 94, 4531–4544.

Walker, J.A., Patino, L.C., Carr, M.J., Feigenson, M.D., 2001. Slab

control over HFSE depletions in central Nicaragua. Earth Planet.

Sci. Lett. 192, 533–543.

Wallace, P.J., Carmichael, I.S.E., 1999. Quaternary volcanism

near the Valley of Mexico: implications for subduction zone

magmatism and effects of crustal thickness variations on

primitive magma compositions. Contrib. Mineral. Petrol. 135,

291–314.

White, W.M., Hofmann, A.W., Puchelt, H., 1987. Isotope geo-

chemistry of Pacific Mid-Ocean Ridge basalt. J. Geophys. Res.

92 (B6), 4881–4983.

Wilson, M., 1989. Igneous Petrogenesis: A Global Tectonic

Approach. Unwin Hyman, London, 446 pp.

adakites mex

Documents

pico de orizaba

nevado de

mexican volcanic

martin del

unrelated

complex fault

red altered

metamorphic