04_gsamemoir_streepey
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04_GSAmemoir_streepeyTRANSCRIPT
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Geological Society of AmericaMemoir 197
2004
Exhumation of a collisional orogen: A perspective from the North American Grenville Province
Margaret M. Streepey*Department of Geological Sciences, Florida State University, Tallahassee, Florida 32306-4100, USA
Carolina Lithgow-BertelloniBen A. van der Pluijm
Eric J. EsseneDepartment of Geological Science, University of Michigan, Ann Arbor, Michigan 48109-1063, USA
Jerry F. MagloughlinDepartment of Earth Resources, Colorado State University, Fort Collins, Colorado 80523-1482, USA
ABSTRACTCombined structural and geochronologic research in the southernmost portion of
the contiguous Grenville Province of North America (Ontario and New York State)show protracted periods of extension after the last episode of contraction. TheGrenville Province in this area is characterized by synorogenic extension at ca. 1040Ma, supported by U-Pb data on titanites and 40Ar-39Ar data on hornblendes, followedby regional extension occurring along crustal-scale shear zones between 945 and 780Ma, as recorded by 40Ar-39Ar analysis of hornblende, biotite, and K-feldspar. By ca.780 Ma the southern portion of the Grenville Province, from Ontario to the Adiron-dack Highlands, underwent uplift as a uniform block. Tectonic hypotheses haveinvoked various driving mechanisms to explain the transition from compression toextension; however, such explanations are thus far geodynamically unconstrained.Numerical models indicate that mechanisms such as gravitational collapse and man-tle delamination act over timescales that cannot explain a protracted 300 m.y. exten-sional history that is contemporaneous with ongoing uplift of the Grenville Province.Rather, the presence of a plume upwelling underneath the Laurentian margin, com-bined with changes in regional stress directions, permitted the observed uplift andextension in the Grenville Province during this time. The uplift history, while on aslightly different timescale from those of most plume models, is similar to that seen inmodels of uplift and extension caused by the interaction of a plume with the base ofthe lithosphere. Some of the protracted extension likely reflects the contribution of far-field effects, possibly caused by tectonic activity in other cratons within the Rodiniansupercontinent, effectively changing the stress distributions in the Grenville Provinceof northeastern North America.
Keywords: Grenville, Rodinia, extension
391
*E-mail: [email protected].
Streepey, M.M., Lithgow-Bertelloni, C., van der Pluijm, B.A., Essene, E.J., and Magloughlin, J.F., 2004, Exhumation of a collisional orogen: A perspective fromthe North American Grenville Province, in Tollo, R.P., Corriveau, L., McLelland, J., and Bartholomew, M.J., eds., Proterozoic tectonic evolution of the Grenvilleorogen in North America: Boulder, Colorado, Geological Society of America Memoir 197, p. 391410. For permission to copy, contact [email protected]. 2004 Geological Society of America.
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INTRODUCTION
Central to many questions in structural geology and tecton-ics regarding the evolution of orogens is how crust overthick-ened by continental collisions is modified and stabilized after anorogenic event. To understand how the crust evolves after oro-genesis, it is necessary to study ancient mountain belts, the deepcores of which are exposed at the surface today in high-grademetamorphic terranes. Because results of studies of the tempo-ral evolution of such areas give insight into the time and ratesinvolved in crustal stabilization, these results can be used bothto study the general problem of crustal stabilization and to pre-dict the deep behavior of young orogenic belts.
The Grenville Province in northeastern North America isan outstanding, well-studied example of an exposed, deeplyeroded, ancient mountain system. The province is affected by aca. 1.0- to 1.3 billion-year-old set of orogenic events, seen incratonic blocks worldwide, and culminating in the formation ofthe supercontinent Rodinia (Hoffman, 1991; Dalziel, 1997).One of the best continuous exposures of Grenville-aged rocksis in northeastern North America between Labrador, Canada,and New York state, where Grenville deformation is thought tohave occurred in an arc-continent collision at ca. 1.31.2 Gaand a continent-continent collision at ca. 1.11.05 Ga (Mooreand Thompson, 1980; Easton, 1992; Rivers, 1997; Davidson,1998; Carr et al., 2000; McLelland et al., 2001). The terrane ischaracterized by slices of crust that are separated by ductileshear zones in which more of the deformation is concentrated,some of which record normal motion overprinting an earliercontractional history. The colliding craton causing continent-continent collision in this segment of Rodinia is not known, asthe proposed collision with Amazonia has recently been ques-tioned by paleomagnetic evidence (Tohver et al., 2002). Earlyrifting attempts are recorded in some of the blocks of Rodinia(Li et al., 1999; Karlstrom et al., 2000; Dalziel and Soper, 2001;Tack et al., 2001; Timmins et al., 2001). Most major riftingevents involving the eastern Laurentian margin (present-daycoordinates) appear to have occurred in the late Neoprotero-zoic. Rifting in this region resulted in the opening of the Iape-tus Ocean, which has been dated in the north at ca. 600 Ma(Torsvik et al., 1996; Svenningsen, 2001) and in the south at570550 Ma (Torsvik et al., 1996). However, with documentedpulses of rifting having occurred in Baltica, Congo, China, andthe southwestern United States from ca. 900 Ma to ca. 700 Ma,any extensional activity in the eastern Laurentian block, pres-ent-day northeastern North America, during this period mayreflect initial stages of Rodinias breakup (Li et al., 1999; Tan-ner and Bluck, 1999; Streepey et al., 2000; Dalziel and Soper,2001; Timmins et al., 2001). Well-exposed Grenville structuresin North America provide strong constraints on the nature ofextensional activity in the area and also, when compared toextensional activity in other Rodinian blocks that occurred dur-ing roughly the same period, on the processes that control thebreakup of supercontinents. The driving mechanism(s) for
extension in the Laurentian part of the Grenville orogen is theprimary focus of this contribution.
Geologic Setting
One of the continuous exposures of rocks that showsGrenville-aged deformation occurs in North America. The east-ern edge of the belt abuts the edge of the Appalachian thrust frontand is bounded to the west by the Archean Superior Province andother Archean and Proterozoic provinces. Because of the later-ally continuous nature of this belt, it offers an excellent opportu-nity to study lithotectonic relationships in the orogen.
The Grenville Province is composed of lithotectonicallydistinct blocks representing the autochthonous terrains of theLaurentian craton as well as allochthonous blocks accreted tothe Laurentian margin during Grenville orogenesis (Easton,1992; Rivers, 1997; Davidson, 1998; Hanmer et al., 2000; Fig.1, inset). These blocks are separated by major crustal-scale shearzones and contain distinct, smaller domains that are also sepa-rated by major ductile shear zones (e.g., Davidson, 1984; Eas-ton, 1992). A significant amount of strain recorded by theserocks is concentrated into these zones of deformation, whichprovide the key to unraveling the tectonic history of the region.In many cases, these shear zones appear to be multiply active,with the latest episode of deformation recording extension, orappearing to record extensional activity, synchronous toGrenville-aged contractional pulses (Mezger et al., 1991b; Cul-shaw et al., 1994; Busch et al., 1997; Martignole and Reynolds,1997; Ketchum et al., 1998; Streepey et al., 2001). The currentstructural expression of the region is of an extensional terrain,and the challenge then lies in determining both the magnitude,timing, and origin of extension as well as the earlier, contrac-tional history of the area.
In this paper, we focus on the eastern Metasedimentary Beltof the Grenville Province and its boundary with the adjacentGranulite Terrane (Fig. 1). This area spans southeastern Ontarioand northwestern New York state. The Metasedimentary Belt isone of three major crustal slices that comprise the GrenvilleProvince in this region (Fig. 1). It lies between the Gneiss Beltand the Granulite Terrane and contains variably metamorphosed(greenschist to granulite-facies) metasediments, metagranitoids,and metavolcanic rocks (Easton, 1992).
The Metasedimentary Belt contains several small shearzones that juxtapose lithologically and geochronologically dis-tinct domains. These shear zones within the MetasedimentaryBelt dip to the southeast, and the two major boundaries, the Ban-croft shear zone and the Robertson Lake shear zone, show lateextensional motion. The Carthage-Colton shear zone is locatedat the eastern edge of the Metasedimentary Belt, and separatesit from the Granulite Terrane of the Adirondack Highlands. Thisshear zone also shows a late extensional history, but dips shal-lowly to the northwest, creating a grabenlike geometry betweenthe Robertson Lake shear zone and the Carthage-Colton shearzone (Fig. 1).
392 M.M. Streepey et al.
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Studies of the deformation histories of these shear zonesrequire a multidisciplinary approach, with emphasis placed onthe field relationships, peak metamorphic pressures and tem-peratures, and the corresponding geochronologic data that con-strain the cooling and exhumation history. Because most of therocks have experienced more than one phase of deformation andmetamorphism, structural relationships in the field can be com-plex, and field analysis alone is not enough to completely con-strain the significance of these boundaries.
This study presents a synthesis of geochronologic informa-tion combined with structural analysis and thermobarometricdata to describe the kinematics of the uplift or exhumation his-tory of a segment of the Grenville Province in northeasternNorth America. A summary of ages is given, adding to regionalcompilations (Cosca et al., 1991, 1992, 1995; Mezger et al.,1991a, 1992, 1993; van der Pluijm et al., 1994). In addition, new40Ar-39Ar ages from amphiboles in the Adirondack Lowlandsand the Adirondack Highlands are presented and further con-strain the geologic history of the area.
Whereas the combination of structural, petrologic, andgeochronologic information is critical to constructing a kine-matic model of the evolution of the region, it does not give a geo-dynamic picture of the development of the late stages ofmodification and stabilization of overthickened crust. Thisinformation allows us to develop reasonable geologic hypothe-ses about timing of late, postorogenic extension and the natureof motion between blocks of crust, but it does not explain thephysical processes behind the evolution. In addition, geochrono-logic data are restricted to lithologies and assemblages that con-tain minerals with the appropriate elements for radiogenicdating. In areas where the appropriate assemblages are not avail-
able, the geochronologic results are limited or incomplete andcannot provide a full, detailed cooling history of the rocks.
In order to develop a more geodynamically complete pic-ture of the exhumation history of the Grenville Province, wehave developed a two-dimensional numerical model of a slice ofcrust representing this region. The structures assigned to themodel are taken directly from field studies in the region, and therheologies are assigned based on existing literature (Ranalli,1995). The numerical models explore possible driving mecha-nisms for the observed phenomenon of extension in this oro-genic belt. From geochronologic and structural information, thetimescales involved in the transition from compression to exten-sion have been evaluated and have placed constraints on theamount of displacement across shear zones. Although how thisorogenic belt extends following collision is known, why itextends is less evident. It remains uncertain whether extensioncan be attributed to a single mechanism, such as gravitationalcollapse, or whether it requires a combination of mechanisms,such as mantle delamination in addition to changes in far-fieldstresses. Whereas numerical models cannot provide constraintsthat uniquely solve this problem, they give insights as to whetheror not proposed mechanisms can act in a way that fits fieldobservations over the period of time dictated by geochronologicconstraints.
GEOCHRONOLOGIC SUMMARY
In studies of ancient metamorphic terranes, motion alongductile shear zones can often be delineated with a combinationof ages that yield information on the timing of latest metamor-phism and ages that record the cooling or exhumation history of
Exhumation of a collisional orogen 393
Figure 1. Generalized map of the Meta-sedimentary Belt (MB) of the GrenvilleProvince (Ontario and New York). Themap shows the Metasedimentary Belt inbetween the Gneiss Belt (GB) and theGranulite Terrane (GT). The Bancroftshear zone (BSZ), Robertson Lake shearzone (RLSZ), and Carthage-Coltonshear zone (CCSZ) are shown in theirmost current expression as normalfaults. Other shear zones shown are theMetasedimentary Belt Boundary Zone(MBBZ) and the Sharbot Lake shearzone. The inset map shows the GrenvilleProvince of northeastern North Americawith the Grenville Front tectonic zone(GFTZ) as it abuts the Archean SuperiorProvince. Other abbreviations: MTMorin terrane; LSZLabelle shearzone. After Streepey et al. (2001).
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the terrane (e.g., van der Pluijm et al., 1994). In such studies itis critical to constrain the pressure-temperature (P-T) conditionsof metamorphism in order to determine whether geochronologicages are ages of cooling from a peak metamorphic event orgrowth ages. Minerals yield cooling ages if the peak conditionsof metamorphism are higher than the closure temperatures of theminerals and growth ages if the minerals can be shown to havegrown during metamorphism but at conditions below their clo-sure temperatures. Therefore, in order to best interpret geo-chronologic data in the eastern portion of the MetasedimentaryBelt, it was necessary to initially assess the metamorphic con-ditions of the terrane.
Figure 2, A and B, shows temperature and pressure maps ofthe Metasedimentary Belt from Streepey et al. (1997; thermo-barometric data from references therein). Metamorphism in thearea reached upper-amphibolite to granulite-facies metamor-phism. Maximum temperatures in the study area from just westof the Robertson Lake shear zone to just east of the Carthage-Colton shear zone ranged from 600 to 650 C in and around theRobertson Lake shear zone and increased to the east to 700750C in and around the Carthage-Colton shear zone. Pressureswere 600 to 800 MPa over the region.
In order to best interpret radiometric ages from polymeta-morphic terranes, it is essential not only to have quantitative
394 M.M. Streepey et al.
Pressures (MPa)
< 600
600-700
700-800
> 800
0 30 km
.
Temperatures (C)
>750
700-750
650-700
600-650
550-600
500-550
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Exhumation of a collisional orogen 395
assessments of P-T conditions but also to have accurate closuretemperatures for minerals used in analysis and some constraintson the diffusion mechanisms active in isotopic resetting. For thisstudy we consider volume diffusion in grains to be the primarymechanism of isotopic resetting. In addition, published andwidely used closure temperatures for the minerals titanite, horn-blende, biotite, and K-feldspar are considered appropriate for thisstudy of a slowly cooled, regionally metamorphosed terrane(titanite: 600700 C, Mezger et al., 1991a, Scott and St-Onge,1995; hornblende: 480500 C, McDougall and Harrison, 1999;biotite: 300 C, McDougall and Harrison, 1999; K-feldspar: 150to 300 C, Zeitler, 1987, McDougall and Harrison, 1999, Loveraet al., 1991). Because peak temperatures of regional metamor-phism are close to or generally exceed the closure temperature oftitanite in the U-Pb system, the U-Pb ages of titanite constraineither the timing of latest metamorphism or cooling ages veryclose to the timing of peak metamorphism in this area. The 40Ar-39Ar ages of hornblende, biotite, and K-feldspar, which havelower closure temperatures than titanite, constrain most of thecooling history of the study area and are considered to have closedto the K-Ar system at some time after peak metamorphism.
The U-Pb ages from zircon, garnet, monazite, and titanitehave been determined for the Metasedimentary Belt in numer-ous studies (Mezger et al., 1993; Corfu and Easton, 1995, 1997;Perhsson et al., 1996; Wasteneys et al., 1999; Corriveau and vanBreemen, 2000; McLelland et al., 2001). We provide a briefsummary of the metamorphic ages of the Metasedimentary Belt;the reader is referred to reviews by Rivers (1997), Carr et al.(2000), Hanmer et al. (2000), and McLelland et al. (2001) fordetailed descriptions of the early metamorphic history of theMetasedimentary Belt. The Metasedimentary Belt yields infor-mation on two major periods of Grenville-aged orogenesis thatrepresent an arc accretion event from ca. 13001190 Ma (theElzevirian orogeny), culminating in a continent-continent colli-sion at ca. 10801020 Ma (the Ottawan orogeny). These eventsrepresent two episodes of contraction, possibly separated byextensional events, which are recorded by magmatic activity andemplacement of large anorthosite complexes during these peri-ods (McLelland et al., 1988; Davidson, 1995). The RobertsonLake shear zone and the Carthage-Colton shear zone separaterocks showing a marked discontinuity in metamorphic age, andso are fundamental boundaries separating blocks with distinctmetamorphic histories. From the Metasedimentary Belt bound-ary thrust zone east to the Robertson Lake shear zone (encom-passing the Bancroft and Elzevir terranes), metamorphicminerals record geochronological evidence of metamorphismduring the latest contractional event during the Ottawan orogeny.
The Frontenac terrane (including the Adirondack Low-lands) from east of the Robertson Lake shear zone to theCarthage-Colton shear zone shows evidence of metamorphismrelated to the earlier Elzevirian orogeny. It does not, however,appear to record metamorphic ages related to the Ottawanorogeny, indicating that this terrane was either laterally sepa-rated from the Elzevir terrane during this period or was at shal-
low crustal levels (Mezger et al., 1993; Streepey et al., 2000,2001). However, some investigators have proposed that at leastportions of the Adirondack Lowlands may have been deformedduring the Ottawan orogeny (Wasteneys et al., 1999), and moredetailed isotopic work may be useful in resolving the extent andnature of Ottawan deformation in the Lowlands. East of theCarthage-Colton shear zone, peak metamorphism in the Adiron-dack Highlands occurred during the Ottawan orogeny, althoughthere is some evidence that this terrane was also deformed dur-ing the Elzevirian orogeny (McLelland et al., 1988; McLellandand Chiarenzelli, 1989; Kusky and Lowring, 2001). In this scenario, the Frontenac terrane, bounded by the east-dippingRobertson Lake shear zone and the west-dipping Carthage-Colton shear zone, is a block of crust that has been largely protected from the Ottawan pulse of orogenesis, while theAdirondack Highlands and the Elzevir terrane recorded meta-morphic ages during this period.
The cooling history of the terranes immediately adjacent tothese two shear zones is discussed in order to evaluate their sig-nificance as postorogenic extensional structures. The ages com-piled in this study include ages determined from regional U-Pband 40Ar-39Ar geochronologic data (Busch and van der Pluijm,1996; Busch et al., 1996b, 1997; Streepey et al., 2000, 2001,2002, and new results) to provide a complete cooling history forthe eastern half of the Metasedimentary Belt. Sample locationsand their corresponding ages are given in Table 1. The U-Pb agesof titanite give the timing of early deformation, thought to havesome transpressive component along both the east-dippingRobertson Lake shear zone and the west-dipping Carthage-Colton shear zone. The 40Ar-39Ar ages of hornblendes, biotites,and K-feldspars, combined with structural analysis of shearzones, record the timing of later extensional motion along bothshear zones. New 40Ar-39Ar ages of hornblendes further detailthe cooling history of the crust adjacent to the Carthage-Coltonshear zone in northwest New York state.
Robertson Lake Shear Zone
The Robertson Lake shear zone is a multiply active, east-dipping shear zone separating the eastern Elzevir terrane (Maz-inaw domain) and the western Frontenac terrane (Sharbot Lakedomain) within the Metasedimentary Belt (Fig. 1; Easton,1988). The latest episode of motion recorded along this zone isdown-to-the-east, as shown by shear-sense indicators includingS-C, CC fabrics, with these crystal plastic structures crosscutby brittle fabrics delineating an uplift history during deforma-tion (Busch and van der Pluijm, 1996). Its early history recordsa transpressive event at ca. 1030 Ma, indicating imbrication viasinistral transpression of the Mazinaw and the Sharbot Lakedomains (Busch et al., 1997). 40Ar-39Ar cooling ages of horn-blendes and micas in the Robertson Lake shear zone show amarked difference across the zone. Combined with the structuralinformation and the nature of the offset, extensional motion hadto have occurred to juxtapose the crustal blocks on either side of
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TAB
LE 1
.SAM
PLE
LOCA
TIO
NSH
ornbl
ende
Biot
iteSa
mpl
eage
age
Dom
ain
Loca
tion
UTM
Coo
rdin
ates
UTM
Coo
rdin
ates
From
Bus
ch e
t al.(
1996
)N
orth
ing
East
ing
RVL1
18A
1011
Ma
n.d
.Sh
arbo
t Lak
e49
7122
537
2600
RVL2
0A12
05 M
an.d
.Sh
arbo
t Lak
e49
7305
036
7025
CDN5
894
7 M
an.d
.El
zevi
r/Maz
inaw
4968
970
3560
50M
TG72
952
Ma
n.d
.El
zevi
r/Maz
inaw
4957
060
3553
00
From
Bus
ch a
nd v
an d
er P
luijm
(199
6)N
orth
ing
East
ing
RVL1
18B
n.d
.96
9 M
aSh
arbo
t Lak
e49
7122
537
2600
LVT1
30B
n.d
.90
1 M
aEl
zevi
r/Maz
inaw
4990
750
3619
20
From
Stre
epey
et a
l.(20
00) a
nd un
publi
shed
dat
aA1
0299
0 M
an.d
.Lo
wla
nds
Popp
le H
ill Fo
rmatio
n, n
ear R
usse
ll.A1
1210
55 M
a94
0 M
aLo
wla
nds
Nea
r Gou
vern
eur,
H
wy
58/8
12, N
Jct
.of P
opl
ar H
ill Rd
.A1
1499
0 M
an.d
.Lo
wla
nds
Alon
g G
rass
Rive
r, H
wy
17, W
sid
e of
road
, 1.5
km
NW
of R
usse
ll.A1
1796
7 M
an.d
.H
ighl
ands
0.5
mi.E
of R
t.27
and
Bro
user
s Co
rner.
A124
1043
Ma
n.d
.Lo
wla
nds
Emor
yville
Rd.
, ca.
0.5
mi.N
W o
f pow
er
plan
t, ca
0.2
5 m
i.W o
f tur
noff
to Ta
lcvi
lle.
A125
1066
Ma
n.d
.Lo
wla
nds
Emor
yville
Rd.
, E o
f Hai
lsbor
o, sm
all
outc
rop
north
of r
oad,
NW
of h
ouse
, 1.
8 m
i.E o
f brid
ge, 2.
1 m
i.fro
m Is
land
Bra
nch
Rd.
A128
1020
Ma
964
Ma
Low
land
sTr
out L
ake R
d., N
of E
dward
s, alo
ng W
sid
e of
Trout L
ake,
S
side,
W o
f 2 is
land
s, W
sid
e of
road
.Cut
abo
ut 4
0 m
long
.A1
2910
79 M
a92
4 M
aLo
wla
nds
S.of T
rout L
ake,
R
t.19
to E
dward
s, ca
.due
W o
f west
ernm
ost
ext
rem
e of
Ced
ar L
ake.
A133
975
Ma
n.d
.H
ighl
ands
Cres
t of W
hite
s H
ill, W
hite
Hill
Rd.
, SE
of P
aris
hville
abo
ut 3
mi.a
t aba
ndon
ed lo
okout.
150
on s
mall
trail
to th
e W
.
A134
972
Ma
n.d
.H
ighl
ands
Very
lo
w o
utc
rops
alo
ng b
oth
sides
of t
he h
ighw
ay.S
side
of W
hite
Hill,
abo
ut 1
mi.S
of l
ooko
ut.
Out
crop
on W
hite
Hill
Rd.
, w
ithin
am
phib
olite
.
A135
1165
Ma
n.d
.H
ighl
ands
Just
N o
f Ste
rling
Rd.
, nea
r pow
er
line,
abo
ut 1
50fro
m ju
nctio
n with
Joe I
ndian
Rd.
A136
943
Ma
937
Ma
Hig
hlan
dsSm
all o
utcr
op o
n Jo
e In
dian
Rd.
at t
he c
rest
of a
sm
all h
ill.Lo
cate
d at
the
N70
W, 60
N s
ymbo
l on
Leon
ard
and
Budd
ingt
ons
map.
A137
1005
Ma
n.d
.H
ighl
ands
Rt.
56, a
bout
3 m
i.S o
f Sta
rk.W
sid
e of
hwy
, ro
adc
ut o
f am
phib
olite
mig
mat
ites.
A138
983
Ma
n.d
.H
ighl
ands
Smal
l out
crop
on
E sid
e of
Hwy
56,
abo
ut 1
mi.S
of 1
37, a
bout
4 m
i.S o
f Sta
rk.
A140
947
Ma
n.d
.H
ighl
ands
Hw
y 3,
just
E of
Pitca
irn.E
xpos
ures
on
emba
nkm
ent N
of t
he ro
ad, a
t cre
st o
f hill.
A142
953
Ma
919
Ma
Hig
hlan
dsSm
all o
utcr
op o
n th
e E
side
of M
ud L
ake R
d.at t
he ju
nctio
n of M
ud La
ke a
nd
Brig
gs R
d.(S
E co
rner
of i
nters
ect
ion).
A145
935
Ma
n.d
.H
ighl
ands
Abou
t 2 m
i.E o
f Tex
as
on T
exas
Rd.
, 6 m
i.fro
m H
wy 8
12.
HM
95n.d
.91
5 M
aLo
wla
nds
NW
of R
usse
ll on
Rt.1
7 in
Dev
ils E
lbow
, 2
mi.S
of H
erm
on.S
ampl
e fro
m E
sid
e of
out
crop
.
SE59
6-49
n.d
.89
5 M
aH
ighl
ands
On
Rt.8
7, N
of D
ana
Hill R
d., 1
.9 m
i.S o
f Whi
ppor
will C
orners
.O
utcr
op o
n NW
sid
e of
road
.LB
596-
31b
n.d
.92
5 M
aLo
wla
nds
4.5
mi.f
rom
inte
rsec
tion
of H
wy 3
and
Hwy
812
, on
812
S of
Bal
mat
.Sam
ple
from
E s
ide
of o
utcr
op.
LB93
n.d
.90
4 M
aLo
wla
nds
Out
crop
just
N of
LB59
6-31b
.
CN59
6-56
n.d
.92
4 M
aH
ighl
ands
0.2
mi.S
of ju
nctio
n of H
anso
n Rd.
and
Ore
bed
Rd.o
n O
rebe
d Rd
., ne
ar C
olto
n.O
utcr
op o
n W
sid
e of
road
.
PP59
6-60
n.d
.89
9 M
aLo
wla
nds
1 m
i.SW
of P
ierre
pont
on
Rt.2
.Out
crop
on
E sid
e of
road
.
From
Stre
epey
et a
l.(20
01)
Latit
ude
Long
itude
RWS-
110
00 M
an.d
.W
ithin
CCS
ZN
orth
44
deg.
, 22
min
.W
est
75
deg.
, 10
min
.RW
S-3c
999
Ma
n.d
.W
ithin
CCS
ZN
orth
44
deg.
, 22
min
.W
est
75
deg.
, 10
min
.EA
198
1 M
an.d
.W
ithin
CCS
ZN
orth
44
deg.
, 22
min
.W
est
75
deg.
, 10
min
.D
H98
-199
8 M
an.d
.W
ithin
CCS
ZN
orth
44
deg.
, 22
min
.W
est
75
deg.
, 10
min
.RW
H-1
973
Ma
n.d
.W
ithin
CCS
ZN
orth
44
deg.
, 22
min
.W
est
75
deg.
, 10
min
.CR
7-DH
198
9 M
an.d
.W
ithin
CCS
ZD
ana
Hill
outc
rop:
On
N sid
e of
Dan
a Hi
ll Rd.
CR1-
DH1
980
Ma
n.d
.W
ithin
CCS
ZD
ana
Hill
outc
rop:
On
N sid
e of
Dan
a Hi
ll Rd.
CR3-
8794
1 M
an.d
.W
ithin
CCS
Z1.
8 km
N o
f int
erse
ctio
n be
tween D
ana
Hill
Rd.
and
Rt.8
7, o
n Rt
.87.
CR2-
A294
8 M
an.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.D
H2-
810
12 M
an.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.CR
6-A4
1005
Ma
n.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.CR
12-A
499
8 M
an.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.CR
9-A4
944
Ma
n.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.H
87-5
b10
19 M
an.d
.W
ithin
CCS
ZD
irect
ly ac
ross
Rt.
87 fr
om C
R3-8
7.n.d
.no
dat
a;CC
SZ
Carth
age-
Colto
n sh
ear z
one;U
TM
Unive
rsal T
ransv
ers
e M
erca
tor.
-
the shear zone (Busch et al., 1996b; Fig. 3). The timing of thetransition from compression to extension can be somewhat con-strained by the age of the latest transpressive event in the regionat ca. 1030 Ma (Busch et al., 1997), but cannot be directly deter-mined. The termination of extension across the Robertson Lakeshear zone cannot be constrained from 40Ar-39Ar analyses ofhornblende and biotite, as both show differences of ca. 70100Ma across the zone. Results from the analysis of K-feldspar inthe region suggest that the entire block was uplifting uniformlyby 780 Ma, suggesting termination of extension between 900and 780 Ma (Streepey et al., 2002).
Ages taken from Busch and van der Pluijm (1996), Buschet al. (1996b, 1997), and Streepey et al. (2002) are compiled inFigure 3. These data constrain the cooling history of the terranefrom immediately after orogenesis in the Robertson Lake shearzone area to the time at which the terrane was uplifting as a uni-form block. In addition, the geometry of normal fault motionand the amount of displacement along the shear zone are evident(Busch et al., 1996a). The U-Pb ages from titanites documentthe difference in metamorphic ages between the Mazinaw andthe Sharbot Lake domains. As the closure temperature of titan-ite is ca. 600700 C (Mezger et al., 1991a; Scott and St-Onge,1995), titanite ages give the timing of metamorphism or a cool-ing age that is very close to the age of metamorphism in theamphibolite to granulite-facies rocks of the Elzevir and theFrontenac terranes. Metamorphism in the Sharbot Lake domain(the hangingwall block of the Robertson Lake shear zone)occurred at ca. 1140 to 1170 Ma (Mezger et al., 1993; Corfu andEaston, 1995; Busch et al., 1997). These ages are generally sim-ilar to those across the entire width of the Frontenac terrane(Mezger et al., 1993). However, the youngest metamorphic agesin the Mazinaw domain (the footwall block of the RobertsonLake shear zone) range from ca. 1010 Ma to 1050 Ma (Mezgeret al., 1993; Busch et al., 1997), showing a ca. 100-m.y. differ-ence in the timing of the latest metamorphic event across thisboundary. Transpressional activity is interpreted to have causedjuxtaposition through imbrication of the two terranes at ca. 1030Ma (Busch et al., 1997).
The 40Ar-39Ar cooling ages of hornblendes, micas, and K-feldspars constrain the post-titanite cooling and unroofing his-tory of the blocks of crust adjacent to the Robertson Lake shearzone and constrain the timing and nature of postorogenic exten-sion along this zone. Hornblende ages for rocks in the vicinityof the Robertson Lake shear zone are shown in Figure 3. Theoffset in ages shown by the titanite U-Pb geochronology is alsoshown by the cooling ages of hornblende, with hornblende agesof ca. 1010 Ma in the Sharbot Lake domain (hangingwall),which are at least 60 m.y. older than rocks immediately acrossthe Robertson Lake shear zone in the Mazinaw domain, wherehornblende ages are ca. 950 Ma (Busch and van der Pluijm,1996; Busch et al., 1996a). Biotite, which closes to the K-Ar sys-tem at ca. 300 C, continues to show an offset across the Robert-son Lake shear zone, with biotites in the Sharbot Lake domainrecording ages of 970 Ma that are at least 70 m.y. older than the
900 Ma biotite ages in the Mazinaw domain (Busch and van derPluijm, 1996). At the time of biotite closure, rocks were at fairlyshallow crustal depths of 10 to 12 km assuming an averagegeothermal gradient. Because of the offsets in cooling ages ofthe rocks that are presently exposed at the surface crustal level,it is clear that extensional activity did not terminate across theRobertson Lake shear zone until sometime after 900 Ma.
The 40Ar-39Ar ages of K-feldspars give some informationon the termination of extension along the Robertson Lake shearzone, but do not completely constrain it. Unlike hornblendes ormicas, which are considered to have one diffusion domain andtherefore a single closure temperature, K-feldspars are thoughtto have multiple diffusion domains and therefore multiple clo-sure temperatures (Lovera et al., 1991). Analysis of K-feldsparsgives, instead of a single age, a temperature-time path for thegrain. Thermal modeling of K-feldspar spectra from the Mazi-naw and the Sharbot Lake domains show that the two domainswere juxtaposed by at least 780 Ma, meaning that the termina-tion of extension across the Robertson Lake shear zone musthave occurred between 900 Ma and 780 Ma (Streepey et al.,2002). Thus, postorogenic extension across the Robertson Lakeshear zone terminated between 140 and 260 m.y. after the finalexpression of contractional tectonics in the area at ca. 1040 Ma.
CARTHAGE-COLTON SHEAR ZONE
The Carthage-Colton shear zone separates the eastern Fron-tenac terrane (Adirondack Lowlands) from the Granulite Ter-rane (Adirondack Highlands; Fig. 1). It is 150 km east of the Robertson Lake shear zone and dips to the west, toward theRobertson Lake shear zone. With this geometry, the Frontenacterrane is a grabenlike block bounded by two shear zones dip-ping toward one another. Upper amphibolite-facies marbles and other metasediments dominate the Adirondack Lowlandslithologies, whereas the Adirondack Highlands are comprisedpredominantly of granulite-facies metaigneous assemblages.The Carthage-Colton shear zone crops out as a zone of intensedeformation between the two terranes, although the exact loca-tion of the boundary has been debated (Geraghty et al., 1981).
The Carthage-Colton shear zone had a long history of activ-ity over the duration of the Grenville orogenic cycle. TheAdirondack Lowlands and Highlands both appear to have beenaffected by the ca. 1190 Ma arc-continent collision at the end ofthe Elzevirian orogeny (Mezger et al., 1991a, 1992; Wasteneyset al., 1999; Kusky and Lowring, 2001). However, only theAdirondack Highlands appear to have been pervasively meta-morphosed by the granulite-facies Ottawan orogeny, which hasbeen dated at 10901040 Ma (McLelland et al., 1996). Theentire Frontenac terrane, from east of the Robertson Lake shearzone to just west of the Carthage-Colton shear zone, appears tohave escaped widespread thermal metamorphism and resettingof isotopic ages from this pervasive deformational event, eitherby being at shallower crustal levels during that period or bybeing laterally separated.
Exhumation of a collisional orogen 397
-
Figu
re 3
. M
aps
show
ing
horn
blen
de,
biot
ite,
and
K-
feld
spar
40A
r-39 A
r age
s acr
oss t
he R
ober
tson
Lake
she
arzo
ne
(RLS
Z) a
nd t
he C
artha
ge-C
olton
she
ar zo
ne(C
CSZ)
. Acr
oss t
he R
LSZ,
the a
ges a
re fr
om B
usch
et al
.(19
96),
Busch
and v
an d
er P
luijm
(199
6), an
d Stre
epey
et a
l. (20
02). H
ornble
nde a
ges a
re ita
licize
d. A
cros
s the
CCSZ
, age
s are
from
Stre
epey
et a
l. (20
00, 2
001,
2002
)an
d ne
w r
esults
. Pai
rs s
epar
ated
by
a co
mm
a in
dica
teho
rnbl
ende
and
bio
tite
ages
from
the
sam
e sa
mpl
e. T
heag
e dist
ributio
ns ac
ross
the R
LSZ
indi
cate
mot
ion
alon
gth
e sh
ear z
one
afte
r ca.
900
Ma
and
befo
re c
a. 78
0 M
a.Th
e ag
e di
strib
utio
ns a
cros
s th
e CC
SZ in
dica
te d
efor
-m
atio
n be
twee
n ca
. 950
and
930
Ma,
mos
t lik
ely
at c
a.94
5 M
a. D
H-1
fie
ld o
utcr
op n
ame;
GB
Gne
iss B
elt;
GFT
ZG
renv
ille
Fron
t tec
toni
c zo
ne; G
TG
ranu
lite
Terr
ane;
MB
M
etas
edim
enta
ry B
elt;
MBB
ZM
eta-
sedi
men
tary
Bel
t Bou
ndar
y Zon
e; M
SZ
Moo
rton s
hear
zone;
MT
Mor
in t
erra
ne;
RW
field
out
crop
nam
e;SL
SZ
Shar
bot L
ake
shea
r zon
e.
-
Exhumation of a collisional orogen 399
McLelland et al. (1996) proposed that the Carthage-Coltonshear zone was the locus for extensional collapse of the Ottawanorogen at ca. 1050 Ma, which resulted in exhumation of thehigh-grade core of the Adirondack Highlands, presumably whilethe orogen was still under a contractional stress field and as adirect result of the orogenic event, either through gravitationalcollapse or through mantle delamination beneath the orogen.Streepey et al. (2001) suggested that the Carthage-Colton shearzone was involved in transpressive deformation similar to thatdocumented across the Robertson Lake shear zone at ca. 1040Ma. It is clear that the Carthage-Colton shear zone was activeduring or immediately after the latest episode of Grenville con-traction. In addition, cooling ages from hornblendes and biotitesshow that the Carthage-Colton shear zone was reactivated in anextensional regime similar to that observed along the RobertsonLake shear zone.
We present sixteen new 40Ar-39Ar hornblende analysesfrom the University of Michigan Radiogenic Isotope Laboratorycombined with published 40Ar-39Ar hornblende and biotite agesnear and along the Carthage-Colton shear zone (Streepey et al.,2000, 2001). Standard operating procedures for the collection ofhornblende and biotite analyses in this laboratory are describedin detail in Streepey et al. (2000). Our results are shown in Fig-ure 3, and isotopic data are presented in Table 2.1 Plateaus weredefined as occurring where 50% or more of the total 39Ar wasreleased in three or more consecutive steps and where the agesof the steps overlapped at the 2 level of error.
The hornblende ages in the Adirondack Lowlands of theFrontenac terrane show that these locations within this slice ofcrust reached 500 C at ca. 1036 Ma (Fig. 3; Table 2). Horn-blende ages across the Carthage-Colton shear zone are 947983Ma. The offset in ages indicates active movement along theCarthage-Colton shear zone after hornblendes closed to the K-Ar system, or after 950 Ma. The nature of the offset, combinedwith the regional fabrics, indicates that this motion must havebeen extensional (Heyn, 1990; Streepey et al., 2000). Somehornblendes in the Dana Hill metagabbro tightly cluster at 945Ma. Though there is some textural complexity in these samples,with young ages coming from a variety of veins and other tex-tures, these ages fit well within the regional framework of exten-sion (bracketed by regional hornblende and biotite 40Ar-39Arages) and indicate that this was likely a time of deformationalong the Carthage-Colton shear zone (Streepey et al., 2001).Biotite 40Ar-39Ar ages are ca. 900930 Ma on both sides of theshear zone, indicating that this block of crust was uniformlyuplifting by this time (Streepey et al., 2000). K-feldspar ages aresimilar to those found in the Robertson Lake shear zone area,further supporting the idea that the entire Metasedimentary Belt
was uplifting as a uniform block by ca. 780 Ma (Heizler andHarrison, 1998; Streepey et al., 2002).
NUMERICAL MODELING
Geochronology paired with structural geology shows thatextensional motion took place along a large segment of theMetasedimentary Belt well after the Grenville contractionalorogeny, during a period that was considered to be relatively qui-escent. Application of 40Ar-39Ar and U-Pb geochronologydetails the kinematics and timing of this transition and theamount and nature of extensional deformation that occurredafter it, but gives few constraints on the mechanisms that pro-duced a regional extensional event during this period.
Extension occurred at least 100 m.y. after the latest con-tractional event in the Grenville Province of New York andsoutheastern Ontario. Given this timescale, it is difficult to makea causal link between orogenesis and extension. Whereas sev-eral attempts have been made to create a Himalayan analog tothe Grenville Province (e.g., Windley, 1986), a component ofmajor extension in the latter is clearly postorogenic, so thetimescales for the two are different. In Tibet, for example, grav-itational potential energy due to the elevated topography of theplateau played a major role in driving collapse (e.g., Shen et al.,2001). However, in the Grenville Province the duration and ter-mination of this extensional event were so much later than com-pression that gravitational collapse became an ineffectivedriving mechanism. Earlier synorogenic extensional events (asproposed by McLelland et al., 2001, and references therein) atca. 1050 Ma were different in nature and almost certainly can beascribed to processes such as gravitational collapse, mantledelamination, or some combination of these driving mecha-nisms. The exhumation of the Grenville orogen was not solelythe result of erosional and isostatic processes, but was due atleast in part to active extension along shear zones, which led touplift of the region. Geochronologic data have allowed con-struction of a kinematic model of denudation and unroofing ofmidcrustal levels of the orogenic belt. When uplift is discussedin the context of this paper, we refer to the exhumation of thecore of the Grenville Province and do not constrain a measureof the paleotopographic surface.
A model investigation has been made of the evolution of ablock of overthickened crust, with three common driving mech-anisms proposed to explain postorogenic extension. We haveevaluated the driving forces necessary to generate uplift andextension that match the kinematics of deformation in theGrenville Province as documented through field and laboratorystudies. Two critical field observations in this area that must beexplained are the continuous regional uplift during the time ofextension and the time lag in termination of extensional motionalong the Robertson Lake shear zone versus the Carthage-Colton shear zone detailed in the geochronology (see earlier andFig. 3).
1GSA Data Repository item 2004059, Appendix, hornblende spectra, is avail-able on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO80301-9140, USA, [email protected], or at www.geosociety.org/pubs/ft2004.htm.
-
TAB
LE 2
.HO
RNBL
ENDE
ARG
ON
DATA
Pow
er
39Ar
frac
39Ar
mol
40Ar
/39Ar
37Ar
/39Ar
36Ar
/39Ar
40Ar
*/39 A
r K%
40Ar
atm
osCa
/KAg
e (M
a)1
err
or
(Ma)
A112
-140
00.
1797
71.
33E-
1582
.671
663.
6246
90.
0103
479
.615
13.
6972
36.
6508
110
442
401
0.12
911
9.53
E-16
82.1
3706
3.89
560.
0005
081
.989
30.
1799
07.
1478
910
682
402
0.04
571
3.37
E-16
80.9
9802
3.88
507
0.
0002
581
.070
60.
0896
17.
1285
710
593
420
0.12
908
9.52
E-16
80.8
0290
3.97
513
0.
0001
080
.831
80.
0357
67.
2938
210
562
440
0.04
952
3.65
E-16
79.8
0750
3.82
902
0.
0005
079
.956
40.
1865
77.
0257
210
483
460
0.06
496
4.79
E-16
80.3
2021
3.94
636
0.
0006
980
.524
70.
2545
97.
2410
310
533
480
0.01
616
1.19
E-16
77.8
2671
3.64
937
0.
0024
778
.557
60.
9391
36.
6960
910
349
560
0.08
421
6.21
E-16
79.8
6897
3.63
473
0.00
025
79.7
954
0.09
212
6.66
923
1046
364
00.
1007
67.
43E-
1680
.251
004.
0008
10.
0000
480
.238
70.
0153
27.
3409
410
503
720
0.03
772
2.78
E-16
79.2
4898
3.52
251
0.00
293
78.3
825
1.09
337
6.46
332
1032
680
00.
0386
32.
85E-
1681
.537
494.
1369
10.
0009
381
.261
50.
3384
97.
5906
610
615
880
0.01
055
7.78
E-17
80.5
4386
4.17
951
0.00
409
79.3
344
1.50
162
7.66
883
1041
1410
000.
0642
74.
74E-
1680
.992
303.
9166
20.
0007
480
.772
70.
2711
47.
1864
610
563
1040
0.02
004
1.48
E-16
78.7
2645
3.90
584
0.
0017
379
.236
80.
6482
67.
1666
810
408
4800
0.02
954
2.18
E-16
80.0
8239
3.91
963
0.
0017
380
.594
40.
6393
57.
1919
810
546
J va
lue
9.84
667E
-03
1.
3818
1E-0
5To
tal 3
9 K v
ol =
2.12
529E
-10
CCNT
P/G
Tota
l gas
age
=10
51.9
7
1.39
196
Ma
A114
-236
00.
0087
16.
42E-
1743
7.13
157
4.65
082
1.19
085
85.2
341
80.5
015
8.53
361
1091
5640
00.
0035
72.
63E-
1784
.831
182.
6434
10.
0696
764
.245
224
.267
04.
8502
987
771
440
0.01
623
1.20
E-16
78.7
9309
2.49
256
0.05
687
61.9
881
21.3
280
4.57
350
853
1748
00.
0342
22.
53E-
1675
.257
002.
5539
30.
0073
973
.072
22.
9031
24.
6861
197
08
520
0.07
799
5.75
E-16
76.4
3780
2.69
612
0.00
273
75.6
316
1.05
471
4.94
701
996
456
00.
1064
27.
85E-
1676
.703
642.
7159
80.
0010
276
.403
20.
3916
94.
9834
510
043
600
0.19
840
1.46
E-15
76.4
4511
2.70
967
0.00
100
76.1
492
0.38
709
4.97
187
1001
264
00.
0650
44.
80E-
1675
.725
332.
7073
30.
0001
775
.675
50.
0658
04.
9675
899
74
680
0.05
337
3.94
E-16
74.3
6980
2.69
303
0.00
144
73.9
429
0.57
402
4.94
134
979
472
00.
1441
91.
06E-
1575
.233
562.
7618
20.
0004
575
.101
80.
1751
35.
0675
699
13
760
0.00
258
1.90
E-17
74.3
0312
2.82
691
0.00
236
73.6
062
0.93
794
5.18
699
976
5784
00.
2090
91.
54E-
1575
.251
752.
7319
80.
0007
275
.037
70.
2844
55.
0128
199
02
880
0.04
428
3.27
E-16
75.1
3989
2.76
550.
0000
575
.123
80.
0214
25.
0743
199
16
2000
0.03
130
2.31
E-16
77.0
6652
3.00
146
0.00
076
76.8
428
0.29
030
5.50
727
1008
650
000.
0046
23.
41E-
1780
.452
623.
7787
40.
0309
371
.312
811
.360
56.
9334
795
240
J va
lue
9.74
593E
-03
1.
6958
8E-0
5To
tal 3
9 K v
ol =
1.50
293E
-10
CCNT
P/G
Tota
l gas
age
=99
2.40
3
1.77
968
Ma
A117
-1R
400
0.06
297
4.65
E-16
113.
3235
55.
0468
90.
0467
599
.509
312
.190
19.
2603
512
263
440
0.13
070
9.64
E-16
74.1
2110
4.74
351
0.00
057
73.9
514
0.22
895
8.70
369
982
348
00.
1721
21.
27E-
1574
.658
904.
7491
30.
0006
074
.480
70.
2386
98.
7140
987
252
00.
1083
47.
99E-
1673
.440
854.
7365
10.
0015
572
.981
60.
6253
48.
6908
497
23
560
0.08
989
6.63
E-16
71.9
3891
4.77
110.
0019
771
.356
30.
8098
78.
7543
195
54
600
0.05
587
4.12
E-16
71.2
9738
4.84
565
0.00
070
71.0
905
0.29
017
8.89
110
952
564
00.
0470
13.
47E-
1670
.750
444.
8344
80.
0025
969
.985
21.
0816
18.
8706
194
14
-
680
0.02
548
1.88
E-16
70.3
0706
4.75
113
0.00
502
68.8
222
2.11
197
8.71
767
929
476
00.
0808
65.
97E-
1674
.379
644.
8044
40.
0020
573
.775
20.
8126
58.
8154
998
03
880
0.04
753
3.51
E-16
72.8
9371
4.88
858
0.00
407
71.6
920
1.64
858
8.96
987
959
610
000.
1361
51.
00E-
1573
.203
745.
3166
30.
0002
573
.130
00.
1007
49.
7552
897
32
2000
0.04
257
3.14
E-16
73.6
1771
5.22
413
0.00
348
72.5
902
1.39
574
9.58
556
968
448
000.
0005
33.
93E-
1898
.697
215.
9871
10.
0895
072
.250
526
.795
810
.985
5296
439
0J
valu
e9.
7801
9E-0
3
1.65
238E
-05
Tota
l 39 K
vol =
1.44
533E
-10
CCNT
P/G
Tota
l gas
age
=98
7.86
9
1.61
561
Ma
A124
-1R
360
0.03
019
2.23
E-16
125.
3363
64.
2134
60.
0474
311
1.32
2011
.181
47.
7311
213
385
400
0.17
033
1.26
E-15
80.5
0973
3.98
635
0.00
127
80.1
340
0.46
669
7.31
440
1051
240
10.
1096
88.
09E-
1680
.733
033.
8988
20.
0014
880
.296
00.
5413
37.
1538
010
533
402
0.04
250
3.14
E-16
81.2
5107
3.85
999
0.00
243
80.5
319
0.88
512
7.08
255
1055
542
00.
0126
39.
32E-
1779
.317
043.
9584
50.
0144
275
.055
85.
3724
17.
2632
110
0014
460
0.21
815
1.61
E-15
81.2
0917
3.91
409
0.00
086
80.9
539
0.31
434
7.18
182
1060
246
10.
0809
95.
98E-
1681
.154
363.
8917
30.
0017
680
.635
70.
6391
17.
1407
910
563
480
0.10
678
7.88
E-16
81.5
2008
3.83
570.
0004
181
.398
60.
1490
27.
0379
810
642
520
0.04
500
3.32
E-16
80.2
3726
3.91
163
0.00
240
79.5
267
0.88
558
7.17
730
1045
456
00.
0218
31.
61E-
1679
.204
674.
0385
80.
0024
978
.468
10.
9299
57.
4102
410
358
600
0.00
773
5.70
E-17
77.3
9229
4.28
706
0.00
899
74.7
364
3.43
173
7.86
617
997
2264
00.
0116
38.
58E-
1778
.559
424.
5639
70.
0019
277
.991
60.
7227
98.
3742
610
3014
720
0.03
076
2.27
E-16
79.9
5281
4.34
586
0.
0001
079
.981
70.
0361
47.
9740
610
506
800
0.02
660
1.96
E-16
80.7
8376
4.17
887
0.00
348
79.7
551
1.27
335
7.66
765
1048
812
000.
0568
54.
19E-
1681
.004
874.
0396
0.00
053
80.8
471
0.19
477
7.41
211
1058
440
000.
0283
72.
09E-
1681
.852
684.
0990
70.
0008
582
.104
80.
3080
27.
5212
310
716
J va
lue
9.87
089E
-03
1.
2059
4E-0
5To
tal 3
9 K v
ol =
2.58
136E
-10
CCNT
P/G
Tota
l gas
age
=10
63.4
3
1.33
794
Ma
A125
-140
00.
2539
01.
87E-
1584
.451
713.
9048
50.
0064
782
.540
22.
2634
37.
1648
610
562
401
0.07
938
5.86
E-16
84.0
4833
3.75
689
0.00
251
83.3
075
0.88
143
6.89
338
1063
444
00.
1303
89.
62E-
1683
.997
653.
7257
50.
0013
683
.594
60.
4798
36.
8362
410
663
480
0.10
856
8.01
E-16
83.7
6073
3.70
631
0.00
069
83.5
557
0.24
478
6.80
057
1065
352
00.
2233
21.
65E-
1584
.004
993.
8024
0.00
102
83.7
027
0.35
984
6.97
688
1067
256
00.
0858
36.
33E-
1685
.409
033.
8426
20.
0009
885
.119
20.
3393
57.
0506
810
804
600
0.00
564
4.16
E-17
77.5
5969
4.87
365
0.00
266
76.7
725
1.01
495
8.94
248
999
3468
00.
0078
35.
77E-
1784
.759
364.
4357
30.
0130
388
.609
74.
5426
78.
1389
511
1329
820
0.01
984
1.46
E-16
83.3
0916
4.05
837
0.
0082
585
.746
82.
9260
27.
4465
510
8614
1000
0.01
869
1.38
E-16
83.4
4706
4.02
577
0.
0084
085
.929
52.
9748
77.
3867
310
8814
4800
0.06
665
4.92
E-16
83.6
6405
4.09
005
0.00
077
83.4
373
0.27
103
7.50
468
1064
4J
valu
e9.
6330
2E-0
3
1.87
146E
-05
Tota
l 39 K
vol=
1.26
569E
-10
CCNT
P/G
Tota
l gas
age
=10
65.0
8
1.92
921
Ma
A128
-136
00.
0200
31.
48E-
1610
3.37
114
0.86
044
0.05
595
86.8
393
15.9
927
1.57
879
1114
538
00.
0097
67.
20E-
1745
.937
180.
5593
70.
0011
845
.587
20.
7618
61.
0263
666
814
420
0.00
899
6.63
E-17
85.6
7338
1.20
975
0.00
381
84.5
478
1.31
382.
2197
210
9213
(conti
nued
)
-
TAB
LE 2
.Co
ntin
ued
Pow
er
39Ar
frac
39Ar
mol
40Ar
/39Ar
37Ar
/39Ar
36Ar
/39Ar
40Ar
*/39 A
r K%
40Ar
atm
osCa
/KAg
e (M
a)1
err
or
(Ma)
460
0.01
472
1.09
E-16
95.1
5639
2.10
311
0.00
229
94.4
805
0.71
029
3.85
892
1186
1150
00.
0614
54.
53E-
1683
.472
604.
6535
10.
0006
783
.275
50.
2361
38.
5385
510
802
520
0.16
436
1.21
E-15
78.3
9011
4.93
948
0.00
060
78.2
127
0.22
632
9.06
327
1029
153
00.
0604
04.
46E-
1678
.093
544.
6488
90.
0006
277
.910
10.
2349
08.
5300
710
262
540
0.02
521
1.86
E-16
71.3
4198
3.67
143
0.00
056
71.1
764
0.23
209
6.73
657
957
556
00.
0405
92.
99E-
1675
.791
474.
5035
10.
0000
275
.786
10.
0070
98.
2633
210
053
620
0.10
396
7.67
E-16
76.9
1635
4.80
667
0.00
048
76.7
755
0.18
312
8.81
958
1015
266
00.
1161
18.
57E-
1678
.493
214.
9517
40.
0005
578
.329
70.
2083
19.
0857
610
312
720
0.11
533
8.51
E-16
79.9
5906
5.11
697
0.00
065
79.7
680
0.23
895
9.38
894
1045
278
00.
0867
66.
40E-
1680
.744
144.
8914
40.
0006
580
.551
10.
2390
88.
9751
210
532
1000
0.06
995
5.16
E-16
80.5
6078
4.96
834
0.00
099
80.2
677
0.36
380
9.11
622
1050
240
000.
1023
97.
55E-
1666
.014
293.
4490
60.
0013
465
.619
60.
5978
86.
3285
589
91
J va
lue
9.83
709E
-03
1.
4414
8E-0
5To
tal 3
9 K v
ol =
2.63
518E
-10
CCNT
P/G
Ttot
al g
as a
ge =
1022
.11
1.
2886
7 M
a
A129
-136
00.
0233
61.
72E-
1697
.701
206.
7107
0.05
614
81.1
131
16.9
784
12.3
1321
1044
1150
00.
5648
54.
17E-
1584
.981
446.
6316
10.
0005
384
.823
80.
1855
012
.168
0910
792
540
0.09
031
6.66
E-16
84.3
7694
6.50
400.
0012
084
.731
70.
4204
511
.933
9410
794
580
0.10
879
8.03
E-16
85.2
8425
6.53
173
0.00
166
84.7
932
0.57
578
11.9
8483
1079
362
00.
0209
31.
54E-
1685
.023
556.
4932
30.
0009
184
.755
50.
3152
711
.914
1810
7913
1000
0.12
513
9.23
E-16
82.4
3000
6.78
991
0.00
165
81.9
417
0.59
238
12.4
5855
1052
320
000.
0635
14.
69E-
1684
.959
447.
4724
80.
0002
984
.872
30.
1025
713
.710
9710
804
4800
0.00
313
2.31
E-17
79.7
7944
6.68
513
0.
0074
581
.981
12.
7596
812
.266
2910
5288
J va
lue
9.65
675E
-03
1.
7966
5E-0
5To
tal 3
9 K V
ol=
1.17
160E
-10
CCNT
P/G
Tota
l gas
age
=10
75.0
1
2.10
352
Ma
A133
-140
00.
1046
67.
72E-
1678
.384
833.
1879
30.
0064
176
.490
92.
4161
95.
8494
110
012
440
0.28
683
2.12
E-15
73.0
6987
3.12
962
0.00
103
72.7
641
0.41
847
5.74
242
963
144
10.
0877
26.
47E-
1673
.686
013.
1416
70.
0012
773
.310
90.
5090
75.
7645
396
83
460
0.02
532
1.87
E-16
73.4
5835
3.18
647
0.00
229
72.7
827
0.91
977
5.84
673
963
850
00.
0496
33.
66E-
1674
.458
303.
2227
60.
0010
274
.156
10.
4058
65.
9133
297
76
540
0.11
704
8.64
E-16
74.8
1581
3.20
948
0.00
134
74.4
197
0.52
945
5.88
895
980
358
00.
0497
13.
67E-
1674
.777
193.
1368
40.
0023
474
.085
50.
9250
5.75
567
976
562
00.
0113
08.
34E-
1771
.758
093.
1344
80.
0105
168
.653
24.
3268
85.
7513
492
018
700
0.12
656
9.34
E-16
73.3
8544
3.21
055
0.00
100
73.0
899
0.40
273
5.89
092
966
278
00.
0451
33.
33E-
1674
.219
913.
2652
70.
0003
974
.105
20.
1545
65.
9913
297
64
880
0.04
618
3.41
E-16
74.4
9200
3.20
771
0.00
037
74.3
841
0.14
485
5.88
571
979
410
000.
0364
52.
69E-
1673
.883
803.
8105
70.
0025
474
.635
71.
0176
86.
9918
798
26
1200
0.00
925
6.83
E-17
74.9
2031
3.98
344
0.00
117
74.5
737
0.46
264
7.30
906
981
2950
000.
0042
33.
12E-
1774
.502
663.
6995
40.
0114
977
.897
54.
5566
76.
7881
510
1533
J va
lue
9.69
066E
-03
1.
7372
2E-0
5To
tal 3
9 K v
ol =
1.89
216E
-10
CCNT
P/G
Tota
l gas
age
=97
2.99
5
1.63
359
Ma
-
A134
-136
00.
0580
64.
28E-
1688
.659
323.
1155
30.
0243
481
.468
28.
1109
65.
7165
710
613
380
0.08
990
6.63
E-16
74.6
7086
2.89
451
0.00
067
74.4
739
0.26
378
5.31
103
991
240
00.
1350
69.
97E-
1672
.878
022.
9391
10.
0003
672
.771
60.
1460
25.
3928
697
32
420
0.13
788
1.02
E-15
72.0
7033
2.91
703
0.
0000
272
.076
60.
0087
15.
3523
596
62
430
0.07
872
5.81
E-16
72.9
9311
2.94
646
0.00
062
72.8
086
0.25
278
5.40
635
973
244
00.
0658
74.
86E-
1672
.615
722.
9357
60.
0007
572
.393
40.
3061
75.
3867
296
93
460
0.08
062
5.95
E-16
72.7
2679
2.93
459
0.00
137
72.3
216
0.55
714
5.38
457
968
248
00.
0572
84.
23E-
1672
.604
682.
9346
90.
0019
172
.040
80.
7766
45.
3847
596
64
500
0.06
910
5.10
E-16
73.4
6718
2.96
128
0.00
186
72.9
177
0.74
792
5.43
354
975
252
00.
0362
32.
67E-
1672
.741
532.
8976
30.
0025
172
.000
91.
0181
65.
3167
596
54
560
0.02
905
2.14
E-16
72.4
6758
2.99
739
0.00
192
71.8
994
0.78
405
5.49
980
964
560
00.
0191
01.
41E-
1670
.952
023.
0573
50.
0021
070
.331
00.
8752
75.
6098
294
86
680
0.03
939
2.91
E-16
72.0
1860
3.25
967
0.00
347
70.9
928
1.42
436
5.98
105
955
376
00.
0351
42.
59E-
1671
.750
963.
2029
80.
0018
571
.204
80.
7611
85.
8770
395
74
840
0.01
835
1.35
E-16
72.6
9965
3.60
576
0.00
535
71.1
194
2.17
367
6.61
607
956
640
000.
0502
63.
71E-
1672
.237
524.
2873
20.
0024
271
.522
50.
9898
27.
8666
496
04
J va
lue
9.82
456E
-03
1.
5083
7E-0
5To
tal 3
9 K v
ol =
3.12
587E
-10
CCNT
P/G
Tota
l gas
age
=97
4.68
0
1.34
455
Ma
A135
-136
00.
0048
03.
54E-
1718
9.06
855
3.53
975
0.38
769
74.5
070
60.5
926
6.49
495
996
2942
00.
0321
52.
37E-
1697
.219
902.
8304
70.
0082
294
.792
02.
4973
35.
1935
211
936
460
0.10
836
8.00
E-16
94.1
6484
2.76
105
0.00
110
93.8
398
0.34
519
5.06
615
1184
252
00.
2854
92.
11E-
1592
.272
922.
8059
90.
0009
691
.988
50.
3082
45.
1486
111
671
540
0.17
551
1.30
E-15
91.5
9555
2.83
532
0.00
085
91.3
458
0.27
267
5.20
242
1161
256
00.
0738
25.
45E-
1693
.826
662.
8451
20.
0023
193
.143
40.
7282
15.
2204
011
783
620
0.14
952
1.10
E-15
91.6
0731
2.84
698
0.00
091
91.3
373
0.29
475
5.22
382
1161
266
00.
0696
25.
14E-
1691
.920
432.
8621
70.
0007
692
.144
90.
2442
05.
2516
911
683
720
0.03
631
2.68
E-16
91.5
3615
2.89
577
0.
0005
991
.710
50.
1904
75.
3133
411
646
840
0.04
446
3.28
E-16
92.4
5542
2.94
274
0.00
034
92.3
555
0.10
808
5.39
952
1170
540
000.
0199
61.
47E-
1692
.069
613.
0966
80.
0057
890
.363
01.
8536
15.
6819
811
529
J va
lue
9.88
469E
-03
1.
1115
2E-0
5To
tal 3
9 K v
ol=
1.54
303E
-10
CCNT
P/G
Tota
l gas
age
=11
67.3
6
1.24
451
Ma
A136
-136
00.
0290
2.14
E-16
107.
5147
33.
1368
40.
0598
089
.843
516
.436
15.
7556
711
498
400
0.08
390
6.19
E-16
70.2
5276
3.13
401
0.00
122
69.8
912
0.51
466
5.75
048
950
442
00.
1658
91.
22E-
1569
.971
593.
0752
50.
0003
669
.866
60.
1500
55.
6426
695
02
440
0.23
971.
77E-
1569
.016
903.
1408
10.
0003
368
.918
50.
1425
85.
7629
593
91
450
0.07
365
5.43
E-16
68.4
6276
3.10
302
0.00
155
68.0
044
0.66
950
5.69
361
930
548
00.
0462
63.
41E-
1668
.160
773.
1885
30.
0012
267
.800
90.
5279
85.
8505
192
85
520
0.08
498
6.27
E-16
67.3
9505
3.13
191
0.00
063
67.2
088
0.27
636
5.74
662
921
256
00.
0204
41.
51E-
1667
.855
533.
2227
0.01
155
64.4
438
5.02
793
5.91
321
891
2058
00.
0132
39.
76E-
1767
.226
983.
0830
40.
0031
368
.153
11.
3776
5.65
695
931
1564
00.
0340
62.
51E-
1670
.514
163.
1958
0.00
225
69.8
502
0.94
159
5.86
385
949
780
00.
1283
79.
47E-
1668
.488
293.
1414
50.
0009
168
.220
00.
3917
45.
7641
393
22
880
0.02
252
1.66
E-16
67.3
3619
3.24
219
0.00
315
66.4
059
1.38
156
5.94
897
913
9
(conti
nued
)
-
TAB
LE 2
.Co
ntin
ued
Pow
er
39Ar
frac
39Ar
mol
40Ar
/39Ar
37Ar
/39Ar
36Ar
/39Ar
40Ar
*/39 A
r K%
40Ar
atm
osCa
/KAg
e (M
a)1
err
or
(Ma)
4000
0.05
804.
28E-
1669
.015
213.
2216
70.
0006
168
.834
60.
2617
5.91
132
939
4J
valu
e9.
9144
5E-0
3
1.20
341E
-05
Tota
l 39 K
vol =
2.21
028E
-10
CCNT
P/G
Tota
l gas
age
=94
3.29
9
1.37
251
Ma
A137
-236
00.
0743
45.
49E-
1679
.545
282.
6555
0.00
766
77.2
828
2.84
427
4.87
248
1010
338
00.
1824
21.
35E-
1576
.643
712.
5629
30.
0005
476
.485
50.
2064
24.
7026
210
022
400
0.29
765
2.20
E-15
77.5
8981
2.57
025
0.00
031
77.4
988
0.11
730
4.71
606
1012
640
10.
0246
21.
82E-
1676
.839
482.
4938
10.
0041
975
.601
21.
6115
14.
5758
099
37
440
0.15
378
1.13
E-15
76.7
6473
2.56
553
0.00
078
76.5
340
0.30
057
4.70
739
1002
146
00.
1135
68.
38E-
1676
.796
232.
5509
70.
0011
776
.451
60.
4487
64.
6806
810
023
480
0.03
633
2.68
E-16
77.3
7406
2.59
891
0.00
191
76.8
109
0.72
784
4.76
864
1005
350
00.
0162
81.
20E-
1676
.301
152.
4661
0.00
684
74.2
795
2.64
957
4.52
495
980
956
00.
0283
62.
09E-
1676
.613
912.
5863
90.
0049
375
.157
11.
9014
94.
7456
798
96
800
0.05
065
3.74
E-16
76.8
3979
2.70
719
0.00
161
76.3
642
0.61
893
4.96
732
1001
440
000.
0220
31.
63E-
1677
.064
613.
4832
20.
0060
375
.281
82.
3134
6.39
123
990
7J
valu
e9.
7086
2E-0
3
1.72
082E
-05
Tota
l 39 K
vol =
2.77
185E
-10
CCNT
P/G
Tota
l gas
age=
1004
.41
2.
3128
3 M
a
A138
-136
00.
0034
12.
51E-
1780
.221
033.
8620
10.
0742
758
.272
827
.359
77.
0862
681
238
400
0.01
336
9.86
E-17
75.3
8258
2.98
881
0.00
238
74.6
796
0.93
255
5.48
406
987
1142
00.
1304
29.
62E-
1674
.158
962.
9600
10.
0004
574
.026
70.
1783
55.
4312
198
02
440
0.10
992
8.11
E-16
74.4
5032
2.96
696
0.00
062
74.2
657
0.24
798
5.44
396
983
246
00.
1022
67.
55E-
1674
.445
562.
9893
30.
0003
974
.561
20.
1553
45.
4850
198
62
480
0.08
788
6.48
E-16
74.5
8835
3.00
933
0.00
059
74.4
137
0.23
416
5.52
171
984
350
00.
1166
48.
61E-
1674
.504
272.
9973
10.
0009
274
.233
10.
3639
75.
4996
598
32
520
0.07
957
5.87
E-16
74.4
4747
2.97
613
0.
0000
374
.455
60.
0109
35.
4607
998
53
560
0.20
707
1.53
E-15
74.3
3688
3.00
375
0.00
039
74.2
214
0.15
535
5.51
147
982
158
00.
0200
11.
48E-
1673
.735
132.
9842
70.
0000
773
.756
20.
0285
85.
4757
297
87
640
0.08
036
5.93
E-16
74.6
8295
2.98
614
0.00
071
74.4
746
0.27
898
5.47
916
985
140
000.
0491
03.
62E-
1674
.240
163.
0346
0.00
125
73.8
720
0.49
591
5.56
807
979
4J
valu
e9.
7523
8E-0
3
1.69
034E
-05
Tota
l 39 K
vol =
2.45
945E
-10
CCNT
P/G
Tota
l gas
age
=98
2.38
0
1.49
725
Ma
A140
-136
00.
0481
13.
55E-
1664
.058
671.
5539
10.
0082
661
.617
83.
8103
72.
8512
185
64
400
0.15
487
1.14
E-15
70.5
3351
2.27
729
0.00
118
70.1
852
0.49
382
4.17
851
949
142
00.
0720
35.
31E-
1670
.739
172.
2903
40.
0004
070
.619
70.
1688
94.
2024
695
32
440
0.12
733
9.40
E-16
70.6
7584
2.34
235
0.00
044
70.5
457
0.18
414
4.29
789
952
346
00.
0507
63.
75E-
1670
.538
672.
2823
10.
0000
170
.541
80.
0044
44.
1877
295
23
500
0.03
876
2.86
E-16
70.6
7347
2.29
519
0.00
156
70.2
130
0.65
155
4.21
136
949
6
-
540
0.10
871
8.02
E-16
72.4
5699
2.38
892
0.00
278
71.6
342
1.13
555
4.38
334
964
260
00.
1307
29.
65E-
1671
.079
792.
3918
80.
0005
170
.928
50.
2128
54.
3887
795
63
640
0.09
072
6.69
E-16
71.1
0540
2.37
214
0.00
069
70.9
027
0.28
507
4.35
255
956
372
00.
0792
05.
84E-
1670
.815
592.
3225
0.00
092
70.5
424
0.38
577
4.26
147
952
310
000.
0668
84.
93E-
1668
.269
672.
1322
10.
0004
368
.143
20.
1852
53.
9123
192
73
4000
0.03
192
2.35
E-16
66.5
2505
1.88
886
0.00
066
66.3
294
0.29
411
3.46
580
908
6J
valu
e9.
8580
6E-0
3
1.30
213E
-05
Tota
l 39 K
vol =
2.00
423E
-10
CCNT
P/G
Tota
l gas
age
=94
6.27
5
1.27
061
Ma
A142
-134
00.
1064
57.
85E-
1686
.984
282.
6341
90.
0301
278
.084
410
.231
64.
8333
810
232
360
0.00
028
2.07
E-18
83.8
7368
1.
9578
90.
2916
32.
3040
110
2.74
703.
5924
641
717
440
0.00
059
4.38
E-18
87.4
3051
3.62
755
0.
0908
211
4.26
8030
.695
86.
6560
613
5215
846
00.
0018
31.
35E-
1780
.862
333.
1329
20.
0345
770
.646
112
.634
15.
7484
894
765
500
0.00
211
1.55
E-17
76.3
35