evidence for the granulite–granite connection ... · the classic cordilleran metamorphic core...

www.elsevier.com/locate/lithos

Lithos 86 (200

Evidence for the granulite–granite connection:

Penecontemporaneous high-grade metamorphism, granitic

magmatism and core complex development in the

Liscomb Complex, Nova Scotia, Canada

Jaroslav Dostala,*, Duncan J. Keppieb, Pierre Jutrasa, Brent V. Millerc,

Brendan J. Murphyd

aDepartment of Geology, Saint Mary’s University, Halifax, Nova Scotia B3H 3C3, CanadabInstituto de Geologia, Universidad Nacional Autonoma de Mexico, Mexico DF 04510, Mexico

cRadiogenic Isotope Geochemistry, Department of Geology & Geophysics, Texas A&M University, College Station, Texas 77843-3115, USAdDepartment of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada

Received 11 June 2004; accepted 14 April 2005

Available online 9 June 2005

Abstract

Upper amphibolite–granulite facies gneisses and granites of the Liscomb Complex (Nova Scotia, Canada), which are

exposed in a core complex within the Cambro–Ordovician Meguma Group of southern Nova Scotia, yielded concordant U–Pb

zircon/monazite ages of 377F2 and 374F3 Ma, respectively. Geochronological and geochemical data suggest a single

Devonian high-grade metamorphic event, which generated the granitic magma by partial melting of the fertile Liscomb gneisses

at a depth of ~30 km. The melting was also synchronous with an extensional event during which the gneisses were uplifted in a

core complex associated with the intrusion of granitoids to a depth of ~10 km. Subsequently, the gneisses and granites

underwent rapid exhumation before the deposition of unconformably overlying late Fammenian rocks at ~364 Ma. These

events took place during terminal stages of the Acadian Orogeny and the onset of extensional tectonics in Atlantic Canada

during the Middle–Late Devonian. The close temporal and spatial association of Liscomb gneisses/granulites and granites, their

major and trace element compositions, and their overlapping isotopic characteristics confirm the hypothesis that high-grade

metamorphism and generation of granitic melt are complementary processes. As the Liscomb granites are of similar age,

mineralogy and chemistry to the voluminous granitoid plutons found throughout the Meguma Terrane, a similar process is

indicated for the rest of the terrane.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Granite; Granulite; Core complex; Zircon dating; Melting

0024-4937/$ - s

doi:10.1016/j.lit

* Correspondi

E-mail addre

6) 77–90

ee front matter D 2005 Elsevier B.V. All rights reserved.

hos.2005.04.002

ng author.

ss: [email protected] (J. Dostal).

J. Dostal et al. / Lithos 86 (2006) 77–9078

1. Introduction

One hypothesis for the origin of voluminous

granitoid rocks that intrude into the upper crust

links it to melt generated during granulite facies

metamorphism in the mid-lower crust (e.g., Viel-

zeuf et al., 1990). Tests for this hypothesis have

been sought in mid-lower crustal granulites (e.g.,

LeFort, 1986; Solar and Brown, 2001) and in lower

crustal xenoliths within volcanic suites (e.g., Braun

and Kriegsman, 2001). These tests have been gen-

erally limited to geochemical and isotopic compar-

Fig. 1. Geological map of the Meguma Terrane of southern Nova Scoti

including the South Mountain Batholith (SMB) as well as the Liscom

(Greenough et al., 1999) and the Cambro–Ordovician Meguma Group. T

the lamprophyres form a swarm of narrow dykes along the eastern shore of

and the location of the map. It also shows the lithotectonic terranes o

G=Gander; D=Dunnage; H=Humber) and the Minas Fault (MF) separat

isons because upper and mid-lower crusts are

rarely exposed together, making a direct connection

difficult. Furthermore, geochronological data for

minerals with high blocking temperatures such as

zircon are generally missing for genetically-related

granulites and granites. However, an unusual situa-

tion in which middle crustal granulite-facies

gneisses and upper crustal granitoid rocks crop

out together occurs in the Liscomb Complex of

southern Nova Scotia, Canada (Fig. 1), thereby

providing a rare opportunity to test the granulite–

granite connection.

a, showing the major intrusions of Late Devonian granitoid rocks,

b Complex, the xenolith-bearing lamprophyre dykes of Tangier

he area of study, shown in Fig. 2, is indicated by a star. Note that

Nova Scotia. The insert displays eastern Canada, northeastern USA,

f the Canadian Appalachians (terranes: M=Meguma; A=Avalon;

ing the Meguma and Avalon terranes.

J. Dostal et al. / Lithos 86 (2006) 77–90 79

2. Geological setting

The Liscomb Complex is located within the

Meguma Terrane of the Canadian Appalachians

(Fig. 1). The Meguma Terrane, most outboard terrane

of the northern Appalachians, is juxtaposed against

the Avalon Terrane along the Minas (Cobequid-Che-

dabucto) Fault Zone. Both these terranes were accret-

ed to North America (Laurentia) during continental

collision in the early to middle Paleozoic (Williams

and Hatcher, 1983). In particular, the Meguma was

accreted in the Devonian during the final closure of

the Rheic Ocean. The Meguma Terrane is composed

mainly of the ~10 km thick Cambro–Ordovician tur-

bidite succession of the Meguma Group which con-

tains Gondwanan fauna (Pratt and Waldron, 1991).

Detrital zircons from a lower unit of the Meguma

Group yielded ~3.0 Ga, 2.0 Ga and 600 Ma ages,

also indicating a Gondwanan (West African) source

(Krogh and Keppie, 1990). The Meguma turbidites

(wackes and pelites) are disconformably to uncon-

formably overlain by Siluro–Devonian shallow-ma-

rine and continental rocks. The youngest of these

rocks contains Early Devonian (Lochkovian to lower

Emsian) fossils (Boucot, 1975; Bouyx et al., 1997).

These Cambrian to Devonian rocks were deformed

and metamorphosed to a lower greenschist to amphib-

olite facies under low pressure metamorphic condi-

tions during the Devonian Acadian Orogeny at about

405–370 Ma (Keppie and Dallmeyer, 1995; Hicks et

al., 1999), shortly after the deposition of the Lower

Devonian rocks. This was accompanied by the intru-

sion of voluminous peraluminous granitoids of the

South Mountain Batholith (SMB), Liscomb Complex

and satellite plutons that were emplaced at a depth of

~10–12 km around 380–370 Ma (Clarke et al., 1997;

Kontak and Reynolds, 1994).

The SMB is the dominant granitoid body of the

Meguma Terrane. It spreads over an area of about

7300 km2 (Fig. 1) and contains rocks ranging from

megacrystic biotite granodiorite, with up to 20% bio-

tite, to equigranular leucogranite containing less than

2% biotite. The granitic bodies produced a distinct

contact metamorphic aureole. This was followed by

rapid exhumation, as documented by 40Ar / 39Ar mica

cooling ages of ~375–360 Ma (Keppie and Dall-

meyer, 1995), before being unconformably overlain

by Upper Devonian to Carboniferous continental and

shallow marine rocks (Martel et al., 1993). The oldest

of these rocks is of late Fammenian age (~365–360

Ma according to Okulitch, 2003).

Many authors have inferred that the Meguma

Group and overlying Siluro–Devonian units repre-

sents a Cambrian to Early Devonian passive margin

bordering northwest Africa that was subsequently

transferred to Laurentia during the Acadian Orogeny

(e.g., Schenk, 1997). This was based primarily upon:

(i) proposed stratigraphic correlations between the

Cambro–Silurian strata in the Meguma Terrane and

coeval seccessions in Morocco (Schenk, 1997), and

(ii) the Middle Devonian age of the Acadian Orogeny,

the oldest accretionary event recognized in the

Meguma Terrane. Alternatively, it has been proposed

that the Cambrian to Early Devonian strata of the

Meguma Terrane was either thrust over the Avalon

Terrane (e.g., Greenough et al., 1999) or may repre-

sent a passive margin bordering the Avalon micro-

continent, which would imply that the Meguma Group

was deposited on Avalonian continental crust (e.g.,

Keppie and Dostal, 1991; Keppie et al., 2003). Detri-

tal zircon studies show contrasting provenance for

Avalonian and Meguma Cambro–Ordovician sedi-

mentary rocks (Krogh and Keppie, 1990; Keppie et

al., 1998), whereas Siluro–Devonian sedimentary

rocks contain similar age suites (Murphy et al., 2004).

The basement of the Meguma Group is only

exposed in the Liscomb Complex (Fig. 2), an assem-

blage of high-grade gneisses and mafic plutonic

rocks that were intruded by granitoid rocks (Giles

and Chatterjee, 1986, 1987; Clarke et al., 1993;

Kontak and Reynolds, 1994). The complex, which

crops out over an area of ~240 km2, cuts across

greenschist facies metasedimentary rocks of the

Meguma Group near the northern margin of the

Meguma Terrane (Fig. 1).

Exposure of the Liscomb Complex is very poor.

Strong shearing and at least 2 m wide contact aureole

were observed in the only exposure of the contact

between a foliated granite/gneiss of the Liscomb

Complex and the Meguma Group. The gneisses

have a distinct foliation that is oblique to that in the

surrounding Meguma Group and the fold traces and

lithologic boundaries of the Meguma Group appear to

be sharply truncated by the border of the Liscomb

Complex, indicating that its emplacement is post-

folding (Fig. 2). Within the Liscomb Complex, field

Fig. 2. Geological map of the Liscomb Complex (modified from Kontak and Reynolds, 1994 and Clarke et al., 1993) showing the sample

locations. Note that due to poor exposure, most contacts are inferred. Structural information is from Faribault (1891), Fletcher and Faribault

(1891a,b) and Kontak and Reynolds (1994). The Late Devonian to Early Carboniferous (Tournaisian) Horton Group consists of nonmarine

clastic sedimentary rocks deposited mainly in alluvial–lacustrine environments.


relationships including rare contacts between the var-

ious units indicate that the sequence of emplacement

is gneisses, gabbros and granites (Kontak and Rey-

nolds, 1994), and that the emplacement of all the units

postdates Acadian deformation of the Meguma meta-

sedimentary rocks. 40Ar / 39Ar dates are interpreted to

record cooling ages from the Liscomb Complex at

375F3 Ma in amphibole (gneisses), 373F4 to

367F3 Ma in muscovite (gneisses and granites),

and 385 to 367 Ma in biotite (gneisses, granites and

gabbros) (Kontak and Reynolds, 1994), providing a

younger limit for the emplacement of the Liscomb

Complex.

Clarke et al. (1993) inferred that the gneisses were

emplaced as a domal uplift that may have intruded the

Meguma Group through diapirism. However, the

presence of paragneisses is more typical of core com-

plexes. The classic Cordilleran metamorphic core

complexes occur in a narrow belt within the magmatic

arc extending from southern Canada to northwestern

Mexico. They record Tertiary extension following the

Laramide Orogeny (Coney, 1980; Dickinson, 2002).

Typically, they consist of an older metamorphic–plu-

tonic basement overprinted upwards by a metamor-

phic carapace of gently dipping, domal, greenschist–

amphibolite facies with lineated and foliated myloni-

tic–gneissic fabrics. This carapace is overlain by a

decollement zone with sliding and detachment kine-

matic indicators. This zone is, in turn, overlain by an

unmetamorphosed cover attenuated by subhorizontal

faults. The amplitude of most of these core complexes

is V4 km (Coney, 1980), and estimates of the pres-

sures of formation for the mylonitic fabrics are 3–3.5

kb (=10–13 km) (Davis et al., 1980). On the other

hand, core complexes in the arc–backarc Cyclades

region (Aegean Sea, Greece) developed at 5–7 kb

(=20–25 km depth) and 700–380 8C, were exhumed

at a rate between 1–2 km/my, and cooled at a rate of


29 8C/my (Lister et al., 1984). Even deeper exhuma-

tion has been reported in the active core complexes of

the D’Entrecasteaux Islands, a rifted arc complex in

Papua New Guinea, in which gneissic domes include

eclogites formed at depths of 45–75 km (=13–21 kb)

and temperatures of 730–900 8C (Hill et al., 1992).

Isothermal exhumation at a rate of 15 km/my was

followed by cooling at N100 8C/my. These core com-

plexes rise through a region of density inversion

where ophiolites overlie less-dense continental crust

and are located in a continental rift that passes later-

ally into the active Woodlark Basin sea-floor spread-

ing system. Unroofing took place by faulting and

shearing at the boundary the gneiss domes. Present

day surface uplift has led to topographic elevations of

up to 2.5 km. Clockwise P–T–t paths and short-lived

thermal pulses associated with extensional deforma-

tion and the intrusion of sills occur in all of these core

complexes (Lister and Baldwin, 1993). Poor exposure

of the Liscomb Complex means that most of these

characteristics cannot be observed. However, the gen-

tle dips in the foliation of the Liscomb gneisses, the

domal shape of the high-grade gneisses and their

discordance with the surrounding Meguma Group

are consistent with a core complex interpretation.

The gneisses of the Liscomb Complex include a

variety of migmatitic and non-migmatitic rocks ranging

from augen gneiss (quartz–K-feldspar–plagioclase–

biotite–muscovite–sillimanite) through hornblende–

biotite gneiss (quartz–K-feldspar–plagioclase–horn-

blende–biotite) to quartzo–feldspathic gneiss (quartz–

K-feldspar–plagioclase–biotite–muscovite–sillimanite–

garnet) and sillimanite schist (quartz–plagioclase–cor-

dierite–biotite–sillimanite) (Clarke et al., 1993). Al-

though these mineral assemblages are typical of the

upper amphibolite facies, that these are mostly ret-

rograde assemblages is indicated by the presence of

coronas around pyroxene cores and zoned minerals,

such as Mn-rich garnet cores and ternary feldspar

cores with compositions indicative of temperatures

N900 8C (Clarke et al., 1993; Kontak and Reynolds,

1994). Clarke et al. (1993) and Kontak and Rey-

nolds (1994) estimated pressures of 640 to 820 MPa

and temperatures of 760 to 980 8C.The mafic rocks form two separate intrusions

(Chatterjee et al., 1989) composed of amphibole/clin-

opyroxene-bearing gabbros and diorites that contain

significant proportions of both cognate and exotic

xenoliths (Clarke et al., 1993). They contain xenoliths

of both Liscomb gneisses and Meguma Group rocks.

The granitic rocks of the complex are mainly grano-

diorites and monzogranites (sensu Streckeisen and Le

Maitre, 1979) similar to those of the SMB. Both

the granodiorites and monzogranites contain biotite

(+/�muscovite). In addition, many granites contain

garnet and other noteworthy accessory minerals, in-

cluding zircon, monazite and apatite.

The only other evidence for the nature of the base-

ment beneath the Meguma Group comes from xeno-

liths in ~368Mamafic lamprophyre dykes (the Tangier

Dykes on Fig. 1), which intrude the Meguma Group to

the south of the Liscomb Complex (Fig. 1: Kempster et

al., 1989). The xenoliths include three rock types:

sapphirine granulites, mafic gneisses and garnetiferous

quartzo–feldspathic gneisses (Owen et al., 1988; Owen

and Greenough, 1991). Mineral core compositions for

the early (pre-dyke) metamorphic event in the sapphi-

rine granulites and quartzo–feldspathic gneisses indi-

cate minimum temperatures ofz600 8C at pressures of

~450–600 MPa (Owen et al., 1988), whereas rim com-

positions and M2 (syn-dyke) assemblages in the meta-

pelitic rocks imply conditions of 725–795 8C and 700–

900 MPa (Owen and Greenough, 1991). These xeno-

liths indicate that a mafic unit was emplaced at or

before 629F4 Ma into pelitic metasedimentary rocks

containing ~880–1050 Ma detrital zircons (Greenough

et al., 1999). The xenoliths underwent a high-grade

metamorphic event at 378F1 Ma (U–Pb concordant

zircon age; Greenough et al., 1999).

3. Geochronology

3.1. Analytical methods

U–Pb isotopic analyses of zircon and monazite

from the Liscomb Complex were done at the Univer-

sity of North Carolina using the procedure of Ratajeski

et al. (2001). All zircon fractions were highly abraded,

but monazites were not. All reported errors are of two

sigma. The zircon and monazite were obtained from

three samples: granite LG-1 (location: N 45814.777Vand W 62846.732V) and garnet–biotite–sillimanite

gneisses LG-120 (Si-poor; probably a residual rock;

location: N 45816.482V W 62839.923V) and LG-122

(location: N 45816.402V W 62840.003V; Fig. 2).

Fig. 3. U–Pb concordia diagrams for (A) the Liscomb granodiorite

(sample LG-1), (B) a garnet–biotite–sillimanite mafic gneiss (sam-

ple LG-120) and (C) a garnet–biotite–sillimanite felsic gneiss (sam-

ple LG-122).


3.2. Results

Analyses from eight single-grain and one four-grain

fractions of zircon from granite LG-1 form a recent Pb-

loss line anchored by two concordant and two nearly-

concordant points (Fig. 3A, Table 1). Regression of the

zircon data yields an upper intercept at 373.8F2.7 and

a lower intercept suggestive of recent Pb loss. The

upper intercept age is interpreted as representing the

time of crystallization of the Liscomb granite. Four

single monazite grains from the same sample fall

above the concordia, likely due to excess 206Pb caused

by the incorporation of 230Th (e.g., Scharer, 1984). In

these cases, the 207Pb / 235U ages (373.4 to 374.0 Ma;

Table 1) yield the most reliable estimates.

Four multi-grain and four single-grain zircon anal-

yses from (probably restitic) gneiss sample LG-120

form a recent Pb-loss discordant trend with an upper

intercept at 376.9F2.3 Ma. This age is supported by

two concordant monazite analyses (Fig. 3B). We inter-

pret the upper intercept age as representing the time of

granulite facies metamorphism in the Liscomb meta-

morphic suite. The lack of any inheritance in these data

suggests that either the pelitic protolith lacked detrital

zircon, or it was all consumed to crystallize new zircon.

Seven single-grain and one two-grain zircon frac-

tions from gneiss sample LG-122 also form a discor-

dant trend anchored by one concordant point (Fig.

3C), but with an upper intercept at 373.9F7.2 Ma.

As these zircons are extremely rich in U and radio-

genic Pb, whereas their common Pb content is small

(Table 1), the error ellipses are much smaller than

those of the other two samples, and thus the upper

intercept age represents a good estimate of the time of

granulite facies metamorphism.

4. Geochemistry

4.1. Analytical methods

The major and trace element analyses of samples

used for geochronology are given in Table 2. Major

and some trace (Rb, Sr, Ba, Zr, Nb, Y, Ga, Co, Cr, Ni,

V and Zn) elements in these samples were analyzed

with an X-ray fluorescence spectrometer at the Geo-

chemical Centre of the Department of Geology, Saint

Mary’s University, Halifax. Additional trace elements

Table 1

U–Pb isotopic data for Liscomb Complex

Analysis #, fraction (number of grains) Weight

(mg)aTotala Totalb Totalb U

(ppm)

Pb

(ppm)

Atomic ratios Ages (Ma)

U

(ng)

Pb

(pg)

Com.Pb

(pg)

206Pbb /204Pb

206Pbc /208Pb

206Pbc /238U

% Errord 207Pbc /235U

% Errord 207Pbc /206Pb

% Errord 206Pb /238U

207Pb /235U

207Pb /206Pb

re

Liscomb granite (LG-1; N 45814.777V W 62846.732V)1) Fragment of acicular prism #1 (1) 0.60 0.82 44.0 4.71 1366 73 614 11.504 0.05379 1.346 0.40119 1.359 0.05410 0.192 337.7 342.5 375.0 0.990

2) Fragment of acicular prism #1 (1) 0.86 0.64 37.0 6.07 749 43 386 9.718 0.05458 1.671 0.40688 1.694 0.05407 0.269 342.6 346.6 374.0 0.987

3) Acicular prism #2 (1) 2.38 2.78 165.7 22.1 1168 70 460 18.326 0.05573 0.399 0.41553 0.432 0.05408 0.161 349.6 352.8 374.4 0.928

4) Acicular prism #3 (1) 2.55 1.94 109.3 10.9 761 43 659 38.741 0.05691 0.550 0.42419 0.569 0.05406 0.146 356.8 359.0 373.7 0.966


6) Stubby prism (1) 0.74 1.12 62.6 5.97 1504 84 710 32.585 0.05807 0.907 0.43279 0.938 0.05405 0.230 363.9 365.2 373.2 0.969



9) Four fragments of acicular prism #4 (4) 0.71 1.09 64.2 6.70 1537 91 632 20.092 0.05947 0.946 0.44362 1.225 0.05410 0.750 372.4 372.8 375.2 0.791

10) Monazite 1 (1) 0.35 2.70 655.3 11.0 7701 1872 942 0.279 0.05998 0.388 0.44451 0.402 0.05375 0.099 375.5 373.4 360.4 0.969

11) Monazite 2 (1) 0.26 1.65 475.8 9.17 6318 1825 701 0.226 0.06017 0.604 0.44529 0.619 0.05367 0.127 376.7 374.0 357.4 0.979

12) Monazite 3 (1) 7.99 16.93 5165.9 24.4 2119 647 2647 0.210 0.06028 0.089 0.44523 0.157 0.05357 0.124 377.3 373.9 353.0 0.612

13) Monazite 4 (1) 2.42 9.08 2101.0 8.02 3756 869 4334 0.297 0.06033 0.121 0.44748 0.136 0.05380 0.062 377.6 375.5 362.6 0.891

Liscomb gneiss (LG-120; N 45816.482V W 62839.923V)1) Large fragment (1) 3.28 3.96 236.3 9.10 1206 72 1500 4.861 0.05388 0.282 0.40045 0.293 0.05390 0.077 338.3 342.0 366.9 0.964

2) Large acicular prism fragment (1) 2.24 1.07 57.2 2.29 478 26 1663 14.131 0.05514 0.139 0.41099 0.203 0.05405 0.142 346.0 349.6 373.3 0.713

3) Small stubby prisms (2) 3.05 0.38 22.3 1.11 125 7 1255 6.593 0.05661 0.244 0.42188 0.437 0.05405 0.346 355.0 357.4 373.0 0.613

4) Small flat prisms (2) 3.41 0.97 65.4 13.2 284 19 284 8.205 0.05754 1.042 0.42697 1.249 0.05381 0.678 360.7 361.0 363.3 0.840

5) Thin acicular prism fragments (6) 5.08 0.90 56.3 1.59 177 11 2143 5.490 0.05889 0.125 0.43930 0.161 0.05410 0.099 368.9 369.8 375.2 0.788

6) Medium stubby prisms (3) 5.29 0.51 32.6 1.31 96 6 1466 4.663 0.05890 0.192 0.43958 0.273 0.05413 0.186 368.9 370.0 376.6 0.732

7) Spheriodal with tips (1) 1.56 0.42 25.7 1.44 269 16 1115 6.719 0.05906 0.194 0.44043 0.259 0.05409 0.164 369.9 370.6 374.7 0.774

8) Fat medium prism (1) 3.53 0.67 39.1 1.55 189 11 1652 10.952 0.05950 0.152 0.44373 0.219 0.05409 0.151 372.6 372.9 374.7 0.722

9) Monazite (1) 1.67 1.28 713.5 12.5 765 427 404 0.104 0.05984 0.889 0.44624 0.919 0.05409 0.222 374.6 374.6 374.6 0.970

10) Monazite (2) 2.83 2.04 1160.8 36.5 721 410 229 0.104 0.05984 0.577 0.44780 0.809 0.05427 0.558 374.7 375.7 382.3 0.724

Liscomb gneiss (LG-122; N 45816.402V W 62840.003V)1) Clear square fragment (1) 4.68 2.97 163.3 1.15 635 35 8456 5.181 0.05123 0.100 0.37936 0.114 0.05370 0.054 322.1 326.6 358.7 0.879

2) Clear flat prism (1) 3.53 2.02 112.1 1.33 571 32 5076 5.676 0.05248 0.069 0.39138 0.128 0.05409 0.108 329.7 335.4 374.7 0.544

3) Medium stubby prism #1 (1) 3.97 2.76 164.5 1.20 696 41 8241 5.680 0.05629 0.067 0.41799 0.091 0.05386 0.062 353.0 354.6 365.2 0.736

4) Large pink fragment #1 (1) 27.77 10.21 600.3 1.13 368 22 32945 7.318 0.05741 0.150 0.42807 0.246 0.05408 0.195 359.9 361.8 374.2 0.610

5) Large pink fragment #2 (1) 21.36 9.74 573.0 1.10 456 27 32440 7.463 0.05757 0.049 0.42922 0.071 0.05408 0.052 360.8 362.6 374.2 0.685

6) Medium stubby prism #2 (1) 10.92 2.97 181.5 1.12 272 17 9845 5.846 0.05794 0.060 0.43089 0.096 0.05394 0.074 363.1 363.8 368.6 0.637

7) Medium thin prisms (2) 2.03 1.34 81.3 1.23 660 40 4100 6.976 0.05893 0.076 0.43925 0.112 0.05406 0.082 369.1 369.7 373.6 0.688

8) Medium stubby pink prism (1) 7.53 2.29 140.5 1.02 304 19 8572 7.342 0.05988 0.068 0.44649 0.090 0.05408 0.058 374.9 374.8 374.4 0.760

a Weight estimated from measured grain dimensions and assuming zircon=4.67 g/cm3, monazite=5.0 g/cm3, ~20% uncertainty affects only U and Pb concentrations.b Corrected for fractionation (0.18F0.09%/amu —Daly) and spike.c Corrected for fractionation, blank, and initial common Pb.d Errors quoted at 2s.e 207 Pb/235 U–206 Pb/238 U correlation coefficient of Ludwig (2001).

J.Dosta

let

al./Lith

os86(2006)77–90

83

Table 2

Chemical compositions of the dated rocks from the Liscomb

Complex

Sample no. Granite LG-1 Gneiss LG-120 Gneiss LG-122

SiO2 (wt. %) 66.30 44.66 53.45

TiO2 0.61 0.94 0.87

Al2O3 15.67 32.01 17.87

Fe2O3 4.22 13.43 8.17

MnO 0.09 1.38 0.18

MgO 1.49 4.93 6.88

CaO 2.24 0.51 7.63

Na2O 3.30 1.13 2.68

K2O 3.57 0.81 1.07

P2O5 0.26 0.05 0.13

LOI 1.00 0.90 1.06

Total 98.75 100.75 99.99

Cr (ppm) 26 243 123

Ni 14 193 30

Co 10 89 38

V 77 211 163

Zn 80 242 77

Rb 172 34 37

Ba 979 300 268

Sr 194 98 320

Ga 22 54 17

Ta 1.34 1.03 0.44

Nb 18.0 18.3 8.1

Hf 5.69 3.80 2.98

Zr 247 157 122

Y 14 12 19

Th 14.2 9.69

La 36.4 28.0 23.4

Ce 77.7 57.7 46.0

Pr 9.48 6.42 5.70

Nd 37.8 24.3 21.5

Sm 7.72 4.55 4.41

Eu 1.33 0.65 0.98

Gd 5.32 3.24 3.68

Tb 0.74 0.51 0.59

Dy 3.59 2.79 3.55

Ho 0.55 0.47 0.74

Er 1.45 1.34 2.19

Tm 0.21 0.19 0.33

Yb 1.32 1.27 2.17

Lu 0.20 0.19 0.3387Sr / 86Sri 0.707926 0.714273

eNd �5.12 �10.43143Nd/ 144Ndi 0.511893 0.511621

Isotopic ratios corrected to 375 Ma; isotopic data from Clarke et al.


(the rare-earth elements [REE], Hf, Ta, Nb and Th)

were analyzed in all these samples by inductively

coupled plasma-mass spectrometry using a Na2O2-

sintering technique at the Department of Earth

Sciences of the Memorial University of Newfound-

land. The precision for the trace elements is between

2% and 8% of the values cited (Dostal et al., 1986;

Longerich et al., 1990). The Sr and Nd isotopic ratios

of rocks from the same outcrops reported in Table 2

are from Clarke et al. (1993).

4.2. Liscomb granite and gneiss

Granitic rocks of the Liscomb Complex (Fig. 4)

typically have SiO2 contents ranging from 66 to 73

wt.%. They are peraluminous (mol. Al2O3NCaO+

Na2O+K2O), with K2ONNa2O and K2ON3.5 wt.%.

Their K/Rb ratios (210–170) are slightly lower than

those of average crustal compositions (~230; Shaw,

1968). The chondrite-normalized patterns are enriched

in light REE, display slightly fractionated heavy REE,

and are accompanied by a negative Eu anomaly. Their

(La /Yb)n ratios range from ~10 to 17, whereas

(Gd /Yb)n ratios range from 1.5 to 4 (Fig. 5). The

eNd values (�2.7 to �5.9) and initial Sr isotopic

ratios (0.70793 to 0.70875) of the Liscomb granites

(Clarke et al., 1993) are typical of crustally-derived

granitic rocks (Faure, 2001), and, more specifically, S-

type granites (Clarke, 1992). The major (Fig. 4) and

trace element abundances (Fig. 5) as well as the Nd

and Sr isotopic characteristics (Fig. 6) of the Liscomb

granites are within the variation range of the SMB,

suggesting that the Liscomb granite probably repre-

sents a satellite body of the SMB derived from a

common or similar source.

The Liscomb gneisses constitute a heterogeneous

group of non-migmatitic and migmatitic rocks with

SiO2 contents ranging from b46 to N72 wt.%, and

Al2O3 contents ranging from 12 to N32 wt.%. Al2O3

shows a negative correlation with SiO2 and is high in

the sillimanite-bearing gneisses (~25 wt.%) but low in

the quartz–feldspathic gneisses (~13 wt.%). The gar-

net–hornblende gneisses are high in CaO (~5 wt.%),

MgO (~4 wt.%) and Al2O3 (~18 wt.%). The Nd and

Sr isotopic ratios of the Liscomb gneisses (Fig. 6) are

highly variable, ranging from relatively low values of

eNd (~+1) and initial Sr isotopic ratios (~0.706–

0.708) in augen gneisses and garnet–hornblende

gneisses, to high radiogenic values in metapelites

(N�10 and 0.714–0.716, respectively). Augen

gneisses are compositionally similar to the peralumi-

nous granites. Most rocks are likely metamorphosed

felsic igneous rocks and clastic sedimentary rocks,

Fig. 4. Albite–orthoclase–anorthite plot for the normative compositions of granitic rocks from the South Mountain Batholith and Liscomb

Complex, showing fields of some granitoid rocks after O’Connor (1965). The field delineated by the dotted line includes the average

compositions of various granitoid rock types from the South Mountain Batholith (MacDonald et al., 1992; Clarke et al., 1997). The average

chemical compositions of four granitoids of the Liscomb Complex (granodiorite L9, monzogranite L10, leucomonzogranite L11 and

leucogranite L12; Clarke et al., 1993) as well as the dated granite sample (LG-1) all plot into the SMB field.


particularly pelites. Some SiO2-poor rocks are proba-

bly residual rocks, related to melt extraction, whereas

other gneisses may represent an untapped but fertile

source rock. These gneisses which resemble the

source rocks have REE patterns very close to those

of the North American shale composite and average

upper continental crust (Fig. 5).

4.3. Source of magma

Peraluminous granites of the Liscomb Complex,

like those of the SMB, were formed predominantly by

the partial melting of metasedimentary rocks. Sr and

Nd isotopic data show that the source of the SMB

cannot be in the Meguma Group (Fig. 6; Clarke and

Halliday, 1985; Clarke et al., 1988). The Liscomb

granitic rocks, like those of the SMB, are probably

products of the partial melting of a deeper-seated

crustal source, the basement of the Meguma Group.

Nd and Sr isotopic analyses show that the Liscomb

granites fall in an intermediate position between Lis-

comb augen gneisses and Liscomb metapelites, im-

plying that the granites could be genetically related to

the gneisses (Clarke et al., 1993). Some Liscomb

gneisses probably represent a fertile source similar

to that from which the Devonian peraluminous gran-

ites of the Meguma Terrane were derived. This is

consistent with the major and trace element composi-

tions, which indicate that partial melting of such

gneisses could generate a peraluminous granitic melt

similar to that which formed the Liscomb granites.

The absence of leucosomes in the Liscomb gneisses

indicates that they were not partially molten. Howev-

er, the presence of a megacrystic gneissic granite

intruding them suggests that partial melting took

place at a greater depth than is presently exposed.

Compositions of the metapelitic xenoliths of the

Tangier Dykes are comparable to those of the Lis-

comb gneisses (Eberz et al., 1991; Clarke et al., 1993),

although the relation between the Liscomb gneisses

and Tangier xenoliths is uncertain. Isotopic data from

the Tangier pelitic xenoliths show relatively uniform

eNd values, but variable Sr values (Eberz et al., 1991).Nevertheless, the Nd–Sr isotopic ratios for the xeno-

liths (Fig. 6) overlap those of the Liscomb gneisses

and of the SMB granites. Dostal et al. (2004) also

show that the Pb isotopic composition of K-feldspar

from the SMB granites overlaps that of xenoliths in

the Tangier Dykes. Thus, the Tangier pelitic xenoliths

could also represent a source material for some of the

SMB granitoids.

4.4. Meguma basement

The Meguma Terrane granitoids appear to have

been derived from a source comparable to the Lis-

comb gneisses and Tangier xenoliths, which are com-

posed of pelitic metasedimentary rocks interpreted as

deep-seated (mid-crustal) basement rocks underlying

the Meguma Group. The isotopic data (Fig. 6) imply

Fig. 5. Chondrite-normalized rare-earth element compositions: (A)

the average of twelve two-mica granodiorites (L9), twelve two-mica

monzogranites (L10) from the Liscomb Complex (Clarke et al.,

1993), and the dated granodiorite LG-1; (B) the average of SMB

granodiorite (GD), monzogranite (MG), as well as the average

leucomonzogranite of the Davis Lake Pluton (LMG), which is

one of the intrusions of the SMB composite (Dostal and Chatterjee,

1995, 2000); (C) the average of 17 garnet–hornblende gneisses

(L2), 10 quartzo–feldspathic gneisses (L3) and 14 sillimanite schists

(L4) of the Liscomb Complex (after Clarke et al., 1993) compared

to the North America shale composite (NASC; Gromet et al., 1984)

and the average for the upper continental crust (UC; Taylor and

McLennan, 1985). Normalizing values are after Sun and McDo-

nough (1989).


that the Tangier metasedimentary xenoliths, like the

Liscomb gneisses, are not high-grade equivalents of

the Meguma Group, but belong to a distinct basement

unit (Clarke et al., 1997). The Pb isotopic composi-

tions and detrital zircon ages of the crustal xenoliths

from the lamprophyre dykes of Tangier suggest that

they are a part of the Avalon basement, which is

thought to underlie/underthrust the Meguma Group

rocks (Greenough et al., 1999; Dostal et al., 2004).

Although no detrital zircons were identified in the

Liscomb gneisses, enough parallels are drawn with

the lithology, geochemistry and geochronology of

these xenoliths to postulate that the gneisses are Ava-

lonian as well. Likewise, the source of the SMB

magma has Pb isotope characteristics comparable to

the Avalon basement in coastal Maine and southern

New Brunswick (Dostal et al., 2004), which suggests

that the Meguma Terrane is, at least in part, underlain

by Avalonian basement.

5. Discussion and conclusions

The U–Pb data from the Liscomb Complex support

an upper amphibolite–granulite facies metamorphism

at 377F2 Ma, which overlaps the 378F1 Ma meta-

morphism recorded in a granulite xenolith from a

lamprophyre dyke located 30 km to the south of the

Liscomb Complex (Greenough et al., 1999). This

metamorphism took place at pressures of 640–820

MPa, which indicate depths of 24–29 and 26–33

km, respectively (Fig. 7; Owen and Greenough,

1991; Owen et al., 1988). On the other hand, crystal-

lization of the Liscomb granite is dated at 374F3 Ma,

and occurred at pressures of ~300 MPa (=depth of

~10–12 km; Fig. 7; Clarke et al., 1993; Kontak and

Reynolds, 1994). Although these ages overlap within

error, the mean ages are consistent with local temporal

observations that the granite cuts the gneiss. This near

synchronicity suggests that middle crustal granulite/

upper amphibolite facies metamorphism and partial

melting were complementary processes.

Granitic magmatism in the Liscomb Complex is

synchronous (within error) with all but one of the

granite plutons in the Meguma Terrane, which range

in age from 378.5F2 to 370F3 Ma (Keppie and

Krogh, 1999). Such voluminous granitic magmatism

suggests a fertile source (Vielzeuf et al., 1990) that

Fig. 6. Initial 87Sr / 86Sr ratio versus qNd (375 Ma) for granites (�) and gneisses (crosses) of the Liscomb Complex (Clarke et al., 1993), as well

as those of the metapelitic xenoliths (open circles; Eberz et al., 1991) of the Tangier Dykes. The field of the South Mountain Batholith (SMB) is

after Clarke and Halliday (1980) and Clarke et al. (1988), whereas that of Meguma Group sedimentary rocks is after Eberz et al. (1991).

Fig. 7. The Liscomb Complex and Tangier xenolith data plotted on

(A) a Pressure–Temperature diagram, and (B) an Age–Temperature

diagram. Note that only the overlapping age range is shown. Data

are from Owen et al. (1988), Owen and Greenough (1991), Clarke

et al. (1993), Kontak and Reynolds (1994), Greenough et al. (1999)

and this study.


was probably dominated by juvenile sedimentary rock

protholiths rather than a reworked older basement

(Sawyer, 1998; Brown, 2001). The peraluminous na-

ture of the Meguma granitoids also suggests a meta-

sedimentary source. The aluminosilicate-bearing

Liscomb and Tangier gneisses, some of which are

compositionally similar to sedimentary rocks, can be

a fertile source of granite magma, and their Nd, Sr and

Pb isotopic signatures suggest that they are the source

of the Meguma granites. The similarity between the

isotopic signatures of the granites and their source

rocks is consistent with the popular assumption that

magmas image their source region (Brown, 2001).

Cooling ages of 369F3 and 368F3 Ma (Kontak

and Reynolds, 1994) on muscovite and biotite, re-

spectively, were obtained from the granite of locality

LG-1. Furthermore, because the northern margin of

the Meguma Terrane is unconformably overlain by

the Horton Group, the oldest part of which is late

Fammenian (~365–360 Ma) (Martel et al., 1993), this

age is consistent with a projection of the cooling

curve through amphibole, muscovite and biotite to

the surface, which suggests exhumation by ~364

Ma (Fig. 7B). This suggests that, whereas develop-

ment of the core complex raised the granulite facies

rocks from a depth of ~30 km to a depth of ~10–11

km in ~3 million years, exhumation to the surface


required an additional ~10 million years (i.e., at a rate

of ~54 8C/my; Fig. 7). These data are consistent with

the rates of melt production, segregation, ascent and

crystallization predicted by experimental studies (Har-

ris et al., 2000). Solar et al. (1998) inferred that the

process of granite generation from the peak of meta-

morphism to the intrusion of granitic plutons takes

less than 1 Ma.

It is noteworthy that these ~375 Ma magmatic and

metamorphic events in the Meguma Terrane, and

exhumation by ~364 Ma, are contemporaneous with

the onset of extensional tectonics in south-eastern

Canada. The extension was initiated in the Middle–

Late Devonian with the rift-related basalts and alluvial

fan deposits of the McAras Brook Formation near the

southern margin of the Maritimes Basin (Dostal et al.,

1983; Keppie, 1993; Keppie et al., 1997). This is

consistent with evidence which suggests that exten-

sion is an essential element in the development of core

complexes (Dickinson, 2002). It is inferred to have

facilitated uplift of the Liscomb gneisses and intrusion

of the granites, which ascended very rapidly. It is

suggested that the onset of pull-apart tectonics along

the Minas Fault system may have generated a sudden

relaxation at the root of the Acadian Orogen, which

led to the rapid ascent of the Liscomb gneiss diapir

and voluminous granitic melts.

Acknowledgements

This study was financially supported by the Natu-

ral Sciences and Engineering Research Council of

Canada. JDK would like to acknowledge support

from the PAPIIT Project IN103003-3. We would

like to thank Ian Buick and Victor Owen for construc-

tive reviews of the manuscript. We also thank Peter

Giles and A.K. Chatterjee for their help in the field

and in the selection of sampling sites, as well as

Randolph Corney and Aaron Vaughan for their help

in the preparation of the manuscript.

References

Boucot, A.J., 1975. Evolution and Extinction Rate Controls: Devel-

opments in Paleontology and Stratigraphy, vol. 1. Elsevier

Scientific, Amsterdam. 427 pp.

Bouyx, E., Blaise, J., Brice, D., Degardin, J.M., Goujet, D., Gour-

vennec, R., Le Menn, J., Lardeux, H., Morzadec, P., Paris, F.,

1997. Biostratigraphie et paleobiogeographie du Siluro–Devo-

nien de la zone de Meguma (Nouvelle-Ecosse, Canada). Cana-

dian Journal of Earth Sciences 34, 1295–1309.

Braun, I., Kriegsman, L.M., 2001. Partial melting in crustal xeno-

liths and anatectic migmatites: a comparison. Physics and

Chemistry of the Earth. Part A: Solid Earth and Geodesy 26,

261–266.

Brown, M., 2001. Orogeny, migmatites and leucogranites: a review.

Proceedings of Indian Academy of Sciences, Earth Planetary

Sciences, vol. 110, pp. 313–336.

Chatterjee, A.K., Richard, L.R., Clarke, D.B., 1989. Magmatic and

subsolidus amphiboles from the Ten Mile Lake intrusion, Lis-

comb Complex, Nova Sotia. Geological Association of Canada-

Mineralogical Association of Canada, Program with Abstracts

14, A98.

Clarke, D.B., 1992. Granitoid Rocks. Chapman & Hall, London.

283 pp.

Clarke, D.B., Halliday, A.N., 1980. Strontium isotope geology of

the South Mountain Batholith, Nova Scotia. Geochimica et

Cosmochimica Acta 44, 1045–1058.

Clarke, D.B., Halliday, A.N., 1985. Sm/Nd isotopic investigation of

the age and origin of the Meguma Zone metasedimentary rocks.

Canadian Journal of Earth Sciences 22, 102–107.

Clarke, D.B., Halliday, A.N., Hamilton, P.J., 1988. Neodymium and

strontium isotopic constraints on the origin of the peraluminous

granitoids of the South Mountain Batholith, Nova Scotia. Chem-

ical Geology 73, 15–24.

Clarke, D.B., Chatterjee, A.K., Giles, P.S., 1993. Petrochemistry,

tectonic history, and Sr /Nd systematics of the Liscomb Com-

plex, Meguma lithotectonic zone, Nova Scotia. Canadian Jour-

nal of Earth Sciences 30, 449–464.

Clarke, D.B., MacDonald, M.A., Tate, M.C., 1997. Late Devonian

mafic–felsic magmatism in the Meguma Zone, Nova Scotia. In:

Sinha, A.K., Whalen, J.B., Hogan, J.P. (Eds.), The Nature of

Magmatism in the Appalachian Orogen, Geological Society of

America Memoir, vol. 191, pp. 107–127.

Coney, P.J., 1980. Cordilleran metamorphic complexes, an over-

view. In: Crittenden, M.D., Coney, P.J., Davis, G.H. (Eds.),

Cordilleran Metamorphic Core Complexes, Geological Society

of America Memoir, vol. 153, pp. 7–31.

Davis, G.A., Anderson, J.L., Frost, E.G., Shakelford, T.J., 1980.

Mylonitization and detachment faulting in the Whipple–Buck-

skin–Rawhide Mountains terrane, southeastern California and

western Arizona. In: Crittenden, M.D., Coney, P.J., Davis, G.H.

(Eds.), Cordilleran Metamorphic Core Complexes, Geological

Society of America Memoir, vol. 153, pp. 79–130.

Dickinson, W.R., 2002. The Basin and Range Province as a com-

posite extensional domain. International Geology Review 44,

1–38.

Dostal, J., Chatterjee, A.K., 1995. Origin of topaz-bearing and

related peraluminous granites of Late Devonian Davis Lake

pluton, Nova Scotia, Canada. Chemical Geology 123, 67–88.

Dostal, J., Chatterjee, A.K., 2000. Contrasting behaviour of Nb/Ta

and Zr /Hf ratios in a peraluminous granitic pluton (Nova Scotia,

Canada). Chemical Geology 163, 207–218.


Dostal, J., Keppie, J.D., Dupuy, C., 1983. Petrology and geochem-

istry of Devono–Carboniferous volcanic rocks in Nova Scotia.

Maritime Sediments and Atlantic Geology 19, 59–71.

Dostal, J., Baragar, W.R.A., Dupuy, C., 1986. Petrogenesis of the

Natkusiak continental basalts, Victoria Island, Northwest Terri-

tories, Canada. Canadian Journal of Earth Sciences 23, 622–632.

Dostal, J., Chatterjee, A.K., Kontak, D.J., 2004. Chemical and

isotopic (Pb, Sr) zonation in a peraluminous granite pluton:

role of fluid fractionation. Contributions to Mineralogy and

Petrology 147, 74–90.

Eberz, G.W., Clarke, D.B., Chatterjee, A.K., Giles, P.S., 1991.

Chemical and isotopic composition of the lower crust beneath

the Meguma lithotectonic zone, Nova Scotia: evidence from

granulite facies xenoliths. Contributions to Mineralogy and

Petrology 109, 69–88.

Faribault, E. R., 1891. Fifteen Mile Stream sheet, Map 41. Geo-

logical Survey of Canada, Part P Annual Report, v. V, Part II,

1890–1891, Scale 1: 63,360.

Faure, G., 2001. Origin of Igneous Rocks; The Isotopic Evidence.

Springer, Berlin. 496 pp.

Fletcher, H., Faribault, E.R., 1891a. Eastville sheet, map 49, Geo-

logical Survey of Canada, Part P Annual Report, v.V, Part II,

1890–1891, Scale 1:63,360.

Fletcher, H., Faribault, E.R., 1891b. Trafalgar sheet, map 49, Geo-

logical Survey of Canada, Part P Annual Report, v.V, Part II,

1890–1891, Scale 1:63,360.

Giles, P.S., Chatterjee, A.K., 1986. Peraluminous granites of the

Liscomb Complex. Nova Scotia Department of Mines and

Energy, Information Series, vol. 12, pp. 83–89.

Giles, P.S., Chatterjee, A.K., 1987. Evolution of the Liscomb Com-

plex and its relevance to metallogeny in the Eastern Meguma

Terrane. Nova Scotia Department of Mines, Report, vol. 87–1,

p. 83.

Greenough, J.D., Krogh, T.E., Kamo, S.L., Owen, J.V., Ruffman,

A., 1999. Precise U–Pb dating of Meguma basement xenoliths:

new evidence for Avalonian underthrusting. Canadian Journal of

Earth Sciences 36, 15–22.

Gromet, L.P., Dymek, R.F., Haskin, L.A., Korotev, R.L., 1984. The

bNorth American Shale CompositeQ: its composition, major and

trace element characteristics. Geochimica et Cosmochimica

Acta 48, 2469–2482.

Harris, N., Vance, D., Ayres, M., 2000. From sediment to granite:

time scales of anatexis in the upper crust. Chemical Geology

162, 155–167.

Hicks, R.J., Jamieson, R.A., Reynolds, P.H., 1999. Detrital and

metamorphic 40Ar / 39Ar ages from muscovite and whole-rock

samples, Meguma Supergroup, southern Nova Scotia. Canadian

Journal of Earth Sciences 36, 23–32.

Hill, E.J., Baldwin, S.L., Lister, G.S., 1992. Unroofing of active

metamorphic core complexes in the D’Entrecasteaux Islands,

Papua New Guinea. Geology 20, 907–910.

Kempster, R.M.P., Clarke, D.B., Reynolds, P.H., Chatterjee, A.K.,

1989. Late Devonian lamprophyric dykes in theMeguma Zone of

Nova Scotia. Canadian Journal of Earth Sciences 26, 611–613.

Keppie, J.D., 1993. Synthesis of Paleozoic deformational events and

terrane accretion in the Canadian Appalachians. Geologische

Rundschau 82, 381–431.

Keppie, J.D., Dostal, J., 1991. Late Proterozoic tectonic model

for the Avalon Terrane in Maritime Canada. Tectonics 10,

842–850.

Keppie, J.D., Dallmeyer, R.D., 1995. Late Paleozoic P–T–t path of

the southwestern Meguma Terrane, Nova Scotia, Canada: a his-

tory of collision, delamination, short-lived magmatism and rapid

denudation. Canadian Journal of Earth Sciences 32, 644–659.

Keppie, J.D., Krogh, T.E., 1999. U–Pb geochronology of Devonian

granites in the Meguma Terrane of Nova Scotia, Canada: evi-

dence for hotspot melting of a Neoproterozoic source. Journal of

Geology 107, 555–568.

Keppie, J.D., Dostal, J., Murphy, J.B., Cousens, B.L., 1997. Palaeo-

zoic within-plate volcanic rocks in Nova Scotia (Canada) rein-

terpreted: isotopic constraints on magmatic source and

palaeocontinental reconstructions. Geological Magazine 134,

425–447.

Keppie, J.D., Davis, D.W., Krogh, T.E., 1998. U-Pb geochronolog-

ical constraints on Precambrian stratified units in the Avalon

composite terrane of Nova Scotia, Canada; tectonic implica-

tions. Canadian Journal of Earth Sciences 35, 222–236.

Keppie, J.D., Nance, R.D., Murphy, J.B., Dostal, J., 2003. Tethyan,

Mediterranean, and Pacific analogues for the Neoproterozoic-

Paleozoic birth and development of peri-Gondwanan terranes

and their transfer to Laurentia and Laurussia. Tectonophysics

365, 195–219.

Kontak, D.J., Reynolds, P.H., 1994. 40Ar / 39Ar dating of metamor-

phic and igneous rocks of the Liscomb Complex, Meguma

Teranne, southern Nova Scotia, Canada. Canadian Journal of

Earth Sciences 31, 1643–1653.

Krogh, T.E., Keppie, J.D., 1990. Age of detrital zircon and

titanite in the Meguma Group, southern Nova Scotia, Canada;

clues to the origin of the Meguma Terrane. Tectonophysics

177, 307–323.

LeFort, P., 1986. Metamorphism and magmatism during the Hima-

layan collision. In: Coward, M., Ries, A.C. (Eds.), Collision

Tectonics, Special Publication-Geological Society London, vol.

19, pp. 159–172.

Lister, G.S., Baldwin, S.L., 1993. Plutonism and the origin of

metamorphic core complexes. Geology 21, 607–610.

Lister, G.S., Banga, G., Feenstra, A., 1984. Metamorphic core

complexes of Cordilleran type in the Cyclades, Aegean Sea,

Greece. Geology 12, 221–225.

Longerich, H.P., Jenner, G.A., Fryer, B.J., Jackson, S.E., 1990.

Inductively coupled plasma-mass spectrometric analysis of geo-

logical samples: a critical evaluation based on case studies.

Chemical Geology 83, 105–118.

Ludwig, K.R., 2001. Isoplot /Ex version 2.49. A geochronological

toolkit for Microsoft Excel. Berkeley Geochronology Center,

Special Publication 1a (55 pp.).

MacDonald, M.A., Horne, R.J., Corey, M.C., Ham, L.J., 1992. An

overview of recent bedrock mapping and follow-up petrological

studies of the South Mountain Batholith, southwestern Nova

Scotia, Canada. Atlantic Geology 28, 7–28.

Martel, A.T., McGregor, D.C., Utting, J., 1993. Stratigraphic sig-

nificance of Upper Devonian and Lower Carboniferous mios-

pores from the type area of the Horton Group, Nova Scotia.

Canadian Journal of Earth Sciences 30, 1091–1098.


Murphy, J.B., Fernandez-Suarez, J., Keppie, J.D., Jeffries, T.E.,

2004. Contiguous rather than discrete Paleozoic histories for

the Avalon and Meguma terranes based on detrital zircon data.

Geology 32, 585–588.

O’Connor, J.T., 1965. A classification for quartz-rich igneous rocks

based on feldspar ratios. Professional Paper-Geological Survey

(U.S.) 525-B, 79–84.

Okulitch, A.V., 2003. Geological time chart. Geological Survey of

Canada.

Owen, J.V., Greenough, J.D., 1991. An empirical sapphirine–spinel

Mg–Fe exchange thermometer and its application to high grade

xenoliths in the Popes Harbour dyke, Nova Scotia, Canada.

Lithos 26, 317–332.

Owen, J.V., Greenough, J.D., Hy, C., Ruffman, A., 1988. Xenoliths

in a mafic dyke at Popes Harbour, Nova Scotia: implications for

the basement to the Meguma Group. Canadian Journal of Earth

Sciences 25, 1464–1471.

Pratt, B.R., Waldron, J.W.F., 1991. A Middle Cambrian trilobite

faunule from the Meguma Group of Nova Scotia. Canadian

Journal of Earth Sciences 28, 1843–1853.

Ratajeski, K., Glazner, A.F., Miller, B.V., 2001. Geology and geo-

chemistry of mafic to felsic plutonic rocks in the Cretaceous

intrusive suite of Yosemite Valley, California. Geological Soci-

ety of America Bulletin 113, 1486–1502.

Sawyer, E.W., 1998. Formation and evolution of granitic magmas

during crustal reworking: the significance diatexites. Journal of

Petrology 39, 1147–1167.

Scharer, U., 1984. The effect of initial 230Th disequilibrium on

young U–Pb ages: the Makalu case, Himalaya. Earth and Plan-

etary Science Letters 67, 191–204.

Schenk, P.E., 1997. Sequence stratigraphy and provenance on Gond-

wana’s margin; the Meguma Zone (Cambrian to Devonian) of

Nova Scotia, Canada. Geological Society of America Bulletin

109, 395–409.

Shaw, D.M., 1968. A review of K–Rb fractionation trends by

covariance analysis. Geochimica et Cosmochimica Acta 32,

176–573.

Solar, G.S., Brown, M., 2001. Petrogenesis of migmatites in Maine,

USA: possible sources of peraluminous granite in plutons.

Journal of Petrology 42, 789–823.

Solar, G.S., Pressley, R.A., Brown, M., Tucker, R.D., 1998. Granite

ascent in convergent orogenic belts: testing a model. Geology

26, 711–714.

Streckeisen, A., Le Maitre, R.W., 1979. A chemical approximation

to the modal QAPF classification of igneous rocks. Neues

Yahrb. Mineral. Abh., vol. 136, pp. 169–206.

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

atics of oceanic basalts: implications for mantle composition and

processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in

the Ocean Basins, Special Publication-Geological Society Lon-

don, vol. 42, pp. 313–345.

Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its

Composition and Evolution. Blackwell Science, Oxford. 328 pp.

Vielzeuf, D., Clemens, J.D., Pin, C., Moinet, E., 1990. Granites,

granulites and crustal differentiation. In: Vielzeuf, D., Vidal, P.

(Eds.), Granulites and Crustal Evolution. Kluwer Academic,

The Netherlands, pp. 59–85.

Williams, H., Hatcher, R.D., 1983. Appalachian suspect terranes.

Geological Society of America Memoir 158, 33–53.

evidence for the granulite–granite connection ... · the classic cordilleran metamorphic core...

Documents