Terrane transfer during the Grenville orogeny: tracing the Amazonian ancestry of southern...

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Earth and Planetary Science Le

Terrane transfer during the Grenville orogeny: tracing the

Amazonian ancestry of southern Appalachian

basement through Pb and Nd isotopes

E. Tohvera,*, J.S. Bettencourta, R. Tosdalb, K. Mezgerc, W.B. Leited, B.L. Payollae

aInstituto de Geociencias, Universidade de Sao Paulo, Rua do Lago, 562, Cidade Universitaria, CEP 05508-900, Sao Paulo, SP BrazilbMineral Deposit Research Unit, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada

cInstitut fur Mineralogie, Universitat Munster, Corrensstrasse. 24 48149, Munster GermanydInstituto de Geociencias e Ciencias Exatas, Universidade Estadual Paulista, Av. 24 A, no. 1515, CEP 13506-900, Rio Claro, Brazil

eCentrais Eletricas do Norte do Brasil S/A, SQN 408, Bloco L, Apto 202, CEP 70856-120, Brasilia, Brazil

Received 14 April 2004; received in revised form 7 September 2004; accepted 20 September 2004

Editor: K. Farley

Abstract

Whole rock Pb isotope data can be used to determine the provenance of different blocks within the Rodinia

supercontinent, providing a test for paleogeographic reconstructions. Calculated isotopic values for the source region of the

Grenville-deformed SW Amazon craton (Rondonia, Brazil), anchored by published U–Pb zircon ages, are compared to those

from the Grenville belt of North America and bGrenvillianQ basement inliers in the southern Appalachians. Both the SW

Amazon craton and the allochthonous Blue Ridge/Mars Hill terrane are defined by a similar Pb isotopic signature, indicating

derivation from an ancient source region with an elevated U/Pb ratio. In contrast, the Grenville Province of Laurentia

(extending from Labrador to the Llano Uplift of Texas) is characterized by a source region with a distinctly lower, time-

integrated U/Pb ratio. Published U–Pb zircon ages (ca. 1.8 Ga) and Nd model ages (1.4–2.2 Ga) for the Blue Ridge/Mars

Hill terrane also suggest an ancient provenance very different from the rest of the adjacent Grenville belt, which is dominated

by juvenile 1.3–1.5 Ga rocks. The presence of mature continental material in rocks older than 1.15 Ga in the Blue Ridge/

Mars Hill terrane is consistent with characteristics of basement rocks from the SW Amazon craton. High-grade

metamorphism of the Blue Ridge/Mars Hill basement resulted in purging of U, consistent with observations of the rest

of the North American Grenville province. In contrast, the bGrenvillianQ metamorphic history of the Amazon appears to have

been much more heterogeneous, with both U enrichment and U depletion recorded locally. We propose that the Blue Ridge/

Mars Hill portion of the Appalachian basement is of Amazonian provenance and was transferred to Laurentia during

Grenvillian orogenesis after ~1.15 Ga. The presence of these Amazonian rocks in southeastern Laurentia records the

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tters 228 (2004) 161–176

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

sl.2004.09.029

ding author.

ess: [email protected] (E. Tohver).

E. Tohver et al. / Earth and Planetary Science Letters 228 (2004) 161–176162

northward passage of the Amazon craton along the Laurentian margin, following the original collision with southernmost

Laurentia at ca. 1.2 Ga.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Rodinia; Grenville orogeny; Amazon craton; Blue Ridge; exotic terrane; Pb isotopes; Mesoproterozoic paleogeography

1. Introduction

Paleogeographic reconstructions rely on a variety

of techniques and criteria that, taken individually,

might be considered nonunique in determining the

paleogeographic position of a given continent or

block relative to another. The well-studied example of

the Paleozoic transfer of the Argentine Precordillera

terrane from Laurentia to the shores of western

Gondwana is illustrative [1]. The overlapping views

of the Preocordillera’s origin and final resting place

reconstructed from faunal [2], geochemical [3],

paleomagnetic [4], and stratigraphic (e.g., [5,6]) data

present a more complete picture of Paleozoic paleo-

geography. Likewise, the transfer of an Amazonian

terrane to SE Laurentia proposed in this contribution

serves as a marker for the evolving paleogeography of

Rodinia in late Mesoproterozoic times.

The usefulness of radioisotope geochemistry lies in

its ability to delineate coherent large-scale isotopic

patterns, which suggests the potential of bfingerprintsQfor paleogeographic reconstructions. Such techniques

have been used to recognize crustal boundaries [7–10],

distinct terranes [11–13], and tectonic and sedimentary

provenance [14,15] as well as for accretionary models

of continental growth [16–18]. The contribution of

Fig. 1. (top inset) Outline of North America emphasizing the location o

Laurentian craton. (bottom inset) Position of the Amazon craton (AC) with

white. The dark grey area is the outline of the state of Rondonia with the A

craton (PC), accreted at ~1.1 Ga [37]. (main) Schematic illustration of pale

late Mesoproterozoic times are shown in light silhouette, from top to bottom

constrained position of the Amazon at 1.2 Ga, interpreted as indicating co

configuration at the time of the transfer of the Blue Ridge/Mars Hills terrane

sinistral displacement of ~2.5 cm/yr offset between Laurentia and the Ama

Laurentia (Labrador [83]; Quebec [17]; reworked portions of Superior crat

Green Mountains [16]; the midcontinental region east of the Grenville Fro

[8]), Grenvillian basement inliers in the Appalachian [78,79,81,84], and t

Appalachians (from Bartholomew [66]) separates Paleozoic accreted terran

the time of Rodinia breakup. Dashed line separating southeastern midcon

Abbreviations for Grenvillian basement occurrences, shown in black out

Adirondack Mountains; GMM—Green Mountian Massif; BR–MH—Blue

LU—Llano Uplift; Van Horn Mountains; FM—Franklin Mountains; HBU

geochronology to the recognition of the amalgamation

of Rodinia has been fundamental; geochronological

studies led the way to deciphering the effects of the

Grenville orogeny in eastern Laurentia and identifying

its worldwide equivalents. Geochronology of closed

systems (e.g., minerals or whole rocks) is based on

calculating the time necessary for a measured amount

of a daughter isotope to accumulate from a known

amount of parent isotope after a differentiation event

such as crystallization. However, of potentially greater

interest for paleogeography and provenance studies are

the original isotopic characteristics of a given craton or

terrane imparted by the source region at the time of

crustal formation. These initial ratios are distinctive,

being the product of coupled evolution between long-

lived isotopic heterogeneities in the mantle and its

associated crust [19,20]. The advantage of the U–Pb

system for such studies is that the paired U-decay

schemes, 238U–206Pb and 235U–207Pb, with their

significantly different decay constants, allow con-

straints to be placed on the timing of processes that

modified the U/Pb ratio.

The many proposed versions of the Amazonia–

Laurentia connection in Rodinia provide a good

starting point for isotopic-based reconstructions of

Rodinia. Evidence for the Amazonia–Laurentia con-

f the Grenville province (dark grey) on the eastern margin of the

in South America with major geochronological provinces outlined in

mazon river basin shown in white; dashed black line shows Paragua

ogeographic positions previously proposed for the Amazon craton in

: [21,23,24,26]. The southernmost position is the paleomagnetically

llision with the southern Laurentia. Dark silhouette is the proposed

to the North American craton (ca. 1.15 Ga). This model requires net

zon craton after the initial collision. Numbers are Nd model ages for

on [18,56]; Central Metasedimentary Belt [58,59]; Adirondacks and

nt (toothed line) [60]; the Llano region and occurrences in W. Texas

he Amazon craton [30,32,35,64,65]. The bold grey line through the

es from ancestral North America at the end of the Proterozoic, i.e., at

tinental region with TDMb1.55 Ga is from Van Schmus et al. [60].

line, are as follows: CMB—Central Metasedimentary Belt; AM—

Ridge/Mars Hill terrane; EGR—Eastern Granite–Rhyolite province;

—Honeybrook Uplands.

E. Tohver et al. / Earth and Planetary Science Letters 228 (2004) 161–176 163

nection has been found in the form of matching

metamorphic belts of ca. 1.0 Ga, Grenvillian age [21],

similar postrift thermal histories [22,23], linking the

igneous ages of basement provinces [24,25], and

paleomagnetic evidence [26–28]. Conflicting inter-

pretations have led to the Amazon craton being

correlated to almost every portion of the 3000-km

expanse of the Grenville belt of North America (Fig.

1). Although differences in the stated age of these

reconstructions may explain many discrepancies,

more data from the Amazon craton itself are essential

for resolving the issue. Recently, 1.2-Ga paleomag-

netic data from the Amazon craton [26] have been

used to support a collision between the Amazon

craton and southernmost Laurentia (Llano region,

Texas), with a younger pole suggesting a mid-


Laurentian position for Amazonia by ca. 1.1 Ga

[27,28]. Geochronological and structural data from

the Grenville-aged belts of the SW Amazon provide

support for long-lived, sinistral strike-slip motion

required by this paleomagnetic-based model [29].

In this paper, we use new whole rock Pb and

published Sm–Nd data from the SW Amazon craton

to decipher an isotopic fingerprint of Amazon source

region characteristics. Comparison of this source

region with the signature from the Grenville Prov-

ince of eastern Laurentia demonstrates the distinc-

tiveness of the two cratons by the end of the

assembly of Rodinia at 1.0 Ga. A paleogeographic

marker for the Amazon craton’s position with respect

to Laurentia is provided by the presence of

Amazonian crust in basement rocks of the south-

eastern Appalachians. We propose that the transfer of

the Blue Ridge/Mars Hills terrane to the margin of

southeastern Laurentia took place at ca. 1.15 Ga

during accumulated strike-slip motion of the Amazon

craton along the Grenville margin of Laurentia,

following the initial collision of the Amazon craton

with southern Laurentia at ca. 1.2 Ga [26].

2. Regional geology—SW Amazon Craton

The Amazon craton is composed of NW–SE

trending domains of chiefly Paleoproterozoic age

(Fig. 1), recognized on the basis of Sm–Nd and U–

Pb ages. Although the boundaries between these

basement domains are diffuse, a general trend of

younging to the SW is observed [30–32]. The SW

margin of the Amazon craton, best exposed in the

western Brazilian state of Rondonia [33], is marked

by multiple intrusive episodes during the Mesoproter-

ozoic, with especially voluminous magmas emplaced

at ca. 1.57–1.53 and 1.41–1.31 Ga [34]. The

metamorphic effects of the latter episode are partic-

ularly widespread, as revealed by both U–Pb and40Ar–39Ar dating of metamorphic monazite, titanite,

and hornblende [29,35]. Magmatic products of the

Grenville interval (1.2–1.0 Ga) are less common, but

the postorogenic period is marked by the shallow

level intrusion of the tin-bearing Younger Granites of

Rondonia at ca. 950 Ma [34].

It is the Grenville-deformed SW margin of the

Amazon craton that is most commonly correlated with

Laurentia via a Grenville collision [21,24,26]. In fact,

the effects of this collision are complex, with at least

two late Mesoproterozoic deformation events

observed: an older 1.20–1.12 Ga event recorded in

the basement rocks of the Paleo- to Mesoproterozoic

basement rocks interpreted as recording the Amazo-

nia–Laurentia collision [29], followed by a younger

1.10–0.95 Ga event exclusively recorded in two

metasedimentary belts, the Nova Brasilandia [36,37]

and Aguapeı–Sunsas belts [38–41]. The former

records sinistral transpressive deformation during the

accretion of the Paragua craton, a Paleoproterozoic

block of subcontinental dimensions, to the Amazon

craton in late Mesoproterozoic times, an event

accompanied by amphibolite to granulite facies meta-

morphism and the emplacement of a synkinematic

granite suite at 1.11 Ga [36,37,42]. The Sunsas belt

marks the western boundary of the Paragua block and

is marked by synkinematic granite emplacement at ca.

1.05 Ga along major strike-slip mylonitic shear zones

with sinistral offsets [38]. The Aguapeı belt appears to

record a minor episode of low-grade intracratonic

deformation towards the end of the Grenville interval

at ca. 950 Ma [40,41].

3. Pb isotope data

Fifty-six whole rock samples were collected from a

region covering ~70,000 km2 of the Amazon craton

basement in Rondonia, Brazil. The rocks were

collected from the cratonic region north of the Nova

Brasilandia metasedimentary belt, with samples taken

from both the metaigneous host rock lithologies (see

[35] for sample locations) and from all the intrusive

suites of the six known episodes of Meso-Neoproter-

ozoic magmatism (see [34] for sample localities). U–

Pb zircon ages from the former range of 1.75–1.43 Ga

[35,43]. The intrusive suites range in age from ca.

1.65 to 0.97 Ga [34].

Whole rock U, Th, and Pb data are included in the

electronic Appendix A [46]. Whole rock dissolution

in closed Savillex vials, column chromatography, and

mass spectrometer analysis were carried out in the

laboratories of the U.S. Geological Survey in Menlo

Park, California, as described by Bouse et al. [44]. A

wide range of 206Pb/204Pb values (16.8–33.4) and207Pb/204Pb values (15.5–16.9) characterize the Ama-


zon craton samples [45]. The 208Pb/204Pb ratios vary

from 36.3 to 54.5, demonstrating time-integrated Th/

U ratios of 3.8 to 6 (Fig. 2a), similar to that observed

by Sinha et al. for the Blue Ridge of the southern

Appalachians [47]. Both the SW Amazon craton and

the Blue Ridge/Mars Hill terrane are marked by

higher thorogenic Pb values than present-day values

of ~3.6 measured from the nearby Honeybrook

Uplands [48] as well as average values for the rest

of the Grenville belt. We will concentrate on the

uranogenic Pb component, simply noting that both

our techniques and conclusions are valid for and

consistent with observations of thorogenic Pb.

The 207Pb/204Pb values for the SWAmazon craton

rocks are clearly elevated for a given range of206Pb/204Pb values, relative to both the Pb evolution

model of average crust and to Laurentian samples

(Fig. 2b). Inasmuch as 207Pb is generated by the decay

of the short-lived 235U, pronounced differences in

present day 207Pb/204Pb must reflect ancient differ-

entiation events; the more recent the differentiation,

the smaller the eventual difference in 207Pb/204Pb

values, given the increasing scarcity of parent 235U.

The coherence of high 207Pb/204Pb values in all

samples, regardless of age, suggests a common

high-l (238U/204Pb) source region (l2 in the two-

stage model of Stacey and Kramers for a differentiated

mantle [49]). In uranogenic Pb space, samples plot

along an apparent secondary isochron with a slope of

0.0875, corresponding to an apparent age of 1372F59

Ma, depicted as a reference line in Fig. 2b. The

present-day whole rock values and their projection

along this reference line indicate an initial Pb initial

ratio well above the Stacey and Kramers [49] second

stage Pb evolution curve for average crust (l2=9.735).

However, in order to be geologically significant as a

secondary isochron, this line must reflect the time

elapsed since the last major U/Pb fractionation. Two

observations suggest that this is not the case: first,

many of the rocks have magmatic ages that are

younger than the age indicated by the slope of the

reference line; and second, 207Pb/206Pb whole rock

isochrons calculated for contemporaneous rock suites

are similar to the U–Pb zircon ages from those rocks.

Hence, we attach no age significance to the line itself,

which is interpreted as the average of an array of

secondary isochrons formed by individual samples,

useful only as a regional indicator of high l2 values.

3.1. Determination of l2 for SW Amazon source

region and l3 for samples

Modern day Pb compositions are tricky to use as

isotopic discriminants, given the many processes

that redistribute Pb within a bulk sample. More

useful would be some measure of the initial Pb

within a sample, which is characteristic of the

source region at the time of the rock’s extraction

from the reservoir and is unaffected by later events

(e.g., metamorphism) that can profoundly alter the

evolution of whole rock Pb isotope compositions to

their modern values. Determinations of the isotopic

composition of initial Pb have been attempted by

two methods: analysis of U- and Th-free minerals

with a supposedly immutable Pb composition (e.g.,

K-feldspar [7,10]) or by correcting for radiogenic Pb

accumulation from the measured amount of U and

Th present in a whole rocks sample over a known

span of time [50]. Unfortunately, for the first

technique, feldspars are not closed to Pb diffusion

during metamorphism, meaning that initial Pb

values at the time of crystallization are not

preserved [10]. The success of the second technique

is foiled by remobilization of soluble U during

weathering [50]. For example, our own attempts to

determine the initial Pb by correcting for radiogenic

Pb using the observed U content and the known

zircon age proved problematic; several samples plot

below the Canyon El Diablo composition for

primordial Pb [51]. This clear overcorrection for in

situ accumulation of radiogenic Pb is probably the

result of recently acquired U, a subject we will

return to later.

We explore a third technique for determining the

initial Pb of a whole rock sample that considers

each sample as a closed system following extraction

from a source reservoir. The projection from a

whole rock–zircon isochron intersects an array of Pb

evolution curves, each of which represents the time-

dependent Pb composition of source region of a

given l2 value (Fig. 3). The best fit l2 value,

solved for iteratively, yields an intercept of the

isochron with the Pb evolution curve at an age

(Tintercept) that is ideally equal to the crystallization

age of the rock (Fig. 3 inset). This calculation is

done by simultaneously solving the three equations

below, first by setting the slope of the secondary

Fig. 2. (a) Present-day thorogenic 208Pb/204Pb (vertical axis) composition vs. 206Pb/204Pb composition, with inset area showing magnified view

of data cluster. Data are from the SWAmazon craton whole rocks (this study): whole rocks of Blue Ridge of North Carolina and Virginia [47],

whole rocks of the Adirondacks [48]; leached feldspar from the Gneiss belt of Ontario [10]; Llano Uplift of Texas (whole rock and feldspars

[62]; Grenville xenoliths [63]); New Mexico and west Texas (whole rock and feldspars [8]); and Grenville belt of Labrador [12]. (b) Uranogenic207Pb/204Pb vs. 206Pb/204Pb compositions; references, inset, and symbols as in panel (a). Note the clear separation in values from the expanse of

the Laurentian Grenville belt vs. data from the Blue Ridge Province, which overlap with Amazon data.


Fig. 3. Graphic demonstrating the calculation of l2 using a two-point isochron consisting of the whole rock composition and the zircon Pb

composition. Crystallization occurs at 2400 Ma, with an increase in U content (i.e., l3Nl2) followed by evolution of the whole rock

compositions to the modern value that plots above and to the right of the average crustal composition. A decrease in U content at the time of

crystallization (i.e., l3bl2) would have resulted in modern whole rock composition that plotted below and to the left of the endpoint of the l2

curve (inset). In determining the initial Pb imparted by the source region, the whole rock–zircon isochron is projected back to a l2 curve so that

the crystallization age and the Pb evolution model age agree. (Inset) Various dotted curve lines represent l2 values 10.2–9.8. Dashed line curve

at the bottom is the Stacey and Kramers value for average crust, 9.735 [49]. The curved, solid line with the arrow is the evolution curve for the

whole rock system with l3. The whole rock–zircon isochron is seen to intersect the l2=10.2 curve at 2400 Ma and the l2=9.8 curve at 2100 Ma

but does not intersect the Stacey and Kramers curve. Solid lines with arrows are paleogeochrons for 100 Ma intervals that project back to the Pb

composition at 3.7 Ga, the beginning of the second stage of the Stacey and Kramers crustal Pb evolution model [49].


whole rock–zircon isochron (206Pb/204Pbxtl,207Pb/204Pbxtl) equal to the 207Pb/206Pb zircon age

according to the right side of Eq. (1) below.

207Pb=204Pbobs � 207Pb=204Pbxtl206Pb=204Pbobs � 206Pb=204Pbxtl

¼ 1

137:88

ðek235Txtl � 1Þðek238Txtl � 1Þ ð1Þ

where

207Pb=204Pbxtl ¼ 207Pb=204Pb3:7 Ga þ1

137:88

� l2ðek235T3:7 Ga � ek235TxtlÞ ð2Þ

206Pb=204Pbxtl ¼ 206Pb=204Pb3:7 Ga

þ l2ðek238T3:7 Ga � ek238TxtlÞ ð3Þ

The values for 207Pb/204Pb3.7 Ga and206Pb/204Pb3.7 Ga

given by Stacey and Kramers [49] are 12.998 and

11.152, respectively. For the SW Amazon craton

rocks, average l2 values of 9.89F0.17 are required

for all the samples, in keeping with the high207Pb/204Pb values observed for all samples (Fig.

4a). Although in practice the intercept of the isochron

with a l2 evolution curve may yield a Pb model age

(Tintercept) different from the U–Pb crystallization age,

filtering the data by excluding data where this age

difference is N50 Ma does not change the underlying

result; the filtered average is 9.94 F0.19.

This model l2 approach has drawbacks in that it

assumes a single stage evolution following differ-

entiation from the Pb source region, thus ignoring the

obvious concern with felsic intrusive rocks of the

effects of crustal differentiation and contamination.

However, TDM for the rocks in question are rarely

Fig. 4. (a) Frequency diagram for calculated l2 values from data above in data bins of 0.25 units. Geochronological data (U–Pb zircon ages) used to

determine l2 values are as follows: SW Amazon craton [34,35]; Blue Ridge [77,79,85]; Adirondacks ([16,48] and references therein); Llano

[86,87]; Labrador ([12] and references therein). (b) Calculated values for l3 following extraction from Pb reservoir. Excluding, for the moment, the

Adirondacks curve, the Blue Ridge/MarsHill basement and the rest of the LaurentianGrenville belt appear to have been depleted in U at some point

in their respective histories, possibly as a result of high-grade (amphibolite to granulite) Grenvillian metamorphism reported for all of these rocks.

The small, secondary peak from the Adirondacks samples centered around l3=25 units are samples taken from a metasedimentary lithology (one

sample) and pegmatitic facies (three samples) of the Mt. Lyon Granite. The latter unit is reportedly the product of extensive Na-rich

hydrothermalism [48], suggesting a rare, localized occurrence of U enrichment. The greater variation in U contents in the SWAmazonmay reflect a

less homogeneous metamorphic history, with the U-enriched massifs generally in the 1.31–1.41-Ga age range. The bin size is 5 A3 units.


more than 200–300 Ma older than the U–Pb

crystallization age (J.S. Bettencourt, unpublished data;

35), an interval that is too short to have much effect on

Pb–Pb systematics [52]. Secondly, the effects of

metamorphism are ignored, although this is probably

a reasonable assumption for whole rock samples [50].

In support of this, we note that model l2 values from

all rock samples yield a coherent range, regardless of

crystallization age and subsequent metamorphic his-

tory. In addition, the calculated l2 values are in

excellent agreement with the range of values (Fig. 4a)

determined from post-Grenvillian, ca. 950 Ma galena

samples (l2=9.78–10.25) reported by Geraldes [53].

This simplified approach to Pb evolution in a

whole rock sample can be extended to calculate values

for l3 required for an individual whole rock sample to

reach the present-day values after crystallization. We

solve for l3 by setting the observed present day Pb


composition equal to the Pb composition calculated

for the rock beginning at Txtl according to the

following equations:

l3 ¼ 207Pb=204Pbobs

��1

137:88ðek235Txtl � 1Þ

þ 207Pb=204Pbxtl

�ð4Þ

l3 ¼ 206Pb=204Pbobs=½ðek238Txtl � 1Þ

þ 206Pb=204Pbxtl� ð5Þ

where 207Pb/204Pbxtl and206Pb/204Pbxtl are determined

from Eqs. (2) and (3), respectively. The calculated

values for the time integrated U/Pb ratio (i.e., l3) for

individual samples following crystallization are gen-

erally lower than the modern measured U/Pb values, a

fact attributed to recent U gain for most samples (Fig.

5). The calculated l3 values for the Amazon rocks

range from 0.8 to 75, with an average value of 15.3,

which signifies that most samples did experience a net

gain in U at the time of crystallization. Most of the

high l3 samples, i.e., those with the most radiogenic

Pb, seem to be restricted to the ca. 1.4–1.3 Ga suites

Fig. 5. Calculated (solid line) and measured values (dashed line) of U (l3)

sets depicting pseudochrons with no geochronological significance, as discu

The calculated values of l3 give a U–Pb pseudochron with the same

(1372F59 Ma) for all samples. The plot of U data measured in sample

demonstrative of recently acquired excess U.

(average l3 of 28F16), in contrast with average l3

values of 8F6 for older rocks (Fig. 4b). This

observation supports widespread U scavenging from

older country rocks (>1.4 Ga) during this period of

extensive magma emplacement and regional meta-

morphism, in keeping with widely preserved ca. 1.3-

Ga metamorphic cooling ages [29,35,54].

4. Discussion

4.1. Isotopic differences between Amazon craton and

Laurentian Grenville

Reconstructions of Rodinia rely on the recognition

and identification of the distinct cratonic elements that

were incorporated via tectonic collisions into the

growing supercontinent. The suturing of Amazonia

and Laurentia along the greater Grenville mountains

provides a tectonic framework for identifying the

origin of individual terranes in the roots of the now

dismembered and deeply exhumed mobile belt. To

this end, Pb isotopic data from the Grenville province

vs. 206Pb/204Pb, with two regressed lines through the respective data

ssed in the text for the 207Pb/206Pb reference line depicted in Fig. 2b.

age (1326F25 Ma), within error, as the 207Pb/206Pb pseudochron

s is much more diffuse and yields a much younger apparent age,


of Laurentia, selected Appalachian basement inliers

with Grenvillian overprints, and Grenville-deformed

basement samples of Amazon are compared in Fig. 2.

Laurentian Grenville samples comprise both whole

rock and feldspar analyses and form a coherent pattern

that plots below the Pb evolution curve for the

average crust in the Stacey and Kramers model [49].

The coherence of Pb isotopic composition for rocks

from the entire extent of the Grenville Province (from

Labrador to Texas) is remarkable and is uniformly

lower than the crustal average [48]. The implication of

such uniformly low 207Pb/204Pb values in Grenville

rocks is that there was a homogeneous long-lived

mantle source characterized by early U depletion, as

has been suggested to be typical of the Superior craton

[55]. The l2 values calculated for the Labrador,

Adirondacks, and Llano portions of the Laurentian

Grenville Province form a tight cluster at ~9.5,

uniformly lower than Amazon values (Fig. 4a).

The episode(s) of Grenville deformation in Lau-

rentia affected crust of widely differing age, although

a coherent mass of juvenile crust forms the outboard

eastern portions of the belt (Fig. 1). In the exposed

Grenville belt of Canada, the Nd and Pb isotopic

systems reveal a pattern of older Paleoproterozoic to

Archean crust immediately adjacent to the Superior

province [10,17,18,56] that was reworked during the

late Mesoproterozoic orogeny, corresponding roughly

to the bpolycyclic parautochthonous beltQ of Rivers

[57]. Both Nd model ages and U–Pb crystallization

ages decrease away from the Superior province, with

increasingly juvenile materials, as defined by both Pb

and Nd isotopes, encountered across a southeast-

trending transect [10], with large expanses of Quebec

[17] and the Metasedimentary belt of Ontario [58,59]

defined by juvenile crust (+eND values) with Nd

model ages of 1.4–1.5 Ga. The Adirondacks and

Green Mountains of the NE United States are marked

by predominantly juvenile material with TDM in the

1.3–1.4-Ga range [16]. The expanse of this juvenile

crust is continuous to the south; in the subsurface of

the midcontinental United States, the Eastern Granite–

Rhyolite province is marked by TDM of 1.3–1.4 Ga

[60,61]. Juvenile crust also predominates in the

southernmost Laurentian basement exposures of the

Llano Uplift (TDM ~1.3–1.4 Ga) and the region to the

west [9,62,63]. The predominantly juvenile character

of the outboard easternmost portions of the Grenville

Province is summarized in Fig. 6, where a unimodal

distribution of eNd values for 1.0 Ga cluster about

positive values, indicating a juvenile mantle source.

Comparing the Nd isotopic data for the Amazon

craton with the Laurentian Grenville belt reveals the

different histories of these two cratons prior to the

Grenville episode. The majority of TDM ages from the

SW Amazon craton are generally in the 1.5–2.3 Ga

range [31,64,65]. Much of this material has been

reworked, as evidenced by eNd values that are

negative or close to CHUR values at the time of

crystallization (Fig. 6). Unlike the Laurentian rocks

deformed during the Grenville orogeny, juvenile

material is rare, as indicated by the overwhelmingly

negative eNd values calculated for Amazon samples at

1000 Ma, the approximate end of all collision-related

deformation in the Grenville Province. These values

cluster loosely around �3 e units, with a wider

variance in model ages than that observed in the

Grenville belt of North America. The similarity

between the SW Amazonian and Blue Ridge/Mars

Hill terrane Nd data will be discussed below.

4.2. Origin of Grenvillian basement inliers of the SE

Appalachians

The Paleozoic orogenies that gave rise to the

Appalachian Mountains complicate efforts to locate

the pre-Iapetan cratonic margin of Laurentia. In spite

of this difficulty, the Blue Ridge/Mars Hill terrane is

widely considered to be part of Laurentia by the end

of Proterozoic times [66–68], given its location west

of the Paleozoic suture zone (Fig. 1) that marks the

western limit of accreted terranes [66,67,69]. In

addition, Neoproterozoic plutons and dikes are wide-

spread throughout these massifs (Robertson River,

Crosnore, Bakersville dikes), having been emplaced

prior to the opening of Iapetus [70–72] and are

overlain by extrusive mafic rocks of the Catoction Fm

[73]. The Blue Ridge/Mars Hill terrane itself lies

above a shallowly dipping seismic reflector, demon-

strating that it is allochthonous to Laurentia [74,75],

although this boundary may have been reactivated

during Taconic and Alleghenian deformation. Resto-

ration of Paleozoic deformation in the Appalachians

of Virginia demonstrates a metamorphic gradient that

decreases to the east, with amphibolite–granulite

facies rocks (Lovingston massif) emplaced on top of

Fig. 6. (a) Sm–Nd data compiled from the outboard juvenile portions of the Laurentian Grenville Province including the Adirondacks; buried

Grenville province of the midcontinental region; the Llano Uplift and W. Texas region. Note the presence of eNdb0 for rocks older than 1.15 Ga

in the Blue Ridge/Mars Hill data set and overlap with data from the SW Amazon craton data. References as in Fig. 1. Samples where147Sm/144NdN0.14 are not considered in this distribution so as to represent only rocks of average crustal composition. Two low eNd samples

from both the Adirondacks and the Llano regions are marked with asterisks, indicating metasedimentary samples of suspect provenance. (b)

Frequency diagram of eNd values from the same data as above, calculated for 1000 Ma, showing the overlap in juvenile values for the Grenville

belt. A secondary peak around �6 e in the Blue Ridge/Mars Hill samples with zircon ages greater than 1.15 Ga shows the presence of older

material, demonstrating clear overlap with Amazonian crust. Bin size is 3 e units.


deeper granulite facies Pedlar River massif to the west

[67,69]. Further south, the Mars Hills block shows

evidence of having been emplaced structurally above

the adjacent Blue Ridge province rocks of North

Carolina and Tennessee [76].

Geochronological constraints on the timing of this

deformation suggest that the early phase of NE–SW

compression took place between 1145 and 1075 Ma

[77], with younger deformation and metamorphism

associated with emplacement of granites, charnockites,


and anorthosites ranging in age from 1077 to ca. 1020

Ma [77–79]. In spite of the similarity of these ages to

typical Grenville Province ages, the Blue Ridge/Mars

Hills domains form an exception to the general isotopic

architecture of Laurentia. Lead compositions from

these rocks display a trend that is clearly separate from

the rest of the Laurentian Grenville belt, as observed by

Sinha et al. [47] and Sinha and McLelland [48].

However, the coherence of the Amazon trend with

the Blue Ridge/Mars Hill Pb data is striking, with both

data sets easily distinguishable from the Laurentian

Grenville data set (Fig. 2b). Indeed, the calculated l2

values for the SW Amazon and the Blue Ridge/Mars

Hill basement are observed to follow the same

distribution about average l2 values of 10, with a

smaller cluster of values at ~10.5 (Fig. 3a).

The high l2 values calculated for the Blue Ridge/

Mars Hills source region strongly suggest extraction

from a source region other than that which gave rise to

the outboard, juvenile regions of the Laurentian Gren-

ville belt for which the present day Pb compositions are

so distinctively and homogeneously nonradiogenic

(Fig. 3a). The uniqueness of the Blue Ridge/Mars Hill

terrane with respect to Laurentia is supported by Nd

isotopic data from metaigneous rocks [79–81], which

reveal a pattern very different from the nearest adjacent

portions of the Grenville belt (Fig. 1). The presence of

mature, continental material with TDM ranging from 1.5

to 2.2 Ga distinguishes the Blue Ridge/Mars Hill

terrane from the rest of the Laurentian Grenville belt.

The bimodal variation in eNd values calculated at 1000

Ma indicates the presence of both reworked continental

material with negative values (�2 to �9) preserved in

rocks older than 1.15 Ga and a more juvenile

contribution (with eNd of �2 to +4) in rocks younger

than 1.15 Ga (Fig. 6). The presence of this anomalous

Paleoproterozoic crust was first recognized on the basis

of 1.8 Ga Rb–Sr mineral isochrons [82] and has been

confirmed by SHRIMP dating of zircons with igneous

cores that yielded ages of ca. 1.8 Ga [79]. There is clear

overlap of the eNd (1000) values from the Amazon and

the older rocks of the Blue Ridge/Mars Hill terrane,

supportive of derivation from the same source region.

The similarity in both Nd and Pb isotopic

signatures from the Amazon and the Blue Ridge/Mars

Hill terrane points to a common ancestry. If the Pb

isotope patterns were solely the product of Grenvillian

metamorphic history, the Blue Ridge/Mars Hill data

would match the pattern observed in the rest of the

Laurentian Grenville belt, inasmuch as the metamor-

phic geochronology of both is practically indistin-

guishable [77,79]. In fact, a high-grade U-depleting

metamorphic history in the late Mesoproterozoic may

be reflected in the low l3, i.e., values calculated for

both (Fig. 4b). Given the distinctiveness of the

modern day Pb compositions for the Blue Ridge/

Mars Hill rocks from the rest of the Laurentian

Grenville Province, later metamorphism and intrusion

did not obliterate the Pb isotopic characteristics

inherited from the source region. In contrast, the

metamorphic effects of Grenvillian orogenesis on the

Amazon craton appear to have been much more

heterogeneous, as observed through both high and

low l3 values, meaning that both localized U enrich-

ment and U depletion occurred.

Our ability to see through the metamorphic veil

to Blue Ridge/Mars Hill source region characteristics

is aided by Nd isotopes. The relative immobility of

Sm and Nd with respect to whole rock samples

means that the effects of high-grade metamorphism

did not prevent the preservation of Paleoproterozoic

Nd model ages in the Blue Ridge/Mars Hill base-

ment. However, unlike Pb, Nd isotopes do demon-

strate the effects of a different source region for

Grenvillian rocks in the Blue Ridge/Mars Hill

basement after ca. 1.15 Ga. This may be explained

through mass balance considerations; Nd concen-

trations do not vary greatly between felsic and mafic

rocks, whereas Pb-poor mafic rocks (anorthosites,

gabbros, basalts) in the post-Grenville interval are

unlikely to have greatly altered the Pb signature

inherited from older Pb-rich felsic rocks. Juvenile

material observed in rocks younger than 1.15 Ga

suggests a transition of source regions for the Blue

Ridge/Mars Hill basement; before this time, Ama-

zonian signatures dominate. Following the tectonic

transfer to Laurentia at ca.1.15 Ga, Nd isotopes

reveal an influx of intrusive rocks with a Laurentian

source (Fig. 6).

5. Conclusions

The ancient, highly radiogenic source region of the

SW Amazon craton provides us with an isotopic

fingerprint for paleogeographic reconstructions. We


interpret the similarity of Amazon craton Pb and Nd

isotopic signatures with the Blue Ridge/Mars Hills

domain of the southern Appalachian to indicate a

common origin. Both are distinct from Laurentian

isotopic signatures for the rest of the Grenville belt. In

our reconstruction, the transfer of the Blue Ridge/

Mars Hill terrane to Laurentia took place during the

assembly of Rodinia, following the collision of the

Amazon with southernmost Laurentia at ca. 1.2 Ga.

Extensive deformation recorded in the southeast

Appalachian region after ca.1.15 Ga gives a geo-

chronological basis for the timing of this terrane

transfer. The ~50 My that elapsed after the original

collision and the suturing of the Blue Ridge/Mars

Hills terrane to Laurentia is evidence of continued

relative motion between the Amazon craton and

Laurentia. This interpretation of a mobile Rodinia

configuration is supported by the diminishing evi-

dence for Amazon source region characteristics in the

Blue Ridge/Mars Hill basement rocks after 1.15 Ga.

This SWAmazonian crust, later stranded in Laurentia

following the breakup of Rodinia, serves as paleogeo-

graphic marker of the northward passage of the

Amazon craton along the Grenville margin of

Laurentia. The net sinistral displacement between

Amazon and Laurentia suggests that Rodinia paleo-

geography evolved throughout the assembly phase of

the supercontinent’s history.

Acknowledgments

E. Tohver thanks Ben van der Pluijm and Jamie

Gleason for stimulating conversations that preceded

this contribution, which was written with support from

NSF grant #INT-0301807. Fieldwork and analytical

costs were underwritten with support from research

grants to J.S. Bettencourt (FINEP/FUNDUNESP

no. 65.94.0249.00, PADCT/FINEP 64.99.027.00.,

FAPESP-Proc. no. 2000/08033-5) and a scholarship

awarded to B.L.Payolla (FAPESP-Proc. no. 95/0290-

9). The authors acknowledge the cooperation of the

U.S. Geological Survey at Menlo Park where R. Tosdal

analyzed 44 samples. The authors would like to

sincerely thank Dr. Kotov from the Institute of

Precambrian Geology and Geochronology, Russian

Academy of Sciences (IPGG-RAS) in St. Petersburg

where analysis of 12 samples was undertaken.

Thoughtful reviews by Peter Gromet and Randy Van

Schmus are acknowledged and appreciated.

Appendix A. Supplementary data

Supplementary data associated with this article can

be found, in the online version, at doi:10.1016/

j.epsl.2004.09.029.

References

[1] W.A. Thomas, R.A. Astini, The Argentine Precordillera: a

traveler from the Ouachita embayment of North American

Laurentia, Science 273 (1996) 752–757.

[2] A.V. Borrello, The Cambrian of South America, in: D.H.

Holland (Ed.), Cambrian of the New World, Wiley-Inter-

science, London, 1971, pp. 385–438.

[3] S.M. Kay, S. Orrell, J.M. Abbruzzi, Zircon and whole rock

Nd–Pb isotopic evidence for a Grenville age and Laurentian

origin for the basement of the Precordillera terrane, J. Geol.

104 (1996) 637–648.

[4] A.E. Rapalini, R.A. Astini, Paleomagnetic confirmation of the

Laurentian origin of the Argentine Precordillera, Earth Planet.

Sci. Lett. 155 (1998) 1–14.

[5] R.A. Astini, Stratigraphic evidence supporting the rifting,

drifting and collision of the Laurentian Precordillera terrane of

western Argentina, in: R.J. Pankhurst, C.W. Rapela (Eds.), The

Proto-Andean Margin of Gondwana, Geol. Soc. London Spec.

Publ. 142 (1998) 11–33.

[6] M. Keller, Argentine Precordillera: sedimentary and plate

tectonic history of a Laurentian crustal fragment in South

America, Geol. Soc. Am. Spec. Pap. 341 (1999) 1–131.

[7] J.L Wooden, P.A. Mueller, A Pb, Sr, and Nd isotopic

compositions of a suite of late Archean, igneous rocks, eastern

Beartooth Mountains; implications for crust–mantle evolution,

Earth Planet. Sci. Lett. 87 (1988) 59–72.

[8] E.W. James, C.D. Henry, Southeastern extent of the North

American craton in Texas and northern Chihuahua as revealed

by Pb isotopes, Geol. Soc. Am. Bull. 105 (1993) 116–126.

[9] P.J. Patchett, J. Ruiz, Nd isotopes and the origin of Grenville-

age rocks in Texas: implications for Proterozoic evolution of

the United States mid-continent region, J. Geol. 97 (1989)

685–695.

[10] C.P. DeWolf, K. Mezger, Lead isotope analyses of leached

feldspars: constraints on the early crustal history of the

Grenville Orogen, Geochim. Cosmochim. Acta 58 (1994)

5537–5550.

[11] R.N. Tosdal, The Amazonia–Laurentia connection as viewed

from the Middle Proterozoic rocks in the central Andes,

western Bolivia and northern Chile, Tectonics 15 (1996)

827–842.

[12] S.L. Loewy, J.N. Connelly, I.W.D. Dalziel, C.F. Gower,

Eastern Laurentia in Rodinia: constraints from whole rock

http://dx.doi.org/doi:10.1016/j.epsl.2004.09.029


Pb and U/Pb geochronology, Tectonophys 375 (2003)

169–197.

[13] J. Ruiz, R.M. Tosdal, P.A. Restrepo, G. Murillo–Muneton, Pb

isotope evidence for Colombia–southern Mexico connections

in the Mesoproterozoic, Geol. Soc. Am. Spec. Pap. 336 (1999)

183–197.

[14] J.D. Gleason, P.J. Patchett, W.R. Dickinson, J. Ruiz, Nd

isotopes link Ouachita turbidites to Appalachian sources,

Geology 22 (1994) 347–350.

[15] R.M. Tosdal, J.L. Wooden, R.W. Kistler, Inheritance of

Nevadan mineral belts from Neoproterozoic continental

breakup, in: J.K. Cluer, J.G. Price, E.M. Struhsacker, R.F.

Hardyman, C.L. Morris (Eds.), Geology and Ore Deposits

2000: The Great Basin and Beyond: Geol. Soc. Nevada Symp.

Proc., 2000, pp. 451–466.

[16] J. Daly, J. McLelland, Juvenile Middle Proterozoic crust in the

Adirondack highlands, Grenville Province, northeastern North

America, Geology 19 (1991) 119–122.

[17] A.P. Dickin, M.D. Higgins, Sm/Nd evidence for a major 1.5

Ga crust-forming event in the central Grenville Province,

Geology 20 (1992) 137–140.

[18] A.P. Dickin, Crustal formation in the Grenville Province: Nd-

isotope evidence, Can. J. Earth Sci. 37 (2000) 165–181.

[19] B.R. Doe, R.E. Zartman, Plumbotectonics I, the Phanerozoic,

in: H.L. Barnes (Ed.), Geochemistry of Hydrothermal Ore

Deposits, 2nd ed. Holt, Rhinehart and Winston, New York.

[20] D.J. DePaolo, Neodymium isotopes in the Colorado Front

Range and crust–mantle evolution in the Proterozoic, Nature

5812 (1981) 193–196.

[21] P.F. Hoffman, Did the breakout of Laurentia turn Gondwana

inside out? Science 252 (1991) 1409–1412.

[22] G.C. Bond, P.A. Nickeson, M.A. Kominz, Breakup of a

supercontinent between 625 Ma and 555 Ma; new evidence

and implications for continental histories, Earth Planet. Sci.

Lett. 70 (1984) 325–345.

[23] I.W.D. Dalziel, Pacific margins of Laurentia and East

Antarctica–Australia as a conjugate rift pair: evidence and

implications for an Eocambrian supercontinent, Geology 19

(1991) 598–601.

[24] G.R. Sadowski, J.S. Bettencourt, Mesoproterozoic tectonic

correlations between eastern Laurentia and the western border

of the Amazon Craton, Precambrian Res. 76 (1996) 213–227.

[25] M.C. Geraldes, W.R. Van Schmus, K.C. Condie, S. Bell,

W. Teixeira, M. Babinski, J.K. Bartley, L.C. Kah, Prote-

rozoic geologic evolution of the SW part of the Amazonian

Craton in Mato Grosso State, Brazil, Precambrian Res. 111

(2001) 91–128.

[26] E. Tohver, B.A. van der Pluijm, R. Van der Voo, G. Rizzotto,

J.E. Scandolara, Paleogeography of the Amazon craton at 1.2

Ga: early Grenville collision with the Llano segment of

Laurentia, Earth Planet. Sci. Lett. 199 (2002) 185–200.

[27] L.J. Pesonen, S.-2. Elming, S. Mertanen, S. Pisarevsky, M.S.

D’Agrella-Filho, J.G. Meert, P.W. Schmidt, N. Abrahamsen,

G. Bylund, Paleomagnetic configuration of continents during

the Proterozoic, Tectonophys 375 (2003) 289–324.

[28] M.S. D’Agrella-Filho, I.G. Pacca, S.2. Elming, R.I. Trindade,

M.C. Geraldes, W. Teixeira, Paleomagnetic and rock magnetic

studies of Proterozoic rocks of western Mato Grosso state,

Amazonian craton, Geophys. Res. Abstr. 5 (2003) 05619.

[29] E. Tohver, B.A. van der Pluijm, K. Mezger, E.J. Essene, J.

Scandolara, G. Rizzotto, Implications of a two stage tectonic

history of the SW Amazon craton: recognizing the Nova

Brasilandia metasedimentary belt as a late Mesoproterozoic

suture zone in Rodinia reconstructions, Geol. Soc. Am. Abstr.

Programs 36 (2003) 301.

[30] C.C.G. Tassinari, M.J.B. Macambira, Geochronological prov-

inces of the Amazonian craton, Episodes 22 (1999) 174–182.

[31] U.G. Cordani, K. Sato, Crustal evolution of the South

American Platform, based on Nd isotopic systematics on

granitoid rocks, Episodes 22 (1999) 167–173.

[32] C.C.G. Tassinari, J.S. Bettencourt, M.C. Geraldes, M.J.B.

Macambria, J.M. Lafon, The Amazonian craton, in: U.G.

Cordani, E.J. Milani, A. Thomaz Filho, D.A. Campos, Rio de

Janeiro (Eds.), Tectonic Evolution of South America, 2000,

pp. 41–95.

[33] J.E. Scandolara, G.J. Rizzotto, J.L. de Amorim, R.B.C. Bahia,

M.L. Quadros, C.R. da Silva, Geological Map of Rondonia

1:1,000,000, Companhia de Pesquisa de Recursos Minerais,

Brasilia, 1998.

[34] J.S. Bettencourt, R.M. Tosdal, J.W.B. Leite, B.L. Payolla,

Mesoproterozoic rapakivi granites of the Rondonia Tin

Province, southwestern border of the Amazonian craton,

Brazil: I. Reconnaissance U–Pb geochronology and regional

implications, Precambrian Res. 95 (1999) 41–67.

[35] B.L. Payolla, J.S. Bettencourt, M. Kozuch, W.B. Leite, A.H.

Fetter, W.R. Van Schmus, Geological evolution of the base-

ment rocks in the east-central part of the Rondonia Tin

Province, SW Amazonian craton, Brazil: U–Pb and Sm–Nd

isotopic constraints, Precambrian Res. 119 (2002) 141–169.

[36] G.J. Rizzotto, Petrologia e geotectonia do Grupo Nova

Brasilandia, Rondonia, Unpublished MSc, Universidade Fede-

ral do Rio Grande do Sul, Porto Allegre, 1999, 131 pp.

[37] E. Tohver, B. van der Pluijm, K. Mezger, E.J. Essene, J.

Scandolara, G. Rizzotto, Significance of the Nova Brasilandia

metasedimentary belt in western Brazil: redefining the

Mesoproterozoic boundary of the Amazon craton, Tectonics

(in press).

[38] M. Litherland, R.N. Annells, D.B.F. Darbyshire, C.J.N.

Fletcher, M.P. Hawkins, B.A. Klinck, W.I. Mitchell, E.A.

O’Connor, P.E.J. Pitfield, G. Power, B.C. Webb, The

Proterozoic of eastern Bolivia and its relationship to the

Andean mobile belt, Precambrian Res. 43 (1989) 157–174.

[39] G.S. Saes, Tectonic and paleogeographic evolution of the

Aguapeı aulacogen (1.2–1.0 Ga) and the basement terranes in

the southern Amazon craton, PhD thesis, Universidade de Sao

Paulo, 1999, 135 pp.

[40] M.C. Geraldes, B.R. Figueiredo, C.C.G. Tassinari, H.D. Ebert,

Middle Proterozoic vein hosted gold deposits in the Pontes e

Lacerda region, southwestern Amazonian craton, Brazil, Int.

Geol. Rev. 39 (1997) 438–448.

[41] C.J. Fernandes, R.M. Kuyumjian, G.M. Pulz, M.C. Geraldes,

F.E. Pinho, Relacao entre a zona de cisalhamento corredor e o

deposito aurıfero Pau-a-Pique, faixa movel Aguapeı, fronteira

Brasil-Bolivia, Rev. Bras. Geocienc. (2004) (in press).


[42] J.L. Luft, G. Rizzotto, F. Chemale, E.F. Lima, Analise

geologica-estrutural do cinturao Sunsas na regiao de Nova

Brasilandia, sudeste de Rondonia, Rev. Pesq. Geocienc. 2

(2000) 65–78.

[43] C.C.G. Tassinari, U.G. Cordani, A.P. Nutman, W.R. Van

Schmus, J.S. Bettencourt, P.N. Taylor, Geochronological

systematics on basement rocks from the Rio Negro-Juruena

Province (Amazonian Craton) and tectonic implications, Int.

Geol. Rev. 38 (1996) 161–175.

[44] R.M. Bouse, J. Ruiz, S.R. Titley, R.M. Tosdal, J.L. Wooden,

Lead isotope compositions of Late Cretaceous and Early

Tertiary igneous rocks and sulfide minerals in Arizona:

implications for the sources of plutons and metals in porphyry

copper deposits, Econ. Geol. 94 (1994) 211–244.

[45] R.M. Tosdal, J.S. Bettencourt, U–Pb zircon ages and Pb

isotopic compositions of Middle Proterozoic Rondonian

Massifs, southwestern margin of the Amazon Craton, Brazil,

Actas VII Cong. Geolog. Chil., Universidad de Concepcion,

Chile, 1994, pp. 1538–1541.

[46] K.R. Ludwig, ISOPLOT—A plotting and regression program

for radiogenic isotope data, U.S. Geol. Surv. Open File Rep.

(1991) 91–445.

[47] A.K. Sinha, J.P. Hogan, J. Parks, Lead isotope mapping of

crustal reservoirs within the Grenville superterrane: I. Central

and southern Appalachians, Earth Processes: reading the

isotopic code, in: A. Basu, S. Hart (Eds.), AGU Geophys.

Monogr. 95 (1996) 297–312.

[48] A.K. Sinha, J.M. McLelland, Lead isotope mapping of

crustal reservoirs within the Grenville superterrane: II.

Adirondack massif, New York, in: A.K. Sinha (Ed.), Proc.

International Conferences on Basement Tectonics, vol. 13,

1999, pp. 297–312.

[49] J.S. Stacey, J.D. Kramers, Approximation of terrestrial lead

isotopic evolution by a two-stage model, Earth Planet. Sci.

Lett. 26 (1975) 207–221.

[50] J.N. Rosholt, R.E. Zartman, I.T. Nkomo, Lead isotope

systematics and uranium depletion in Granite Mountains,

Wyoming, Geol. Soc. Am. Bull. 84 (1973) 989–1002.

[51] J.H. Chen, G.J. Wasserburg, A search for primordial Pb in iron

meteorites, Meteoritics 18 (1983) 279–280.

[52] S. Moorbath, P.N. Taylor, R. Goodwin, Origin of granitic

magma by crustal remobilization: Rb–Sr and Pb–Pb geo-

chronology and isotope geochemistry of the late Archean

Qorqut granite complex of southern West Greenland, Geo-

chim. Cosmochim. Acta 45 (1981) 1051–1060.

[53] M.C. Geraldes, Estudos geoquımicos e isotopicos das minera-

lizacoes aurıferas e rochas associadas da regiao de Pontes e

Lacerda (MT), MSc. thesis, Universidade Estadual de Campi-

nas, 1996, 104 p.

[54] W. Teixeira, C.C.G. Tassinari, U.G. Cordani, K. Kashawita,

A review of the geochronology of the Amazonian

craton: tectonic implications, Precambrian Res. 42 (1989)

213–227.

[55] C. Gariepy, C.J. Allegre, The lead isotope geochemistry and

geochronology of late-kinematic instrusives from the Abitibi

greenstone belt, and implications for late Archean crustal

evolution, Geochim. Cosmochim. Acta 49 (1985) 2371–2383.

[56] A.P. Dickin, R.H. McNutt, Nd model age mapping of the

southeast margin of the Archaen foreland in the Grenville

Province of Ontario, Geology 17 (1989) 299–302.

[57] T. Rivers, T., Lithotectonic elements of the Grenville Province:

review and tectonic implications, Precambrian Res. 86 (1997)

117–154.

[58] D.P. Moecher, E.C. Anderson, C.A. Cook, K. Mezger, The

petrogenesis of metamorphosed carbonatites in the Grenville

Province, Ontario Can. J. Earth Sci. 34 (1997) 1185–1201.

[59] O. Blein, M.R. LaFleche, L. Corriveau, Geochemistry of the

granulitic Bondy gneiss complex: a 1.4 Ga arc in the Central

Metasedimentary Belt, Grenville Province, Canada, Precam-

brian Res. 120 (2003) 193–217.

[60] W.R. Van Schmus, M.E. Bickford, A. Turek, Proterozoic

geology of the east-central midcontinent basement, Geol. Soc.

Am. Spec. Pap. 308 (1996) 7–32.

[61] W.R. Van Schmus, M.E. Bickford, J.L. Anderson, E.E.

Bender, R.R. Anderson, P.W. Bauer, J.M. Robertson, S.A.

Bowring, K.C. Condie, R.E. Denison, M.C. Gilbert, J.A.

Grambling, C.K. Mawer, C.K. Shearer, W.J. Hinze, K.E.

Karlstrom, E.B. Kisvarsanyi, E.G. Lidiak, J.C. Reed, P.K.

Sims, O. Tweto, L.T. Silver, S.B. Treves, M.L. Williams, J.L.

Wooden, Transcontinental Proterozoic provinces, Chapter 4

in: The Geology of North America, Precambrian: Contermi-

nous U.S., Geol. Soc. Am., Boulder, CO, Vol. C-2, 1993, pp.

171–334.

[62] D.R. Smith, C. Barnes, S. Shannon, R. Roback, E. James,

Petrogenesis of Mid-Proterozoic granitic magmas: examples

from central and west Texas, Precambrian Res. 85 (1997)

53–79.

[63] K.L. Cameron, R.L. Ward, Xenoliths of Grenvillian granulite

basement constrain models for the origin of voluminous

Tertiary rhyolites, Davis Mountains, west Texas, Geology 26

(1998) 1087–1090.

[64] J.O.E. Santos, L.A. Hartmann, H.E. Gaudette, D.I. Groves,

N.J. Mcnaughton, I.R. Fletcher, A new understanding of the

provinces of the Amazon craton based integration of field

mapping and U–Pb and Sm–Nd geochronology, Gondwana

Res. 3 (2000) 454–488.

[65] M.A.S.B. Pinho, F. Chemale, W.R. Van Schmus, F.E.C. Pinho,

U–Pb and Sm–Nd evidence for 1.76–1.77 Ga magmatism in

the Moriru region, Mato Grosso, Brazil: implications for

province boundaries in the SW Amazon craton, Precambrian

Res. 126 (2003) 1–25.

[66] M.J. Bartholomew, Palinspastic reconstruction of the Grenville

terrane in the Blue Ridge Geologica Province, southern and

central Appalachians, USA, Geol. J. 18 (1983) 241–253.

[67] H. Williams, R.D. Hatcher, Appalachian suspect terranes,

Geol. Soc. Am., Mem. 158 (1983) 33–53.

[68] M.J. Bartholomew, S.E. Lewis, Appalachian Grenville mas-

sifs: pre-Appalachian translational tectonics, Basement Tecton.

7 (1997) 363–374.

[69] R.D. Hatcher, Southern and central Appalachian basement

massifs, Geol. Soc. Am. Spec. Pap. 194 (1984) 149–153.

[70] D.W. Rankin, T.W. Stern, J. McLelland, R.E. Zartman, A.L.

Odom, Correlation chart for Precambrian rocks of the eastern

United States, in: J.E. Harrison, Z.E. Peterman (Eds.),


Correlation of Precambrian rocks of the United States and

Mexico: USGS Prof. Paper 1241-E, 1983, 18 pp.

[71] S.A. Goldberg, J.R. Butler, P.D. Fullagar, The Bakersville dike

swarm: geochronology and petrogenesis of late Proterozoic

basaltic magmatism in the southern Appalachian Blue Ridge,

Am. J. Sci. 286 (1986) 403–430.

[72] S. Qi, S.A. Goldberg, P.D. Fullagar, Precise U–Pb zircon ages

of Neoproterozoic plutons in the Southern Appalachian Blue

Ridge and their implications for the initial rifting of Laurentia,

Precambrian Res. 68 (1994) 81–95.

[73] J.N. Aleinikoff, R.E. Zartman, M. Walter, D.W. Rankin, P.T.

Lyttle, W.C. Burton, U–Pb ages of metarhyolites of the

Catoctin and Mount Rogers formations, Central and Southern

Appalachians; evidence for two pulses of Iapetan rifting, Am.

J. Sci. 295 (1995) 428–454.

[74] C.J. Ando, F.A. Cook, J.E. Oliver, L.D. Brown, S. Kaufman,

Crustal geometry of the Appalachian orogen from seismic

reflection studies, Geol. Soc. Am. Mem. 158 (1983) 83–101.

[75] L. Glover, R.E. Sheridan, W.S. Holbrook, J. Ewing, M.

Talwani, R.B. Hawman, P. Wang, Paleozoic collisions,

Mesozoic rifting, and structure of the Middle Atlantic states

continental margin: an bEDGEQ Project report, Geol. Soc. Am.

Spec. Pap. 314 (1997) 107–135.

[76] M.J. Bartholomew, S.E. Lewis, Evolution of Grenville

massifs in the Blue Ridge geologic province, southern and

central Appalachians, Geol. Soc. Am. Spec. Pap. 194 (1984)

229–254.

[77] J.N. Aleinikoff, W.C. Burton, P.T. Lyttle, A.E. Nelson, C.S.

Southworth, U–Pb geochronology of zircon and monazite

from Mesoproterozoic granitic gneisses of the northern Blue

Ridge, Virginia and Maryland, USA, Precambrian Res. 99

(2000) 113–146.

[78] H.S. Pettingill, A.K. Sinha, M. Tatsumoto, Age and origin of

anorthosite, charnockites, and granulites in the central Virginia

Blue Ridge, Nd and Sr isotopic evidence, Contrib. Mineral.

Petrol. 85 (1984) 279–291.

[79] C.W. Carrigan, C.F. Miller, P.D. Fullagar, B.R. Bream, R.D.

Hatcher, C.D. Coath, Ion microprobe age and geochemistry of

southern Appalachian basement, with implications for Protero

zoic and Paleozoic reconstructions, Precambrian Res. 120

(2003) 1–36.

[80] P.J. Berquist, C. Miller, P.D. Fullagar, C.W. Carrigan, S.

Ownby, B.R. Bream, R.D. Hatcher, J. Wooden, Anomalous

ancient crust in the southeastern USA: implications for the

assembly of North America and Rodinia, Geol. Soc. Am.

Abstr. Programs 35 (2003).

[81] S.E. Ownby, C.F. Miller, P.J. Berquist, C.W. Carrigan, J.L.

Wooden, P.D. Fullagar, U–Pb geochronology and geochemis-

try of a portion of the Mars Hill Terrane, North Carolina-

Tennessee: constraints on its origin, history and tectonic

assembly, Geol. Soc. Am. Mem. 197 (2004) 609–632.

[82] J.R. Monrad, G.L. Gulley, Age and P–Y conditions during

metamorphism of granulite facies gneisses, Roan Mountain,

NC–TN, in: S.E. Lewis (Ed.), Geological Investigations in the

Blue Ridge of Northwestern North Carolina, Carolina Geo-

logical Society Field Trip Guidebook, Virginia Polytechnic

Institute, 1983, pp. 41–52.

[83] S.A. Prevec, R.H. McNutt, A.P. Dickin, Sr and Nd isotopic

and petrological evidence for the age and origin of the White

Bear Arm Complex and associated units from the Grenville

Province in eastern Labrador, in: C.F. Gower, T. Rivers, B.

Ryan (Eds.), Mid-Proterozoic Laurentia-Baltica, Geol. Assoc.

Can. Spec. Pap. 38 (1990) 65–78.

[84] P.D. Fullagar, S.A. Goldberg, J.R. Butler, Nd and Sr isotopic

characterization of crystalline rocks from the southern

Appalachian Piedmont and Blue Ridge, North and South

Carolina, Geol. Soc. Am. Mem. 191 (1997) 165–179.

[85] A.K. Sinha, M.J. Bartholomew, Evolution of the Grenville

terrane in the central Virginia Appalachians, Geol. Soc. Am.

Spec. Pap. 194 (1984) 175–186.

[86] N. Walker, Middle Proterozoic geologic evolution of Llano

uplift, Texas: evidence from U–Pb zircon geochronometry,

Geol. Soc. Am. Bull. 104 (1992) 494–504.

[87] M.E. Bickford, K. Soegaard, K.C. Nielsen, J.M. McLelland,

Geology and geochronology of Grenville-age rocks in the Van

Horn and Franklin Mountains area, West Texas; implications

for the tectonic evolution of Laurentia during the Grenville,

Geol. Soc. Am. Bull. 112 (2000) 1134–1148.

Terrane transfer during the Grenville orogeny: tracing the Amazonian ancestry of southern...

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