Tethyan, Mediterranean, and Pacific analogues for the Neoproterozoic–Paleozoic birth and development of peri-Gondwanan terranes and their transfer to Laurentia and Laurussia

Abstract

Modern Tethyan, Mediterranean, and Pacific analogues are considered for several Appalachian, Caledonian, and Variscan terranes (Carolina, West and East Avalonia, Oaxaquia, Chortis, Maya, Suwannee, and Cadomia) that originated along the northern margin of Neoproterozoic Gondwana. These terranes record a protracted geological history that includes: (1) ∼1 Ga (Carolina, Avalonia, Oaxaquia, Chortis, and Suwannee) or ∼2 Ga (Cadomia) basement; (2) 750–600 Ma arc magmatism that diachronously switched to rift magmatism between 590 and 540 Ma, accompanied by development of rift basins and core complexes, in the absence of collisional orogenesis; (3) latest Neoproterozoic–Cambrian separation of Avalonia and Carolina from Gondwana leading to faunal endemism and the development of bordering passive margins; (4) Ordovician transport of Avalonia and Carolina across Iapetus terminating in Late Ordovician–Early Silurian accretion to the eastern Laurentian margin followed by dispersion along this margin; (5) Siluro-Devonian transfer of Cadomia across the Rheic Ocean; and (6) Permo-Carboniferous transfer of Oaxaquia, Chortis, Maya, and Suwannee during the amalgamation of Pangea. Three potential models are provided by more recent tectonic analogues: (1) an “accordion” model based on the orthogonal opening and closing of Alpine Tethys and the Mediterranean; (2) a “bulldozer” model based on forward-modelling of Australia during which oceanic plateaus are dispersed along the Australian plate margin; and (3) a “Baja” model based on the Pacific margin of North America where the diachronous replacement of subduction by transform faulting as a result of ridge–trench collision has been followed by rifting and the transfer of Baja California to the Pacific Plate. Future transport and accretion along the western Laurentian margin may mimic that of Baja British Columbia. Present geological data for Avalonia and Carolina favour a transition from a “Baja” model to a “bulldozer” model. By analogy with the eastern Pacific, we name the oceanic plates off northern Gondwana: Merlin (≡Farallon), Morgana (≡Pacific), and Mordred (≡Kula). If Neoproterozoic subduction was towards Gondwana, application of this combined model requires a total rotation of East Avalonia and Carolina through 180° either during separation (using a western Transverse Ranges model), during accretion (using a Baja British Columbia “train wreck” model), or during dispersion (using an Australia “bulldozer” model). On the other hand, Siluro-Devonian orthogonal transfer (“accordion” model) from northern Africa to southern Laurussia followed by a Carboniferous “Baja” model appears to best fit the existing data for Cadomia. Finally, Oaxaquia, Chortis, Maya, and Suwannee appear to have been transported along the margin of Gondwana until it collided with southern Laurentia on whose margin they were stranded following the breakup of Pangea. Forward modeling of a closing Mediterranean followed by breakup on the African margin may provide a modern analogue. These actualistic models differ in their dictates on the initial distribution of the peri-Gondwanan terranes and can be tested by comparing features of the modern analogues with their ancient tectonic counterparts.

Full text

Tethyan, Mediterranean, and Pacific analogues for the
Neoproterozoic–Paleozoic birth and development of
peri-Gondwanan terranes and their transfer to Laurentia
and Laurussia
J. Duncan Keppie
a,
*, R. Damian Nance
b
, J. Brendan Murphy
c
, J. Dostal
d
a
Instituto de Geologia, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F., Mexico
b
Department of Geological Sciences, Ohio University, Athens, OH 45701, USA
c
Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Canada B2G 2W5
d
Department of Geology, St. Mary’s University, Halifax, Nova Scotia, Canada B3H 3C3
Received 8 January 2002; accepted 14 August 2002
Abstract
Modern Tethyan, Mediterranean, and Pacific analogues are considered for several Appalachian, Caledonian, and Variscan
terranes (Carolina, West and East Avalonia, Oaxaquia, Chortis, Maya, Suwannee, and Cadomia) that originated along the
northern margin of Neoproterozoic Gondwana. These terranes record a protracted geological history that includes: (1) f1Ga
(Carolina, Avalonia, Oaxaquia, Chortis, and Suwannee) or f2 Ga (Cadomia) basement; (2) 750–600 Ma arc magmatism that
diachronously switched to rift magmatism between 590 and 540 Ma, accompanied by development of rift basins and core
complexes, in the absence of collisional orogenesis; (3) latest Neoproterozoic –Cambrian separation of Avalonia and Carolina
from Gondwana leading to faunal endemism and the development of bordering passive margins; (4) Ordovician transport of
Avalonia and Carolina across Iapetus terminating in Late Ordovician– Early Silurian accretion to the eastern Laurentian margin
followed by dispersion along this margin; (5) Siluro-Devonian transfer of Cadomia across the Rheic Ocean; and (6) Permo-
Carboniferous transfer of Oaxaquia, Chortis, Maya, and Suwannee during the amalgamation of Pangea. Three potential models
are provided by more recent tectonic analogues: (1) an ‘‘accordion’’ model based on the orthogonal opening and closing of
Alpine Tethys and the Mediterranean; (2) a ‘‘bulldozer’’ model based on forward-modelling of Australia during which oceanic
plateaus are dispersed along the Australian plate margin; and (3) a ‘‘Baja’’ model based on the Pacific margin of North America
where the diachronous replacement of subduction by transform faulting as a result of ridge – trench collision has been followed
by rifting and the transfer of Baja California to the Pacific Plate. Future transport and accretion along the western Laurentian
margin may mimic that of Baja British Columbia. Present geological data for Avalonia and Carolina favour a transition from a
‘‘Baja’’ model to a ‘‘bulldozer’’ model. By analogy with the eastern Pacific, we name the oceanic plates off northern
Gondwana: Merlin ( uFarallon), Morgana ( uPacific), and Mordred ( uKula). If Neoproterozoic subduction was towards
Gondwana, application of this combined model requires a total rotation of East Avalonia and Carolina through 180jeither
during separation (using a western Transverse Ranges model), during accretion (using a Baja British Columbia ‘‘train wreck’’
model), or during dispersion (using an Australia ‘‘bulldozer’’ model). On the other hand, Siluro-Devonian orthogonal transfer
(‘‘accordion’’ model) from northern Africa to southern Laurussia followed by a Carboniferous ‘‘Baja’’ model appears to best fit
0040-1951/03/$ - see front matter D2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0040-1951(03)00037-4
* Corresponding author.
E-mail address: duncan@servidor.unam.mx (J.D. Keppie).
www.elsevier.com/locate/tecto
Tectonophysics 365 (2003) 195– 219

the existing data for Cadomia. Finally, Oaxaquia, Chortis, Maya, and Suwannee appear to have been transported along the
margin of Gondwana until it collided with southern Laurentia on whose margin they were stranded following the breakup of
Pangea. Forward modeling of a closing Mediterranean followed by breakup on the African margin may provide a modern
analogue. These actualistic models differ in their dictates on the initial distribution of the peri-Gondwanan terranes and can be
tested by comparing features of the modern analogues with their ancient tectonic counterparts.
D2003 Elsevier Science B.V. All rights reserved.
Keywords: Analogues; Neoproterozoic – Paleozoic birth; Peri-Gondwanan terranes
1. Introduction
The Appalachian–Caledonian orogen was once
considered a two-sided, symmetrical system that was
interpreted in terms of geosynclinal theory in which a
major syncline was telescoped into an orogen (Kay,
1951; Williams, 1964). With the advent of plate
tectonics, this interpretation was replaced by orthog-
onal opening and closing of an ocean, now termed
Iapetus, between eastern Laurentia and a continental
landmass (Avalonia–Carolina: defined below)
thought to border Western Europe and northwest
Africa (Dewey, 1969). The terms Avalonia, Carolina,
and Cadomia are used here to include a collection of
terranes previously grouped as the Avalon Zone or
Composite Terrane (Fig. 1) (e.g. Williams, 1979;
Keppie, 1985), the Carolina Zone, which includes
the Carolina, Spring Hope, and Roanoke Rapids
terranes (e.g. Williams, 1979), or the Avalonian–
Cadomian belt (e.g. Murphy and Nance, 1989). How-
ever, data accumulated over the past 25 years suggests
that Avalonia– Carolina and eastern Laurentia were
not conjugate rift margins during the opening of
Iapetus (e.g. Keppie, 1977; Dalziel, 1992; Nance
and Thompson, 1996; Keppie et al., 1998). This
evidence includes: (1) the recognition that the north-
western margin of Neoproterozoic Avalonia–Caro-
lina–Cadomia was an active margin at the same
time that the eastern margin of Laurentia was a
developing rift-passive margin (Keppie, 1985, 1989;
Cawood et al., 2001); (2) the realization that Neo-
proterozoic subduction in Avalonia– Carolina – Cado-
mia was both long-lived ( f170 Ma) and terminated,
not in collisional orogenesis, but with a transition to
an early Cambrian platform (Keppie, 1982; Murphy
and Nance, 1989; Nance et al., 1991); (3) the accu-
mulation of isotopic data indicating that Avalonia and
Carolina are underlain by a f1 Ga basement and
contain a f1 Ga detritus in Neoproterozoic units that
have been linked with f1 Ga orogens that encircle
the Amazon craton ( f1 Ga orogens are absent in the
West African craton)(Keppie and Krogh, 1990; Mur-
phy et al., 1996, 2000; Keppie et al., 1998; Hibbard et
al., 2002); and (4) the evolution of models based on
subsidence curves, f1 Ga Rodinia supercontinent
reconstructions, and paleomagnetic data, that suggest
eastern Laurentia lay adjacent to western South Amer-
ica prior to the birth of Iapetus (e.g. Figs. 2 and 3)
(Bond et al., 1984; Hoffman, 1991; Dalziel, 1992;
Keppie, 1993; Keppie and Ramos, 1999). Paleonto-
logical and paleomagnetic data suggest that Avalo-
nia–Carolina– Cadomia originated as peri-Gond-
wanan terranes distributed along the northern margin
of Amazonia–northwest Africa, although their rela-
tive locations along this margin may have varied with
time (e.g. Keppie et al., 1996; Keppie and Ramos,
1999). This evidence has spawned a series of models
for the transfer of these terranes from Gondwana to
Laurentia (from Cambrian separation to Late Ordovi-
cian – Early Silurian accretion) (e.g. Keppie, 1993;
Strachan et al., 1996; Keppie et al., 1996; Keppie
and Ramos, 1999; Murphy et al., 1999; Hibbard,
2000; Linnemann et al., 2000; Franke et al., 2000;
Hibbard et al., 2002; Nance et al., 2002). The
improved database has reached the stage where more
actualistic models may be constructed. This paper
presents a summary of the geological records of these
peri-Gondwanan terranes from which are derived
actualistic plate tectonic models for their transfer to
eastern Laurentia and Laurussia.
Potential modern analogues include Alpine Tethys,
the Pacific Ocean, and the Mediterranean Sea. We
conclude that the Late Paleozoic – Cenozoic plate tec-
tonics of the eastern Pacific Ocean (e.g. Debiche and
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219196

Fig. 1. Pangea A reconstruction (modified after Keppie and Ortega-Gutie
´rrez, 1999; Weil et al., 2001) showing the location of peri-Gondwanan terranes and the inferred polarity of
Neoproterozoic subduction. Abbreviations: A = Atlanta, B = Boston, Br = Brunia (includes Moravo-Silesia and W. Sudetes), CBI = Cape Breton Island, Ch = Chortis, CI = Central
Iberia, Cp = Chiapas, F = Floresta , G = Garzo
´n, Gu = Guajira, H = Huiznopala, I = Ireland, M = Mixtequit a, MA= Me
´rida Andes, MN = Moldanubian, N = Newfoun dland,
No = Novillo, OM = Ossa-Morena Ox = Oaxacan Complex, Q = Quetame, RH = Rheno-Hercynian, S = Santander, SM = Santa Marta, ST = Saxo-Thuringian, W = Washington.
OAXAQUIA comprises Huiznopala, Mixtequita, Novillo, and Oaxacan Complex.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 197

Engebretson, 1987; Van Staal et al., 1998) provides the
closest analogue for the Neoproterozoic –Early Cam-
brian history of the peri-Gondwanan terranes, whereas
the future history of Australian invasion of the Pacific
Ocean provides a reasonable analogue for their Early
Paleozoic history. Application of Pacific models to
these terranes has an important bearing on their initial
arrangement, which can be evaluated using a variety of
provenance data including basement signatures, Cam-
brian faunal provinciality, paleomagnetic data, and
detrital zircon ages.
2. Peri-Gondwanan terranes
Peri-Gondwanan terranes in this paper are limited to
those presently located in the Appalachian, Caledo-
nian, and Variscan orogens that originated adjacent to
Amazonia and northwest Africa. These comprise Ava-
lonia and Carolina, which were accreted during the
Late Ordovician–Early Silurian (N.B. some authors
prefer a Carboniferous time of accretion for Carolina),
Cadomia and Bohemia, which were accreted during the
Siluro-Devonian, and Oaxaquia, Chortis, Maya, and
Fig. 2. An end member, side-by-side arrangement of the peri-Gondwanan terranes at 550 Ma (see text for detailed discussion). Abbreviations as
in Fig. 1 plus: C = Carolina, EA = East Avalonia, G = Gander terrane, M = Meguma terrane, WA= West Avalonia (modified after Keppie and
Ramos, 1999).
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219198

Suwannee, which were accreted in the Permo-Carbon-
iferous. Several reviews of the peri-Gondwanan ter-
ranes have been published recently (Keppie, 1994;
Nance and Thompson, 1996; Ramos and Keppie,
1999; Murphy et al., 1999; Franke et al., 2000; Hibbard
et al., 2002; Nance et al., 2002). This paper represents a
companion to Nance et al. (2002). Consequently, the
summaries presented below will focus on those points
essential for establishing actualisitic plate tectonic
models: (1) basement age; (2) polarity of Neoproter-
ozoic subduction; (3) timing of the cessation of sub-
duction and the switch from arc to rift magmatism; (4)
factors bearing on the provenance of the terranes; (5)
timing of separation from Gondwana; and (6) timing of
accretion with Laurentia –Laurussia.
2.1. f1 Ga basement terranes
2.1.1. Oaxaquia–Chortis
The f1 Ga basements of Oaxaquia and the
Chortis block underlie most of Mexico and Honduras,
an area of 1,000,000 km
2
(Fig. 1). Currently, there are
widely divergent views on their provenance. One
view holds that they represent an autochthonous
extension of the Grenville Orogen of eastern and
southern Laurentia (e.g. Karlstrom et al., 1999),
whereas another view proposes that they are exotic
terranes derived either from Amazonia or northeastern
Laurentia (Ortega-Gutie
´rrez and Keppie, 2000; Kep-
pie et al., 2001, 2003, and references therein). The
Oaxacan Complex of southern Mexico, which appears
to be representative of Oaxaquia and the Chortis
block, consists of (1) a metavolcanic-metasedimentary
juvenile arc sequence of unknown polarity and age;
(2) a f1140 Ma, bimodal, within-plate intrusive
suite that was deformed, metamorphosed, and mig-
matized at f1100 Ma; (3) a f1012 Ma anortho-
site-gabbro that was deformed and metamorphosed in
the granulite facies at f980–1104 Ma; and (4) a
f920 Ma post-tectonic calc-alkaline pluton that has
been related to subduction of unknown polarity (Kep-
pie et al., 2001, 2003; Ortega-Obregon, 2002).
This basement complex is unconformably overlain
by the Lower Ordovician Tin
˜u Formation, which
contains trilobites of Gondwanan affinity in outer
shelf-slope deposits (Robison and Pantoja-Alor,
1968; R. Robison, written comm., 1998). On these
grounds, together with their mutually similar Meso-
proterozoic geological records, it has been suggested
that Oaxaquia and the Chortis block may have been
derived from the gap north of Colombia in the circum-
Gondwanan, Ordovician facies belts on the northwest-
ern margin of Amazonia (e.g. Figs. 2 and 3)(Cocks
and Fortey, 1988; Keppie and Ortega-Gutierrez, 1995;
Keppie et al., 2001). The same location was chosen by
Keppie (1977) and Boucot et al. (1997) based on the
close affinity between Silurian fauna in rocks uncon-
formably overlying the f1 Ga Novillo Gneiss in
northeastern Mexico and those in Venezuela (Fig. 1).
Such a provenance is also in accord with the detrital
zircon ages (980–1230 Ma) in the Tin
˜u Formation,
which may be derived from the Oaxacan Complex
and f1 Ga basement found in many northern
Andean massifs (Gillis et al., 2001). The absence of
Cambrian rocks in Mexico coincides with the separa-
tion of the peri-Gondwanan terranes, and may be
related to the thermal uplift and erosion that com-
monly precedes thermal requilibration and deposition
of rift–drift sequences.
The lower Paleozoic rocks of Oaxaquia (Fig. 1) are
unconformably overlain by Carboniferous and Per-
mian rocks that herald the appearance of fauna with
Laurentian affinities in the Mississippian (Sour-Tovar
et al., 1996; Stewart et al., 1999). This interpretation is
borne out by the detrital zircon record, which indi-
cates that Oaxaquia was isolated from the southern
margin of Laurentia until the Carboniferous (Gillis et
al., 2001). It is also consistent with paleomagnetic
data that would locate Oaxaquia off either Amazonia
or northeastern Laurentia (Ballard et al., 1989; Keppie
and Ortega-Gutie
´rrez, 1999). Such data led Keppie
and Ramos (1999) to place an ocean between Oax-
aquia and Laurentia until Permo-Carboniferous times,
in contrast to Ortega-Gutie
´rrez et al. (1999) who
propose a collision between Oaxaquia and eastern
Laurentia in the Late Ordovician – Silurian.
2.1.2. Maya terrane
The Maya terrane of the Yucatan Peninsula (Fig. 1)
represents a block that was rotated f60janticlock-
wise during the Early Mesozoic opening of the Gulf
of California (Molina-Garza et al., 1992; Dickinson
and Lawton, 2001). Restoration of this rotation sug-
gests former continuity with Oaxaquia (Fig. 1). The
Mixtequita inlier near the southern border of the
terrane contains f1.23 Ga orthogneisses metamor-
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 199

phosed under granulite facies at 990 – 975 Ma (Weber
and Ko¨hler, 1999; Ruiz et al., 1999), factors that
suggest it represents part of Oaxaquia. Zircons from
plutonic rocks found in boreholes in the Yucatan
Peninsula have yielded late Neoproterozoic ages
(Krogh et al., 1993), and Late Silurian ages have been
recorded in plutons in the Maya Mountains (Steiner
and Walker, 1996). The relationship between these
units is not exposed. But, if the f1 Ga rocks form
the basement beneath the Maya terrane, a history
similar to that of Oaxaquia may be assumed (Keppie
and Ramos, 1999).
2.1.3. Suwannee terrane: Florida
Although the Suwannee terrane (Fig. 1) is covered
by Phanerozoic rocks, boreholes have yielded the
following sequence: (1) a Mesoproterozoic basement
recorded by 1060 –1240 Ma
207
Pb/
206
Pb zircon ages
in a granitoid (Heatherington et al., 1993) and T
DM
model ages of 1580–1040 Ma in latest Neoprotero-
Fig. 3. An end member, end-to-end arrangement of the peri-Gondwanan terranes between 700 and 600 Ma, assuming the present order and
subduction polarity applies to the Neoproterozoic, and backward modeled to remove 150– 200 million years of subduction (see text for detailed
discussion). Abbreviations are as in Figs. 1 and 2. Modified after Keppie and Ramos (1999).
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219200

zoic igneous suites (Heatherington et al., 1996); (2)
f625 and f552 Ma, calc-alkaline igneous suites
related to subduction of unknown polarity (Heather-
ington et al., 1996); and (3) unconformably overlying,
undeformed Ordovician –Devonian rocks containing
high-latitude trilobite and acritarch fauna of Gond-
wanan affinity that have generally been correlated
with the Bove Basin of West Africa (Whittington
and Hughes, 1974; Cramer and Diez, 1974).Sucha
provenance is consistent with available paleomagnetic
data (Opdyke et al., 1987). The Cambrian hiatus may
have a similar origin to that of Oaxaquia. The
Suwannee terrane was accreted to southern Laurentia
during the Permo-Carboniferous amalgamation of
Pangea at f300 Ma (Heatherington et al., 1996).
2.1.4. Carolina
Carolina comprises many Neoproterozoic terranes
(e.g. Carolina, Spring Hope, Roanoke Rapids, etc.)
located along the eastern margin of the southern
Appalachians. It surrounds on three sides and is in
tectonic contact with the f1 Ga Goochland terrane,
which has been interpreted as either Laurentian base-
ment or an exotic terrane (Hibbard et al., 2002).
Carolina consists of a f635–580 Ma juvenile oce-
anic-continental arc that was deformed in the Virgilina
orogeny prior to the deposition of a f580 – 540 Ma
mature arc sequence (Hibbard et al., 2002).The
mature arc is unconformably overlain by Middle
Cambrian sedimentary and bimodal volcanic rocks
containing mixed Tethyan– Avalonian, cool-water tri-
lobites that share faunal affinities with Armorica,
Gondwana, and Avalonia (Theokritoff, 1979; Samson
et al., 1995). 1.1 –1.8 Ga detrital zircons in these
Cambrian quartzites (Samson et al., 1999, 2001)
suggest a provenance in Amazonia. The age of the
basement beneath Carolina has been inferred from ion
microprobe analyses on igneous zircons in Neoproter-
ozoic volcanic suites, which yielded ages of 965 –
1229 Ma (Mueller et al., 1996). This is consistent with
the T
DM
model ages of 1.1–0.7 Ga reported on the
f635–580 Ma juvenile arc sequence (Samson et al.,
1995; Wortman et al., 2000). In contrast to the high
paleolatitudes of other peri-Gondwanan terranes, pale-
omagnetic data from latest Precambrian – Cambrian
units indicate a low paleolatitude for Carolina
(15jS: Vick et al., 1987), but may have undergone
remagnetization (Van der Voo, 1993). Based upon
arc–backarc spatial geometry, Dennis and Wright
(1997) have proposed that subduction was towards
the southeast (present coordinates) during the Neo-
proterozoic. This is consistent with the proposal that
the switch in isotopic arc signatures from juvenile to
mature was related to eastward thrusting of the f1
Ga Goochland terrane under Carolina during the
Virgilina orogeny (Hibbard and Samson, 1995).
Although separation of Carolina from Gondwana
has not been documented, its oblique sinistral accre-
tion to eastern Laurentia appears to have taken place
in the Late Ordovician–Early Silurian (Hibbard,
2000; Hibbard et al., 2002), although other authors
argue for Carboniferous accretion (e.g. Hatcher,
1989).
2.1.5. Avalonia
Avalonian rocks have been recorded on both sides
of the Atlantic Ocean and include West Avalonia from
Boston (USA) through Maritime Canada to the Ava-
lon Peninsula of Newfoundland, and East Avalonia
from southeast Ireland, Wales, and southern England,
through the Rheno–Hercynian zone and the Czech
West Sudetes, into the Moravo– Silesian and Brunia
zones on the southeastern side of the Bohemian
massif (Fig. 1) (Murphy et al., 1999; Freidl et al.,
2000; Kro¨ner et al., 2000, 2001; Nance et al., 2002,
and references therein). Unequivocal basement is not
exposed. However, T
DM
model ages in Late Neo-
proterozoic and Paleozoic ( f730–370 Ma) igneous
suites range from 0.8 to 1.1 Ga in West Avalonia and
from 1.0 to 1.8 Ga in East Avalonia (Thorogood,
1990; Murphy et al., 2000; Hegner and Kro¨ ner, 2000;
Nance et al., 2002, and references therein). These ages
are in accord with the few available SHRIMP analyses
of xenocrystic zircons that cluster around 1.2 Ga
(Hegner and Kro¨ner, 2000; Freidl et al., 2000, and
references therein). However, the model ages older
than 1.2 Ga suggest the additional presence of Pale-
oproterozoic source rocks in East Avalonia. In north-
western Cape Breton Island, an allochthonous f1
Ga basement block (Blair River Complex) has been
correlated with both the type Grenville orogen (Miller
et al., 1996) and Oaxaquia (Keppie et al., 2000).
Ayuso et al. (1996) inferred that the Pb isotopic data
from Neoproterozoic igneous rocks across Cape Bre-
ton Island represent mixtures of this Blair River
basement and typical Avalonian crust implying that
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 201

they were juxtaposed by the Neoproterozoic. The
Blair River Complex consists of gneiss with a proto-
lith age of z1.2 Ga that was metamorphosed at
f1035 Ma, intruded by syenite at 1080 Ma, and then
remetamorphosed in the upper amphibolite – granulite
facies between 1000 and 970 Ma (Miller et al., 1996).
The Neoproterozoic rocks of Avalonia record three
stages of arc development: (1) an early stage (750 –
635 Ma) represented by isolated inliers with both arc-
and rift-related igneous rocks; (2) a main stage
recorded in voluminous magmatic arc rocks associ-
ated with a variety of intra-arc, interarc, and backarc
basin deposits dominated by volcanogenic turbidites
that started synchronously at f635 Ma but switched
diachronously into (3) late stage, rift-related volcan-
ism and sedimentation at f590 Ma in New England,
f560 Ma in southern New Brunswick, f550 Ma in
Cape Breton Island, f570 Ma in Newfoundland,
f550–540 Ma in Britain, and f550 Ma in Brunia
(Murphy et al., 1999; Kro¨ner et al., 2000, 2001;
Nance et al., 2002). In East Avalonia, south-directed
subduction is indicated by the presence of late stage,
550–560 Ma blueschists in Angelsey (Dallmeyer and
Gibbons, 1987). In West Avalonia (southern New
Brunswick and Nova Scotia), on the other hand, arc
to backarc spatial relationships and variations in q
Nd
and rare earth elements during the main and late
stages suggest that the subduction zone dipped
towards the northwest (present coordinates) (Dostal
et al., 1996; Keppie et al., 1998; Murphy et al., 1999).
In Cape Breton Island, the apparent northward migra-
tion (present coordinates) of the main – late stage arc
may be due to shallowing of the subduction zone
(Keppie et al., 1998). The possibility that this migra-
tion is due to subduction erosion is not supported by
the presence of material with velocities of 6.6 – 6.8
km/s in southern Cape Breton Island, which, if this
material is Neoproterozoic (Jackson et al., 2000),
suggests that the lower crust has not been removed.
A nonaccreting margin is also suggested by the
synchronous compressive deformation in the backarc
region of mainland Nova Scotia and central Cape
Breton Island. In parts of West Avalonia (Cobequid
and Antigonish Highlands), 690– 630 Ma sinistral
transtension produced backarc basins that were
inverted by dextral transpression at 610 Ma (Nance
and Murphy, 1990; Keppie et al., 2000). In central
Cape Breton Island, mainland Nova Scotia, and south-
ern New Brunswick, a f550 Ma, initially subhor-
izontal shear zone (now near-vertical in southern New
Brunswick) separating low from high grade (low
pressure–high temperature) Neoproterozoic metamor-
phic rocks (Nance and Murphy, 1990; Raeside and
Barr, 1990; Nance and Dallmeyer, 1994) may be
interpreted in terms of core complex tectonics (Keppie
et al., 1998, 2000), and indicates that the region had
passed into extension by this time.
A paleolatitude for West Avalonia of 34jF8jat
575 Ma (McNamara et al., 2001) is consistent with a
location either off northwest Africa or Amazonia and/
or Oaxaquia (Murphy et al., 2002). Ages of 977 –
1223 Ma for euhedral detrital zircons in locally
derived sedimentary rocks of the early and main arc
stages favour a nearby source in Amazonia and/or
Oaxaquia (Murphy and MacDonald, 1993; Keppie et
al., 1998). 980–1255 Ma ages from detrital zircons in
the West Sudetes and Moravo– Silesian point to a
similar source (Hegner and Kro¨ner, 2000).
Latest Neoproterozoic –Cambrian rocks in Avalo-
nia show a general NW to SE trend from marginal to
inner platform (Landing, 1996) associated, in the
Antigonish Highlands, with a dextral pull-apart basin
(e.g. Keppie and Murphy, 1988). These Cambrian
sequences contain a unique Avalonian fauna that is
distinct from those in Gondwana, Baltica, and Lau-
rentia (Landing, 1996), suggesting the existence of a
barrier to faunal migration in the Cambrian. In Nova
Scotia, these Cambrian sedimentary rocks are inter-
bedded with bimodal volcanic rocks that are tholeiitic,
where they lie above 580 – 550 Ma arc rocks, and
alkalic, where they rest on older Neoproterozoic arc
rocks. In East Avalonia, subsidence curves indicate
that the rift –drift transition occurred during the early
Ordovician (Prigmore et al., 1997). This is consistent
with the increasing faunal endemism (Cocks, 2000)
and paleomagnetic data (Trench and Torsvik, 1992).
Accretion of Avalonia to Laurentia and Baltica is
indicated by (1) paleomagnetic data, which indicates
similar Early Silurian paleolatitudes for Avalonia and
eastern Laurentia (Miller and Kent, 1988; Trench and
Torsvik, 1992; Potts et al., 1993; Hodych and Buchan,
1994; Mac Niocaill et al., 1997); (2) faunal linkages
by the Late Ordovician (Williams et al., 1995); (3) a
switch from primitive to mature Nd isotopic signa-
tures in sedimentary rocks at the base of the Silurian
in West Avalonia (Murphy et al., 1996); (4) an Early
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219202

Silurian sequence interpreted to overstep the entire
Canadian Appalachian orogen (Chandler et al., 1987);
and (5) Late Ordovician –Early Silurian accretionary
deformation with a sinistral transpressional compo-
nent (Pickering et al., 1988; Currie and Piaseki, 1989;
Doig et al., 1990; Soper et al., 1992; Keppie, 1993;
Cawood et al., 1994).
Avalonia is tectonically bordered by Cambro-
Ordovician continental rise prisms represented by
the Gander–Greenore and Meguma (limited to West
Avalonia) terranes (Fig. 2). The age of the Gander
rocks is constrained between 545 m.y. (youngest
detrital titanite) and the conformably to unconform-
ably overlying late Arenig – Llanvirn volcano sedi-
mentary rocks containing a Celtic fauna (Neuman,
1984; Colman-Sadd et al., 1992; Van Staal et al.,
1996). Detrital zircons in the Gander rocks have also
yielded the following ages: 540 – 550 Ma, 600–800
Ma, 1.0–1.55 Ga, and 2.5–2.7 Ga (Van Staal et al.,
1996, and references therein). In the Meguma terrane,
the age of the Meguma Group is constrained between
552 Ma (youngest detrital titanite) near the base, and
the Tremadocian (graptolites) near the top: it is dis-
conformably overlain by Silurian–Devonian rocks
that have been correlated with the sequence inter-
preted to overstep the Appalachian orogen (Krogh and
Keppie, 1990; Keppie and Krogh, 2000). Detrital
zircons in the Meguma Group fall into the following
age groups: 560 –680 Ma, f2 Ga, and f3Ga
(Krogh and Keppie, 1990). On the other hand, xen-
oliths in f370 Ma mafic dykes cutting the Meguma
terrane yielded upper intercept ages of 880 –1050 Ma
inferred to indicate a f1 Ga basement (Greenough et
al., 1999).Greenough et al. (1999) infer that the
source of these f1 Ga zircons lies in Avalonian
basement thrust beneath the Meguma terrane in the
Devonian. However, the potential presence of a
Siluro-Devonian trans-Appalachian overstep sequence
in the Meguma terrane suggests that by Silurian times
it already lay adjacent to Avalonia and may have been
depositedonanAvalonianbasement(Keppie and
Krogh, 2000).
2.2. f2 Ga basement terranes: Cadomia and
Bohemia
Terranes with f2 Ga basements, such as the
Central Iberian zone, the Armorican Massif, the
Massif Central, and the Saxo-Thuringian and Molda-
nubian zones, have generally been included in the
Armorican Terrane Assemblage (Tait et al., 2000;
Linnemann et al., 2000) and are here called Cadomia
and Bohemia (Fig. 1). Cadomia includes the Ossa-
Morena and Central Iberian zones of the Iberian
massif, and the French Armorican and Central mas-
sifs. The Saxo-Thuringian and Moldanubian zones in
the Bohemian massif of central Europe may also be
included in Cadomia.
Cadomian basement is represented by the 2.2 –
1.8 Ga Icart Gneiss exposed in Brittany (Samson
and D’Lemos, 1998). Sm–Nd isotopic data for the
crustally derived Neoproterozoic arc rocks of Cado-
mia in northern France and the Channel Islands
record T
DM
model ages that range from 1.0 to 1.9
Ga and are interpreted to reflect mixing of material
derived from the mantle at ca. 600 Ma with the ca.
2.1 Ga Icartian continental basement (D’Lemos and
Brown, 1993). This basement is isotopically indis-
tinguishable from that of the ca. 2.0 Ga Eburnian
Province in the West Africa craton (Nance and
Murphy, 1994, 1996). A similar Eburnian (2.1–1.7
Ga) event has been recorded in U – Pb analyses of
zircon from igneous bodies of the Saxo-Thuringian
and Moldanubian zones (Wendt et al., 1993; Linne-
mann et al., 2000).
Two Neoproterozoic magmatic stages are recog-
nized in Cadomia: (1) an early phase represented by
the 746 F17 Ma Pentevrian orthogneisses in north-
west France, which were deformed and metamor-
phosed at 650–615 Ma; and (2) a main stage that
lasted from f615 to 560 Ma and terminated with
tectonothermal activity at 570–540 Ma (Quesada,
1990; Chantraine et al., 1994, 2001; Egal et al.,
1996; Strachan et al., 1996; Linnemann et al., 2000;
Eguı
´luz et al., 2000; D’Lemos et al., 2001,and
references therein). Polarity inferred from the relative
locations of the arc and backarc suggests that the
subduction zone dipped northwards in France (Chan-
traine et al., 2001) swinging around the Armorican arc
to dip southwards towards the Ossa Morena ( uNW
Africa craton) basement in Iberia (Quesada, 1997) (all
present coordinates). Weil et al. (2001) published
paleomagnetic data that suggest the Armorican arc
results from Permo-Carboniferous oroclinal bending
of an originally N –S linear belt. Arc magmatism in
Cadomia ended with sinistral wrench tectonics, fol-
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 203

lowed by widespread migmatization, and post-tec-
tonic granitoid emplacement at f570–540 Ma
(Rabu et al., 1990; Chantraine et al., 1994, 2001;
Strachan et al., 1996; Egal et al., 1996). Proximity of
Cadomia to the West African craton is indicated by
the presence of residual bauxitic and lateritic sedi-
mentary rocks in Central Iberia that correlate with
those in the NW African craton (Quesada, 1997), and
1.8–2.2 Ga and Archean detrital zircon ages (coupled
with the lack of f1 Ga ages) in latest Neoproter-
ozoic sedimentary rocks from the northern part of
French Armorica, the Ossa-Morena zone of Iberia,
and the Saxo-Thuringian zone (Gebauer et al., 1989;
Samson et al., 1999; Gutie
´rrez-Alonso et al., 2001;
Tichomirowa et al., 2001). Such ages are accompa-
nied by 950–1300 Ma ages in detrital zircons from
the Central Iberian zone, the Montagne Noire (French
Central Massif), and the Moldanubian zone (Bohe-
mian massif) (Gebauer, 1994; Gebauer et al., 1989;
Fernandez-Sua
´rez et al., 2000). Since these latter
regions are underlain by f2 Ga basement, the record
of f1 Ga detrital zircons suggests water-borne
transport from a Mesoproterozoic source.
The Neoproterozoic rocks are unconformably over-
lain by Cambrian, bimodal volcanic rocks and sedi-
mentary rocks that contain Tethyan faunas and
Archeocyathids, common to the northern Gondwanan
margin (Dore
´, 1994; Robardet et al., 1994).The
Arenigian Armorican quartzite is widespread through-
out Cadomia and contains 1.0 – 1.1 Ga detrital zircons
(Gutie
´rrez-Alonso, 2001), which indicates either a
primary source in Mesoproterozoic orogens or recy-
cling of underlying sediments, such as those found in
the Central Iberian zone. Paleomagnetic data suggest
that, by the Late Ordovician, Armorica had rifted
away from Africa and lay at 40jS(Taitetal.,
2000). This is consistent with the presence of Ashgil-
lian glacial deposits interpreted to represent drop-
stones from floating ice during a period of global
cooling (Brenchley et al., 1991). Late Silurian to Early
Devonian paleomagnetic data record paleolatitudes of
20–30jS and indicate a continued northward drift of
Cadomia (Tait et al., 2000). Faunal endemism per-
sisted throughout the Silurian and into the Emsian and
Givetian, but disappeared in mid-Devonian times with
the closure of the Rheic Ocean as Armorica collided
with Laurussia (Kriz and Paris, 1982; Tait et al.,
2000).
2.3. Summary and questions
Peri-Gondwanan terranes may be separated into two
groups on the basis of the age of their basement, either
f2or f1Ga(Fig. 1). The f2 Ga basement of
Cadomia extends from Iberia and NW France into the
Saxo-Thuringian and Moldanubian zones of central
Europe. This distribution matches the areal extent of
similar basement in northwest Africa, which, combined
with faunal, paleomagnetic, and paleoclimatic data,
suggests that these terranes are of local provenance.
On the other hand, terranes with f1 Ga basement may
be traced from Mexico through eastern Laurentia
(Carolina–West Avalonia), the southern British Isles,
and the Rheno–Hercynian zone of northern Europe,
around the Bohemian massif into Brunia. With some
gaps, a f1 Ga orogenic belt surrounds the Amazon
craton, and one approach has been to derive the f1
Ga peri-Gondwanan terranes from areas adjacent to the
northwest and northern margins of Amazonia (e.g.
Nance and Murphy, 1994, 1996; Keppie and Ramos,
1999; Hegner and Kro¨ner, 2000). But at this point, a
question arises: is it possible that the f1 Ga orogen
encircling Amazonia had a branch around the northern
margin of Africa? This would drastically reduce the
amount of lateral motion (up to 7000 km) required to
disperse the peri-Gondwanan terranes to their present
positions along the Appalachian –Caledonian –Varis-
can orogen. However, such a branch has not been
proposed by anyone and would be difficult to reconcile
with the complete absence of f1 Ga detrital zircons in
the Neoproterozoic sedimentary successions of south-
ern Iberia, NW France, and the Saxo-Thuringian zone
(Gebauer et al., 1989; Samson et al., 1999; Gutie
´rrez-
Alonso et al., 2001; Tichomirowa et al., 2001). Dis-
placements of up to 5000 km have been proposed for
Baja British Columbia along the Cordilleran margin of
western Laurentia (e.g. Beck, 1991; Cowan et al., 1997;
Keppie and Dostal, 2001, and references therein), and
forward modeling of Australia shows that accreted
terranes will be bulldozed and dispersed along the side
of Australia for up to 8000 km (Van Staal et al., 1998).
Could either of these mechanisms be applied to the
displacements required for the f1 Ga peri-Gond-
wanan terranes?
Current interpretations show that the polarity of the
Neoproterozoic subduction zones, in present-day
coordinates, changes along the orogen: SE in Caro-
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219204

lina, NW in West Avalonia, SE in East Avalonia, and
N to SW beneath French and Iberian Cadomia,
respectively (Fig. 1).Isthisvariationanoriginal
feature, or have some of the terranes been rotated
about a vertical axis? Mesozoic – Cenozoic rotation of
terranes about vertical axes has been recorded along
the western margin of Laurentia, during both separa-
tion and accretion (Nicholson et al., 1994; Johnston,
2002). Could such mechanisms be applied to the f1
Ga peri-Gondwanan terranes?
Given that all the terranes considered in this paper
originated adjacent to the Gondwanan margin, is it
possible to locate them more accurately? Two end
member configurations can be envisaged: (1) the
terranes are arranged side-by-side (e.g. Fig. 2), and
(2) the terranes are arranged end-to-end, either as
presently observed or in a different order (Fig. 3).
As will be shown below, each potential modern
analogue for terrane dispersal partly predicts the
relative location of the terranes. Thus the analogues
may be tested using subtle distinctions in fauna,
paleomagnetic data, and detrital zircons suites. In an
end-to-end arrangement, for example, the mixed fau-
nal affinities of the Middle Cambrian trilobites in
Carolina would favour a model that placed Carolina
between Avalonia and Cadomia/West Africa, an
arrangement used in Section 3.3 below. On the other
hand, backward modeling to f700 Ma of the side-
by-side arrangement to allow for 150 – 200 million
years of subduction would produce three synchronous
arc terranes separated by several thousand kilometers,
and would place some of the terranes within the peri-
Rodinian ocean, far from any continent. This scenario
is not in accord with either the presence of continent-
derived, Archean, Paleoproterozoic, and Mesoproter-
ozoic detrital zircons in the early arc sediments of
West Avalonia, or the close correlation between West
and East Avalonia. Note that the presence or absence
of f1 Ga detrital zircons appears to be independent
of the basement age: f1 Ga detrital zircons are
found in northern Iberia ( f2 Ga basement) whereas
they are absent in the Meguma terrane (f1Ga
basement). The mismatch between ages of basement
and detrital zircons in overlying clastic rocks is typical
of modern drainage systems, such as the Mississippi,
Amazon, and Ganges, in which detritus is transported
across a continent. Similarly, the potential extent of
longshore marine transport is shown by the presence
of Archean detrital zircons in Cambrian–Triassic
miogeoclinal rocks from Canada to Mexico (Gehrels
et al., 1995).
Current estimates for the switch from arc to rift
magmatism is diachronous among these peri-Gond-
wanan terranes: f540 Ma in Carolina, f590 Ma in
New England, f560 Ma in southern New Bruns-
wick, f550 Ma in Cape Breton Island, f570 Ma in
Newfoundland, f550–540 Ma in Britain, 550 Ma in
Brunia, and 560 Ma in Cadomia. In view of this,
could termination of the arc be due to flattening of the
subducting slab, intra-arc rifting, or collision of a mid-
ocean ridge with the trench? Can the rifting be related
to the separation of terranes from Gondwana?
In the following section, we present some potential
modern analogues for the northern margin of Neo-
proterozoic–Paleozoic Gondwana, and then apply
them to the peri-Gondwanan terranes. These ana-
logues are then evaluated in light of the data.
3. Modern analogues
3.1. Alpine Tethyan and Mediterranean (‘‘accor-
dion’’) model
The Mesozoic –Cenozoic history of the Alpine
Tethys Ocean involves orthogonal (‘‘accordion’’)
opening and closing of a small ocean basin with some
lateral displacements (Stampfli et al., 2001).This
could be a modern analogue for the traditional Iapetus
model, which involves orthogonal opening and clos-
ing of Iapetus between Gondwana and Laurentia (e.g.
Williams, 1979; Van der Voo, 1993). But, for reasons
presented earlier, this model does not fit the geo-
logical data, and current reconstructions of Neopro-
terozoic Rodinia place eastern Laurentia against
western South America (e.g. Dalziel, 1997). In such
a reconstruction, the peri-Gondwanan terranes prob-
ably faced an open ocean at the time of inception of
Iapetus, and so lay beyond the Laurentia–South
American suture (e.g. Figs. 2 and 3). But while the
orthogonal opening of Iapetus does not appear to be
valid, it is possible that (a) Avalonia was transferred
orthogonally to Laurentia in the Ordovician once
Laurentia lay opposite northwestern Gondwana; and
(b) Cadomia was transferred orthogonally to Laurus-
sia in the Siluro-Devonian.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 205

3.1.1. Application of the ‘‘accordion’’ model to
Avalonia
An ‘‘accordion’’ model including the orthogonal
transfer of Avalonia from northern Gondwana to
Laurentia has been proposed by Dalziel (1997), who
swings Avalonia around a pole of rotation near the
coast of Colombia. In this scenario, the presently
observed relative locations and Neoproterozoic sub-
duction polarity reversals in the peri-Gondwanan
terranes would be an original feature. Fig. 3 ex-
plores this model. Given the 150 – 200 million years
of Neoproterozoic subduction with opposite polar-
ities observed in the geological record, the East
Avalonia and Carolina arcs could have lain along
the fringe of Gondwana, whereas West Avalonia
would have to have lain several thousand kilometers
offshore in the circum-Rodinian ocean in order to
provide oceanic lithosphere for subduction. Such a
possibility seems to be negated by the close corre-
lation between West and East Avalonia during the
Neoproterozoic, and by the Archean, Paleoprotero-
zoic, and Mesoproterozoic detrital zircon record in
the early arc sedimentary rocks of West Avalonia,
which would be unexpected in an intra-oceanic arc
(Keppie et al., 1998).
3.1.2. Application of ‘‘accordion’’ model to Cadomia
and Bohemia
Tait et al. (2000) have proposed that Cadomia and
Bohemia ( uArmorican Terrane Assemblage) were
transferred orthogonally from northwestern Africa to
southern Laurussia based on paleomagnetic and fau-
nal data. Stampfli and Borel (2002) have placed this
scenario in a plate tectonic framework including the
following stages: (1) southward subduction of the
Rheic–Rheno–Hercynian ocean beneath north Africa
and trench rollback triggering detachment of the
Gothic ( uCadomia and Bohemia) terrane in the Late
Silurian leaving a widening Paleotethys in its wake;
(2) Middle–Late Devonian collision of the Gothic
(Cadomia and Bohemia) terrane with Laurussia; (3)
latest Devonian jump and flip of the subduction zone
to the southern margin of the Gothic terrane; and (4)
Carboniferous ridge–trench collision inducing a
strike-slip regime analogous to the Gulf of California.
The southward polarity of Neoproterozoic subduction
throughout Cadomia, after unfolding the Armorican
arc, is consistent with orthogonal transfer of Cadomia
to Laurussia, followed by oroclinal folding in the
Permo-Carboniferous.
3.1.3. Application of the ‘‘accordion’’ model to
Oaxaquia, Chortis, Maya, and Suwannee
The Permo-Caroniferous collision of Oaxaquia,
Chortis, Maya, and Suwannee, lying along the northern
margin of Amazonia, with southern Laurentia may be
analogous to the closing of the Mediterranean Sea
between North Africa and Europe (Stampfli and Borel,
2002, and references therein). These peri-Amazonian
terranes were then stranded on the southern Laurentian
margin during the Early Mesozoic breakup of Pangea.
3.2. Australian (‘‘bulldozer’’) model
Van Staal et al. (1998) have compared the
development of the Appalachian – Caledonian orogen
with the forward-modeled northward motion of
Australia into the Pacific Ocean ending in collision
with Asia some 45 million years in the future. One
potential consequence of this bulldozing motion is
that oceanic plateaus, such as the 4000 1500 km
Caroline–Ontong plateau, are dispersed along the
Australian plate margin over a distance of 8000 km
(Fig. 4a).
3.2.1. Application of the ‘‘bulldozer’’ model to
Avalonia and Carolina
If Fig. 5a is turned over and relabeled, the result
is comparable with the present distribution of Car-
olina and Avalonia along the southeastern margin of
Laurentia (Fig. 4b).Infact,Dalziel (1991) has
proposed that Laurentia performed an ‘‘end-run’’
around western Gondwana in which Laurentia
would act as a ‘‘bulldozer’’. If the peri-Gondwanan
terranes were placed in front of the advancing
Laurentia, they would be bulldozed and dispersed
along its eastern margin. Such a model has impli-
cations for the relative positions of these terranes in
the Neoproterozoic. Applying this mechanism to the
side-by-side arrangement of the peri-Gondwanan
terranes would require them to be distributed as
shown in Fig. 2, with East Avalonia closest to
Laurentia, followed by West Avalonia, and Carolina
farthest outboard. During the bulldozing action
Carolina would end up farthest south (present coor-
dinates) along the Laurentian margin, as is now the
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219206

case. On the other hand, applying this mechanism
to the end-to-end arrangement of the terranes would
require the reverse west to east order (present
coordinates): East Avalonia, West Avalonia, Caro-
lina. This is precisely the opposite of that shown in
Fig. 3.
3.3. Baja California and Baja British Columbia
(‘‘Baja’’) models
The diachronous switch from calc-alkaline arc to
tholeiitic/alkaline rift magmatism in the peri-Gond-
wanan terranes is analogous to that recorded by the
oblique collision of the East Pacific Rise and Cocos
Ridge with the Middle America Trench (Dickinson and
Snyder, 1979; Protti et al., 1995; Murphy et al., 1999;
Keppie et al., 2000). In both cases, the trench is
replaced by a transform fault as the ridge is overridden
leading to a switch from arc to rift magmatism. As the
ridge–trench–transform (R-T-F) triple point migrates,
the magmatic switch moves in tandem with the triple
point (see Fig. 5 in Dickinson and Snyder, 1979).
Where two differently oriented ridges are being over-
ridden, the R-T-F triple points may migrate towards
Fig. 4. Australian ‘‘bulldozer’’ model: (a) present and future locations of Australia and the Caroline-Ontong plateau; (b) same diagram reversed
and relabeled: Australia to Laurentia, and Caroline-Ontong plateau to Avalonia and Carolina. Dashes= arc and periarc, crosses = Australian
plate, dark shade = Caroline-Ontong plateau.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 207

each other (as in Middle America—see figures in Protti
et al., 1995), or they may move apart. If the ridge is
offset by a transform fault, the F-F-T triple point may
also migrate. In the case of the Mendocino transform
offset of the East Pacific Ridge, migration occurs in the
opposite direction to that of the R-T-F triple point,
producing a widening zone of rift magmatism (see
Figs. 1–3 in Dickinson and Snyder, 1979). Other
features of ridge –trench collision include flattening
of the subduction zone prior to collision, the develop-
ment of a slab window with mantle upwelling, diapir-
ism and eruption of adakites leading to uplift,
extension, and increased heat flow (Dickinson and
Snyder, 1979; Thorkelson and Taylor, 1989; Goring
et al., 1997). Flattening of the subducting slab produces
a landward migration of the arc and causes shortening,
both of which have been observed in West Avalonia for
the 630–550 Ma arcs (Keppie et al., 1998). Such arc
migration may also be the result of subduction erosion
in which the lower part of the lithosphere is removed,
but this is inconsistent with available geophysical data
for West Avalonia. If the continental margin is irregu-
lar, the R-T-F and T-F-F triple points may be unstable
leading to extension or compression, and the separation
of blocks. This is the case for the Humbolt, Salinian,
and Baja California blocks, which are presently being
transferred from the North American plate to the
Pacific plate (Fig. 5) (Stock and Hodges, 1989). Such
a mechanism might likewise be responsible for the
separation of the peri-Gondwanan terranes from Gond-
wana. The development of such microplates can also
lead to the rotation of the blocks, as is the case for the
western Transverse Ranges, which have rotated
through f120j(Fig. 5) (Nicholson et al., 1994). Such
rotation would, in turn, produce apparent subduction
polarity reversals like those presently observed in the
Fig. 5. Tectonic model for the separation of blocks from the North American continental margin after collision of the East Pacific Rise with the
trench, showing the rotation of the western Transverse Ranges, and migration of the arc-rift magmatic boundary between 20 Ma and the present
(modified after Nicholson et al., 1994; Dickinson and Snyder, 1979). Cross section shows a core complex developed beneath the accretionary
complex-arc boundary (after Crouch and Suppe, 1993).
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219208

peri-Gondwanan terranes of the Appalachian – Caledo-
nian orogen. In the North American Cordillera, this
extension and rotation is accompanied by the develop-
ment of Basin-and-Range tectonics, extensional basins,
and core complexes in which high temperature – low
pressure metamorphic rocks are brought up into contact
with low-grade rocks along a sub-horizontal shear zone
(Fig. 5 cross-section) (Crouch and Suppe, 1993).Such
structures, which can form anywhere between the
accretionary prism and the backarc region (Che
´ry,
2001), have been recorded in the arc–backarc region
of West Avalonia in Cape Breton Island (Keppie et al.,
1998, 2000).
A more advanced stage in the transport of terranes
such as Baja California may be found in Baja British
Columbia and Baja Alaska. Some workers believe
these terrane assemblages originated off Mexico, were
transferred to the Kula Plate in the Late Cretaceous,
and transported northwards to accrete to western
Laurentia in British Columbia and Alaska in the
Cenozoic (for review and figures see Cowan et al.,
1997). A potential consequence of such transport is
the transcurrent fault slicing of the allochthonous
terranes into discrete ribbon blocks (see figures in
Keppie and Dostal, 2001). This may be followed by
oroclinal folding of a ribbon continent (‘‘train wreck’’
model of Johnston, 2002) upon encountering a con-
vergent bend in the active margin (Fig. 6), which
would produce reversals of polarity. Another result of
fault slicing is that initially outboard terranes are
transported farther than inboard terranes. Furthermore,
sequential transport places originally inboard terranes
on the ocean side of originally outboard terranes, as
illustrated by the Yukatat terrane assemblage of
Alaska (see figures in Plafker and Berg, 1994).
3.3.1. Application of the ‘‘Baja’’ model to peri-
Gondwanan terranes
The shuffling of terranes recorded in Alaska could
account for the apparent reversals of subduction polar-
ity deduced from arc –backarc geometry in the peri-
Gondwanan terranes. Examination of the peri-Gond-
wanan terranes in the Appalachian, Caledonian, and
Variscan orogens reveals two Variscan oroclines: the
Armorican arc through Iberia and France, and the
distribution of Avalonia around the eastern border of
the Bohemian massif. Although the Armorican arc has
been attributed to two orthogonal superposed com-
pressional events (Weil et al., 2001), the application of
the ‘‘Baja’’ model by Stampfli and Borel (2002) to the
southern margin of Laurussia during the Carbonifer-
ous may indicate the operation of a ‘‘train wreck’’
model in Bohemia. However, the oroclines may have
been produced by other mechanisms, such as rotation
during oblique Gondwana –Laurussia collision. Fur-
Fig. 6. ‘‘Train wreck’’ model for SAYBIA (Siberia – Alaska –
Yukon – British Columbia) ribbon continent (modified from John-
ston, 2002): (a) reconstruction of SAYBIA at 85 Ma, and (b) present
distribution of SAYBIA. IM = Intermontane domain.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 209

ther analysis is required to evaluate these alternative
models. Elsewhere in Carolina and Avalonia, orocli-
nal folds appear to be absent, although it is possible
that subsequent dispersion could have sliced segments
apart making their recognition difficult. Thus, the
reversals of subduction polarity may be the result of
rotation produced either during separation of ribbon
blocks or during their accretion to a continental
margin.
With the exception of adakites, all the features of
ridge–trench collision occur in the geological record
of Carolina and Avalonia. Thus it seems appropriate
to apply the ‘‘Baja’’ model to the arc–rift transition in
the peri-Gondwanan terranes and this has been
attempted in Figs. 7 and 8. In this model, several
assumptions are made: (1) by analogy with the Pacific
Ocean, where subduction polarity is predominantly
towards the continents, it is assumed that subduction
was beneath Gondwana; (2) it is assumed that Caro-
lina and Avalonia represent several slices that were
transferred to an oceanic plate in the Cambrian and
transported longitudinally into Iapetus, from which
they were accreted to Laurentia in the Late Ordovi-
cian–Early Silurian: this dictates that the initial
arrangement of terranes from west to east (present
coordinates: top to bottom in Fig. 7) along the north-
ern margin of Amazonia was: East Avalonia, West
Avalonia, Carolina; (3) it is assumed that f1Ga
basement was only present around Amazonia; (4) it is
assumed that Cadomia originated adjacent to north-
west Africa and was transferred orthogonally to south-
ern Laurussia in the Siluro-Devonian with relatively
little orogen-parallel transport; and (5) it is assumed
that Oaxaquia, and the Chortis, Maya (Yucatan), and
Suwannee (Florida) terranes were distributed between
northwestern Amazonia and Carolina – Avalonia, and
that they were not transferred to Laurentia until the
amalgamation of Pangea.
The diachronism in the switch from arc to rift
magmatism in the peri-Gondwanan terranes can be
Fig. 7. Neoproterozoic reconstructions using the Baja California analogue for the peri-Gondwanan terranes (modified from Ramos and Keppie,
1999). See text for discussion. Abbreviations as in Figs. 1 and 2.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219210

Fig. 8. Lower Paleozoic reconstructions using the Baja California and Baja British Columbia analogue for the peri-Gondwanan terranes (modified fromKeppie and Ramos (1999).
See text for discussion. Abbreviations as in Figs. 1 and 2.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 211

used to track the movement of R-T-F and T-F-F triple
points. In order to simplify discussion of the model,
the oceanic plates are given names analogous to those
in the Pacific Ocean: Merlin uFarallon, Morga-
na uPacific, and Mordred uKula (Fig. 7). Subduc-
tion of the Merlin Plate beneath northern Gondwana
prior to 600 Ma is followed between 590 and 540 Ma
by collision of the Merlin – Morgana and Merlin–
Mordred ridge–transform systems with the northern
Gondwana trench, causing a diachronous switch from
arc to rift magmatism as subduction was replaced by
transform motions. In West Avalonia, this switch
appears to be bi-directional, from 590 Ma in New
England to 560 Ma in southern New Brunswick, and
from 570 Ma in eastern Newfoundland to 550 Ma in
Cape Breton Island, and is likened to the subduction
of the Cocos Plate (Keppie et al., 2000). On the other
hand, the relatively young, 550 –540 Ma switch in
East Avalonia and Carolina is explicable in terms of a
ridge offset by transform faults, which allowed sub-
duction of small remnants of the Merlin Plate to
continue until 550 Ma. By analogy with Baja Cal-
ifornia, it is further inferred that the development of a
transform system along the northern Gondwanan
margin was accompanied by latest Neoproterozoic
migration of the R-F-F (Mordred – Morgana–Gond-
wana) triple point, microplate capture, and the rifting
of East and West Avalonia relative to Gondwana. The
separation caused by this rifting was wide enough to
produce a faunal barrier and the development of the
unique Avalonian fauna by the Early Cambrian (Land-
ing, 1996). This was synchronous with initial deposi-
tion of Early Cambrian turbidites in the Gander and
Meguma terranes. The Meguma terrane is placed
adjacent to West Avalonia and close to northwest
Africa to account for its f1 Ga basement and the
North African provenance of its detrital zircons. On
the other hand, the Gander terrane may have lain
between Oaxaquia and West Avalonia, either of which
would be a ready source for the f1 Ga zircons
recorded in the Gander turbidites (Van Staal et al.,
1996).
In addition, the Baja-type rifting may have been
approximately synchronous with the anticlockwise
rotation of East Avalonia and Carolina in a manner
analogous to the western Transverse Ranges (Fig. 8).
This latter rotational model is favoured over the
alternatives (‘‘train wreck’’ rotation as the leading
end of Avalonia encountered Laurentia, or ‘‘bull-
dozer’’ rotation during dispersion as the terranes were
swept along the eastern margin of Laurentia) because
oroclinal folds are absent. During the Cambrian and
Ordovician, this terrane ribbon was displaced sinis-
trally along the northern margin of Amazonia into
Iapetus, while Laurentia was advancing northwards in
bulldozer fashion along the western margin of South
America (Keppie and Murphy, 1988; Keppie, 1993;
Hibbard, 2000). The Early –Middle Ordovician posi-
tions of Avalonia and Carolina south of 15jS are
consistent with their graptolite and trilobite faunal
provinces (Fig. 8). Following accretion of Avalonia
and Carolina to Laurentia in the Late Ordovician –
Early Silurian, the terranes were swept along the
eastern margin of the Laurentian ‘‘bulldozer’’. Further
advance of Laurussia relative to Gondwana may have
dispersed Avalonia around the eastern end of the
Bohemian massif.
4. Conclusions
Several modern analogues have been presented for
the Neoproterozoic and Early Paleozoic evolution of
terranes in the Appalachian, Caledonian, and Variscan
orogen that were derived from the northern periphery
of Gondwana. End member models are (1) the Alpine
Tethys (‘‘accordion’’) model; (2) the Australian (‘‘bull-
dozer’’) model; and (3) Baja California and Baja
British Columbia (‘‘Baja’’) models. For Avalonia and
Carolina, the ‘‘accordion’’ model is least supported by
the geological data: (1) the juxtaposing of eastern
Laurentian and western South American in the Neo-
proterozoic requires vast relative lateral displacements
to reach a Pangea A reconstruction in the Permo-
Carboniferous, and (2) the synchroneity of a passive
eastern Laurentian margin and an active margin along
Carolina–Avalonia – Cadomia during the Neoprotero-
zoic implies that they were not opposing margins.
Instead, it appears that a ‘‘Baja’’ model for the Neo-
proterozoic–Early Cambrian followed by a Lower
Paleozoic ‘‘bulldozer’’ model best fit the geological
data for Avalonia and Carolina. Thus, the development
of magmatic arcs along the northern margin of Gond-
wana, the gradual shallowing of the Benioff zone
followed by the diachronous switch to rift magmatism,
the accompanying replacement of a trench by a trans-
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219212

form plate margin, and the associated extension pro-
ducing rifts and core complexes, are all analogous to
features found in the western margin of Mesozoic –
Cenozoic North America. For North America, these
phenomena have been related to subduction of the
Farallon Plate followed by collision of the East Pacific
Rise with the Middle America Trench. Separation and
lateral transport of Avalonia and Carolina from Gond-
wana is likened both to the break-off of Baja California
and its transfer to the Pacific Plate, and to the detach-
ment of Baja British Columbia and its transport on the
Kula Plate. By analogy, we name the oceanic plates for
Neoproterozoic peri-Gondwana: Merlin uFarallon,
Mordred uKula, and Morgana uPacific (Figs. 7 and
8). In Cambro-Ordovician times, Avalonia and Caro-
lina were transported on the Mordred Plate into the
Iapetus Ocean where they encountered Laurentia,
which was bulldozing its way northwards (present
coordinates) from a position off western South Amer-
ica to one off northwest Africa. This led to the
accretion of Carolina and Avalonia to Laurentia in
the Late Ordovician, following which they were swept
along its eastern margin.
For Cadomia, the ‘‘Baja’’ model also best fits the
Neoproterozoic–Cambrian record of subduction ter-
minating in rifting rather than collision. This was
followed by orthogonal Siluro-Devonian transfer from
northern Africa to southern Laurussia, which is con-
sistent with the relative location of Laurentia – Baltica
and North Africa in the mid-Paleozoic. Application of
the ‘‘Baja’’ model to the Permo-Carboniferous is
supported by strike-slip tectonics adjacent to the
Paleotethys Ocean (Stampfli and Borel, 2002).
Permo-Carboniferous, continent–continent colli-
sion between Amazonia and southern Laurentia
welded terranes along the leading edge of Gondwana
(Oaxaquia, and the Chortis, Maya, and Suwannee) to
Laurentia. Following the Early Mesozoic breakup of
Pangea, these terranes were stranded on the southern
Laurentian margin.
Application of these modern analogues provides
constraints on the provenance of Avalonia, Carolina,
and Cadomia. Thus, we believe they were probably
distributed from west to east (present coordinates) off
northern Amazonia in the following order: East Ava-
lonia, West Avalonia, and Carolina, with Cadomia
located off northwest Africa (Fig. 7). Data bearing on
the polarity of Neoproterozoic subduction suggests
that certain segments of the active margin have been
rotated. This is based upon (1) the presence of con-
tinental detritus in the early–main stages of the Neo-
proterozoic arc; and (2) the close correlation between
East and West Avalonia. This requires East Avalonia
and Carolina to be rotated through 180jrelative to
West Avalonia. Such rotation probably took place
during separation (by analogy with the western Trans-
verse Ranges), however, rotation either during accre-
tion to Laurentia (by a ‘‘train wreck’’ model:
considered unlikely given the absence of oroclines),
or during dispersion along the eastern Laurentian
margin, or some combination of these mechanisms,
is also possible. Data pertaining to the original
arrangement of the peri-Gondwanan terranes appears
to favour an original, end-to-end arrangement based
on the close correlation between East and West
Avalonia. But it is possible that, following separation,
terranes originally in an end-to-end distribution could
have been moved by transcurrent faulting into a side-
by-side arrangement before being dispersed by the
Laurentian ‘‘bulldozer’’.
The presentation of actualistic models for the
Neoproterozoic and Early Paleozoic histories of the
peri-Gondwanan terranes provides the basis for tests
of the models. For example, the approach and colli-
sion of a ridge with a trench produces many tectonic
features besides diachronous termination of arc mag-
matism, such as changes in structural kinematics,
opening of slab windows, and complex extension
and shortening associated with microplate capture
and block rotation. The actualistic model has addi-
tionally generated a whole new set of questions for
which additional data is required. For example, what
evidence is there for block rotation during separation,
accretion or dispersion? Can the relative locations of
the peri-Gondwanan terranes be more precisely
located along the northern margin of Gondwana?
Both improved paleomagnetic and geological data
can be brought to bear on these and other questions
arising from the ‘‘Baja, bulldozer, and accordion’’
models.
Acknowledgements
This paper (a contribution to International Geo-
logical Correlation Programme Project #453) was
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 213

supported by grants from Programa de Apoyo a
Proyectos de Investigacio
´n e Innovacio
´n Tecnolo
´gica
to JDK, the Ohio Research Challenge Program to
RDN, North American Mobility in Higher Education
to JDK and RDN, and Natural Sciences and
Engineering Research Council to JBM and JD. We
are grateful to Drs. R. Strachan, C. Hepburn, and J.
Hibbard for their constructive reviews of the manu-
script.
References
Ayuso, R.A., Barr, S.M., Longstaffe, F.J., 1996. Pb and O isotopic
constraints on the source of granitic rocks from Cape Breton
Island, Nova Scotia, Canada. American Journal of Science 296,
789 – 817.
Ballard, M.M., van der Voo, R., Urrutia-Fucugauchi, J., 1989. Pa-
leomagnetic results from Grenvillian-aged rocks from Oaxaca,
Mexico: evidence for a displaced terrane. Precambrian Research
42, 343 – 352.
Beck Jr., M.E., 1991. Case for northward transport of Baja and
coastal southern California: paleomagnetic data, analysis, and
alternatives. Geology 19, 506 – 509.
Bond, C.G., Nickerson, P.A., Kominz, M.A., 1984. Breakup of a
supercontinent between 625 Ma and 555 Ma: new evidence and
implications for continental histories. Earth and Planetary Sci-
ence Letters 70, 325 – 345.
Boucot, A.J., Blodgett, R.B., Stewart, J.H., 1997. European Province
Late Silurian brachiopods from the Ciudad Victoria area, Tam-
aulipas, northeastern Mexico. In: Klapper, G., Murphy, M.A.,
Talent, J.A. (Eds.), Paleozoic Sequence Stratigraphy, Biostratig-
raphy, and Biogeography: Studies in Honor of J. Grenville
(‘‘Jess’’) Johnson. Geological Society of America, Boulder,
CO, Special Paper, vol. 321, pp. 273 – 293.
Brenchley, P.J.M., Romano, T.P., Young, G.C., Storch, P., 1991.
Hirnantian glaciomarine diamictites—evidence for the spread
of glaciation and its effect on Upper Ordovician faunas. In:
Barnes, C.R., Williams, S.H. (Eds.), Advances in Ordovician
Geology. Geological Survey of Canada, Ottawa, Ontario,
pp. 325 – 336.
Cawood, P.A., Dunning, G.R., Lux, D., van Gool, J.A.M., 1994.
Timing of peak metamorphism and deformation along the Ap-
palachian margin of Laurentia in Newfoundland. Geology 22,
399 – 402.
Cawood, P.A., McCausland, P.J.A., Dunning, G.R., 2001. Opening
Iapetus: constraints from the Laurentian margin in Newfound-
land. Geological Society of America Bulletin 113, 443 – 453.
Chandler, F.W., Loveridge, D., Currie, K.L., 1987. The age of the
Springdale Group, western Newfoundland, and correlative
rocks—evidence for a Llandovery overlap sequence in the
Canadian Appalachians. Transactions of the Royal Society of
Edinburgh 78, 41 – 49.
Chantraine, J., Auvray, B., Brun, J.P., Chauvel, J.J., Rabu, D., 1994.
The Cadomian Orogeny in the Armorican Massif. In: Keppi,
J.D. (Ed.), Pre-Mesozoic Geology in France and Related Areas.
Springer, Berlin, pp. 75 – 128.
Chantraine, J., Egal, E., Thie
´blemont, D., Le Goff, E., Guerrot, C.,
Balle
`vre, M., Guennoc, P., 2001. The Cadomian active margin
(North Armorican Massif, France): a segment of the North At-
lantic Panafrican belt. Tectonophysics 331, 1 – 18.
Che
´ry, J., 2001. Core complex mechanics: from the Gulf of Corinth
to the Snake Range. Geology 29, 439–442.
Cocks, L.R.M., 2000. The Early Paleozoic of Europe. Geological
Society of London Journal 157, 1 – 10.
Cocks, L.R.M., Fortey, R.A., 1988. Lower Paleozoic facies and
faunas around Gondwana. In: Audley-Charles, M.G., Hallam,
A. (Eds.), Gondwana and Tethys. Geological Society, London,
Special Publication, vol. 37, pp. 183 –200.
Colman-Sadd, S.P., Dunning, G.R., Dec, T., 1992. Dunnage – Gan-
der relationships and Ordovician orogeny in central Newfound-
land: a sediment provenance and U/Pb study. American Journal
of Science 292, 317 – 355.
Cowan, D.S., Brandon, M.T., Garver, J.I., 1997. Geologic tests of
hypotheses for large coastwise displacements—a critique illus-
trated by the Baja British Columbia controversy. American Jour-
nal of Science 297, 117– 173.
Cramer, F.H., Diez, M. del C.R., 1974. Early Paleozoic paly-
nomorph provinces and paleoclimate. Society of Economic
Paleontologists and Mineralogists Special Publication 21,
177 – 188.
Crouch, J.K., Suppe, J., 1993. Late Cenozoic tectonic evolution of
the Los Angeles basin and inner borderland: a model for core
complex-like crustal extension. Geological Society of America
Bulletin 105, 1415 – 1434.
Currie, K.L., Piaseki, M.A.J., 1989. Kinematic model for south-
western Newfoundland based upon Silurian sinistral shearing.
Geology 17, 938 – 941.
Dallmeyer, R.D., Gibbons, W., 1987. The age of blueschist meta-
morphism in Anglesey, North Wales: evidence from
40
Ar/
39
Ar
mineral ages of the Penmynydd Schists. Geological Society of
London Journal 144, 843 – 850.
Dalziel, I.W.D., 1991. Pacific margins of Laurentia and East
Antarctica – Australia as a conjugate rift pair: evidence and
implications for an Eocambrian supercontinent. Geology 19,
598 – 601.
Dalziel, I.W.D., 1992. On the organization of American plates in the
Neoproterozoic and the breakout of Laurentia. GSA Today 2
(11), 238 – 241.
Dalziel, I., 1997. Overview: Neoproterozoic – Paleozoic geography
and tectonics: review, hypotheses and environmental specula-
tions. Geological Society of America Bulletin 109, 16 –42.
Debiche, M.G., Engebretson, D.C., 1987. The motion of allochth-
onous terrane across the North Pacific Basin. Geological Society
of America Special Paper 207, 49 pp., Boulder, Colorado.
Dennis, A.J., Wright, J.E., 1997. The Carolina terrane in northwest-
ern South Carolina, USA: Late Precambrian –Cambrian defor-
mation and metamorphism in a peri-Gondwana oceanic arc.
Tectonics 16, 460 – 473.
Dewey, J.F., 1969. Evolution of the Appalachian/Caledonian Oro-
gen. Nature 222, 124 – 129.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219214

Dickinson, W.R., Lawton, T.F., 2001. Carboniferous to Cretaceous
assembly and fragmentation of Mexico. Geological Society of
America Bulletin 113, 1142 – 1160.
Dickinson, W.R., Snyder, W.S., 1979. Geometry of subducted
slabs related to San Andreas transform. Journal of Geology
87, 609 – 627.
D’Lemos, R.D., Brown, M., 1993. Sm –Nd isotopic characteristics
of late Cadomian granite magmatism in northern France and the
Channel Islands. Geological Magazine 130, 797 – 804.
D’Lemos, R., Samson, S.D., Nagy, E., Miller, B., 2001. Tectono-
thermal evolution of the Cadomian arc, northwest Europe-con-
straints from U –Pb zircon analyses and comparisons to
Avalonia. Geological Society of America Abstracts with Pro-
grams 33 (6), A-206.
Doig, R., Nance, R.D., Murphy, J.B., Casseday, R.P., 1990. Evi-
dence for Silurian sinistral accretion of Avalon composite ter-
rane in Canada. Geological Society of London Journal 147,
927 – 930.
Dore
´, F., 1994. The Variscan orogeny in the Armorican Massif:
Cambrian of the Armorican Massif. In: Keppie, J.D. (Ed.),
Pre-Mesozoic Geology of France and Related Areas. Springer,
Heidelberg, Germany, pp. 136 – 141.
Dostal, J., Keppie, J.D., Cousens, B.L., Murphy, J.B., 1996. 550–
580 Ma magmatism in Cape Breton Island (Nova Scotia, Can-
ada): the product of NW-dipping subduction during the final
stage of assembly of Gondwana. Precambrian Research 76,
96 – 113.
Egal, E., Guerrot, C., Le Goff, D., Thieblemont, D., Chantraine, J.,
1996. The Cadomian orogeny revisited in northern France. In:
Nance, R.D., Thompson, M.D. (Eds.), Avalonian and Related
Peri-Gondwanan Terranes of the Circum-North Atlantic. Geo-
logical Society of America, Boulder, CO, Special Paper, vol.
304, pp. 281 – 318.
Eguı
´luz, L., Gil Ibarguchi, J.I., A
´balos, B., Apraiz, A., 2000. Super-
posed Hercynian and Cadomian orogenic cycles in the Ossa –
Morena zone and related areas of the Iberian Massif. Geological
Society of America Bulletin 112, 1398 – 1413.
Fernandez-Sua
´rez, J., Gutie
´rrez-Alonso, G., Jenner, G.A., Turbrett,
M.N., 2000. New ideas on the Prote rozoic – Early Paleozoic
evolution of NW Iberia: insights from U – Pb detritial zircon
ages. Precambrian Research 102, 185 – 206.
Franke, W., Haak, V., Oncken, O., Tanner, D., 2000. Oro-
genic Processes: Quantification and Modeling in the Variscan
Belt. Geological Society, London, Special Publication, vol. 179.
102 pp.
Freidl, G., Finger, F., McNaughton, N.J., Fletcher, I.R., 2000. De-
ducing the ancestry of terranes: SHRIMP evidence for South
America-derived Gondwana fragments in central Europe. Geol-
ogy 28, 1035 – 1038.
Gebauer, D., 1994. Ein Modell der Entwicklungsgeschichte des
ostbayerischen Grundgebirges auf der Basis plattentektonischer
Vorstellungen und radiometrischer Datierungen 1994. Erla¨uter-
ungen zur geologischen Karte von Bayern 1:25,000, Bl. 6439
Ta¨nnesburg. Bayerische Geologische Landesamt.
Gebauer, D., Williams, I.S., Compston, W., Gru
¨nenfelder, M., 1989.
The development of the Central European continental crust
since the Early Archaean based on conventional and ion-mi-
croprobe dating of detrital zircons up to 3.84 b.y. old. Tectono-
physics 157, 81 – 96.
Gehrels, G.E., Dickinson, W.R., Ross, G.M., Stewart, J.H., Ho-
wells, D.G., 1995. Detrital zircon reference for Cambrian to
Triassic miogeoclinal strata of western North America. Geology
23, 831 – 834.
Gillis, R.J., Gehrels, G.E., Flores de Dios, A., Ruiz, J., 2001. Paleo-
geographic implications of detrital zircon ages from the Oaxaca
terrane of southern Mexico. Geological Society of America
Abstracts with Programs 33 (6), A-428.
Goring, M.L., Kay, S.M., Zeitler, P.K., Ramos, V.A., Rubiolo, D.,
Fernandex, M.I., Panza, J.L., 1997. Neogene Patagonian plateau
lavas: continental magmas associated with ridge collision at the
Chile Triple Junction. Tectonics 16, 1 – 17.
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 Avalonia underthrusting. Canadian Journal of
Earth Sciences 36, 15 – 22.
Gutie
´rrez-Alonso, G., 2001. LAM U –Pb dating of detrital zircons
from the Armorican quartzite. Geological Association of Canada
Abstracts 26, 56.
Gutie
´rrez-Alonso, G., Ferna
´ndez-Sua
´rez, J., Jeffries, T.E., Jenner,
G.A., Cox, R.A., 2001. Towards a deconstruction of the west-
ern European Cadomian – Avalonian belt: detrital zircons tell
their tale. IGCP Project No. 453 Abstracts and programme,
65 – 66.
Hatcher Jr., R.D., 1989. Tectonic synthesis of the U.S. Appala-
chians. In: Hatcher, R.D., Thomas, W., Viele, G. (Eds.), The
Appalachian – Ouachita Orogen in the United States. Geological
Society of America, Boulder, CO, Geology of North America,
vol. F-2, pp. 511 – 535.
Heatherington, A.L., Mueller, P.A., Spencer, J., Isachsen, C.E.,
1993. Terrane accretion in southeastern North America: con-
straints of geochronologic data from Paleozoic and Proterozoic
granitoids. Geological Society of America Abstracts with Pro-
grams 25, A-322.
Heatherington, A.L., Mueller, P.A., Nutman, A.P., 1996. Neopro-
terozoic magmatism in the Suwannee terrane: implications for
terrane correlation. In: Nance, R.D., Thompson, M.D. (Eds.),
Avalonian and Related Peri-Gondwanan Terranes of the Cir-
cum-North Atlantic. Geological Society of America, Boulder,
CO, Special Paper, vol. 304, pp. 257– 268.
Hegner, E., Kro¨ner, A., 2000. Review of Nd isotopic data and
xenocrystic and detrital zircon ages from the pre-Variscan base-
ment in the eastern Bohemian Massif: speculations on palins-
pastic reconstructions. In: Franke, W., Haak, V., Oncken, O.,
Tanner, D. (Eds.), Orogenic Processes: Quantification and Mod-
eling in the Variscan Belt. Geological Society, London, Special
Publication, vol. 179, pp. 113 – 129.
Hibbard, J.P., 2000. Docking Carolina: Mid-Paleozoic accretion in
the southern Appalachians. Geology 28, 127 – 130.
Hibbard, J., Samson, S., 1995. Orogenesis exotic to the Iapetan
cycle in the southern Appalachians. In: Hibbard, J., van Staal,
C., Cawood, P. (Eds.), Current Perspectives in the Appala-
chian – Caledonian Orogen. Geological Association of Canada,
Ottawa, Ontario, Special Paper, vol. 41, pp. 191– 205.
Hibbard, J.P., Stoddard, E.F., Stoddard, E.F., Secor, D.T., Dennis,
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 215

A.J., 2002. The Carolina Zone: overview of Neoproterozoic to
Early Paleozoic peri-Gondwanan terranes along the eastern
flank of the southern Appalachians. Earth Science Reviews
57, 299 – 339.
Hodych, J.P., Buchan, K.L., 1994. Paleomagnetism of the Early
Silurian Cape Marys sills of the Avalon Peninsula of Newfound-
land. Eos, Transactions of American Geophysical Union 75, 16.
Hoffman, P.F., 1991. Did the breakout of Laurentia turn Gondwana-
land inside out? Science 252, 1409 – 1412.
Jackson, H.R., Chian, D., Salisbury, M., Shimeld, J., 2000. Prelimi-
nary crustal structure from the Scotian margin to the Maritimes
Basin from wide angle seismic reflection/refraction profiles.
Abstracts Volume 25, 73.
Johnston, S.T., 2002. The Great Alaskan Terrane Wreck: reconcili-
ation of paleomagnetic and geological data in the northern Cor-
dillera. Earth and Planetary Science Letters 193, 259 –272.
Karlstrom, K.E., Williams, M.L., McLelland, J., Geissman, J.W.,
Aha¨ll, K.-I., 1999. Refining Rodinia: geologic evidence for the
Australia – western U.S. connection in the Proterozoic. GSA To-
day 9, 1 – 7.
Kay, M., 1951. North American geosynclines. Geological Society
of America Memoir 48, 143 pp.
Keppie, J.D., 1977. Plate tectonic interpretation of Paleozoic world
maps (with emphasis on circum-Atlantic orogens and southern
Nova Scotia). Nova Scotia Department of Mines Paper 77-3,
45 pp.
Keppie, J.D., 1982. Tectonic Map of Nova Scotia, Scales 1:500,000
and 1:2,000,000.
Keppie, J.D., 1985. The Appalachian collage. In: Gee, D.G., Sturt,
B.A. (Eds.), The Caledonide Orogen: Scandinavia and Related
Areas. J. Wyllie and Sons, New York, pp. 1217 – 1226.
Keppie, J.D., 1989. Northern Appalachian terranes and their accre-
tionary history. Geological Society of America Special Paper
230, 159 – 192.
Keppie, J.D., 1993. Synthesis of Paleozoic deformational events
and terrane accretion in the Canadian Appalachians. Geologi-
sche Rundschau 82, 381 – 431.
Keppie, J.D., 1994. Pre-Mesozoic Geology in France and Related
Areas. Springer, New York. 514 pp.
Keppie, J.D., Dostal, J., 2001. Evaluation of the Baja controversy
using paleomagnetic and faunal data, plume magmatism, and
piercing points. Tectonophysics 339 (3 – 4), 427 – 442.
Keppie, J.D., Krogh, T.E., 1990. Detrital zircon ages from Late
Precambrian conglomerate, Avalon Composite Terrane, Anti-
gonish Highlands, Nova Scotia. Geological Society of America
Abstracts with Programs 22, 27 – 28.
Keppie, J.D., Krogh, T.E., 2000. 440 Ma igneous activity in the
Meguma terrane, Nova Scotia, Canada: part of the Appalachian
overstep sequence? American Journal of Science 300, 528 – 538.
Keppie, J.D., Murphy, J.B., 1988. Anatomy of a telescoped pull-
apart basin: an example from the Cambro-Ordovician of the
Antigonish Highlands. Maritime Sediments and Atlantic Geol-
ogy 24, 123 – 138.
Keppie, J.D., Ortega-Gutierrez, F., 1995. Provenance of Mexican
terranes: isotopic constraints. International Geology Review 37,
813 – 824.
Keppie, J.D., Ortega-Gutie
´rrez, F., 1999. Middle American Precam-
brian basement: a missing part of the reconstructed 1 Ga orogen.
In: Ramos, V.S., Keppie, J.D. (Eds.), Laurentia – Gondwana
Connections before Pangea. Geological Society of America,
Boulder, CO, Special Paper, vol. 336, pp. 199–210.
Keppie, J.D., Ramos, V.A., 1999. Odyssey of terranes in the Iape-
tus and Rheic oceans during the Paleozoic. In: Ramos, V.A.,
Keppie, J.D. (Eds.), Laurentia – Gondwana Connections before
Pangea. Geological Society of America, Boulder, CO, Special
Paper, vol. 336, pp. 267 – 276.
Keppie, J.D., Dostal, J., Murphy, J.B., Nance, R.D., 1996. Terrane
transfer between eastern Laurentia and western Gondwana in
the Early Paleozoic: constraints on global reconstructions. In:
Nance, R.D., Thompson, M.D. (Eds.), Avalonian and Related
Peri-Gondwanan Terranes of the Circum-North Atlantic. Geo-
logical Society of America, Boulder, CO, Special Paper, vol.
304, pp. 369 – 380.
Keppie, J.D., Davis, D.W., Krogh, T.E., 1998. U – Pb geochrono-
logical 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., Dostal, J., Dallmeyer, R.D., Doig, R., 2000. Super-
posed Neoproterozoic and Silurian magmatic arcs in central
Cape Breton Island, Canada: geochemical and geochronological
constraints. Geological Magazine 137, 137 – 153.
Keppie, J.D., Dostal, J., Ortega-Gutierrez, F., Lopez, R., 2001. A
Grenvillian arc on the margin of Amazonia: evidence from the
southern Oaxacan Complex, southern Mexico. Precambrian Re-
search 112 (3 – 4), 165 – 181.
Keppie, J.D., Dostal, J., Cameron, K.L., Solari, L.A., Ortega-Gu-
tie
´rrez, F., Lopez, R., 2003. Geochronology and geochemistry of
Grenvillian igneous suites in the northern Oaxacan Complex,
southern Me
´xico: tectonic implications. Precambrian Research
122, 365 – 389.
Kriz, J., Paris, F., 1982. Ludlovian, Pridolian and Lockhovian in
La Meignanne (Massif Armoricaine): biostratigraphy and cor-
relations based on bivalvia and chitinozoa. Geobios 15 (3),
391 – 421.
Krogh, T.E., Keppie, J.D., 1990. Age of detrital zircon and
titanite in the Meguma Group, southern Nova Scotia, Canada:
clues for the orgin of the Meguma Terrane. Tectonophysics
177, 307 – 323.
Krogh, T.E., Kamo, S.L., Sharpton, B., Marin, L., Hildebrand,
A.R., 1993. U – Pb ages of single shocked zircons linking distal
K/T ejecta to the Chicxulub crater. Nature 366, 731 – 734.
Kro¨ ner, A., Stı
´pska
´, P., Schulmann, K., Jaeckel, P., 2000. Chrono-
logical constraints on the pre-Variscan evolution of the north-
eastern margin of the Bohemian Massif, Czech Republic. In:
Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.), Orogenic
Processes: Quantification and Modeling in the Variscan Belt.
Geological Society, London, Special Publication, vol. 179,
pp. 175 – 197.
Kro¨ ner, A., Jaeckel, P., Hegner, E., Opletal, M., 2001. Single zircon
ages and whole-rock Nd isotopic systematics of early Paleozoic
granitoid gneisses from the Czech and Polish Sudetes (Jizerske
´
hory, Krkonose Mountains and Orlice – Sceznı
´k Complex). In-
ternational Journal of Earth Sciences (Geologische Rundschau)
90, 304 – 324.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219216

Landing, E., 1996. Avalon: insular continent by the latest Precam-
brian. In: Nance, R.D., Thompson, M.D. (Eds.), Avalonian and
Related Peri-Gondwanan Terranes of the Circum-North Atlan-
tic. Geological Society of America, Boulder, CO, Special Paper,
vol. 304, pp. 29 – 63.
Linnemann, U., Gehmlich, M., Tichomirowa, M., Buschmann, B.,
Nasdala, L., Jonas, P., Lu
¨tzner, H., Bombach, K., 2000. From
Cadomian subduction to Early Paleozoic rifting: the evolution
of Saxo-Thuringia at the margin of Gondwana in the light of
single zircon geochronology and basin development (Central
European Variscides, Germany. In: Franke, W., Haak, V., Onck-
en, O., Tanner, D. (Eds.), Orogenic Processes: Quantification
and Modeling in the Variscan Belt. Geological Society, London,
Special Publication, vol. 179, pp. 131 – 153.
Mac Niocaill, C., van der Pluijm, B.A., Van der Voo, R., 1997.
Ordovician paleogeography and the evolution of the Iapetus
ocean. Geology 25, 159 – 162.
McNamara, A.K., Mac Niocaill, C., van der Pluijm, B.A., Van der
Voo, R., 2001. West African proximity of Avalon in the latest
Precambrian. Geological Society of America Bulletin 113,
1161– 1170.
Miller, J.D., Kent, D.V., 1988. Paleomagnetism of the Siluro-Dev-
onian Andreas redbeds: evidence of a Devonian supercontinent?
Geology 16, 195 – 198.
Miller, B.V., Dunning, G.R., Barr, S.M., Raeside, R.P., Jamieson,
R.A., Reynolds, P.H., 1996. Magmatism and metamorphism in a
Grenvillian fragment: U – Pb and
40
Ar/
39
Ar ages from the Blair
River Complex, northern Cape Breton Island, Nova Scotia, Can-
ada. Geological Society of America Bulletin 108, 127 – 140.
Molina-Garza, R.S., Van der Voo, R., Urrutia-Fucugauchi, J., 1992.
Paleomagnetism of the Chiapas massif, southern Me
´xico: evi-
dence for rotation of the Maya block and implications for the
opening of the Gulf of Me
´xico. Geological Society of America
Bulletin 104, 1156 – 1168.
Mueller, P.A., Kozuch, M., Heatherington, A.L., Wooden, J.L.,
Offield, T.W., Koeppen, R.P., Klein, T.L., Nutman, A.P.,
1996. Evidence for Mesozporterozoic basement in the Caro-
lina Terrane and speculations on its origin. In: Nance, R.D.,
Thompson, M.D. (Eds.), Avalonian and Related Peri-Gond-
wanan Terranes of the Circum-North Atlantic. Geological
Society of America, Boulder, CO, Special Paper, vol. 304,
pp. 207 – 218.
Murphy, J.B., MacDonald, D.A., 1993. Geochemistry of late Pro-
terozoic arc-related volcaniclastic turbidite sequences, Antigon-
ish Highlands, Nova Scotia. Canadian Journal of Earth Sciences
30, 2273 – 2282.
Murphy, J.B., Nance, R.D., 1989. Model for the evolution of the
Avalonian– Cadomian belt. Geology 17, 735 – 738.
Murphy, J.B., Keppie, J.D., Dostal, J., Waldron, J.W.F., Cude, M.P.,
1996. Geochemical and isotopic characteristics of Early Silurian
clastic sequences in Antigonish Highlands, Nova Scotia, Cana-
da: constraints on the accretion of Avalonia in the Appalachian –
Caledonide Orogen. Canadian Journal of Earth Sciences 33,
379 – 388.
Murphy, J.B., Keppie, J.D., Dostal, J., Nance, R.D., 1999. Neo-
proterozoic – early Paleozoic evolution of Avalonia. In: Ramos,
V.A., Kep pie, J.D. (Eds.), Laurentia – Gondwana Connections
before Pangea. Geological Society of America, Boulder, CO,
Special Paper, vol. 336, pp. 253– 266 .
Murphy, J.B., Strachan, R.A., Nance, R.D., Parker, K.D., Fowler,
M.B., 2000. Proto-Avalonia: a 1.2 – 1.0 Ga tectonothermal event
and constraints for the evolution of Rodinia. Geology 29,
1071 – 1075.
Murphy, J.B., Nance, R.D., Keppie, J.D., 2002. West African
proximity of Avalon in the latest Precambrian by McNamara,
A.K., Mac Niocaill, C., van der Pluijm, B.A., Van der Voo, R.,
2001: discussion. Geological Society of America Bulletin 114,
1049 – 1050.
Nance, R.D., Dallmeyer, R.D., 1994. Structural and
40
Ar/
39
Ar min-
eral age constraints for the tectonothermal evolution of the
Green Head Group and Brookville Gneiss, southern New Bruns-
wick, Canada: implications for the configuration of the Avalon
composite terrane. Geological Journal 29, 293 – 322.
Nance, R.D., Murphy, J.B., 1990. Kinematic history of the Bass
River Complex, Nova Scotia: Cadomian tectonostratigraphic
relations in the Avalon terrane of the Canadian Appalachians.
In: D’Lemos, R.S., Strachan, R.A., Topley, C.G. (Eds.), The
Cadomian Orogeny. Geological Society of London Special Pub-
lication, vol. 51, pp. 395 –406.
Nance, R.D., Murphy, J.B., 1994. Contrasting basement isotopic
signatures and the palinspastic restoration of peripheral orogens:
example fr om the Neoproterozoic Avalonian– Cadomia n belt.
Geology 22, 617 – 620.
Nance, R.D., Murphy, J.B., 1996. Basement isotopic signatures and
Neoproterozoic paleogeograp hy of Avalonian – Cadomian a nd
related terranes in the circum-North Atlantic. In: Nance, R.D.,
Thompson, M.D. (Eds.), Avalonian and Related Peri-Gondwanan
Terranes of the Circum-North Atlantic. Geological Society of
America, Boulder, CO, Special Paper, vol. 304, pp. 333– 346.
Nance, R.D., Thompson, M.D. (Eds.), Avalonian and Related
Peri-Gondwanan Terranes of the Circum-North Atlantic.
Geological Society of America, Boulder, CO, Special Paper,
vol. 304.
Nance, R.D., Murphy, J.B., Strachan, R.A., D’Lemos, R.S., Taylor,
G.K., 1991. Late Proterozoic tectonostratigraphic evolution of
the Avalonian and Cadomian terranes. Precambrian Research
53, 41 – 78.
Nance, R.D., Murphy, J.B., Keppie, J.D., 2002. A Cordilleran mod-
el for the evolution of Avalonia. Tectonophysics 352, 11 – 31.
Neuman, R.B., 1984. Geology and paleobiology of islands in the
Ordovician Iapetus Ocean: review and implications. Geological
Society of America Bulletin 94, 1188 – 1201.
Nicholson, C., Sorlien, C.C., Atwater, T., Crowell, J.C., Luyendyk,
B.P., 1994. Microplate capture, rotation of the western trans-
verse ranges, and initiation of the San Andreas transform as a
low-angle fault system. Geology 22, 491 – 495.
Opdyke, N.D., Jones, D.S., McFadden, B.J., Smith, D.L., Mueller,
P.A., Shuster, R.D., 1987. Florida as an exotic terrane: paleo-
magnetic and geochronologic investigation of lower Paleozoic
rocks from the subsurface of Florida. Geology 15, 900 – 903.
Ortega-Gutie
´rrez, F., Keppie, J.D., 2000. Proterozoic Australia –
Western United States (AUSWUS) fit between Laurentia and
Australia: comment. Geology 28, 863.
Ortega-Gutie
´rrez, F., Elias-Herrera, M., Reyes-Salas, M., Lo
´pez, R.,
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 217

1999. Late Ordovician – early Silurian continental collision or-
ogeny in southern Mexico and its bearing on Gondwana – Lau-
rentia connections. Geology 27, 719 – 722.
Ortega-Obregon, C., 2002. Geologia, geoquı
´mica y Geocronologı
´a
del granito Etla, en el Estado de Oaxaca. Licenciatura en Ingen-
ierı
´a Geologica Tesis. Universidad Nacional Automona de Me
´x-
ico. 108 pp.
Pickering, K., Basset, M.G., Siveter, D.J., 1988. Late Ordovician –
Early Silurian destruction of the Iapetus Ocean: Newfoundland,
British Isles and Scandinavia—A discussion. Transactions of
Royal Society of Edinburgh 79, 361 – 382.
Plafker, G., Berg, H.C., 1994. Overview of the geology and tectonic
evolution of Alaska. In: Plafker, G., Berg, H.C. (Eds.), The
Geology of North America, vol. G-1. Geological Society of
America, Boulder, CO, pp. 989 – 1021.
Potts, S., Van der Pluijm, B., Van der Voo, R., 1993. Discordant
Silurian paleolatitudes for central Newfoundland: new paleo-
magnetic evidence from the Springdale Group. Earth and Plan-
etary Science Letters 120, 1 – 12.
Prigmore, J.K., Butler, A.J., Woodcock, N.H., 1997. Rifting during
separation of Eastern Avalonia from Gondwana: evidence from
subsidence analysis. Geology 25, 203 – 206.
Protti, M., Gu
¨endal, F., McNally, K., 1995. Correlation between the
age of the subducting Cocos Plate and the geometry of the Wa-
dati – Benioff zone under Nicaragua and Costa Rica. In: Mann, P.
(Eds.), Geologic and Tectonic Development of the Caribbean
Plate Boundary in Southern Central America. Geological Society
of America, Boulder, CO, Special Paper, vol. 295, pp. 309 – 326.
Quesada, C., 1990. Precambrian terranes in the Iberian Variscan
foldbelt. In: Strachan, R.A., Taylor, G.K. (Eds.), Avalonian
and Cadomian Geology of the North Atlantic. Blackie, London,
pp. 109 – 133.
Quesada, C., 1997. Evolucio
´n geodina
´mica de la zona Ossa-Mor-
ena durante el ciclo Cadomiense. In: Livro de Homenagem ao
Prof. Francisco Goncalves: Estudio sobre a Geologia de zona
de Ossa-Morena (Macico Ibe
´rico). IGME, Madrid, Spain,
pp. 205 – 230.
Rabu, D., Chantraine, J., Chauvel, J.J., Denis, E., Bale
´, P., Bardy,
Ph., 1990. The Brioverian (Upper Proterozoic) and the Cado-
mian orogeny in the Armorican Massif. In: D’Lemos, R.S.,
Strachan, R.A., Topley, C.G. (Eds.), The Cadomian Orogeny.
Geological Society of London Special Publication, vol. 51,
pp. 81 – 94.
Raeside, R.P., Barr, S.M., 1990. Geology and tectonic development
of the Bras d’Or suspect terrane, Cape Breton Island, Nova
Scotia. Canadian Journal of Earth Sciences 27, 1371 – 1381.
Ramos, V.A., Keppie, J.D. (Eds.), 1999. Laurentia – Gondwana
Connections before Pangea. Geological Society of America,
Boulder, CO, Special Paper, vol. 336. 276 pp.
Robardet, M., Bonjour, J.L., Paris, F., Morzadec, P., Racheboeuf,
P.R., 1994. The Variscan orogeny in the Armorica Massif: Ordo-
vician, Silurian, and Devonian of the medio-north-Armorican
domain. In: Keppie, J.D. (Ed.), Pre-Mesozoic Geology of France
and Related Areas. Springer, Heidelberg,Germany, pp. 142 –151.
Robison, R., Pantoja-Alor, J., 1968. Tremadocian trilobites from
Nochixtlan region, Oaxaca, Mexico. Journal of Paleontology
42, 767 – 800.
Ruiz, J., Tosdal, R.M., Restrepo, P.A., Marillo-Mun
˜eton, G.,
1999. Pb is otope evid ence fo r Colombi a – southern Me
´xico
connections in the Proterozoic. In: Ramos, V.A., Keppie,
J.D. (Eds.), Laurentia – Gondwana Connections before Pangea.
Geological Society of America, Boulder, CO, Special Paper,
vol. 336, pp. 183 – 198.
Samson, S.D., D’Lemos, R.S., 1998. U – Pb geochemistry and Sm –
Nd isotopic composition of Proterozoic gneisses, Channel Is-
lands, UK. Journal of the Geological Society of London 155,
609 – 618.
Samson, S.D., Hibbard, J.P., Wortman, G.L., 1995. Nd isotopic
evidence for juvenile crust in the Carolina terrane, southern
Appalachians. Contributions Mineralogy and Petrology 121,
171 – 184.
Samson, S.D., Secor, D.T., Stern, R., 1999. Provenance and paleo-
geography of Neoproterozoic circum-Atlantic arc-terranes: con-
straints from U – Pb ages of detrital zircons. Geological Society
of America Abstracts and Programs 31 (7), A-429.
Samson, S.D., Secor, D.T., Hamilton, M.A., 2001. Wandering
Carolina: tracking exotic terranes with detrital zircons. Geo-
logical Society of America Abstracts with Programs 33 (6),
A-263.
Soper, N.J., Strachan, R.A., Holdsworth, R.E., Gayer, R.A., Greiling,
R.O., 1992. Sinistral transpression and the Silurian closure of
Iapetus. Geological Society of London Journal 149, 871 – 880.
Sour-Tovar, F., Quiroz-Barroso, S.A., Navarro-Santillan, D., 1996.
Carboniferous invertebrates from Oaxaca, southern Mexico:
mid-continent paleogeographic extension. Geological Society
of America Abstracts with Programs 28 (7), A365.
Stampfli, G.M., Borel, G.D., 2002. A plate tectonic model for the
Paleozoic and Mesozoic constrained by dynamic plate bounda-
ries and restored synthetic ocean isochrons. Earth and Planetary
Science Letters 196, 17 – 33.
Stampfli, G.M., Borel, G., Cavazza, W., Mosar, J., Ziegler, P.A.,
2001. The paleotectonic atlas of the Peritethyan domain. Euro-
pean Geophysical Society (CD ROM).
Steiner, M.B., Walker, J.D., 1996. Late Silurian plutons in Yucatan.
Journal of Geophysical Research 101, 17727 – 17735.
Stewart, J.H., Blodgett, R.B., Boucot, A.J., Carter, J.L., Lo
´pez, R.,
1999. Exotic Paleozoic strata of Gondwanan provenance near
Ciudad Victoria, Tamaulipas, Me
´xico. In: Ramos, V.A., Keppie,
J.D. (Eds.), Laurentia – Gondwana Connections before Pangea.
Geological Society of America, Boulder, CO, Special Paper,
vol. 336, pp. 227 – 252.
Stock, J.M., Hodges, K.V., 1989. Pre-Pliocene extension around the
Gulf of California and the transfer of Baja California to the
Pacific plate. Tectonics 8, 99 – 115.
Strachan, R.A., D’Lemos, R.S., Dallmeyer, R.D., 1996. Late Pre-
cambrian evolution of an active plate margin: North Armorican
Massif, France. In: Nance, R.D., Thompson, M.D. (Eds.), Ava-
lonian and Related Peri-Gondwanan Terranes of the Circum-
North Atlantic. Geological Society of America, Boulder, CO,
Special Paper, vol. 304, pp. 319 – 332.
Tait, J., Scha¨tz, M., Bachtadse, V., Soffel, H., 2000. Paleomagnetism
and Paleozoic paleogeography of Gondwana and European ter-
ranes. In: Franke, W., Haak, V., Oncken, O., Tanner, D. (Eds.),
Orogenic Processes: Quantification and Modeling in the Varis-
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219218

can Belt. Geological Society, London, Special Publication, vol.
179, pp. 21 – 34.
Theokritoff, G., 1979. Early Cambrian provincialism and biogeo-
graphic boundaries in the North Atlantic region. Lethaia 12,
281 – 295.
Thorkelson, D.J., Taylor, R.P., 1989. Cordilleran slab windows.
Geology 17, 833 – 836.
Thorogood, E.J., 1990. Provenance of the pre-Devonian sediments
of England and Wales: Sm – Nd isotopic evidence. Journal Geo-
logical Society of London 147, 591 – 594.
Tichomirowa, M., Berger, H.J., Koch, E.A., Belyatski, B.V., Go¨ tze,
J., Kempe, U., Nasdala, L., Schaltegger, U., 2001. Zircon ages
of high grade gneisses in the Eastern Ergebirge (Central Euro-
pean Variscides)—constraints on origin of the rocks and Pre-
cambrian to Ordovician magmatic events in the Variscan
foldbelt. Lithos 56, 303 – 332.
Trench, A., Torsvik, T.H., 1992. The closure of the Iapetus Ocean
and Tornquist Sea: new paleomagnetic constraints. Journal Geo-
logical Society of London 149, 867 – 870.
Van der Voo, R., 1993. Paleomagnetism of the Atlantic, Tethys and
Iapetus Oceans. Cambridge Univ. Press, Cambridge, 411 pp.
Van Staal, C.R., Sullivan, R.W., Whalen, J.B., 1996. Provenance
and tectonic history of the Gander Zone in the Caledonian/
Appalachian Orogen: implications for the origin and assembly
of Avalon. In: Nance, R.D., Thompson, M.D. (Eds.), Avalonian
and Related peri-Gondwanan Terranes of the Circum-North
Atlantic. Geological Society of America, Boulder, CO, Special
Paper, vol. 304, pp. 347 – 368.
Van Staal, C.R., Dewey, J.F., Mac Niocaill, C., McKerrow, W.S.,
1998. The Cambria–Silurian tectonic evolution of the northern
Appalachians and British Caledonides: history of a complex, west
and southwest Pacific-type segment of Iapetus. In: Blundell, D.J,
Scott, A.C. (Eds.), Lyell: The Past is the Key to the Present.
Geological Society Special Publication, vol. 143, pp. 199 – 242.
Vick, H.K., Channell, J.E.T., Opdyke, N.D., 1987. Ordovician
docking of the North Carolina Slate Belt: paleomagnetic data.
Tectonics 6, 573 – 583.
Weber, B., Ko¨ hler, H., 1999. Sm/Nd, Rb/Sr, and U– Pb geochro-
nology of a Grenville terrane in southern Mexico: origin and
geologic history of the Guichicovi complex. Precambrian Re-
search 96, 245 – 262.
Weil, A.B., Ban der Voo, R., van der Pluijm, B., 2001. Oroclinal
bending and evidence against the Pangea megashear: the Can-
tabrian – Asturias arc (northern Spain). Geology 29, 901 – 904.
Wendt, J.I., Kro¨ner, A., Fiala, J., Todt, W., 1993. Evidence from
zircon dating for existence of approximately 2.1 Ga old crystal-
line basement in southern Bohemia, Czech Republic. Geologi-
sche Rundschau 82, 42 – 50.
Whittington, H.B., Hughes, C.P., 1974. Geography and faunal prov-
inces in the Tremadoc epoch. Society of Economic Paleontolo-
gists and Mineralogists Special Publication 21, 203 – 218.
Williams, H., 1964. The Appalachians in northeast Newfound-
land—a two-sided symmetrical system. American Journal of
Science 262, 1137 – 1158.
Williams, H., 1979. The Appalachian Orogen in Canada. Canadian
Journal of Earth Sciences 16, 792 – 807.
Williams, S.H., Harper, D.A.T., Neuman, R.B., Boyce, W.D., Mac
Niocaill, C., 1995. Lower Paleozoic fossils from Newfoundland
and their importance in understanding the history of the Iapetus
Ocean. In: Hibbard, J., van Staal, C., Cawood, P. (Eds.), Current
Perspectives in the Appalachian –Caledonian Orogen. Geolog-
ical Association Canada, Ottawa, Ontario, Special Paper, vol.
41, pp. 115 – 126.
Wortman, G.L., Samson, S.D., Hibbard, J.P., 2000. Precise U – Pb
zircon constraints on the earliest magmatic history of the Caro-
lina terrane. Journal of Geology 108, 321 – 338.
J.D. Keppie et al. / Tectonophysics 365 (2003) 195–219 219