Contrasting metamorphic terranes near Chéticamp, Cape Breton Highlands, Nova Scotia

Two contrasting metamorphic terranes can be recognized in northwestern Cape Breton Island. One terrane (Pleasant Bay complex) consists of biotite gneiss and quartzite with minor calc-silicate lenses that were metamorphosed in Late Precambrian time (about 550 Ma) and were subsequently intruded by Silurian salic and mafic plutons that were, in turn, deformed and intruded by granite in Devonian time. The other terrane (Jumping Brook complex) consists of volcanogenic and sedimentary schists of probable Silurian age that were metamorphosed in Devonian time. P–T estimates indicate that the older parts of the Pleasant Bay complex were metamorphosed at about 790 °C and 7 kbar (1 kbar = 100 MPa) at low to moderate water fugacities during a major intrusive episode. The Jumping Brook complex exhibits a single progressive metamorphic sequence now disrupted by faulting. P–T conditions during this Devonian (370–390 Ma) metamorphism varied from greenschist (300 °C at <3 kbar) to amphibolite (650 °C at 4 kbar) facies. Metamorphism probably occurred in a thermal dome. The data suggest a moderately deformed basement–cover relation between the Pleasant Bay and Jumping Brook complexes.

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U-Pb geochronological constraints on Precambrian stratified units in the Avalon Composite Terrane of Nova Scotia, Canada: tectonic implications

Canadian Journal of Earth Sciences ◽

10.1139/e97-109 ◽

1998 ◽

Vol 35 (3) ◽

pp. 222-236 ◽

Cited By ~ 71

Author(s):

J Duncan Keppie ◽

D W Davis ◽

T E Krogh

Keyword(s):

Nova Scotia ◽

Shear Deformation ◽

Volcanic Activity ◽

Detrital Zircons ◽

Published Data ◽

Cape Breton Island ◽

Magmatic Arc ◽

Cape Breton ◽

Facies Metamorphism ◽

George River

Concordant U-Pb ages of detrital zircons in several Proterozoic units in the Avalon Composite Terrane of Nova Scotia, along with previously published data, indicate that deposition of low- and high-grade stratified units in the Cobequid Highlands (Gamble Brook Formation) and central Cape Breton Island (variously assigned to the George River Group or George River Metamorphic Suite and the Bras d'Or Gneiss) started after ~977 Ma, extended through a period of volcanic activity between ~694 and 637 Ma, and ended before the ~629-612-600 Ma volcanic activity associated with deposition of the Georgeville and Jeffers groups in the Antigonish and Cobequid highlands, and the East Bay Hills and Coxheath groups in southern Cape Breton Island. These age data, along with U-Pb analyses of metamorphic and igneous zircon and monazite, also constrain three Late Proterozoic tectonothermal events: (i) oblique sinistral ductile shear deformation and greenschist-amphibolite-facies metamorphism probably occurred between ~694 and 629 Ma; (ii) oblique dextral deformation and greenschist-facies metamorphism is bracketed between ~612 and 607 ± 2 Ma; and (iii) low-angle, normal shear deformation associated with low-pressure, high-temperature metamorphism took place at ~553-550 Ma. These three events may record (i) opening and (ii) closing of the Antigonish-Cobequid back-arc basin, followed by (iii) gravitational collapse of the central Cape Breton magmatic arc following cessation of subduction, respectively. The combination of ~700-550 Ma arc magmatism and ~1.3-1.0 Ga concordant detrital zircon ages in the Avalon Composite Terrane suggests provenance in the Amazon craton or Oaxaquia in Mexico.

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Stratigraphy, tectonic setting, and geological history of late Precambrian volcanic-sedimentary-plutonic belts in southeastern Cape Breton Island, Nova Scotia

10.4095/208235 ◽

1996 ◽

Cited By ~ 4

Author(s):

S M Barr ◽

C E White ◽

A S Macdonald

Keyword(s):

Nova Scotia ◽

Tectonic Setting ◽

Geological History ◽

Cape Breton Island ◽

Late Precambrian ◽

Cape Breton ◽

History Of

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Paleomagnetism of the Late Precambrian Fourchu Group, Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e86-155 ◽

1986 ◽

Vol 23 (11) ◽

pp. 1673-1685 ◽

Cited By ~ 28

Author(s):

Rex J. E. Johnson ◽

Rob Van der Voo

Keyword(s):

Nova Scotia ◽

Eastern Cape ◽

Early Paleozoic ◽

Cape Breton Island ◽

Late Precambrian ◽

Cape Breton ◽

Younger Age ◽

Recent Origin ◽

Gabbroic Intrusion ◽

Dual Polarity

Volcanogenic sediments of the Fourchu Group and a gabbroic intrusion, which are found in the Avalonian terrane of south-eastern Cape Breton Island, have been sampled for paleomagnetic analysis. Upon detailed thermal and alternating-field demagnetization, three often-superimposed components of magnetization are obtained. One of these is aligned with the present-day geomagnetic field direction in Nova Scotia and is assumed to be of recent origin. The second group of directions is south-southeasterly and shallow, is postfolding in age, and is inferred to represent a Carboniferous overprint. The third direction, carried almost always by hematite, is also postfolding and yields a dual-polarity mean direction to the northwest or south-east, with a fairly steep inclination (D = 132°, I = −63°). This last direction is not seen in Avalonian or other North American rocks of Devonian or younger age; it is, therefore, bracketed in age between the earliest folding of the rocks and the latest Silurian. Given that Taconic folding has not been reported for this area, we assume that this magnetization was introduced in the rocks during uplift and oxidation after an Avalonian folding phase. For the Avalon terrane of Nova Scotia, the available paleomagnetic data reveal a set of moderately high paleolatitudes for the Late Precambrian and early Paleozoic, in contrast to the near-equatorial values predicted for the area under the assumption that it remained fixed with respect to the craton. On the other hand, strong similarities exist between Avalonian paleolatitudes and those for Armorica and Gondwana; a tentative reconstruction is proposed in which Avalon is adjacent to Armorica and Gondwana in the Late Precambrian and early Paleozoic.

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Contrasting U–Pb ages from plutons in the Bras d'Or and Mira terranes of Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e90-127 ◽

1990 ◽

Vol 27 (9) ◽

pp. 1200-1208 ◽

Cited By ~ 27

Author(s):

S. M. Barr ◽

G. R. Dunning ◽

R. P. Raeside ◽

R. A. Jamieson

Keyword(s):

Nova Scotia ◽

Close Similarity ◽

Zircon Age ◽

Middle Cambrian ◽

Cape Breton Island ◽

Early Ordovician ◽

Late Precambrian ◽

Cape Breton ◽

Devonian Age

U–Pb dates from zircon, titanite, and monazite in plutons of the Bras d'Or and Mira terranes of southern Cape Breton Island, combined with 40Ar/39Ar and other radiometric age data, indicate that the Bras d'Or and Mira terranes had separate magmatic and metamorphic histories until at least the Middle Cambrian and possibly until the Devonian. The Bras d'Or Terrane is characterized by abundant late Precambrian (ca. 565–555 Ma) dioritic to granitic plutons, as exemplified by the Shunacadie granodiorite ([Formula: see text], U–Pb zircon). Early Ordovician granitic plutons, such as the Kellys Mountain leucogranite with a U–Pb (zircon) age of 498 ± 2 Ma, occur locally. Titanite and 40Ar/39Ar (hornblende) ages from plutons and metamorphic units suggest that widespread metamorphism may have occurred between these plutonic events and (or) during the Early Ordovician plutonism.Plutons in the Mira Terrane appear to have been emplaced at about 620 Ma or before, as exemplified by the Chisholm Brook granodiorite ([Formula: see text]), and to have been unaffected by younger thermal events, as indicated by close similarity of U–Pb (zircon and titanite) and 40Ar/39Ar (hornblende) ages. Plutons of Devonian age are localized in an easterly trending belt in the central part of the terrane. In contrast to the Bras d'Or Terrane, widespread latest Precambrian (ca. 565–555 Ma) to Early Ordovician plutonism and metamorphism appear to have been absent. It is unlikely that the Mira and Bras d'Or terranes were juxtaposed before the Early Ordovician.

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