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

1990 ◽  
Vol 27 (9) ◽  
pp. 1200-1208 ◽  
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.

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

1987 ◽  
Vol 24 (12) ◽  
pp. 2422-2435 ◽  
Author(s):  
K. L. Currie
Keyword(s):  
Nova Scotia ◽  
The Other ◽  
Biotite Gneiss ◽  
Cape Breton Island ◽  
Late Precambrian ◽  
Cape Breton ◽  
Facies Metamorphism ◽  
Cover Relation ◽  
Metamorphic Terranes

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.

Upper Placentian—Branchian series of mainland Nova Scotia (middle-upper Lower Cambrian): Faunas, paleoenvironments, and stratigraphic revision

1995 ◽  
Vol 69 (3) ◽  
pp. 475-495 ◽  
Author(s):  
Ed Landing
Keyword(s):  
Nova Scotia ◽  
Lower Cambrian ◽  
Preliminary Evidence ◽  
Middle Cambrian ◽  
Cape Breton Island ◽  
Cape Breton ◽  
History Of ◽  
Placentia Bay ◽  
Stratigraphic Nomenclature ◽  
Eastern Massachusetts

Lithostratigraphy and depositional and epeirogenic history of the upper Placentian Series (Cuslett-Fosters Point Formations of the Bonavista Group) and Branchian Series (Brigus Formation) are identical in the northern Antigonish Highlands; Cape Breton Island; and eastern Placentia Bay, southeastern Newfoundland. Preliminary evidence suggests that the lower Middle Cambrian is present in the field area. A unified, uppermost Precambrian–Lower Cambrian, formation- and member-level nomenclature is appropriate to Avalonian North America, and the stratigraphic nomenclature of southeastern Newfoundland is applied in northern mainland Nova Scotia.Latest Placentian shoaling and deposition of a peritidal carbonate lithosome and unconformable onlap of the trilobite-bearing Branchian Series occurred in shallow Avalonian shale basins from eastern Massachusetts to central England.Uppermost Placentian Series faunas are very diverse in the Fosters Point Formation. Limited similarities with the South Australian Lower Cambrian are indicated by the presence of Camenella sp. cf. C. reticulosa, Conotheca australiensis, and Hyptiotheca sp., but these forms do not contribute to highly resolved correlation.Twenty-eight taxa are illustrated from the upper Placentian and Branchian Series. Caveacus rectus n. gen. and sp., a phosphatic problematicum, is limited to the upper Placentian Series. The oldest, skeletalized, macrophagous predators are the Pseudoconodontida and the later appearing Protoconodontida (n. orders). The Pseudoconodontida includes the Protohertzinacea n. superfamily and Strictocorniculacea n. superfamily (with the Rhombocorniculidae and Strictocorniculidae n. families). Strictocorniculum vanallerum n. gen. and sp. is described. The tommotiid family Sunnaginiidae emend. includes Eccentrotheca, Sunnaginia, Kulparina, and Jayceia deltiformis n. gen. and sp.

Middle Cambrian paleomagnetism of the Avalon Terrane in Cape Breton Island, Nova Scotia

Tectonics ◽  
1985 ◽  
Vol 4 (7) ◽  
pp. 629-651 ◽  
Author(s):  
Rex J. E. Johnson ◽  
Rob Van der Voo
Keyword(s):  
Nova Scotia ◽  
Middle Cambrian ◽  
Cape Breton Island ◽  
Cape Breton

Cambrian acritarchs from the Bourinot belt, Cape Breton Island, Nova Scotia: age and stratigraphic implications1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

2012 ◽  
Vol 49 (1) ◽  
pp. 289-307 ◽  
Author(s):  
Teodoro Palacios ◽  
Sören Jensen ◽  
Chris E. White ◽  
Sandra M. Barr
Keyword(s):  
Nova Scotia ◽  
Special Issue ◽  
Middle Cambrian ◽  
Cape Breton Island ◽  
Cape Breton

We present the first description of organic-walled microfossils from Cambrian strata of the Bourinot belt, central Cape Breton Island. Age-diagnostic acritarchs have been recovered from the Dugald and MacMullin formations and from probable levels within the upper part of the Eskasoni Formation, which permit detailed correlations with acritarch-based zones in Newfoundland and Spain. The assemblage of acritarchs from the Dugald Formation confirms earlier assignments to the early middle Cambrian eteminicus Zone, but it also indicates that the upper part of the formation belongs to the hicksi Zone of the Drumian Stage. Acritarchs from the MacMullin Formation provide the first biostratigraphic evidence that this unit extends into the forchhammeri Zone of the Guzhangian Stage. These acritarchs are present in the lower part of the MacMullin Formation, putting into question earlier identification of hicksi Zone trilobites in this unit and raising the possibility of an unconformity. The data from the Bourinot belt provide additional evidence for the biostratigraphic utility of acritarchs in the Cambrian Acado-Baltic province.

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

1986 ◽  
Vol 23 (11) ◽  
pp. 1673-1685 ◽  
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.

40Ar/39Ar mineral ages from Kellys Mountain, Cape Breton Island, Nova Scotia: implications for the tectonothermal evolution of the Avalon composite terrane

1989 ◽  
Vol 26 (8) ◽  
pp. 1509-1516 ◽  
Author(s):  
J. Duncan Keppie ◽  
R. D. Dallmeyer
Keyword(s):  
Nova Scotia ◽  
Contact Aureole ◽  
Rapid Cooling ◽  
Middle Cambrian ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Mineral Assemblages ◽  
Plutonic Complex ◽  
High Level

Hornblende from a diorite stock within the Kellys Mountain plutonic complex within the Avalon composite terrane, and hornblende, muscovite, and biotite from amphibolite and gneiss within the contact aureole record similar 40Ar/39Ar plateau ages of 493–498 Ma. These data indicate relatively rapid cooling through the contrasting temperatures appropriate for intracrystalline retention of argon in the different minerals. This is consistent with the relatively high level of intrusion of the pluton (3–10 km) suggested previously from the study of mineral assemblages developed in the contact aureole. These relationships suggest that intrusion of the Kellys Mountain complex took place at approximately 500 Ma, indicating an age close to the Cambro-Ordovician boundary. The complex may have formed in the same within-plate rifting regime as the Middle Cambrian Bourinot Group volcanic sequences exposed within the Avalon composite terrane.

U – Pb zircon date from Avalonian Cape Breton Island and geochronologic calibration of the Early Ordovician

1997 ◽  
Vol 34 (5) ◽  
pp. 724-730 ◽  
Author(s):  
Ed Landing ◽  
Samuel A. Bowring ◽  
Kathleen L. Davidek ◽  
Richard A. Fortey
Keyword(s):  
New Brunswick ◽  
Eastern Cape ◽  
Associated Fauna ◽  
Zircon Age ◽  
Cape Breton Island ◽  
Early Ordovician ◽  
Cape Breton ◽  
Fossil Evidence ◽  
North Wales ◽  
Saint John

A U–Pb zircon date of 483 ± 1 Ma is recorded from an uppermost Tremadoc K-bentonite from the Chesley Drive Group on McLeod Brook, eastern Cape Breton Island. The associated fauna, with the trilobite Peltocare rotundifrons, is also known from the Reversing Falls section in Saint John, New Brunswick, and the traditional reference of the latter section to the Arenig is incorrect. A 483 ± 1 Ma age is significantly older than a U – Pb zircon age reported from the classical base of the Arenig Series in north Wales and about 10 Ma older than strata regarded herein as upper Arenig in central Newfoundland. If the global standard for the base of the Arenig is defined at the Tetragraptus approximatus Zone base, then the base of the type Arenig in Wales is younger than the latter horizon. The McLeod Brook occurrence is from an uppermost Tremadoc (Hunnebergian Stage) interval that has been removed below the unconformity in north Wales. The age of the Tremadoc –Arenig series boundary remains uncertain; however, a tentative estimate that it is significantly younger than 483 Ma is suggested by fossil evidence.

Cambrian volcanism in Nova Scotia, Canada

1985 ◽  
Vol 22 (4) ◽  
pp. 599-606 ◽  
Author(s):  
J. B. Murphy ◽  
K. Cameron ◽  
J. Dostal ◽  
J. Duncan Keppie ◽  
A. J. Hynes
Keyword(s):  
Nova Scotia ◽  
Lower Cambrian ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Felsic Magma ◽  
Middle Cambrian ◽  
Cape Breton Island ◽  
Shallow Marine ◽  
Cape Breton ◽  
Pull Apart Basin

Cambrian volcanic rocks in Nova Scotia occur in small grabens or half grabens in the Avalon Zone (Composite Terrane) as part of a thin sequence of continental to shallow-marine Cambro-Ordovician rocks. In the northern Antigonish Highlands, the volcanic rocks occur mainly in the Lower Cambrian McDonalds Brook Group. In southern Cape Breton Island, they occur predominantly in the Middle Cambrian Bourinot Group. The chemistry of these volcanic rocks indicates that they are bimodal (basalts–rhyolites) and within plate. The basalts are alkalic in the Antigonish Highlands and tholeiitic in Cape Breton Island. The rising basaltic magma is postulated to have produced the felsic magma by anatexis of the crust. It is proposed that the Antigonish Highlands volcanic rocks erupted in a small pull-apart basin. A similar structural setting is probable in southern Cape Breton Island, but there the bounding faults are poorly exposed. These basins probably formed during a period of transpression in the last stages of the late Hadrynian Cadomian deformation.

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