Paleomagnetism of Siluro-Devonian and Cambrian granitic rocks from the Avalon zone in Cape Breton Island, Nova Scotia

1981 ◽  
Vol 18 (7) ◽  
pp. 1187-1210 ◽  
Author(s):  
K. V. Rao ◽  
M. K. Seguin ◽  
E. R. Deutsch
Keyword(s):  
Granitic Rocks ◽  
High Coercivity ◽  
Early Paleozoic ◽  
Early Devonian ◽  
Cape Breton Island ◽  
Polar Wander ◽  
Cape Breton ◽  
Northern Latitudes ◽  
Two Generations ◽  
Radiometric Ages

As part of a major study of the Avalon zone in Cape Breton Island, we describe the paleomagnetism of radiometrically well-studied granitic rocks of two generations, representing the Acadian (350–450 Ma) and the Avalonian (520–580 Ma) Orogenies, respectively. Detailed alternating field (AF) and thermal experiments performed on the younger granites indicate that they are characterized by three different mean directions of magnetization in the 10–60 mT coercivity spectra: SE (D = 149°, I = +70°; K = 160, N = 4 sites); NE-1 (D = 72°, I = −70°; K = 320, N = 3 sites); and NE-2 (D = 31°, I = −24°; K = 67, N = 3 sites) with corresponding paleopole positions at CB-1 (16°N, 41°W; δp, δm = 6°, 7°); CB-2 (32°N, 97°W; δp, δm = 7°, 8°); and CB-3 (27°S, 96°W; δp, δm = 6°, 11°). The radiometric ages of these three remanence directions do not differ from each other by more than 50 Ma; these remanences are also present as low coercivity (5–25 mT) magnetizations in the Avalonian granites (10 sites). Antipole CB-3 agrees with other recently reported Early Devonian paleomagnetic results from the northern Appalachians. In contrast, the two other antipoles (CB-1 and CB-2) are located in southerly latitudes but do not differ significantly from poles of contemporaneous rocks in New Brunswick and Newfoundland. The "aberrancy" of southerly located Siluro-Devonian poles with respect to those in northern latitudes is discussed in the context of possible transcurrent motion of the "Acadia" displaced terrain with respect to cratonic North America. Presently available paleomagnetic data are not conclusive and cannot confirm or negate this possibility. The CB-1, CB-2, and CB-3 poles are interpreted as representing rapid apparent polar wander with respect to Cape Breton Island during Siluro-Devonian time.In the older Cambrian granites, pole CB (37°N, 176°E; δp, δm = 2°, 3°), derived from a high coercivity (20–70 mT) mean remanence direction NW (D = 318°, I = +15°; K = 298, N = 10 sites), probably corresponds to the Avalonian Orogeny. Further results are needed to interpret the paleogeographic setting of the Avalon microcontinent in early Paleozoic time.

Radiometric Ages of Granitic Rocks, Cape Breton Island, Nova Scotia

1972 ◽  
Vol 9 (9) ◽  
pp. 1074-1086 ◽  
Author(s):  
Randall F. Cormier
Keyword(s):  
Nova Scotia ◽  
Mean Value ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Granitic Intrusion ◽  
Radiometric Ages ◽  
Northern Highlands

Rubidium–strontium whole-rock and mineral ages of granitic rocks from fourteen localities on Cape Breton Island have been measured. The ages cluster about a mean value of about 560 m.y. and indicate that most of the granitic rocks on the island have primary ages that are close to the Cambrian–Precambrian (Hadrynian) boundary. Some of the granitic rocks, particularly in the northern highlands, may have considerably younger, Siluro–Devonian (Acadian?), primary ages. Evidence is presented suggesting that simple biotite ages are not always reliable for the measurement of primary ages of granitic rocks. It. is suggested that, the granitic rocks having primary ages close to the Cambrian-Precambrian boundary be referred to a hitherto generally unrecognized episode of granitic intrusion, the Bretonian.

Radiometric Ages of Granitic Rocks, Cape Breton Island, Nova Scotia: Discussion

1973 ◽  
Vol 10 (1) ◽  
pp. 112-112
Author(s):  
Randall F. Cormier
Keyword(s):  
Nova Scotia ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Radiometric Ages

Radiometric Ages of Granitic Rocks, Cape Breton Island: Discussion

1973 ◽  
Vol 10 (9) ◽  
pp. 1470-1470 ◽  
Author(s):  
R. F. Cormier
Keyword(s):  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Radiometric Ages

Origin and Emplacement of Acadian Granitic Rocks, Northern Cape Breton Island

1975 ◽  
Vol 12 (2) ◽  
pp. 252-262 ◽  
Author(s):  
Robert A. Wiebe
Keyword(s):  
Country Rock ◽  
Source Region ◽  
Spatial Arrangement ◽  
High Water ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Northern Cape ◽  
Areal Variation ◽  
Differentiation Index

Acadian granitic rocks in northern Cape Breton Island consist entirely of even-grained leucocratic granodiorite and adamellite. The compositional range is small, and the average composition corresponds well with melts that could be generated in the crust. Abundant pegmatites in the contact zone suggest high water content.Within the major plutons these granitic rocks show: (1) high scatter on a Rb–Sr isochron (Cormier 1972), (2) apparently random areal variation in K and Ca, but a systematic areal variation in K/Rb and Ca/Sr, and (3) high scatter of Na2O and K2O on plots against differentiation index. The minor compositional heterogeneity indicated by these relations could have originated within the source region of melting or by assimilation during emplacement.The granitic plutons are elongate north–south and occur in an en echelon pattern within a NNE-trending migmatite zone. The spatial arrangement of pre-emplacement structures in the country rock and the distribution of xenoliths in the intrusions suggest that emplacement was accommodated by east–west expansion, upbowing of the surrounding country rock, faulting, and minor stoping.

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.

Pb and O isotopic constraints on the source of granitic rocks from Cape Breton Island, Nova Scotia, Canada

1996 ◽  
Vol 296 (7) ◽  
pp. 789-817 ◽  
Author(s):  
R. A. Ayuso ◽  
S. M. Barr ◽  
F. J. Longstaffe
Keyword(s):  
Nova Scotia ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Isotopic Constraints

scholarly journals Formation of Anorthositic Rocks within the Blair River Inlier of Northern Cape Breton Island, Nova Scotia (Canada)

Lithosphere ◽  
2021 ◽  
Vol 2020 (1) ◽  
Author(s):  
J. Gregory Shellnutt ◽  
Jaroslav Dostal ◽  
J. Duncan Keppie ◽  
D. Fraser Keppie
Keyword(s):  
Nova Scotia ◽  
Crustal Contamination ◽  
Parental Magma ◽  
Intrusive Complex ◽  
Early Devonian ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Iapetus Ocean ◽  
Northern Cape ◽  
Mineral Compositions

Abstract Rocks from the Blair River inlier of Northern Cape Breton Island (Nova Scotia, Canada) have been correlated with either the Grenville basement of eastern Laurentia or the accreted Avalon terrane. Additional zircon U-Pb dates of spatially associated anorthositic dykes (425.1±2.2 Ma) and a metagabbro (423.8±2.5 Ma) from the Fox Back Ridge intrusion of the Blair River inlier reveal Late Silurian emplacement ages. Their contemporaneity suggests that they may be members of a larger intrusive complex. The anorthositic rocks have high Eu/Eu∗ values (>2.5), and bulk compositions are similar to the mineral compositions of labradorite (An50-70) and andesine (An30-50). The metagabbro is compositionally similar to alkali basalt and does not seem to have been affected by crustal contamination (Nb/U>24; Th/NbPM≤1.1) although it was metamorphosed. The high Tb/YbN (1.8-1.9) ratios suggest that the parental magma of the metagabbro was derived from a garnet-bearing peridotite. Fractional crystallization and mass balance calculations indicate that the anorthositic rocks can be derived by mineral accumulation from a mafic parental magma similar in composition to the metagabbro of this study. The Late Silurian ages suggest that the rocks were emplaced into the Avalon terrane after the closure of the Iapetus Ocean but before Early Devonian (415-410 Ma) sinistral transpression.

Grenvillian basement in the northern Cape Breton Highlands, Nova Scotia

1987 ◽  
Vol 24 (5) ◽  
pp. 992-997 ◽  
Author(s):  
Sandra M. Barr ◽  
Robert P. Raeside ◽  
Otto van Breemen
Keyword(s):  
Nova Scotia ◽  
Long Range ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Basement Rocks ◽  
Northern Cape ◽  
Granitoid Rocks

The northernmost Cape Breton Highlands are underlain by the Blair River Complex, a distinctive assemblage of basement rocks including felsic and mafic gneisses, foliated gabbroic to granitic rocks, anorthosite, and foliated and unfoliated varieties of syenite. Major faults and mylonite zones separate the complex from schists, gneisses, and granitoid rocks typical of the rest of the Cape Breton Highlands. U–Pb dating of zircon from the Lowland Brook syenite of the Blair River Complex indicates a metamorphic age of [Formula: see text] and an igneous age of 1100–1500 Ma. These ages and the distinctive rock assemblage allow the Blair River Complex to be correlated with the Grenvillian rocks in the Long Range Inlier and Indian Head Range Complex of western Newfoundland. This is the first confirmed report of Grenvillian basement in Cape Breton Island, and it places new constraints on correlations between Newfoundland and the northern mainland Appalachians.

Northeastern extension and crustal expression of terranes from Cape Breton Island, Nova Scotia, based on geophysical data

1989 ◽  
Vol 26 (11) ◽  
pp. 2255-2267 ◽  
Author(s):  
B. D. Loncarevic ◽  
S. M. Barr ◽  
R. P. Raeside ◽  
C. E. Keen ◽  
F. Marillier
Keyword(s):  
High Pressure ◽  
Seismic Reflection ◽  
Granitic Rocks ◽  
Early Cambrian ◽  
Seismic Reflection Profile ◽  
The West ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Reflection Profile ◽  
Appalachian Orogen

The narrowest section of the Appalachian Orogen in Atlantic Canada (from Grenville-age basement in the west to the Avalon Terrane in the east) is preserved in Cape Breton Island, where components of four terranes display distinctive stratigraphic, igneous, metamorphic, aeromagnetic, and gravity characteristics. The Blair River Complex of northwestern Cape Breton Island is a fragment of Grenvillian rocks that is similar to units in western Newfoundland. The Aspy Terrane is characterized by mid-Paleozoic granitic rocks and high-pressure paragneisses and appears to continue across the Cabot Strait as the Gander Terrane of the Hermitage Flexure in Newfoundland. The Bras d'Or Terrane is composed of Hadrynian to Early Cambrian low-pressure metasedimentary units and dioritic to granitic plutonic rocks. As indicated by aeromagnetic anomalies, this terrane continues across the Laurentian Channel to the south coast of Newfoundland, where it may be terminated by the Hermitage Fault. The Avalon Terrane of southeastern Cape Breton Island bears many similarities to the Avalon Terrane of Newfoundland.A seismic reflection profile obtained as part of the Lithoprobe-East project shows that the Blair River Complex is juxtaposed against the Aspy Terrane by steeply dipping fault systems that cut through the entire crust and that the Bras d'Or Terrane is similarly juxtaposed with the Avalon Terrane. The nature of the boundary between the Aspy and Bras d'Or terranes is less clear, although metamorphic conditions and the seismic reflection profile both suggest that the Aspy Terrane represents a deeper crustal level, over which the Bras d'Or Terrane has been emplaced.

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