Geology and tectonic development of the Bras d'Or suspect terrane, Cape Breton Island, Nova Scotia

1990 ◽  
Vol 27 (10) ◽  
pp. 1371-1381 ◽  
Author(s):  
Robert P. Raeside ◽  
Sandra M. Barr
Keyword(s):  
Sedimentary Rocks ◽  
Early Cambrian ◽  
Significant Component ◽  
Southeastern Part ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Appalachian Orogen ◽  
Tectonic Development ◽  
Eastern Highlands

The Bras d'Or Terrane is defined in Cape Breton Island and consists of four distinctive components, (i) Low-pressure, regionally metamorphosed aluminous and calcareous gneiss of the Proterozoic Bras d'Or metamorphic suite is restricted to the southeastern part of the terrane. (ii) Late Proterozoic clastic-volcanic-carbonate units (Blues Brook, Malagawatch, McMillan Flowage, and Benacadie Brook formations, and Barachois River and Bateman Brook metamorphic suites) occur throughout the terrane and are generally at low metamorphic grades, although sillimanite grade has locally been achieved, (iii) A suite of 555–565 Ma calc-alkalic dioritic to granitic plutons was emplaced at pressures ranging from about 900 to less than 100 MPa. (iv) Early Ordovician granitic plutonism and Ordovician 40Ar/39Ar ages record regional heating.The Bras d'Or Terrane docked with the Mira Terrane to the southeast no earlier than the Ordovician. Cambro-Ordovician sedimentary rocks of the Mira Terrane appear locally to be thrust over the Bras d'Or Terrane. Mississippian sedimentary rocks overlap both terranes. The present boundary, the Macintosh Brook Fault, is mainly a Carboniferous feature. Docking with the Aspy Terrane to the northwest occurred along the Eastern Highlands shear zone and is constrained by a 375 Ma stitching pluton, the Black Brook Granitic Suite. Docking may have been initiated as early as 415 Ma, as indicated by reset 40Ar/39Ar ages near the boundary. The three Proterozoic components of the Bras d'Or Terrane have been recognized in the Brookville Terrane of southern New Brunswick, and Late Proterozoic gneiss, Late Proterozoic – early Cambrian calc-alkalic plutons and Ordovician granitic plutons have been reported in parts of the Hermitage Flexure of southern Newfoundland. The Bras d'Or Terrane may therefore be a regionally significant component of the northern Appalachian Orogen.

scholarly journals Reactivation of the Eastern Highlands Shear Zone, Cape Breton Island, Appalachian Orogen

2019 ◽  
Author(s):  
N Piette-Lauzière ◽  
R Graziani ◽  
K P Larson ◽  
D A Kellett
Keyword(s):  
Shear Zone ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Appalachian Orogen ◽  
Eastern Highlands

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.

40Ar/39Ar ages of detrital muscovite within Lower Cambrian and Carboniferous clastic sequences in northern Nova Scotia and southern New Brunswick: implications for provenance regions

1997 ◽  
Vol 34 (2) ◽  
pp. 156-168 ◽  
Author(s):  
R. D. Dallmeyer ◽  
J. D. Keppie ◽  
R. D. Nance
Keyword(s):  
Nova Scotia ◽  
New Brunswick ◽  
Lower Cambrian ◽  
Source Region ◽  
Regional Distribution ◽  
Coarse Grained ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Meguma Terrane

Detrital muscovite from lowermost Cambrian sequences exposed in the Avalon Composite Terrane in Nova Scotia and New Brunswick record 40Ar/39Ar plateau ages of ca. 625–600 Ma. These are interpreted to date times of cooling in source areas. The regional distribution of coarse-grained detrital muscovite in Lower Cambrian rocks of Avalonian overstep sequences suggests a source region of dimensions considerably larger than any presently exposed in Appalachian segments of the Avalon Composite Terrane. Late Proterozoic tectonic reconstructions locate the Avalon Composite Terrane adjacent to northwestern South America, thereby suggesting a possible source within Late Proterozoic PanAfrican – Brasiliano orogens. Detrital muscovite from clastic sequences of the proximally derived, Lower Carboniferous (Tournaisian) Horton Group and the more distal Upper Carboniferous (Westphalian D – Stephanian) Pictou Group in Nova Scotia records 40Ar/39Ar spectra that define plateau ages of ca. 390–380 Ma (Horton Group) and and ca. 370 Ma (Pictou Group). Finer grained fractions from samples of the Horton Group display more internally discordant age spectra defining total-gas ages of ca. 397–395 Ma. A provenance for the finer muscovite may be found in southern Nova Scotia where Cambrian–Ordovician turbidites of the Meguma Group display a regionally developed micaceous cleavage of this age. The ca. 390–380 Ma detrital muscovites probably were derived from granite stocks presently exposed in proximal areas of northernmost Cape Breton Island. A more distal source for the ca. 370 Ma detrital muscovites in the Pictou Group is suggested by its original extensive distribution, although a local, possibly recycled, source may also have been present. The presence of only 400–370 Ma detrital muscovite suggests a rapidly exhumed orogenic source with characteristics similar to those of crystalline rocks presently exposed in the Cape Breton Highlands and (or) the Meguma Terrane.

Tectonic significance of the Carboniferous Big Pond Basin, Cape Breton Island, Nova Scotia

1986 ◽  
Vol 23 (12) ◽  
pp. 2000-2011 ◽  
Author(s):  
Dwight C. Bradley ◽  
Lauren M. Bradley
Keyword(s):  
Sedimentary Rocks ◽  
Sedimentary Basins ◽  
Strike Slip ◽  
Fault System ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Pull Apart Basin ◽  
Tectonic Significance ◽  
Basin Margin ◽  
Faulted Basin

Detailed mapping in southeastern Cape Breton Island has revealed a strike-slip origin for the small Carboniferous outlier at Big Pond. Topographically low Carboniferous sedimentary rocks occur between splays of a previously unrecognized, northeast-trending set of high-angle faults, the Big Pond fault system. The section is dominated by fanglomerates, which coarsen toward the faulted basin margins and which were deposited and (or) reworked by currents flowing toward the basin's center and along its axis. We interpret the fanglomerates as syntectonic. Interbedded limestones of Visean age (Windsor B Subzone) provide age control for the upper part of the 300 m section and, by inference, for at least some of the fault motion. Dextral motion on the Big Pond fault system is indicated by (1) slickenside stepping directions on minor faults, which juxtapose basement against basement and which parallel the main northeast-striking fault; (2) northeast-striking mesoscale faults within the basin, which produce dextral offsets; and (3) shear and extension fractures in fanglomerate clasts along the northeast-striking basin margin faults, which reveal dextral and down-to-basin motion. The location of the basin at a right step in the through-going dextral fault system implies that it is a pull-apart basin. We suggest that during Visean times, southern Cape Breton Island was cut by several such dextral wrench faults and associated sedimentary basins and that the tectonic climate was similar to that recognized by previous workers in Newfoundland and New Brunswick. No evidence was found in support of the paleomagnetically based hypothesis for sinistral strike slip during this time.

The age of igneous and metamorphic events in the western Cape Breton Highlands, Nova Scotia

1986 ◽  
Vol 23 (12) ◽  
pp. 1891-1901 ◽  
Author(s):  
R. A. Jamieson ◽  
O. van Breemen ◽  
R. W. Sullivan ◽  
K. L. Currie
Keyword(s):  
Metamorphic Rocks ◽  
Western Cape ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
The North ◽  
Cape Breton ◽  
Gneiss Complex ◽  
Form Part ◽  
Plutonic Rocks ◽  
High Level

Plutonic rocks of four different ages have been recognized in the Cape Breton Highlands on the basis of U–Pb dating of zircons. Two plutons, the North Branch Baddeck River leucotonalite [Formula: see text] and the Chéticamp pluton (550 ± 8 Ma), give dates that fall within the range of Late Proterozoic to Cambrian ages considered characteristic of the Avalon tectonostratigraphic zone of the eastern Appalachians. Late Ordovician to Silurian tonalite (Belle Côte Road orthogneiss, 433 ± 20 Ma) was metamorphosed, deformed, and incorporated into the central Highlands gneiss complex by approximately 370–395 Ma. High-level subvolcanic plutons (Salmon Pool pluton, [Formula: see text]) postdate all metamorphic rocks in the area. The presence of the older plutons is consistent with interpretation that the Cape Breton Highlands form part of the Avalon zone, but the presence of Ordovician–Silurian plutonic rocks and Devonian amphibolite-facies metamorphism is anomalous in comparison with the Avalon zone of Newfoundland and southeastern Cape Breton Island. Terranes with similar Late Proterozoic to mid-Paleozoic plutonic and metamorphic histories form a discontinuous belt along the northwest side of the Avalon zone southwest of Cape Breton Island. These rocks probably reflect events during and after the accretion of the Avalon zone to North America.

Relationship between the Aspy and Bras d'Or "terranes" in the northeastern Cape Breton Highlands, Nova Scotia

1993 ◽  
Vol 30 (9) ◽  
pp. 1773-1781 ◽  
Author(s):  
Shoufa Lin
Keyword(s):  
Shear Zone ◽  
Sedimentary Rocks ◽  
The West ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Cape Breton ◽  
Basal Conglomerate ◽  
Back Arc ◽  
Eastern Highlands ◽  
Basin System

According to previous interpretations, the Eastern Highlands shear zone separates Ordovician–Silurian volcano-sedimentary rocks to the west (Cheticamp Lake Gneiss of the Aspy "terrane") from late Precambrian sedimentary rocks and dioritic – tonalitic plutons and Early Ordovician granite to the east (Bras d'Or "terrane"). New mapping discovered a basal conglomerate of the Cheticamp Lake Gneiss that rests on deformed diorite of the Bras d'Or "terrane" and contains clasts similar or identical to rocks of the Bras d'Or "terrane." The late Precambrian rocks of the Bras d'Or "terrane" are also overlain by a volcano-sedimentary sequence of Silurian age (Clyburn Brook formation). These observations suggest that rocks of the Aspy "terrane" lie unconformably on those of the Bras d'Or "terrane." The Eastern Highlands shear zone is therefore not a terrane boundary. The Ordovician–Silurian rocks of the Aspy "terrane" are interpreted to have formed in an arc–back-arc basin system. The back-arc basin is interpreted to have formed by rifting in the Bras d'Or "terrane" and the Eastern Highlands shear zone to have been related to the closure of the basin.

Geological correlations between Cape Breton Island and Newfoundland, northern Appalachian orogen

1998 ◽  
Vol 35 (11) ◽  
pp. 1252-1270 ◽  
Author(s):  
S M Barr ◽  
R P Raeside ◽  
C E White
Keyword(s):  
Sensu Stricto ◽  
Mobile Belt ◽  
Cape Breton Island ◽  
Small Areas ◽  
Isotopic Signatures ◽  
The North ◽  
Rock Types ◽  
Cape Breton ◽  
Appalachian Orogen ◽  
Back Arc

Geological correlations between Cape Breton Island and Newfoundland are apparent both in surface geology and at deeper crustal levels, based on similarities in Sm-Nd isotopic signatures. The Mira terrane of southeastern Cape Breton Island is part of the Avalon terrane sensu stricto and is composed of Neoproterozoic volcanic-sedimentary-plutonic belts and overlying Cambrian rocks directly comparable to those in the western part of the Newfoundland Avalon terrane. The Bras d'Or terrane is also mainly of Neoproterozoic age, but shows lithological and isotopic contrasts with the Mira terrane. Small areas of similar Neoproterozoic rocks occur in southern Newfoundland and to the north as inliers in the Exploits terrane. The Bras d'Or terrane and similar rocks in Newfoundland are interpreted to represent a peri-Gondwanan terrane where rocks of the Gander terrane were later formed. Hence this area is part of the Central Mobile Belt and distinct from Avalon terrane sensu stricto. The Aspy terrane is a complex area that may include fragments of Bras d'Or crust and components of the Gander, Exploits, and possibly Notre Dame terranes of Newfoundland. It formed by subduction and back-arc basin opening and closure during the Silurian to Early Devonian. The Blair River Inlier is a fragment of Grenvillian rocks, similar to those in the Grenvillian inliers in the Humber zone of western Newfoundland in terms of age, rock types, and isotopic composition. Silurian and Devonian promontory-promontory collision resulted in juxtaposition and stacking of these elements in Cape Breton Island, as in the Hermitage Flexure - Port aux Basques area of Newfoundland. Because the lower crust under Bras d'Or - Gander - Aspy terranes seems distinct from that under Avalon terrane sensu stricto, it is preferable to use the term peri-Gondwanan rather than Avalonian to refer to these areas.

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