Geochemistry of Late Proterozoic basaltic rocks from southeastern Cape Breton Island, Nova Scotia

1990 ◽  
Vol 27 (5) ◽  
pp. 619-631 ◽  
Author(s):  
J. Dostal ◽  
J. D. Keppie ◽  
J. B. Murphy
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Progressive Increase ◽  
Cape Breton Island ◽  
Basaltic Rocks ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Intermediate Units ◽  
Light Rare Earth Elements ◽  
Greenschist Facies Metamorphism

Late Proterozoic volcanic rocks of the Fourchu Group from the Avalon Zone in southeastern Cape Breton Island, Nova Scotia, are composed predominantly of mafic and felsic types with subordinate intermediate units that were all affected by subgreenschist- to greenschist-facies metamorphism. The rocks crop out in four fault blocks (Coastal, Stirling, East Bay Hills, and Coxheath) and have geochemical characteristics of ensialic orogenic volcanic suites. The basaltic rocks range from tholeiitic to calc-alkaline and show a distinct compositional zonation that resembles the across-arc variation observed in recent volcanic-arc systems. The variations include a progressive increase in abundances of light rare-earth elements, Th, Zr, Hf, Nb, and Ta and in the ratios of Zr/SiO2, Th/SiO2, Zr/Y, La/Yb, and Th/Hf from the Coastal block in the southeast to the Coxheath block in the northwest. The zonation may be explained in terms of a northwesterly-dipping subduction zone, with the trench lying to the southeast of Nova Scotia.

Birth of the Avalon arc in Nova Scotia, Canada: geochemical evidence for ∼700–630 Ma back-arc rift volcanism off Gondwana

1998 ◽  
Vol 135 (2) ◽  
pp. 171-181 ◽  
Author(s):  
J. D. KEPPIE ◽  
J. DOSTAL
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Benioff Zone ◽  
Calc Alkaline ◽  
Cape Breton Island ◽  
Mafic Rocks ◽  
Cape Breton ◽  
Arc Setting ◽  
Oceanic Island Basalts ◽  
Back Arc

Central Cape Breton Island in Nova Scotia, Canada, is host to ∼700–630 Ma felsic and associated mafic volcanic rocks that are relatively rare in other parts of the Avalon Composite Terrane, occurring elsewhere only in the Stirling Block of southern Cape Breton Island and in parts of eastern Newfoundland. The mafic rocks of central Cape Breton Island are typically intraplate tholeiitic basalts generated by melting of a garnet-bearing mantle source. They lack a continental trace element and εNd imprint although they were emplaced on continental crust; they resemble oceanic island basalts. Contemporaneous volcanism in the Stirling Block is calc-alkaline and formed in a volcanic arc setting. In the absence of evidence for an intervening trench complex or suture, it may be inferred that the central Cape Breton tholeiites formed in a back-arc setting relative to the Stirling Block. This rifting may represent the initial stages of separation of an Avalonian arc from western Gondwana. The arc rifted further between ∼630–610 Ma when the younger Antigonish-Cobequid back-arc basin formed. Subsequently, the extensional arc became convergent, telescoping the back-arc basin. Northwestward migration of calc-alkaline arc magmatism may be related to shallowing of the associated Benioff zone through time.

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.

Appalachian basement and its intrusion by Cretaceous dykes, offshore southeast Nova Scotia, Canada

1993 ◽  
Vol 30 (12) ◽  
pp. 2495-2509 ◽  
Author(s):  
L. F. Jansa ◽  
G. Pe-Piper ◽  
B. D. Loncarevic
Keyword(s):  
Nova Scotia ◽  
Short Wavelength ◽  
Lower Grade ◽  
Aeromagnetic Data ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Depleted Mantle ◽  
Half Graben ◽  
Meguma Terrane

Aeromagnetic data collected between eastern Nova Scotia and southern Newfoundland provide new information about the offshore extension of the Avalon and Meguma terranes. A zone of short-wavelength anomalies that delineates Scatarie Ridge extends westward to the Late Proterozoic Fourchu Group in southeastern Cape Breton Island and eastward towards the Burin Peninsula of Newfoundland, suggesting that both regions belong to the same tectono-stratigraphic province of the Avalon composite terrane. A different zone of short-wavelength, discontinuously lineated anomalies at the northern edge of the Canso Ridge correlates with amphibolite-facies metamorphic rocks of the Meguma terrane on the Canso Peninsula, interpreted as an exhumed deeper metamorphic level of the Meguma terrane at its boundary with the Avalon terrane. The S-shaped pattern of long linear magnetic trends, characteristic of lower grade Meguma rocks on the southern flank of the Canso Ridge, indicates plastic deformation of the Meguma terrane during the Acadian orogeny when emplaced against the rigid Cape Breton Island block indentor. Analogous patterns occur off western Nova Scotia, suggesting little strike-slip motion occurred between the Meguma and Avalon terranes since the Acadian orogeny.Late Proterozoic rocks on Scatarie Ridge are intruded by Cretaceous diabase dykes. The diabase is alkaline with a within-plate geochemical signature, similar in composition to basalt flows in the Orpheus half-graben. A depleted-mantle model age TDM (Nd) of 731 Ma, εNd = +6.5, suggests that the magma was sourced from a lithospheric mantle reservoir involved in Late Proterozoic magmatic activity. Aeromagnetic data interpretation confirms the distribution of Cretaceous basalt flows and sills within Mesozoic sedimentary strata of the Orpheus half-graben previously outlined by seismic methods but was unable to differentiate between Proterozoic and Mesozoic intrusive rocks where the Proterozoic rocks lay near to the ocean floor.

ABSOLUTE AGE OF THE FISSET BROOK FORMATION AND THE DEVONIAN-MISSISSIPPIAN BOUNDARY, CAPE BRETON ISLAND, NOVA SCOTIA

1964 ◽  
Vol 1 (3) ◽  
pp. 159-166 ◽  
Author(s):  
R. F. Cormier ◽  
A. M. Kelly
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Cape Breton Island ◽  
Rock Samples ◽  
Cape Breton ◽  
Absolute Age ◽  
Age Determinations ◽  
Good Agreement

The Fisset Brook formation of sedimentary and volcanic rocks crops out in the Cheticamp area of Cape Breton Island, Nova Scotia. Its stratigraphic age has been determined as earliest Mississippian using spores contained in the sedimentary members. A rubidium–strontium age determination using whole-rock samples of the volcanic members has yielded an age of 349 ± 15 million years. This is in good agreement with age determinations elsewhere for the Devonian–Mississippian boundary. Similar rocks exposed to the east of Lake Ainslie, some thirty miles to the southwest, give an identical age, 348 ± 20 million years. These rocks are clearly correlative with the Fisset Brook formation. Mixed sedimentary and volcanic rocks in the Cape St. Lawrence area, some thirty miles to the northeast of Fisset Brook, appear to be significantly older, 462 ± 25 million years, and should be considered tentatively as Ordovician in age.

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.

Chronology of Devonian to early Carboniferous rifting and igneous activity in southern Magdalen Basin based on U-Pb (zircon) dating

2002 ◽  
Vol 39 (8) ◽  
pp. 1219-1237 ◽  
Author(s):  
Greg R Dunning ◽  
Sandra M Barr ◽  
Peter S Giles ◽  
D Colin McGregor ◽  
Georgia Pe-Piper ◽  
...  
Keyword(s):  
Nova Scotia ◽  
Fault Zone ◽  
Middle Devonian ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Late Devonian ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Igneous Activity ◽  
Age Determinations

Fifteen U–Pb (zircon) radiometric age determinations have been made on igneous rocks of Middle Devonian to Early Carboniferous age from the southern margin of the Magdalen basin in Cape Breton Island and northern mainland Nova Scotia. Volcanic rocks interbed with early rift-basin sedimentary rocks with some palynological biostratigraphy; dated intrusive rocks cut these sedimentary units. Our biostratigraphically constrained ages are in close agreement with the current Devonian time scale. Combined with previously published data, the age determinations show that igneous activity occurred in four pulses: Middle Devonian (390–385 Ma), early Late Devonian (375–370 Ma), latest Devonian to early Tournaisian (365–354 Ma), and late Tournaisian to early Visean (ca. 339 Ma). Middle Devonian (385–389 Ma) volcanic rocks are confined to the Guysborough Group. The Fisset Brook Formation (basalt and minor rhyolite) in the type area and elsewhere in Cape Breton Island and northern mainland Nova Scotia is Late Devonian (ca. 373 Ma), whereas the biostratigraphically distinct succession at Lowland Cove is younger (365 Ma). These Late Devonian rocks are synchronous with plutonism in the Cape Breton Highlands and the Meguma terrane. In the Cobequid Highlands, rhyolite of the Fountain Lake Group was synchronous with Horton Group deposition and with widespread granite plutons (362–358 Ma) emplaced during shear on the Cobequid fault zone. The overlying Diamond Brook Formation basalts are slightly younger (355 Ma). Late Tournaisian – early Visean mafic intrusions and minor basalt occur along the Cobequid – Chedabucto fault zone and in a belt from southern New Brunswick through Prince Edward Island to southwestern Cape Breton Island.

Cape Breton ruby, a new Canadian gemstone discovery, Cape Breton Island, Nova Scotia

2007 ◽  
Vol 30 (5) ◽  
pp. 279-286 ◽  
Author(s):  
David J. Mossman ◽  
James D. Duivenvoorden ◽  
Fenton M. Isenor
Keyword(s):  
Nova Scotia ◽  
Cape Breton Island ◽  
Cape Breton
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