scholarly journals Very low- and low-grade metamorphism of mafic volcanic rocks of the Mira terrane (Avalonia), southeastern Cape Breton Island, Nova Scotia

2010 ◽  
Vol 46 (0) ◽  
pp. 95-126 ◽  
Author(s):  
David W.A. McMullin ◽  
Sandra M. Barr ◽  
Robert P. Raeside
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Cape Breton Island ◽  
Grade Metamorphism ◽  
Cape Breton

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.

scholarly journals Effects of fluid flow, cooling and deformation as recorded by 40Ar/39Ar, Rb–Sr and zircon fission track ages in very low- to low-grade metamorphic rocks in Avalonian SE Cape Breton Island (Nova Scotia, Canada)

2014 ◽  
Vol 152 (5) ◽  
pp. 767-787 ◽  
Author(s):  
ARNE P. WILLNER ◽  
SANDRA M. BARR ◽  
JOHANNES GLODNY ◽  
HANS-JOACHIM MASSONNE ◽  
MASAFUMI SUDO ◽  
...  
Keyword(s):  
Nova Scotia ◽  
Fission Track ◽  
White Mica ◽  
Low Grade ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Zircon Fission Track ◽  
Meguma Terrane ◽  
Fission Track Ages ◽  
Oriented Parallel

Abstract40Ar/39Ar in situ UV laser ablation of white mica, Rb–Sr mineral isochrons and zircon fission track dating were applied to determine ages of very low- to low-grade metamorphic processes at 3.5±0.4 kbar, 280±30°C in the Avalonian Mira terrane of SE Cape Breton Island (Nova Scotia). The Mira terrane comprises Neoproterozoic volcanic-arc rocks overlain by Cambrian sedimentary rocks. Crystallization of metamorphic white mica was dated in six metavolcanic samples by 40Ar/39Ar spot age peaks between 396±3 and 363±14 Ma. Rb–Sr systematics of minerals and mineral aggregates yielded two isochrons at 389±7 Ma and 365±8 Ma, corroborating equilibrium conditions during very low- to low-grade metamorphism. The dated white mica is oriented parallel to foliations produced by sinistral strike-slip faulting and/or folding related to the Middle–Late Devonian transpressive assembly of Avalonian terranes during convergence and emplacement of the neighbouring Meguma terrane. Exhumation occurred earlier in the NW Mira terrane than in the SE. Transpression was related to the closure of the Rheic Ocean between Gondwana and Laurussia by NW-directed convergence. The 40Ar/39Ar spot age spectra also display relict age peaks at 477–465 Ma, 439 Ma and 420–428 Ma attributed to deformation and fluid access, possibly related to the collision of Avalonia with composite Laurentia or to earlier Ordovician–Silurian rifting. Fission track ages of zircon from Mira terrane samples range between 242±18 and 225±21 Ma and reflect late Palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid-absent conditions during rifting prior to opening of the Central Atlantic Ocean.

scholarly journals Employing contact metamorphism to assess the conditions of pluton emplacement and timing of recrystallization in southwestern Kellys Mountain, Cape Breton Island, Nova Scotia

2017 ◽  
Vol 54 (11) ◽  
pp. 1165-1178 ◽  
Author(s):  
Nabil A. Shawwa ◽  
Robert P. Raeside ◽  
David W.A. McMullin ◽  
Christopher R.M. McFarlane
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Low Pressure ◽  
Contact Metamorphism ◽  
Contact Aureole ◽  
Low Grade ◽  
Cape Breton Island ◽  
Metasedimentary Rocks ◽  
Cape Breton ◽  
George River

At Kellys Mountain, Cape Breton Island, Nova Scotia, the late Neoproterozoic Glen Tosh formation (a low-grade metapsammite–metapelite unit of the George River Metamorphic Suite) has been intruded by diorite, granodiorite, and granite plutons, and the diorite hosts a narrow contact metamorphic aureole. New mapping and sampling in the contact aureole reveals that the metasedimentary rocks have reached amphibolite-facies metamorphism resulting in the development of neoformed biotite, muscovite, cordierite, ilmenite, garnet, andalusite, sillimanite, monazite, and spinel within the meta-pelite, a mineral assemblage also found in the Kellys Mountain Gneiss as a result of low-pressure regional metamorphism. Neoformed minerals and the disappearance of foliation defines a contact metamorphic aureole within 300 m of the pluton contacts. Petrographic and microprobe analyses of equilibrium assemblages in metapelitic units of the contact aureole yielded metamorphic pressures of 250 MPa, implying an intrusion depth of ∼9 km, with temperatures ranging from 365 to 590 °C. The presence of earlier-formed andalusite and garnet indicates the rocks may have initially undergone a low-pressure regional metamorphic event prior to contact metamorphism. Monazite in the contact aureole was dated using in-situ U–Pb methods and yielded an age of 480.9 ± 3.7 Ma, interpreted as the time of formation of the contact metamorphic aureole.

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.

U–Pb and 40Ar/39Ar mineral ages from Cape North, northern Cape Breton Island: implications for accretion of the Avalon Composite Terrane

1992 ◽  
Vol 29 (2) ◽  
pp. 277-295 ◽  
Author(s):  
J. D. Keppie ◽  
R. D. Dallmeyer ◽  
T. E. Krogh
Keyword(s):  
Point Group ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Isotopic Studies ◽  
Northern Cape ◽  
Point Groups ◽  
Uplift And Erosion ◽  
Tectonothermal Event

Isotopic studies have been used to determine protolith and tectonothermal ages in rocks of the Cape North and Money Point groups and two plutons, that form part of the Avalon Composite Terrane. Colourless, euhedral zircon crystals from low-grade metarhyolite in the Money Point Group record a concordant U–Pb age of 427.5 ± 4 Ma, which is interpreted to date the time of extrusion. This provides a maximum age of middle Silurian for polyphase deformation and concomitant greenschist–amphibolite-facies metamorphism that affected the Cape North area in the eastern half of a major, sinistral, positive flower structure. Monazite from the Cape North granite, intruded during peak metamorphic conditions, yielded nearly concordant data with a 207Pb/235U age of 414 ± 3 Ma. This dates the time of crystallization of the Cape North granite. Metamorphic hornblende from the Cape North and Money Point groups records variably discordant 40Ar/39Ar age spectra that define plateau and (or) isotope correlation ages of ca. 380–390 Ma. Muscovite from these units displays generally concordant spectra that define plateau ages ranging between ca. 365 and 375 Ma. Muscovites from the syntectonic Cape North granite and the posttectonic Relay Station granite record plateau ages of ca. 380–382 Ma. The 40Ar/39Ar ages suggest that relatively rapid postmetamorphic cooling occurred during the Devonian. These isotopic results and petrological data indicate that burial of the Cape North units to ca. 18 km, metamorphism, uplift, and erosion occurred in ca. 60 Ma. Such rates are comparable with those recorded in modern transpressive tectonic regimes. The calc-alkaline nature of the Money Point volcanic rocks suggests derivation above a subduction zone. A correlative Silurian–Devonian tectonothermal event recorded in southern Newfoundland probably records the accretion of the Avalon Composite Terrane with the Dunnage Zone.

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.

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.

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