An 40Ar/39Ar study of the Cape Breton Highlands, Nova Scotia: thermal histories and tectonic implications

1989 ◽  
Vol 26 (10) ◽  
pp. 2081-2091 ◽  
Author(s):  
P. H. Reynolds ◽  
R. A. Jamieson ◽  
S. M. Barr ◽  
R. P. Raeside
Keyword(s):  
Nova Scotia ◽  
Middle Devonian ◽  
Closure Temperature ◽  
Metamorphic Rocks ◽  
The West ◽  
Rapid Cooling ◽  
Cape Breton ◽  
Appalachian Orogen ◽  
Thermal Histories ◽  
Tectonothermal Event

Forty new 40Ar/39Ar age spectra on micas and amphiboles from both granitic and metamorphic rocks show that two geologically distinct terranes in the Cape Breton Highlands (Nova Scotia) have had contrasting thermal histories. Some plutons in the Bras d'Or Terrane in the southeastern highlands apparently cooled through the hornblende (or muscovite) closure temperature immediately following Precambrian to Cambrian intrusion. Other rock units in this terrane, particularly in the west, have been variably overprinted by a Silurian tectonothermal event, probably associated with juxtaposition of the Bras d'Or Terrane with the Aspy Terrane to the northwest. Gneisses at Kellys Mountain in the southeastern Bras d'Or Terrane apparently were not overprinted by this event.Argon data from the Aspy Terrane suggest that Silurian deposition, deformation, and metamorphism were followed by rapid cooling through hornblende and biotite closure temperatures in the Middle Devonian. This probably resulted from uplift and exhumation of the terrane as it collided with the Appalachian Orogen to the northwest. The Cheticamp Pluton in the western part of the Aspy Terrane, which does not appear to have been significantly affected by Silurian–Devonian tectonothermal events, may represent an outlier of the Bras d'Or Terrane. The Aspy Terrane records an Acadian tectonothermal history similar to that of the Gander Zone in southwestern Newfoundland.

Regional significance of new U–Pb age data for Neoproterozoic igneous units in Avalonian rocks of northern mainland Nova Scotia, Canada

1997 ◽  
Vol 134 (1) ◽  
pp. 113-120 ◽  
Author(s):  
J. BRENDAN MURPHY ◽  
J. DUNCAN KEPPIE ◽  
DON DAVIS ◽  
TOM E. KROGH
Keyword(s):  
Nova Scotia ◽  
Volcanic Arc ◽  
Cape Breton Island ◽  
North West ◽  
Cape Breton ◽  
Pan African ◽  
Appalachian Orogen ◽  
Back Arc ◽  
Age Range ◽  
Arc Deposition

Gondwanan Neoproterozoic tectonothermal events (Pan-African and Brasiliano) are represented in northern mainland of Nova Scotia by volcanic and sedimentary rocks assigned to the Jeffers and Georgeville groups and by gabbroic to granitoid plutons. These rocks comprise part of Avalonia, an exotic terrane in the Appalachian orogen that was deposited in an arc-related environment along the periphery of Gondwana prior to accretion to Laurentia. Lavas sampled in the basal units of the Jeffers and Georgeville groups yielded slightly discordant U–Pb zircon and monazite data that fall on chords with upper intercept ages of 628 Ma and 617.7±1.6 Ma, respectively. Syntectonic to late syntectonic plutons intruded into these groups yielded U–Pb zircon ages of 606.6±1.6 Ma and 603+9−5 Ma. The former intrusion also yielded a concordant titanite age of 607±3 Ma. When combined with previously published ages, these data indicate that the back-arc deposition recorded in these groups lasted 10–15 million years (628–613 Ma) and was closely followed by c. 613–595 Ma metamorphism, intrusion and heterogeneous strike-slip related deformation. Assuming no significant shuffling of fault blocks, the relative locations of the Cobequid–Antigonish back-arc basin and the southern Cape Breton Island volcanic arc are consistent with their genesis above a north-west-dipping subduction zone. The age range of arc-related magmatism in Nova Scotia is similar to that of Avalonian rocks in southeastern Newfoundland and Britain, lending support to hypotheses of Neoproterozoic linkages.

The Cheticamp pluton: a Cambrian granodioritic intrusion in the western Cape Breton Highlands, Nova Scotia

1986 ◽  
Vol 23 (11) ◽  
pp. 1686-1699 ◽  
Author(s):  
Sandra M. Barr ◽  
Alan S. Macdonald ◽  
John Blenkinsop
Keyword(s):  
Nova Scotia ◽  
Chemical Compositions ◽  
Western Cape ◽  
Fractionation Process ◽  
Cape Breton Island ◽  
Stratigraphic Unit ◽  
The North ◽  
Rock Types ◽  
Cape Breton ◽  
Appalachian Orogen

The Cheticamp pluton consists of biotite granodiorite (locally megacrystic) in the north and museovite–biotite granodiorite in the south, in probable faulted contact. These two rock types, especially the biotite granodiorite, show a broad range in modal and chemical compositions. They are interpreted to be cogenetic, with the museovite–biotite grandiorite derived from the biotite granodiorite by crystal fractionation involving mafic minerals, plagioclase, and sphene. The overall peraluminous composition of the suite resulted from the fractionation process, probably enhanced by alteration, rather than from derivation from peraluminous source rocks.A seven-point, whole-rock, Rb–Sr isochron indicates an age of 525 ± 40 Ma. The pluton intruded dioritic rocks and quartzo-feldspathic gneisses, thus indicating Precambrian ages for these units. It probably also postdates the Western Highlands volcanic–sedimentary complex, a major undated stratigraphic unit in the Cape Breton Highlands. Although the age overlaps the range of Rb–Sr ages from plutons of the Avalon Terrane of the Appalachian orogen, the geological setting of the Cheticamp pluton differs from that of true Avalonian plutons, such as those in southeastern Cape Breton Island.

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.

A comparative 40Ar/39Ar conventional and laserprobe study of muscovite from the Port Mouton pluton, southwest Nova Scotia

2001 ◽  
Vol 38 (3) ◽  
pp. 347-357 ◽  
Author(s):  
Raymond P Fallon ◽  
Peter H Reynolds ◽  
D Barrie Clarke
Keyword(s):  
Nova Scotia ◽  
Mantle Plume ◽  
Late Carboniferous ◽  
Rapid Cooling ◽  
Age Variations ◽  
Thermal Histories ◽  
Plutonic Rocks ◽  
Meguma Terrane

We report 40Ar/39Ar age spectrum and laserprobe data for primary magmatic or fluido-magmatic muscovite minerals from the Port Mouton pluton, one of several weakly peraluminous peripheral plutons in the Meguma terrane, southwestern Nova Scotia. Laserprobe data from the cores of thin grain fragments suggest that this pluton cooled rapidly following intrusion at 373 ± 1 Ma, the U–Pb monazite age. The rims of thicker more complete grains record ages of 315–325 Ma, even in cases where there have been no apparent changes in grain rim chemistry and where deformation is minimal. The observed age gradients may be the result of prolonged reheating during the Late Carboniferous Alleghanian Orogeny or, alternatively, the result of rapid cooling at this time to temperatures below the closure value for muscovite rims. Conventional age spectra obtained from muscovite separates record neither the older intrusion age nor the younger reset–cooling age. Instead, these intermediate ages appear to reflect the averaging of intragrain (core–rim) age variations in thick grains and thus have no chronological significance. For these Port Mouton muscovite minerals, the record of initial cooling appears to reside only in certain limited regions of a given grain, a record that can be recovered by the laserprobe technique applied to carefully prepared subgrain fragments. A contrast in the early tectono-thermal histories of plutonic rocks in southwestern Nova Scotia relative to those in the northeast may be the result of perturbation by a mantle plume.

scholarly journals Geology of the west - central Cape Breton Highlands, Nova Scotia

1987 ◽  
Author(s):  
R A Jamieson ◽  
P Tallman ◽  
J A Marcotte ◽  
H E Plint ◽  
K A Connors
Keyword(s):  
Nova Scotia ◽  
The West ◽  
Cape Breton ◽  
West Central

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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