New U-Pb (zircon) data from the northern Boisdale Hills show that rhyolite on Long Island and syenogranite of the nearby Mount Cameron pluton have similar ages of SOS ± 3 Ma and 509 ± 2 Ma, respectively. These ages are similar to those known or inferred from some felsic piutonic units elsewhere in central Cape Breton Island and suggest that latest Cambrian to earliest Ordovician igneous activity was widespread in the Bras d'Or terrane. The new dates also suggest that stratigraphic and structural relationships in the Boisdale Hills arc more complex than previously interpreted.
The dated rhyolite and other volcanic and sedimentary rocks in the northern Bourinot belt in the Boisdale Hills were previously included in undivided Middle Cambrian Bourinot Group. In the southern Bourinot belt, the Bourinot Group was subdivided into the Eskasoni, Dugald, and Gregwa formations. The Eskasoni Formation is dominantly a bimodal volcanic suite with petrological characteristics indicative of origin in a continental within-plate tectonic setting. Its present contacts, both with adjacent older metamorphic and plutonic rocks and with the apparently overlying fossiliferous Dugald and volcanogenic Gregwa formations, are faulted. Our new mapping demonstrates that the Eskasoni, Dugald and Gregwa formations can be extended into the central Bourinot belt where they were previously undivided. However, continuity cannot be demonstrated between these Middle Cambrian units and the dated volcanic and associated sedimentary units in the northern Bourinot belt Hence, assuming that both U-Pb and fossil ages are correct, our interpretation is that the Upper Cambrian -Lower Ordovician Northern Boisdale Hills volcanic unit is younger than the Bourinot Group, although petrochemical data suggest that it formed in a similar tectonic regime.
The presence in the Bourinot belt of fauna characteristic of the Acado-Baltic faunal province appears to tie the Bras d'Or terrane to other Avalonian (peri-Gondwanan) terrenes. However, the Bras d'Or terrane differs from the adjacent Mira terrane which includes Lower as well as Middle and Upper Cambrian units and lacks volcanic and plutonic rocks of this age.
RÉSUMÉ
De nouvelles données U-Pb (zircon) provenant de la partie nord des collines Boisdale montrent que la rhyolite sur l'ile Long et le syénogranite du pluton du mont Cameron à proximité ont des âges similaires, de 505 ± 3 Ma et 509 ± 2 Ma respectivement. Ces âges sont similaires à ceux connus ou supposés pour quelques unités plutoniques felsiques ailleurs dans le centre de l'ile-du-Cap-Breton, et suggèrent que l'activité ignée de la fin du Cambrien au début de l'Ordovicien etait répandue dans le terrain de Bras d'Or. Ces nouvelles datations suggèrent aussi que les relations stratigraphiques et structurales dans les collines Boisdale sont plus complexes que ne le montraient les interprétations antérieures.
La rhyolite datée et d'autres roches volcaniques et sédimentaires de la partie nord de la ceinture de Bourinot dans les monts Boisdale étaicnt auparavant incluses dans le Groupe de Bourinot non divisé, du Cambrien moyen. Dans la partie sud de la ceinture de Bourinot, le Groupe de Bourinot était divisé en formations d'Eskasoni, de Dugald et de Gregwa. La Formation d'Eskasoni est principalement une suité volcanique bimodale avec des caractéristiques pétrologiques indiquant un environnement tectonique intracontinental. Ses contacts actuels, à la fois avec les roches métamorphiques et plutoniques plus vieilles et avec les formations apparemment susjacentes de Dugald, fossilifere, et de Gregwa, volcanique, sont failles. Notre nouvelle cartographic montre que les formations d'Eskasoni, de Dugald et de Gregwa peuvent être distinguees dans le centre de la ceinture de Bourinot où elles ne l'étaient pas auparavant. Toutefois, on ne peut pas démontrer de continuité entre ces unités du Cambrien moyen et les volcanites datées et les unités sédimentaires associées dans la partie nord de la ceinture de Bourinot. Ainsi, en assumant que les ages U-Pb et palcbntologiques sont corrects, notre interprétation est que cette unité volcanique du Cambrien tardif - Ordovicien inférieur du nord des collines Boisdale soit plus jeune que le Groupe de Bourinot, quoique les données pétrologiques suggèrent qu'elle se soit formée dans un environnement tectonique similaire.
La présence dans la ceinture de Bourinot de fossiles caractéristiques de la province faunique acado-baltique semble relier le terrain de Bras d'Or aux autres terrains avaloniens (péri-Gondwana). Toutefois, le terrain de Bras d'Or diffère du terrain adjacent de Mint qui comprend des unités du Cambrien infeérieur autant que moyen et supérieur et ne présente pas de roches volcaniques et plutoniques de cet âge.
[Traduit par la rédaction]
The Miramichi Highlands of New Brunswick are underlain by subgreenschist- to greenschist-facies sedimentary and volcanic rocks of the Cambro-Ordovician Tetagouche Group and by amphibolite-facies paragneisses, amphibolites, and felsic orthogneisses of the Trousers Lake and Sisson Brook suites. New field, geochemical, and geochronologic data for the amphibolites and felsic orthogneisses suggest that they are high-grade metamorphic equivalents of the Tetagouche volcanic rocks and their associated intrusions.Amphibolites in the Miramichi Highlands occur as striped and unstriped varieties that possess chemical characteristics indicative of an igneous origin. However, the two types are compositionally distinct: the striped amphibolites resemble volcanic-arc tholeiites, whereas the unstriped amphibolites are like within-plate tholeiites. The geochemically inferred tectonic origin of these amphibolites is compatible with a recently proposed intracontinental back-arc tectonic setting for the Tetagouche Group.Felsic orthogneisses (Fox Ridge augen granite and Trousers Lake felsic orthogneiss) exhibit concordant contacts with the unstriped amphibolites. U–Pb zircon ages for the Fox Ridge augen granite [Formula: see text] and Trousers Lake felsic orthogneisses [Formula: see text] indicate a Late Ordovician intrusive event. Thus, there is no evidence for Precambrian granite and orthogneiss in the Miramichi Highlands, as had been previously inferred from a correlation with purported Precambrian rocks in the Gander Zone of Newfoundland. The age of the unstriped amphibolites is interpreted as being the same as that of the felsic orthogneisses because these two rock types always exhibit close relationships in the field. The age of the striped amphibolites is less certain, although a correlation with Ordovician basalts of the Tetagouche Group is consistent with their field relationships and tectonic setting.
Research Article| July 01, 1989 A lead and strontium isotopic study of the Anahim volcanic belt, British Columbia: Additional evidence for widespread suboceanic mantle beneath western North America MARY LOU BEVIER MARY LOU BEVIER 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information MARY LOU BEVIER 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (7): 973–981. https://doi.org/10.1130/0016-7606(1989)101<0973:ALASIS>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation MARY LOU BEVIER; A lead and strontium isotopic study of the Anahim volcanic belt, British Columbia: Additional evidence for widespread suboceanic mantle beneath western North America. GSA Bulletin 1989;; 101 (7): 973–981. doi: https://doi.org/10.1130/0016-7606(1989)101<0973:ALASIS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Mantle-derived alkali basalts and their peralkaline differentiates of the late Cenozoic Anahim volcanic belt occur in a 500-km-long, east-west-trending belt that cuts across the predominantly north-northwest structural grain of the accreted terranes in southern British Columbia. Pb and Sr isotopic ratios of these rocks indicate that heterogeneous, suboceanic depleted mantle is present in their source region beneath Alexander, Stikinia, and Kootenay terranes. This widespread suboceanic mantle source is characterized 206Pb/204Pb = 18.62-19.18, 207Pb/204Pb = 15.52-15.63, 208Pb/204Pb = 38.15-38.68, and 87Sr/86Sr = .7026-.7033. These values are similar to those of the source for northeast Pacific Ocean seamounts; that is, the Anahim source is not as depleted as the MORB-source in the northeast Pacific. No evidence exists for the presence of radiogenic, subcontinental mantle in the zone of melting beneath the Anahim belt. Locally, very radiogenic initial isotopic ratios from Bella Bella and King Island centers on the coast, and the Wells Gray-Clearwater centers on the far eastern end of the Anahim belt, reflect contamination from a radiogenic, Precambrian(?) crustal component derived from Alexander and Kootenay terranes, respectively. The mantle source for Anahim belt volcanic rocks appears isotopically continuous with the source for alkali basalts in the Basin and Range of the western United States and distinct from the subcontinental mantle source proposed for some Snake River Plain and Columbia River Basalt Group lavas. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Trans-Hudson Orogen in Canada represents an early Proterozoic mountain belt similar to Phanerozoic orogens formed by plate tectonic processes. Volcanic rocks in northern Manitoba and Saskatchewan resemble island arc terranes, while continental rift and oceanic volcanic rocks dominate in the Cape Smith Belt in northern Quebec. Pb-Pb whole rock isotopic data for the ophiolitic Watts Group of the Cape Smith Belt yield an age of 1980 ± 30 Ma. Pb-Pb metamorphic (?) ages of 1890 Ma and 1700 Ma were determined for rift-related igneous rocks of the Povungnituk Group and transitional volcanic rocks of the Chukotat Group, respectively. Sm-Nd isotopic compositions are consistent with a magmatic evolution characterized by involvement of lithospheric mantle in Povungnituk Group volcanism, and depleted asthenospheric magma sources for MORB-like Chukotat Groupbasalts Sm-Nd isotopic compositions of the Watts Group show the characteristics of both Povungnituk and Chukotat Group basalts, suggesting similar sources.
Research Article| May 01, 1990 Tectonic significance of Silurian magmatism in the Canadian Appalachians Mary Lou Bevier; Mary Lou Bevier 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar Joseph B. Whalen Joseph B. Whalen 1Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar Geology (1990) 18 (5): 411–414. https://doi.org/10.1130/0091-7613(1990)018<0411:TSOSMI>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mary Lou Bevier, Joseph B. Whalen; Tectonic significance of Silurian magmatism in the Canadian Appalachians. Geology 1990;; 18 (5): 411–414. doi: https://doi.org/10.1130/0091-7613(1990)018<0411:TSOSMI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract New U-Pb ages for granites from the New Brunswick part of the Canadian Appalachians indicate that >90% of the undeformed felsic plutons are Silurian and not Devonian as previously thought. Silurian igneous and sedimentary assemblages were recently recognized throughout the Canadian Appalachians, although the petrogenetic types of magmas as well as the grades of metamorphism and deformation vary widely. Our data support proposed tectonic models that suggest relatively continuous subduction and orogenic activity in the Canadian Appalachians from Middle Ordovician to Middle Devonian time. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Thin, flat-lying basalt flows of the Mio-Pliocene Chilcotin Group, erupted from central vents, coalesce to form a 50,000 km2 lava plateau in south-central British Columbia. Olivine-bearing transitional basalt is the predominant rock type; alkali basalt and quartz tholeiite are also present. Sr and Pb isotopic ratios indicate a mantle source for the magmas. Based on Mg values of 45–65, and Ni contents of <250 ppm, Chilcotin basalts are differentiated magmas. The genesis of Chilcotin basalt magma can be modelled in two steps, (1) partial melting of spinel lherzolite to produce picritic basalt, and (2) fractionation of olivine from picritic magma to produce transitional basalt. Residual peridotite left over from the partial melting event is similar in mode and composition to ultramafic nodules found in many alkali basalt flows from western North America. Magma was not trapped in the crust long enough to react with it or to produce silicic differentiates. Individual flows of Chilcotin basalt from different vents are isotopically distinct and cannot be related to each other by any reasonable crystal fractionation model, suggesting that the mantle source for Chilcotin basalt is heterogenous on the scale of the basalt plateau, and that many batches of slightly different primary magma were parental to the basalts that make up the volcanic field.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)