Tectonic Significance Of The Akaitcho Group, Wopmay Oreogen, Northwest Territories, Canada

Easton, R. M. (1982) Tectonic Significance Of The Akaitcho Group, Wopmay Oreogen, Northwest Territories, Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The early Proterozoic Akaitcho Group consists of 6 to 8 km of metasedimentary and metavolcanic rocks located in the central metamorphic core zone of the Wopmay, Orogen (Bear Province). In the northern part of the orogen, the following generalized stratigraphic sequence has been recognized: 1) a lower mainly basaltic sequence, 2) 1-2 km of arkosic turbidites intruded by sills of rhyolite porphyry, 3) basalt and rhyolite volcanic complexes, and 4) 1 to 2 km of pelite and tuffaceous sedimentary rocks, locally, intruded by gabbro sills. The Akaitcho Group is conformably overlain by the Odjick Formation, part of an inferred passive-continental margin sequence (the Epworth Group). -- Two types of chondrite-normalized REE patterns are present in the Akaitcho Group basalts: a sloping pattern similar to recent continental tholeiites, and a flat pattern similar to type II ocean tholeiites. The basalt geochemistry in the Akaitcho Group evolves from older, evolved continental tholeiites, through continental tholeiites, to younger oceanic tholeiites. The Akaitcho Group rhyolites are probably crustally-derived. REE patterns of the Akaitcho Group sedimentary rocks indicate that the arkosic turbidites were derived from a granodiorite source terrane (i.e. average continental crust), whereas the upper pelites were derived from a volcanic source terrane similar to the Akaticho Group volcanic complexes and a granodiorite source terrane. -- Bimodal volcanism (subalkaline basalt and rhyolite) in association with continent-derived sediments, the temporal evolution of the basalt geochemistry, and the similarity of the Akaitcho Group to recent rift sequences indicate that the Akaitcho Group was deposited in a rift. The stratigraphic position of the Akaitcho Group beneath the Epworth Group suggests that the Akaitcho Group is related to continental break-up along the western Slave Craton about 1.9 Ga. Zircon dates from central Wopmay Orogen indicate that sea-floor spreading associated with continental break-up was short-lived.

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