The structural and time-temperature history of Banks Island, Northwest Territories
SPEAKER: Keith Dewing (Speaker), Kalin McDannell and Elizabeth Atkinson | Geological Survey of Canada
LOCATION: ConocoPhillips Auditorium, Gulf Canada Square, 401-9th Ave. S.W. Calgary, AB
DATE & TIME: 12:00 Noon Wednesday, September 25th, 2019
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Banks Island is the southwestern most of the Canadian Arctic Islands, about 250 km northeast of the Tuktoyaktuk Peninsula, Northwest Territories. Banks Island is underlain by rocks from numerous geological provinces, including (i) Neoproterozoic Shaler Supergroup, (ii) sediments of the lower Paleozoic Franklinian Basin. These rocks were folded by a compressional event at some time between deposition of the youngest sediments (U. Devonian) and the age of sediments above the angular unconformity (L. Jurassic). Above deformed Devonian strata are (iii) clastic sediments deposited in the Jurassic-Cretaceous Banks Graben, and (iv) Cenozoic strata that blanket much of the island. Multi-generational faults of different orientations cut Jurassic to Cenozoic strata.
The complex structural history is deciphered using a combination of field studies, seismic mapping, and low-temperature thermochronology (organic petrology and apatite fission track). Maximum thickness for the entire Paleozoic succession was between 7.4 km and 9.9 km on northern Banks Island, with timing of maximum burial between Late Devonian (based on youngest preserved strata) and Early Permian (youngest allowable age based on thermochronology). Folded strata on northwestern Banks Island (NE-SW trending) are nearly orthogonal to Late Devonian Ellesmerian folds in the central Arctic Islands. Apatite fission-track data indicate rapid cooling and unroofing during Late Permian and Triassic time (ca. 300-200 Ma), coincident with large, southerly-derived deltaic rocks deposited on the southern Sverdrup Basin margin during this time. The timing of fold development on Banks Island is unclear. There is no thermochronological evidence of cooling on Banks Island co-incident with Late Devonian-Early Carboniferous Ellesmerian Orogeny farther north and there is no geological or geodynamic evidence for a collisional event in Permian or Triassic time when erosion took place.
Regional extension related to the formation of the Arctic Ocean likely caused Mesozoic and Cenozoic strata to be cut by numerous faults, most of which have a dominantly normal sense of motion and parallel the Banks Graben. Some of these faults show a component of strike-slip motion, however there is no compelling evidence for extensive strike-slip movement. A series of NW-SE trending faults on the southeast side of the Banks Graben show normal sense of movement in the Late Cretaceous (Kanguk Formation) time. These appear to be associated with the development of hydrothermal dolomite and a major zinc anomaly in till overlies the trend of one of these faults.
Keith Dewing is a research scientist at GSC-Calgary where he works on Paleozoic strata, petroleum systems, and mineral deposits from the Canadian Arctic Islands. He obtained a PhD from the University of Western Ontario. Kalin McDannell is a post-doctoral fellow at GSC Calgary with expertise in low temperature thermochronology. He has a PhD from Lehigh University. Elizabeth Atkinson is a geophysicist at GSC Calgary. She has a PhD from the University of Calgary and extensive industry experience in Canada, Libya and Indonesia.