Banks Island, Northwest Territories is in the southwest Arctic Islands, bordering the Arctic Ocean about 250 km northeast of Tuktoyaktuk. Banks Island is underlain by: i) Neoproterozoic Shaler Supergroup; and ii) sediments of the lower Paleozoic Franklinian Basin. Compressional folding of these rocks occurred sometime between deposition of the youngest Paleozoic sediments (Upper Devonian) and the age of sediments above the Lower Jurassic angular unconformity. Rocks that overlie deformed Devonian strata are: iii) Jurassic-Cretaceous strata deposited in the Banks Graben; and iv) Cenozoic strata that blanket much of the island.
Interpretation of the complex structural history was carried out through a combination of field studies, seismic mapping and low temperature thermochronology. Numerous faults at several orientations and of multiple generations crosscut Mesozoic and Cenozoic strata. Most faults within the Banks Graben have a dominantly normal sense of motion, and most are parallel to the NE-SW trend of the Banks Graben. Local indications of strike-slip movement are present at the eastern margin of the Banks Graben where Cenozoic strata are folded. Regional extension during opening of the Arctic Ocean likely drove growth and movement of these faults.
A series of NW-SE trending faults are present on the southeast side of the Banks Graben and extend onto northwestern Victoria Island. These NW-SE oriented faults are at a high angle to the dominant extensional trend related to the opening of the Arctic Ocean. They show normal sense of movement and are mapped on the surface, imaged on seismic and on gravity data. One of these faults is well exposed at Nelson Head on southern Banks Island. A detrital apatite fission track sample from the Shaler Supergroup at this location contains three age populations with pooled ages of ca. 385 Ma, 205 Ma, 85 Ma. Thermal history modelling indicates two thermal events, one in the Paleozoic (400-300 Ma) followed by cooling from Carboniferous to Early Cretaceous, and a thermal event in the Cretaceous between 130 Ma and 80 Ma with models indicating cooling occurring subsequent to 80 Ma. This is in agreement with a seismic imagery in Amundsen Gulf that shows that these NW-SE faults were active in Late Cretaceous time because the Kanguk Formation thickens across these faults. The faults were active into the Cenozoic as demonstrated by faulting offsets in Eureka Sound Formation at Nelson Head.
The NW-SE trending faults appear to be associated with hydrothermal dolomite in the Kusrhaak D-16 hydrocarbon exploration well, where Devonian Blue Fiord Formation carbonates contain dolostone breccias, vertical stylolites, dissolution features, saddle dolomite, quartz, and late-stage bitumen. Till sampling by the GSC on NW Victoria Island in the 1980s identified one zinc anomaly. This anomaly overlies a NW-SE trending fault. The NW-SE faults appear to have focussed hydrothermal fluids either in Late Cretaceous time, or at some as-yet unresolved time of motion in the late Paleozoic or early Mesozoic.