40Ar/39Ar thermochronology of the thor-odin – pinnacles area, Southeastern British Columbia: Tectonic implications of cooling and exhumation patterns
The Thor-Odin dome is a basement-cored tectonothermal culmination in southern British Columbia, containing high-grade metamorphic rocks that were polydeformed during the Cordilleran orogenesis. A north–south40Ar/39Ar thermochronology transect was carried out throughout a ~7 km thick tilted section in the Thor-Odin dome and structurally overlying rocks to construct thermochronological histories using existing U–Pb geochronology data with new40Ar/39Ar data and to determine the nature of the boundary between the dome and overlying rocks at Cariboo Alp. Hornblende cooling dates are ~62–58 Ma at the highest structural level, ~57–55 Ma in the middle, and ~57–53 Ma at Cariboo Alp on the upper boundary of the dome. Muscovite and biotite cooling dates are ~53–50.5 Ma; identical throughout the dome, margin, and overlying panel. The Cariboo Alp area separating the Thor-Odin dome from overlying rocks did not accommodate major post-cooling extensional deformation; rather, it is a Late Cretaceous to Paleocene compressional shear zone. These domains cooled at different rates from >700 to ca. 300 °C, with upper structural levels cooling at rates of ca. 20 °C/Ma and the lowest levels at rates in excess of 120 °C/Ma. All levels passed through the closure temperature for argon in biotite (here calculated to be 320–330 °C) together at ca. 52–51 Ma. Differential cooling rates are the result of interaction between northeast-directed compressional transport of rocks towards the foreland of the orogen overlapping with activity on the Columbia River fault zone, reflecting crustal-scale extension that reached a peak in the Eocene.
|Journal||Canadian Journal of Earth Sciences|
van Rooyen, D., & Carr, S. (2016). 40Ar/39Ar thermochronology of the thor-odin – pinnacles area, Southeastern British Columbia: Tectonic implications of cooling and exhumation patterns. Canadian Journal of Earth Sciences, 53(10), 993–1009. doi:10.1139/cjes-2015-0196