科研之友
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摘要
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-south Ar-40/Ar-39 thermochronology transect was carried out throughout a similar to 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 new Ar-40/Ar-39 data and to determine the nature of the boundary between the dome and overlying rocks at Cariboo Alp. Hornblende cooling dates are similar to 62-58 Ma at the highest structural level, similar to 57-55 Ma in the middle, and similar to 57-53 Ma at Cariboo Alp on the upper boundary of the dome. Muscovite and biotite cooling dates are similar to 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 degrees C, with upper structural levels cooling at rates of ca. 20 degrees C/Ma and the lowest levels at rates in excess of 120 degrees C/Ma. All levels passed through the closure temperature for argon in biotite (here calculated to be 320-330 degrees 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.
- 出版日期2016-10
