Open Collections

Kulchycki, Anastasia

University of British Columbia

The western margin of North America was shaped by the Cordilleran orogen. In the mid-Cretaceous, northeast-directed convergence resulted in compression-related structures that span the Cordillera, including the Selwyn thrust and fold belt in central Yukon. Bordering the Keno Hill area are two northwest-southeast extending thrust faults of the Selwyn thrust and fold belt. These faults are the Robert Service Thrust (RST), to the south, and the underlying Tombstone Thrust (TT), to the north. Previous detailed studies of the Keno Hill area have focussed on the late, brittle structures that host vein mineralization, leaving the structural evolution of the early, ductile structures largely unresolved. To investigate the geological evolution of the early structures, this study incorporates 1:25000 scale structural field mapping, microstructural analysis, and geochronology, including: c-axis crystallographic preferred orientation investigations, grain size piezometry, crystallographic vorticity axis investigations, in situ ⁸⁷Rb/⁸⁷Sr and ⁴⁰Ar/³⁹Ar geochronology, and Raman spectroscopy-based thermometry of carbonaceous materials. The in situ geochronology and thermometry investigations on weakly metamorphosed, clastic metasedimentary rocks from the hanging wall and footwall of the RST show a break across the approximate fault trace, with higher temperatures (>480 °C) and older dates in the hanging wall (130-102 Ma), with both the temporal and thermometry data showing a general decrease in the footwall, moving towards the approximate trace of the TT. This coincides with microstructural investigations which showed less grain boundary area reduction farther north. While the strain investigations did not show any obvious spatial or structural relationships, the area was dominated by predominantly non-coaxial constrictional strain. Contrary to other studies that have tried to date movement along the regionally extending thrust faults, the data could support that movement along the TT potentially continued until ca. 88 Ma as opposed to cessation ca. 100-104 Ma.

Text

2024-09-19

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89269

Earth and Environmental Sciences

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/