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Structural, geochronological, and metamorphic characterization of the Monashee décollement and its role in the tectonic evolution of the Canadian Cordillera Holt, Katharina
Abstract
The Monashee décollement (MD) is a crustal-scale shear zone within the southern Omineca belt of the Canadian Cordillera. The MD marks the contact between the autochthonous Precambrian basement core rocks of the Monashee metamorphic complex and the allochthonous rocks of the Lower Selkirk Allochthon. Both packages were metamorphosed at mid-crustal depths (>20 km) but are now exposed at ~ 2200 m elevation. The timing and style of deformation along the MD are disputed. Studies have proposed that the MD is: 1) the base of a mid-crustal ductile “channel”; 2) a complex normal-sense (top-to-the-west) extensional shear zone; or 3) a major reverse-sense (top-to-the-east) contractional shear zone that possibly forms the basal detachment of the Rocky Mountain thrust and fold belt. This study was conducted to investigate those different interpretations through characterizing the detailed temperature-time deformation histories of the rocks within and adjacent to the MD at the Probity Peak field site, ~ 50 km northwest of Revelstoke, British Columbia. This was achieved through: 1) geological field mapping; 2) microstructural analyses of oriented thin sections; 3) quartz c-axis crystallographic preferred orientation (CPO) investigation and opening angle geothermometry; 4) titanium-in-biotite (Ti-in-Bt) geothermometry; and 5) titanite and monazite petrochronology. The data acquired from this study, combined with that from published literature indicate that the MD was active as a reverse-sense contractional shear zone at Probity Peak between ca. 85-80 and 70-65 Ma. The MD was then crosscut by high-angle, brittle-ductile normal faults during extension between ca. 60 and 49 Ma. This extension facilitated exhumation of the Monashee Complex, which continued through Eocene time.
Item Metadata
| Title |
Structural, geochronological, and metamorphic characterization of the Monashee décollement and its role in the tectonic evolution of the Canadian Cordillera
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| Creator | |
| Supervisor | |
| Publisher |
University of British Columbia
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| Date Issued |
2022
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| Description |
The Monashee décollement (MD) is a crustal-scale shear zone within the southern
Omineca belt of the Canadian Cordillera. The MD marks the contact between the autochthonous Precambrian basement core rocks of the Monashee metamorphic complex and the allochthonous rocks of the Lower Selkirk Allochthon. Both packages were metamorphosed at mid-crustal depths (>20 km) but are now exposed at ~ 2200 m elevation. The timing and style of deformation along the MD are disputed. Studies have proposed that the MD is: 1) the base of a mid-crustal ductile “channel”; 2) a complex normal-sense (top-to-the-west) extensional shear zone; or 3) a major reverse-sense (top-to-the-east) contractional shear zone that possibly forms
the basal detachment of the Rocky Mountain thrust and fold belt. This study was conducted to investigate those different interpretations through characterizing the detailed temperature-time deformation histories of the rocks within and adjacent to the MD at the Probity Peak field site, ~ 50 km northwest of Revelstoke, British Columbia. This was achieved through: 1) geological field mapping; 2) microstructural analyses of oriented thin sections; 3) quartz c-axis crystallographic preferred orientation (CPO) investigation and opening angle geothermometry; 4) titanium-in-biotite (Ti-in-Bt) geothermometry; and 5) titanite and monazite petrochronology. The data acquired from this study, combined with that from published literature indicate
that the MD was active as a reverse-sense contractional shear zone at Probity Peak between ca. 85-80 and 70-65 Ma. The MD was then crosscut by high-angle, brittle-ductile normal faults during extension between ca. 60 and 49 Ma. This extension facilitated exhumation of the Monashee Complex, which continued through Eocene time.
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| Genre | |
| Type | |
| Language |
eng
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| Date Available |
2022-05-04
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| Provider |
Vancouver : University of British Columbia Library
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| Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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| DOI |
10.14288/1.0413222
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| URI | |
| Degree | |
| Program | |
| Affiliation | |
| Degree Grantor |
University of British Columbia
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| Graduation Date |
2022-05
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| Campus | |
| Scholarly Level |
Graduate
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| Rights URI | |
| Aggregated Source Repository |
DSpace
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Attribution-NonCommercial-NoDerivatives 4.0 International