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Ministry of Energy Mines and Responsible for Core Review

Geology Adjacent to the Western Margin of the Shuswap Metamorphic Complex
(NTS 82L, 82M)

BCMEMPR Open File 1990-30

by B.J. Johnson


Map (PDF, 46.5MB) 

Entire Document (PDF, 7.44 MB)


Open File 1990-30 portrays the geology adjacent to the western margin of the Shuswap metamorphic complex in parts of NTS sheets 82L and 82M. A 1:100 000 scale geology maps accompanies the report. 

The boundary of the Shuswap metamorphic complex has long been recognized as a sharp transition between upper amphibolite fades rods within the complex and rocks of greenschist facies that overlie it. Mapping and geochronology during the - decade have demonstrated that the Shuswap and other metamorphic complexes in the southern Omineca Belt are bounded by Eocene normal faults which juxtapose rocks of different metamorphic grades and with different cooling histories. The present work undertaken as part of a Ph.D. study focused on the Eagle River fault, and the Shuswap complex, which forms its footwall, in the Shuswap-Adams Lake area.

Detailed mapping has identified stratigraphic successions in both the hanging and footwall of the Eagle River fault, which will allow comparison with known miogeoclinal strata in other parts of the southern Omineca Belt. These data have implications for exploration in the Omineca Belt and for construction and restoration of crustal cross-sections through the Omineca Belt.

The west margin of the Shuswap metamorphic complex is bounded by low to moderate-angle, ductile-brittle, west-side-down, Eocene normal faults of the Okanagan - Eagle River fault system, which between 50 30'N and 51030'N latitude juxtapose upper amphibolite facies rocks of the Shuswap assemblage against greenschist to lower amphibolite facies rocks of the Eagle Bay and Mount Ida assemblages. The Shuswap assemblage contains a succession of migmatitic semipelite, psammite, calcareous amphibolite, calcsilicate gneiss and marble that is inferred to be correlative with the Hadrynian Horsethief Creek Group. The Eagle Bay and Mount Ida assemblages contain quartzite, semipelite, marble, calcsilicate schist, metabasite, and calcareous and graphitic phyllites that are interpreted to be correlative with uppermost Hadrynian to lower Paleozoic rocks of the Hamill Group, Badshot Formation and Lardeau Group.

Compositional layering and subparallel S1 foliation in all three assemblages are folded by tight to isoclinal, recumbent to gently inclined, synmetamorphic D2 folds. The metamorphic peak predated or was synchronous with development of upright (in the Eagle Bay) to moderately inclined (in the Shuswap), gently northwest and southeast plunging D3 folds. S3 crenulation cleavage is well developed in the Eagle Bay and Mount Ida assemblages and in the Shuswap assemblage near Adams Lake. 

Footwall mylonites in the Eagle River and northern Adams Lake segments of the Okanagan - Eagle River fault system consistently display west-directed shear sense and are overprinted by retrograde metamorphism and cataclasis beneath a brittle detachment. In the Scotch Creek segment, strain is partitioned in a zone of ductile-brittle and brittle faults that strike at low angles to the shearing direction.


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