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Geology and thermal history of an area near Okanagan Lake, Southern British Columbia

University of British Columbia

Five phases of deformation are recognized in Shuswap (Monashee Group) gneiss in an area east of Okanagan Lake, southern British Columbia. The first is delineated by north trending mesoscopic structures. The second comprises a south closing megascopic synform with a horizontal ESE axial direction. This structure has in turn been coaxially refolded into a more open phase 3 synform. The second deformation was associated with extensive introduction of synkinematic quartz monzonite and granodiorite that comprises much of the area, and culminated with amphibolite grade metamorphism. Phase 3 deformation was followed by extensive local recrystal1ization and metasomatism which destroyed earlier fabric elements of the gneisses. Phases 1 to 3 are pre-mid-Carboniferous based on poor fossil evidence whereas phases 4 and 5 are Tertiary. Phase 4 comprises open flexural slip folding about NE trending axes and Phase 5 consists of broad warps about horizontal ESE axes. These deformational events were associated with high level thermal and hydrothermal activity which appears to be most intense in areas of high grade Shuswap gneiss, where it has reset K-Ar dates to about 50 million years (paper no. 1). Thermally sensitive fission track apatite dates indicate that the high thermal gradients can be traced into the plutonic rocks west of the Okanagan Valley in which K-Ar dates have been much less affected and range between 130 and 200 million years. Thus perhaps only the oldest dates represent minimum emplacement dates. The statistical methods used in acquiring the apatite dates are discussed and developed beyond that available in the literature (paper no. 2).

Text

2010-02-11

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http://hdl.handle.net/2429/20098

Geological Sciences

University of British Columbia

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