LATE PALEOZOIC GABBROIC ROCKS OF THE BRIDGE RIVER ACCRETIONARY COMPLEX, SOUTHWESTERN BRITISH-COLUMBIA - GEOLOGY AND GEOCHEMISTRY

Gabbroic bodies in the Bralorne-Gold Bridge area of southwestern Briti sh Columbia are associated with the oceanic Bridge River complex of th e western Canadian Cordillera, one of the ''suspect'' terranes accrete d to North America in the Jurassic. The gabbros are locally cut by ton alites and are structurally interleaved with ultramafic rocks, phyllit es, graphitic cherts, and carbonate lenses that comprise the lower par t of the Bridge River complex. Their late Carboniferous crystallizatio n age overlaps the depositional age of affiliated supracrustal rocks ( Mississippian-Jurassic), some of which have been metamorphosed to blue schist facies. Compositionally, the gabbros resemble mafic plutonic ro cks of ophiolitic complexes and gabbroic rocks of the nearby Shulaps R ange. They display some affinity to oceanic island are tholeiitic suit es. The Bralorne and Shulaps gabbros include cumulates and appear to h ave been derived from a single, light REE-depleted, peridotitic source by melting and subsequent fractional crystallization/accumulation of various combinations of plagioclase, pyroxenes, and olivine. The tonal ites are compositionally distinct from typical ophiolitic plagiogranit es, but might be related to the associated gabbros. The gabbroic bodie s occur within tectonic slivers derived from the oceanic crust that fl oored a deep ocean basin that existed during the late Paleozoic and ea rly Mesozoic. The Bridge River complex comprises fragments of oceanic crust that were tectonically incorporated into an east-verging accreti onary prism during a middle/late Triassic to Jurassic collisional even t.