Architecture of the imbricate Upper Paleozoic To Jurassic Oceanic Cache Creek Terrane, Central British Columbia
Résumé
Upper Paleozoic to Lower Jurassic oceanic rocks of the Cache Creek Terrane
near Fort St. James, in central British Columbia, form a stack of thrust
sheets cut by steeply dipping strike slip faults. Paleontologically dated
upper Paleozoic strata include bioclastic shallow water limestone and ribbon
chert. Isotopically dated Permian rocks consist of small tonalite
intrusions and rhyolite flows in basalt flows. Paleontologically dated
lower Mesozoic rocks include greywacke, sandstone, siltstone, argillite,
ribbon chert, conglomerate, limestone and basalt tuff. Trembleur Ultramafic
unit of the Cache Creek Group, in places a layer of an ophiolite suite,
forms thrust sheets and klippe above lower Mesozoic sediments.
Sedimentological, lithochemical, paleontological, petrological and textural
comparisons with that of other areas and established models demonstrate the
Cache Creek Terrane is a structurally stacked assemblage of diverse and
disparate oceanic paleoenvironments. Represented environments include:
spreading ridge, oceanic plateau, atoll, trench fill and possibly arc.
Internal imbrication of the terrane is as young as Early Jurassic, and the
minimum age of obduction of the thrust stack westward onto Stikine Terrane
is Middle Jurassic. Triassic blueschist and eclogite of Cache Creek Terrane
are interpreted to have been exposed by strike slip motion along the Pinchi
Fault in the easternmost part of the terrane. Cache Creek Terrane is
presumed to be overthrust from the east by the Triassic and Jurassic arc of
Quesnel Terrane.