Stratigraphy and detrital zircon U-Pb-Hf isotope provenance of the Faro Peak formation, Central Yukon: implications for the Early Jurassic evolution of the Northern Canadian Cordillera

Abstract

Late Triassic to Early Jurassic plate convergence and crustal thickening along the Cordilleran margin led to exhumation of the Intermontane terranes and subsequent deposition of multiple syntectonic stratigraphic assemblages in northwestern Canada. The Faro Peak formation is exposed in central Yukon along the Vangorda fault, the local suture between the Yukon-Tanana and Slide Mountain terranes, and constrains the timing and spatial extent of Early Jurassic tectonic exhumation. The Faro Peak formation unconformably overlies Yukon-Tanana terrane basement rocks (Snowcap assemblage) and unnamed Triassic strata (formerly lower member of the Faro Peak formation) and consists of Sinemurian to Toarcian massive sandstone and pebble to boulder conglomerate units. Field stratigraphic and detrital zircon U-Pb-Hf isotope studies indicate that the Faro Peak formation was locally sourced from Late Triassic to Early Jurassic arc- to syn-collisional intrusive rocks and mid- to upper Paleozoic arc and marine sedimentary successions. Snowcap assemblage rocks were recycled into the overlying Faro Peak formation and mostly consist of quartz-mica schist and quartzite units with Cryogenian and older maximum depositional ages and Precambrian detrital zircon grains that indicate northwestern Laurentian provenance. The Faro Peak formation was deposited in an isolated, structural basin by sediment gravity flows along the proto-Vangorda fault and separated from coeval, syn-tectonic deposition in the Whitehorse trough of southern Yukon by a regional drainage divide.