Overlap assemblages: Laberge Group of the Whitehorse Trough, northern Canadian Cordillera

Abstract

The Laberge Group was deposited during the Early to Middle Jurassic in a marginal marine environment, in the northern Canadian Cordillera. It occurs as a narrow, elongated siliciclastic unit along more than 600 km of strike length, overlapping the Intermontane terranes of southern Yukon and northwestern British Columbia. The Laberge Group was deposited on the Late Triassic Stuhini and Lewes River groups, a volcano-plutonic complex of the Stikine terrane (Stikinia), and, locally, the Kutcho Arc. It is overlain by Middle Jurassic to Cretaceous clastic units. The variations in clast composition and detrital zircon populations among these units indicate major changes in depositional environment, basin extent, and sources during the latest Triassic to Middle Jurassic. Detrital zircon populations are dominated by near contemporary Stuhini-Lewes River arc grains, consistent with dissection of an active arc. Detrital rutile and muscovite data show rapid cooling and exhumation of metamorphic rocks during the Early Jurassic. Thermochronological data indicate that basin thermal evolution was domainal, with at least five regional temperature-time histories.