LATEST TRIASSIC-EARLIEST JURASSIC CONTRACTIONAL DEFORMATION, UPLIFT AND EROSION IN STIKINIA, NW B.C

An aerially extensive latest Triassic-earliest Jurassic unconformity recognized in the late 1980's in NW Stikinia is considered to be of “orogenic” extent and significance, yet it remains unaccounted for in tectonic models for the northern Cordillera. The unconformity is expressed throughout Stikinia, one of the largest tectonic elements in the Cordillera, and its areal extent of exceeds the areal extent of many more well-known North American orogenic belts, such as the Taconic, Antler and Sonoman.

Structural relations, clast compositions of conglomerate, and bio- and geochronologic data indicate that Paleozoic strata and plutons as young as Late Triassic were were uplifted and unroofed, all during an event of finite duration in the latest Triassic to earliest Jurassic. Terrane collision (amalgamation) is considered the most likely cause of Tr-Jr tectonism in NW Stikinia, mainly because of its contractional nature and limited duration, but also because of a coeval hiatus in volcanism, and a general change in arc-volcanic style, from mafic in the Late Triassic, to more evolved (high-K calc-alkaline, andesitic) in the Early Jurassic.

Examples are drawn from Stikinia in NW BC, from the Telegraph Creek area on the north, through Oweegee Dome and the Sulphurets area (Jack Glacier, Brucejack Creek), to Kinskuch Lake on the south, a distance of over 250km. The Tr-Jr event is also expressed elsewhere in Stikinia, such as in thick polylithic conglomeratic sequences above the u/c, both to the north in Tulsequah and Whitehorse areas, to the south near Terrace, and well to the east, in McConnell Creek and Toodoggone areas.

Did this event, which probably reflects significant crustal thickening, correspond to a change in tectonic regime, such as the amalgamation of Stikinia with Yukon-Tanana (and possibly Quesnellia)? Furthermore, did the proposed collisional event ultimately facilitate the emplacement of magmatic-hydrothermal systems which produced the rich Early Jurassic Cu and Au deposits of the northern Cordillera? If so, tectonic models for the northern Cordillera need to be reconsidered.