Six fission-track analyses were conducted on samples taken across a fault in the Takhini Hotsprings area, Yukon. The results indicate that samples taken on the east side of the fault cooled through 100°C at 104.4 ± 11.9 Ma, while the samples taken on the west side of the fault cooled through 100° C at 63.9 ± 8.5 Ma. Differential uplift and faster erosion on the west side of the fault between the mid-Cretaceous and Early Paleocene could account for this difference in cooling history. This fault forms the approximate western edge of the Whitehorse Trough, and is marked by a dramatic change in the isopach of Jurassic and Triassic sedimentary and volcanic rocks which form a thin veneer over rocks of the Coast Plutonic Complex on the west side, and a very thick sedimentary sequence on the east side where basement rocks are not seen. Based on these observations, the fault is inferrred to be a major zone of crustal weakness which could form the boundary betweeen the Northern Stikine Terrane and the Coast Plutonic Complex in southern Yukon.
Similar results were obtained in a previous study of samples collected across the Llewellyn Fault Zone, which forms the boundary between the Northern Stikine Terrane and rocks of the Nisling Terrane and Coast Plutonic Complex in northwest B.C.
