(U-Th)/He Thermochronology of the Aishihik Batholith, Central Yukon: Evidence for Stable Crust in the Cretaceous

Abstract

The 190-180 Ma Aishihik batholith is located in southcentral Yukon in the North American Cordillera. Low-temperature (U-Th)/He thermochronology is used to assess the thermal history of the batholith and the surrounding host rock to provide an understanding of the Jurassic-Cretaceous tectonism. The Yukon Tanana terrane (YTT) shows a steady cooling of ~5°C/m.y from the Early Jurassic to the Late Cretaceous, when it reaches the surface. Sections of YTT adjacent to the batholith exhibits moderate cooling rates of 7°C/m.y from the Early to Late Jurassic and then slows down to 1.5°C/m.y until reaching the surface in the Late Cretaceous. The batholith itself exhibits relatively fast cooling from the Early to Late Jurassic (15°C/m.y) and then slows down (1.5°C/m.y) until it reaches surface conditions in the Late Cretaceous. All rocks are at the surface at the latest by the Late Cretaceous with no evidence that there were any subsequent substantial thermal events, which indicates that the Yukon has a mature landscape compared to the rest of the North American Cordillera.