Thermotectonic history of Mt Logan, Yukon Territory, Canada: implications of multiple episodes of middle to late Cenozoic denudation

Abstract

The extreme relief of the St. Elias Mountains, including Mt. Logan, is suggestive of a young mountain belt. New apatite fission track data indicate that the Mt. Logan massif experience rapid low-temperature cooling during three distinct periods: during the middle Eocene, Middle Miocene and Pliocene. Each cooling episode, the magnitude of which varies due to temporal variations in recorded paleogeothermal gradients, can be tentatively linked to a tectonic cause. Eocene cooling may be due to re-equilibration of isotherms following normal faulting, caused by a combination of thermal weakening of the crust and a decrease in regional compressional stress, due to the ∼ 43 Ma change in relative motions between the Pacific and North American plates. The cause of Miocene cooling is problematic, and could reflect denudation in response to initial underplating of the Yakutat terrane, or a recorded change in heat flow unrelated to denudation. Pliocene cooling reflects erosion due to surface uplift that produced the spectacular present-day topography of the St. Elias Mountians. This surface uplift is probably related to the coeval significant change in relative motion between the North American and Pacific plates and/or resistance to subduction by the Yakutat terrane.