Thermochronometric reconstruction of the prethrust paleogeothermal gradient and initial thickness of the Lewis thrust sheet, southeastern Canadian Cordillera foreland belt

Abstract

The Lewis thrust, which is >225 km long and has a maximum displacement of >80 km, is a major Foreland belt structural element in the southeastern Canadian Cordillera. We use low-temperature thermochronometry in the preserved Lewis thrust sheet stratigraphic succession to constrain variations in both paleogeothermal gradient and Lewis thrust sheet thickness immediately prior to motion on the Lewis thrust fault. Fission-track and vitrinite reflectance data combined with stratigraphic data suggest that maximum Phanerozoic burial and heating occurred in the Lewis thrust sheet during a short interval (<15 m.y.) in late Campanian time immediately prior to thrusting (ca. 75 Ma). The data suggest th..