Apatite fission track and (U-Th-Sm)/He thermochronology of in-situ bedrock, western Marie Byrd Land, West Antarctica

New low-temperature thermochronological data from granitic basement of western Marie Byrd Land provide insights into the still poorly constrained tectonic and topographic evolution of West Antarctica during and after continental breakup. Here we present the first apatite (U-Th-Sm)/He data from the Devonian Ford Granodiorite and the mid-Cretaceous Byrd Coast Granite suites from the Ford Ranges and the Edward VII Peninsula. Thermal history modeling integrating apatite (U-Th-Sm)/He dates of 109–68 Ma with revised apatite fission track data in combination with geologic information indicates a thermal history with diachronous enhanced cooling at ~100–60 Ma and subsequent slow cooling until the present-day. Enhanced cooling at ~100–70 Ma was related to activity of the West Antarctic rift system and to continental breakup, thereby exhuming most samples to shallow crustal levels. Localized cooling at ~75–60 Ma is interpreted as resulting from faulting in the eastern Ross Sea region. Slow cooling after ~70–60 Ma corresponds with formation of erosion surfaces in western Marie Byrd Land. Comparison of our results from western Marie Byrd Land with data from the literature indicates progressive formation of erosion surfaces from west to east along the Marie Byrd Land-Thurston Island crustal blocks. Late Cenozoic WARS rifting and Marie Byrd Land dome uplift appear to have collectively caused only minor exhumation of <1.5 km in western MBL.