COLLAPSE OF A MESOZOIC WEST ANTARCTIC PLATEAU: EVIDENCE FROM LOW TEMPERATURE THERMOCHRONOLOGY AND GEODYNAMICAL MODELLING

The existence and collapse of a Mesozoic West Antarctic Plateau has been suggested on the basis of geomorphic evidence of major paleo-drainage systems flowing from West Antarctica through the Transantarctic Mountains into East Antarctica, as well as geodynamic models. A large suite of low-temperature thermochronological data from the Byrd Glacier Outlet in the Transantarctic Mountains supports the existence and collapse of a Mesozoic West Antarctic Plateau. Apatite fission track and (U-Th)/He analyses were obtained from samples collected from the base of the mountains along the Byrd Glacier, as well as up selected ridges on the sides of the glacier. Apatite fission track ages from 18 initial samples range from ~147 Ma to 31 Ma. Apatite (U-Th)/He ages from 6 of these samples from the base of the mountains range from ~72 to 31 Ma. Two patterns are evident in the data: 1) the oldest ages are from the highest elevations on near-vertical ridge transects, and 2) ages from the base of the mountains decrease along the Byrd Glacier outlet towards the Ross Sea. Preliminary age/elevation patterns and thermal models derived from the fission track and (U-Th)/He analyses with HeFTy (Ketcham, 2005) document two distinct phases of rapid cooling, from ~85 to 75 Ma and from ~35 to 25 Ma.

The data obtained in this study are consistent with the existence of a Mesozoic highland incised by rivers flowing off of the plateau towards the craton (the rapid cooling seen from 85 to 75 Ma), followed by continued Tertiary incision by rivers, with a final Oligocene stage of incision as the result of glacial erosion (the rapid cooling seen from ~35 to 25 Ma). These results are in good agreement with geodynamic models developed to mimic the unique two-phase evolution of the West Antarctic Rift System (Huerta & Harry, 2007) and models developed to simulate the development of the Transantarctic Mountains as the margin of a collapsed plateau (Bialas et. al, 2007).