The Thiel Mountains are part of the Transantarctic Mountains (TAM) and occupy a strategic position close to the East-West Antarctic boundary.  They occur in a region of relatively subdued topography distal from high topography and high relief of most of the TAM adjacent to the West Antarctic rift system.  Low-temperature thermochronology on samples collected from the Reed Ridge granite on the north flank of the Thiel Mountains constrain the thermal and hence tectonic history. Apatite fission track data plus thermal models indicate cooling from ca. 165-150 Ma. In conjunction with 40Ar/39Ar K-feldspar data, the results indicate cooling was due to relatively slow erosional denudation, and not thermal relaxation following Jurassic tholeiitic magmatism. Denudation was most likely associated with the formation of the Jurassic rift system across Antarctica that marked the initial breakup of Gondwana. This is the oldest episode of denudation associated with formation of the present day TAM.