MULTIMINERAL THERMOCHRONOMETRY INDICATES THERMAL WEAKENING OF THE DEEP CRUST DROVE UPLIFT OF THE TRANSANTARCTIC MOUNTAINS

Knowledge of the thermal, mechanical and rheological state of the deep crust in regions of elevated topography is crucial to understanding how these systems evolve. Modern constraints are available from geophysical data, but in order to understand longer-timescale processes, direct observations from the deep crust are required. In this presentation, we focus on lower crustal xenoliths from the Transantarctic Mountains (TAM), a >4 km high ~3,500 km long ‘rift’ shoulder uplift, in order to illustrate the power of accessory phase thermochronometry in decoding the long-term thermal evolution of the lower crust. Laser Ablation Split Stream (LASS) analysis of a range of accessory minerals record heating of the deep crust beneath the TAM to ultra-high temperature conditions that were sustained from the mid-Cenozoic through to the time of eruption and coincident with rifting and uplift of the TAM. Accessory phase geochemistry documents recrystallization and growth during widespread influx of externally-derived high-SiO₂ melts during rifting. Our data indicate that formation of the TAM occurred as a result of thermal-weakening of the deep crust during rift-related heating which drove crustal excision and resulted in upper crustal exhumation and surface uplift. These data reinforce the importance of multimineral thermochronometry in studies of the deep crust.