New approaches in fission track geochronology as a tectonic tool. Examples from the transantarctic mountains

Apatite fission track analysis has been applied to study the uplift history and tectonics of the Transantarctic Mountains (TAM). An uplifted fossil apatite annealing zone has been identified in the apatite age vs elevation profile and is confirmed by track length data. A 'break in slope' in the apatite age profile marks the base of the uplifted partial annealing zone and approximates the time of initiation of uplift of the mountains. Samples below the 'break in slope' give information on the rate(s) of uplift. Samples above the break have apatite ages that vary significantly with elevation, but the gradient is not equal to an apparent uplift rate. Rather, it is due to inherited characteristics from the pre-existing partial annealing zone. These samples above the 'break in slope' can be used as indicators of paleo-depth in the pre-uplift crust to determine the structure of an area and the displacement across faults. Mountain ranges adjacent to extensional tectonic regimes most likely represent the classical area for finding uplifted partial annealing zones because stable thermo-tectonic conditions needed to establish the distinctive shape of an apatite annealing zone prior to uplift are often present, and the amount of uplift is such that the annealing zone is likely to be preserved in the rock column.