UPLIFT AND COOLING PATHWAYS DERIVED FROM FISSION-TRACK ANALYSIS AND MICA DATING - A REVIEW

Definition of time and temperature pathways for episodes of lithospheric movement provides not simply a chronological framework for crustal dynamism but also permits estimation of rates of crustal cooling and uplift. Important aspects of such pathways are the constraints provided for timing of both plate collision and lithospheric extension. Classically Rb-Sr and K-Ar mica ages have been used to delineate rates of cooling and exhumation in the Central Alps, by comparison of the measured ages with estimates of temperatures for the retention of daughter isotopes. Similar use of fission track apatite and zircon ages has provided data for lower temperature intervals (approximately 100 and approximately 200-degrees-C respectively). Recent detailed studies of the annealing kinetics of fission tracks in apatite yield more precise estimates of cooling rate and permit predictive modelling of age and length parameters for given T,t pathways. In continental collision zones, fast episodic uplift in the western Alps can be contrasted with contemporaneous monotonic uplift in the Central Alps. Additional examples may be seen in the Tibet-Himalayan orogenic belt, in the southern Alps of New Zealand and in the Bolivian Andes. In divergent tectonic regimes, the record of uplift associated with rifting has been recorded by fission track ages in the southeastern Australian margin and around the Red Sea. In an intra-plate tectonic setting, our current fission track reconnaissance study in the British Isles is revealing a hitherto unrecognised thermal history for crystalline and sediment alike.