Application of Detrital Grain Thermochronology on the Exhumation History of the Source Areas
Detrital grain fission-track thermochronology is a promising method for analyzing the exhumation history of the detrital source areas and the process of mountain building and basin deposition. For an unreseted sample from a sedimentary basin, the zircon or apatite fission track grain-age (FTGA) populations and their related FTGA peaks can be obtained by Gaussian or binomial peak-fitting. Then, the lag time (△f) , defined as the difference between the peak age tc and the corresponding depositional age ti, can provide a measure of the exhumation, such as the exhumation rate E= Zc/At where Zc is the FT closure depth. Changes in tc with tA can be approximated by a linear relationship, tc=A-\-Btd where A and B are fit parameters. Moreover, conversion to lag time gives △t=A+(B - l)￡j which shows that A is the present lag time and (B- 1) is the change in lag time with depositional age. It is inferred that the upsection trends in lag time can be represented by B, with B<1 associated with orogenic construction, B=l with steady state, and B>1 with decay. Therefore, a decrease trend in lag time indicates an increase of the orogenic exhumation rate along with an intensive tectonic activity and a sufficient deposits supply inducing a rapid subsidence of the adjacent foreland basin, and vice versa.
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