The exhumation evolution of the Micang Shan-Hannan uplift since Cretaceous: Evidence from apatite (U-Th)/He dating

The apatite (U-Th)/He dating results of 13 granitic samples collected in NanjiangNanzheng transect are used to systematically study Micang Shan s exhumation and thermotectonic evolution. While taking into consideration of the influence of the sample s cooling rates and crystal sizes on (U-Th)/He closure temperatures of respective apatites, this research also quantifies the effects of topography, heat conduction, advection and production on regional geothermal gradients. The inversion results reveal a period of rapid exhumation with an average rate of ∼70 m/Ma in the southern sedimentary area of Micang Shan since about 50 Ma B. P., which removed above 3 km-thick sub-surface rock in the region; the Guangwushan Complex in the middle part of Micang Shan-Hannan Uplift experienced a fast exhumation event at -90 Ma B. P. with an exhumation rate of >75 m/Ma; the northern Hannan Uplift was exhumed to the surface with a fast rate above 40 m/Ma before -100 Ma B. P. , and then slowly with an average exhumation rate of -10 m/Ma. The whole research region, Micang Shan-Hannan Uplift experienced a very slow exhumation with an average rate of 10-25 m/Ma during 90-50 Ma B. P.