Exhumation history of the Huangshan granite pluton, southern Anhui Province: New insights from fission-track analysis

The dating of the uplift onset of the Huangshan pluton in the southern part of Anhui Province associated with the collision between paleo-Pacific Block and the Eurasian Block is a fundamental issue to better understand the uplift mechanisms and the regional tectonic evolution. χ₂ values of seven zircon fission track (ZFT) samples collected from the south part of the Huangshan pluton were all <5%. Based on the grain ages of four typical ZFT samples, three thermal overprints ranging in 113-123, 72-95 and 49-66 Ma were distinguished respectively using the binomial peak-fitting method in accordance with the tectonic thermal events after south China shifted into circum-Pacific tectonic region. Apatite fission track (AFT) study of the Huangshan pluton shows ages lie between 15±3 and 56±6 Ma with all χ₂ values >5%, and all are significantly younger than their host rock formation ages, indicating that the samples have experienced post-formation thermal history. Based on the AFT results and topography characteristics in the Huangshan pluton, three zones with different denudation intensities caused by the differential uplift of the fault blocks were recognized in this paper, indicating that denudation was driven by the increase in elevation significantly. Modeling of the AFT data shows that the earlier cooling phase took place in the early Cenozoic and involved 3.3, 3.8 and 6.0°C/Ma of cooling rates equivalent to the exhumation rates of 90, 104 and 167 m/Ma in different fault blocks. The last phase of cooling took place from ~10 Ma with average cooling rate of ~5. 6°C/Ma, equivalent to average denudation rates of ~156 m/Ma. The fission track results imply that the regional compression field plays an important role for the differential exhumation between individual fault blocks of the Huangshan pluton.