40 Ar/ 39 Ar Thermochronology on Central China Orogen: Cooling, uplift and implications for orogeny dynamics

Abstract

Abstract 40 Ar/ 39 Ar geochronology was carried out on the non-deformed synorogenic granitoid plutons from the Qinling–Dabie Orogen. The new model cooling history (MCH) method is applied to K-feldspar to obtain information about its cooling history. MCH is a quicker and easier method of calculating cooling histories compared with the multi-domain diffusion (MDD) model. Cooling histories indicate that Qinling–Dabie suffered differential uplift and denudation processes since the collision in the Late Triassic. East Qinling uplifted and denuded rapidly from c. 181–187 to c. 150 Ma at a rate of c. 20 °C Ma −1 , three times as fast as west Qinling which was exhumed at a rate of c. 6.6 °C Ma −1 from c. 195–190 to c. 100 Ma. Although west and east Qinling started uplift and denudation at the same time, east Qinling reached the 150 °C geothermal line ( c. 7.5 km deep) at c. 150 Ma, earlier than west Qinling by c. 50 myr, suggesting that earliest collision and strongest compression occurred in east Qinling. Dabie is characterized with a polyphased process of uplift and denudation, implying that the subduction of south China block in this region was multi-staged. The emplacement of the granitoids and uplift pattern along Qinling–Dabie may be due to delamination of the root of the mountains or the slab break-off. Cooling histories suggest that more mass had been removed from the root of east Qinling than west Qinling and Dabie; the final delamination occurred in Dabie at c. 100 Ma but affected the whole Qinling–Dabie orogen.