Isotope chronological trace of granite gravel in Hefei Basin

The discovery of granite gravel in Hefei Jurassic backland basin, which cam e from the Dabie Shan or North Huaiyang, has a great significance for probi ng into uplift and exhumation of the Dabie orogenic belt Lithochemical and isotope chronological analyses on the granite gravel in the Sanjianpu Forma tion and the Fenghuangtai Formation in Jinzhai County prove that post-oroge nic granite was developed in the major provenance of the Hefei Basin, that is, Dabie Shan or North Huaiyang. Discordant lower intersection point age o f zircon U-Pb of granite gravel is about 214 Ala, and Ar-40/Ar-39 age of mu scovite about 196 Ma, K-Ar age of K-spar about 181 Ma. The former is the di agenetic age of the sample, and the latter two represent the sealed ages of muscovite and K-spar respectively. The age of sedimentary rocks in which a lot of granite gravels appear m the sedimentary section may represent the newest age of the exhumation of the granite body, so we assume that the age is 166 Ma. Therefore, we calculated the uplift rates of the granite body f rom Late Triassic to early Middle Jurassic; that is about 0.08 km/Ma and 0. 4-0.3 km/Ma in the early slowly uplifting stage and later fast uplifting st age respectively, after the formation of the body at 214 Ma. These results, are basically identical to the uplifting ages of the Dabie ultrahigh press ure metamorphic (UHPM) belt and the North Huaiyang thrust belt.