Tracing exhumation of the Dabie Shan ultrahigh-pressure metamorphic complex using the sedimentary record in the Hefei Basin, China

摘要

Jurassic rocks in the Hefei Basin were deposited by braided-fluvial and alluvial-fan systems, characterized by a general coarsening-upward sequence. Multiproxy provenance analyses demonstrate that the sediment source areas for the Hefei Basin are composed of a variety of rocks, including ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic rocks and Yangtze basement rocks of the axial Dabie Shan metamorphic complex, the Luzhenguan complex granite, low- and medium-grade metamorphic rocks, and the Yangshan Group sandstone in the North Huaiyang fold and thrust belt. A Middle Jurassic section in the western part of the basin is characterized by relatively high _Nd values (at 176 Ma), ranging from –13.8 to –11.3, whereas a section in the middle part of the basin has higher 147Sm/144Nd ratios, from 0.1168 to 0.1266 and somewhat lower _Nd values (at 176 Ma), from –15.0 to –14.5. Sediments in a section in the eastern part of the basin have the lowest _Nd values (at 176 Ma), ranging from –22.0 to –14.6, the highest T_DM values, from 1.8 to 2.4 Ga, and low 147Sm/144Nd ratios, from 0.0937 to 0.1067.