CONDUCTING AMBIENT NOISE TOMOGRAPHY TOGETHER WITH TWO-PLANE-WAVE TOMOGRAPHY IN THE MIDDLE-LOWER YANGTZE RIVER REGION

The 3-D model shows that in the upper crust, the basin regions including the JiangHan, HeHuai, SuBei, HeFei and NanYang basin, are all featured with low velocities, and the mountain regions with high velocities. We also notice that the high velocity is observed beneath the Dabie orogenic belt in the upper crust in the upper crust, however, but disappears in the lower crust which may imply that the HP/UHP metamorphic rock only concentrated in the upper crust of the Dabie orogenic belt. In the uppermost mantle, our tomography results show that a low-velocity zone at between 100 and 200 km depth has been widely revealed beneath the Middle-Lower Yangtze River Metallogenic Belt. Meanwhile, our results also reveal a pronounced updip low velocity zone with a southwest-northeast strike under the TongLing and NingWu ore districts in a depth range from 200 km to 80 km. The low-velocity zone may represent the hot upper mantle materials in the past due to the partial melts of paleo-Pacific plate or melting of an enriched mantle source induced by the westward subduction of the paleo-Pacific plate and then upwelling of these mantle-derived magmas resulted in the formation of these granitic rocks and coeval ores deposits along the Middle-Lower Yangtze River Metallogenic Belt.