ON THE CRUST VELOCITY LEVELS AND DYNAMICS OF THE DABIESHAN OROGENIC BELT
DONG SHU-WEN1) WU XUAN-ZHI2) GAO RUI3) LU DE-YUAN3) LI YING-KANG4)HE YI-QUAN5) TANG JIA-FU5) CAO FEN-YANG5) HOU MING-JIN5) HUANG DE-ZHI5)1) Nanjing Intstitute of Geology and Mineral Mesources, MGMR,Nanjing 210016, China 2) Institute of Mineral Deposits, M
Seismic sounding data along a 420km long profile was collected in 1994. From north to south the profile goes across three tectonic units, namely North China Block,Dabieshan Orogenic Belt and Yangtze Block. By forward modeling, a vertically layered and laterally blocked crust velocity model as well as its Poisson's ratio section was obtained. According to the seismic experiment associated with geological and geochemical research, the following inferences are drawn. The crust can be divided into three layers. The upper crust exhibits a multiple napped-sheets structure and the middle crust ductile deformed layers. The lower crust of the Dabieshan Belt appears to be acidic in composition as a whole. The Debieshan's UHP metamorphic rocks are characterized by a typical thin skin sheet structure. Anasynchronous dual subduction mountain-building model and opposite wedging and drawing exhumation machanism of the UHP rocks are suggested. It is quite evident that there exists a mountain root of about 6-8km thick under the Dakieshan mountain.