Shrimp Dating And Geotectonic Features Of Maotang Group In West Henan And Their Constraints On The Breakup Of Yangtze Block

The Maotang group in the northern margin of the Yangtze block recorded important information of Rodinia breakup. These data could be helpful in constraining the breakup process of the Yangtze block, and thus make great significance in understanding the evolution of Yangtze block.In comprehensive analysis of field observation, SHRIMP and LA-ICP-MS zircon U-Pb dating and whole rock geochemistry data, we could obtain the following conclusions:1. Maotang group was formed in rifting envirenment of the inner continent during middle Neoproterozoic. The magmatic activity continnued for a long period, and ended at about 600Ma.2. The felsic volcanic formation from Maotang group was characterized by crust source, with primitive rocks possibly derived from the remelting of the upper crust; the basic volcanic formation, Maotang group was characterized by mantle source, and was indicated to be the production of mantle plume contaminated by crust in various degree during ascending. The mantle plume could be sourced from the transition zone from spinel phase to garnet phase, with a relative high degree of paritial melting.3. Zircon dating of the vocanic rocks from Maotang group indicate that this area exist a similar magmatic event to the inner and margin of the Yangtze block at 830～780Ma. This indicates the existence of the basement of the Jinningian in this area, which suggest that the area from the south part of the Qinling to the Wudang where the Maotang group occurred should be a part of the north margin of the Yangtze block.4. Regional stratigraphic correlation indicates that the Maotang group, Wudangshan group and Yaolinghe group could be correlated. The Yaoyingzhai formation of Maotang group is similar to the Liantuo formation in the Xiadong area, and recorded more information of the extension and sedimentation event of the Yangtze block at the beginning of the Neoproterozoic Nanhua Period. The Maotoushan foramtion could not be correlated with the Nantuo foramtion in the Xiadong area, and could represent another tectonic-magmatic event in the north margin of the Yangtze block.5. The vocanic event indicated by the Maotang formation is a part of the globle rifting and volcanic activity event which is thought to be triggered by mantle plume and affect areas such as Middle Asia-East Asia (including the middle and west part of China and the South China), Austrilia, north America, the south part of the Africa and Antarctic.6. The passive rifting in the north margin of the Yangtze block began at 760±10Ma and finished at about 600Ma. The appearence of stable land clastic sedimentation and carbonate deposition in shallow water indicate the formation of the passive continental margin and the finish of the Yangtze block breakup in Neoproterozoic.