Study On The Geochemstry Of Granitoid Intrusives Of Douling Group In The East Qiling And Its Geological Significance

The geological events were quite active during the Tinning period(1000~800Ma) both in North Qinling and South Qinling, accompanied by strong structural deformation and magma activities. At the same time, the regime of Qinling tectonic begun to transformate from vertical accretion imaged by rift system and limited ocean basins to lateral accretion of plate tectonics. In addition, the major geological events of Jinning period are coincidence with the information and the breakup of Rodinia supercontinent during the Neoproterozoic as suggested by some foreign geologists. So it becomes very important to study the granitoids related to the Jinning movement.The Neoproterozoic granitoid intrusions in the South Qinling belt include the Gangou, the Sanpinggou and the Fengzishan plutons, Which are mainly composed by diotite, quartz-diorite, granodiorites and some hornblende gabbros. Geochemically, they are enriched in LILE and LREE, and relatively depleted in HFSE, suggesting that they were formed in an island-arc or active continental margin environment. According to Bernand Barbarin, these intrusions are similar to those of ACG(Amphibole-rich Calc-alkaline) type. Both crustal and mantle materals were involved in their sources.The dating of zircon U-Pb from these granitoids range from 683 + 4Ma to 756+19 Ma, evidently later the peak regional metamorphism (833 + 17Ma ) of Douling Group.Geochemical features of these granitoids, together with their regional geology, indicate that they were probably related to the subduction of regional small ocean basin during the Neoproterozoic, which shows complicated characteristics of small ocean basins and continental blocks existing at the same time. Therefore, it can be concluded that the North China block and Yangtze block were separated from each other at least the late Neoproterozoic.