GEOCHEMISTRY OF THE CALEDONIAN BASIC VOLCANIC ROCKS IN THE SOUTH MARGIN OF QINLING OROGENIC BELT AND THEIR TECTONIC IMPLICATIONS
Dong Yunpeng; Zhou Dingwu; Zhang Guowei;Liu Xiaoming (Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640)(Department of Geology, Northwest University, Xi'an 710069)
The geochemistry of basic volcanic rocks in the south margin of Qinling Orogenic Belt (SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks strongly enriched in LREE with higher REE, and their trace elements geochemistry is similar to that of continental flood basalt. All above evidences suggest that the Caledonian basic volcanic rocks in SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting. The study of regional geology implies that there was an intraplate spreading-rift tectonic setting between South Qinling Block and Yangtz Block in Caledonian epoch,and the dynamic mechanism of spreading in this district was begun in early Caledonian and then the intraplate spreading-initial rifts were formed in late Caledonian.The Mianlue-Huashan limited oceanic basin was formed in Devonian for the reasons of the spreading of paleo-Tethys and geodynamics in deep mantle, and the Qinling microplate was separated from the northern part of the Yangtz plate.