Petrogeochemistry and sedimentary environment of the Early Cretaceous strata from the Shiquanhe-Gegyai area in Tibet and their geological significance

Through comprehensive analysis of Early Cretaceous volcanic petrogeochemistry, sedimentary sequence, sedimentary characteristics and environment in the Shiquanhe-Gegyai area, the calc-alkaline volcanic rocks of the Wumulongqianbo Formation may represent plate subduction. The Duoai Formation, Tuocheng Formation and Langjiu Formation make up three partial melting series, indicating presence of arc crust thickening process under the condition of steepened subduction angle. The alkaline volcanic rock of the Langjiu Formation indicates subduction-induced arc crack. The sediments of the Jiega Formation and the Langshan Formation show the same residual basin under the transgression condition after closure of the Shiquanhe ophiolite mélange. The depth of the residual basin is deep in the south and shallow in the north, and deep in the east and shallow in the west. At the same time, angular unconformity occurred at the edge of the basin, which gradually evolved into weak angular unconformity-conformity towards the interior of the basin.