Genesis of Heishibeihu Cenozoic potassic volcanic rocks from northern Qinghai-Tibet Plateau, China

Cenozoic potassic volcanism of Kunlun area recorded the deep geodynamic processes of northern Qinghai-Tibet Plateau. There have always been major cognitive divergences about the source characteristics and generation mechanism of Cenozoic magma of Kunlun volcanic belt. In this paper, petrological and geochemical characteristics of Heishibeihu potassic volcanic rocks in Kunlun volcanic belt are discussed, and further genesis comparison of the Cenozoic volcanic rocks among Heishibeihu, Kangxiwa and Quanshuigou of west-Kunlun area are made. According to research, the K2O and Na2O contents of basaltic rocks of Kunlun volcanic belt vary largely, from sodic to potassic, and all the basaltic magma displays an evolution tendency of potassic latite in TAS diagram. Magmatic source of Heishibeihu volcanic rocks display EMⅡ characteristics in the composition of high field-strength element (HFSE) and Sr, Nd isotopic system. The Cenozoic volcanic rocks are intensively enriched in LREE and have strong differentiation in HREE, which indicates the magma was originated form garnet-bearing enriched mantle. The ratios of incompatible elements, such as K/Nb and Ba/La, show transitional features between island arc volcanic rocks and OIB (ocean island basalt), which indicates the magmatic source is an ancient subduction mantle wedge undergone metasomatism of asthenosphere fluid.