Geochemical characteristics and geodynamic significance of the Linzizong Group volcanic rocks in the Gangdise area

Abstract：The Cuowomo-Chengxiangcuo volcano-sedimentary basin is located on the south-central edge of the Gangdise block, Tibet. Volcano-sedimentary rocks in this basin are called the Linzizong Group, which is Paleocene-Eocene in age. Geochemical analysis indicates that the Linzizong volcanic rocks belong to a calc-alkaline series, exhibiting enrichment in LREE, different degrees of negative Eu, Ce and Nb anomalies and enrichment in the trace elements K, Rb, Th and Ce and depletion in the trace elements Sr and Ba，especially in Nb, P and Ti. Therefore, the authors tentatively suggest that the Linzizong volcanic rocks formed in a tectonic environment of subduction and arc making and resulted from mixing of basic differentiated magma and crustal anatectic acid magma in different proportions and in different time intervals. In addition, mixing between abyssal sediments on the subducted plate and basic magma is also a factor that can not be negligible. On the basis of an integrated analysis, the authors suggest that the collision between the India plate and Eurasian plate was initiated after 45 Ma.