Geochemistry and genesis of the Nyixung rock body in northern Tibet
WU Xu-ling1,2, CHEN Zhen-hua2(1. China University of Geosciences, Wuhan 430074, Hubei, China;2. Jiangxi Institute of Geological Survey, Nanchang 330201, Jiangxi, China)
The Nyixung rock body is distributed along the Muzhidin-Nyixung-Shasong-Ria zone in Coqên County, Tibet, covering an area of 180.14 km2. It consists of four plutons, which are irregularly elliptical and circular in plan view and occur as a string of beads. The rock types are norite, granodiorite, monzogranite and granite. On the basis of the information obtained through field geological survey and indoor integrated petrological and petrochemical studies, it has been found that there is a clear and sharp pulsatory intrusive contact between various rock units of the rock body and a number of dark dioritic microinclusions are present. The rocks are characterized by a relatively low total REE content, relative enrichment in K, Rb, Ba and Th and relative depletion in Cr, Ti, Nb, Sr and P. Study suggests that the Nyixung rock body formed in an active continental-margin volcanic arc tectonic environment, which is related to northward subduction of the Yarlung Zangbo oceanic plate. So the rock body is believed to be continental arc granite.