Characteristics of Cenozoic Volcanic Rocks in Gongjue Basin, Eastern Tibet, and Their Tectonic Implications
青藏高原东部贡觉盆地新生代火山岩特征及其构造意义

Cenozoic volcanic rocks in Gongjue basin of eastern Tibet were formed in a post-collisional extensional tectonic setting, and volcanic activities were controlled by a strike-slip shear zone. Chemical composition of volcanic rocks indicates that they belong to the high-K calc-alkaline magmatic system, with volcanic rocks possessing relatively high SiO-2, Al-2O-3, K-2O and Na-2O and comparatively low MgO and TiO-2 components. Petrological and chemical studies also indicate that volcanic rocks are intermediate to acidic rocks. This suite of rocks are enriched in LILE (Rb,Ba,K,Sr,Th) and LREE, and must have experienced marked depletion of HFSE and a group of compatible elements (Cr,Ni,V,Sc), similar to characteristics of post-collisional arc-type rocks. There exist weak Ce anomalies but no Eu anomalies in these rocks. The sources of the volcanic rocks might be the enriched metasomtic mantle which experienced multiple mixture of components mainly derived from previously subducted continental/oceanic crust.