西藏冈底斯中段碰撞后岩浆作用及其地球动力学意义

Research work in present project mainly includes geochronological, petrological, geochemical, and isotope geochemical studies of samples from both Wuyu basin, Nanmulin (in the middle of Gangdese belt), Tibet and Majiang district. Ar-Ar geochronological studies have been carried out on volcanics and intrusive granite porphyries, respectively. Ages of the volcanics turn out to be 12.00±0.13Ma to 13.63±0.14Ma, while that of granite porphyries to be 10.84±0.34Ma. Results of trace element geochemical studies of high-K calc-alkaline trachyte trachyandesite suite and the granite porphyries intrusive into it from Gaza formation of Wuyu group within Wuyu basin suggest that Wuyu group volcanics are the surface expression of partial melting of the crustal rocks in Gangdese belt exemplified by Yalungzangbu ophiolite suite representative of Tethyan oceanic crust, and that Neo-Tethyan oceanic crust was subducted northward, retarded beneath Gangdese belt and eventually recycled to the upper surface through Neogene magmatism. Moreover, an Sm-Nd isochron age of 177±23Ma has been determined from bulk and mineral separates of the basic lithologies in Luobusha ophiolite suite, and the Nd isotopic characteristics of the suite calls for Tethyan mantle to be of Indian type. Therefore, studies of the post-colisional magmatism will render important evidence for the interpretations of such events as structure of continent collision belt, tectonics after collision, and so forth. There leaves, however, much work to do in these aspects.

详细研究冈底斯中段几个关键地区的碰撞后火山岩和花岗岩的地质学、岩石学、地球化学特征；通过氩氩热年代学，准确厘定碰撞后岩浆岩形成（或者侵位）的年龄，根据花岗岩氩氩年龄谱估算区域剥蚀（或抬升）速率；微量元素及同位素示踪岩浆起源与演化特征，从岩浆成因模式反演本地区碰撞后岩石圈构造演化的动力学机制