Mesozoic To Cenozoic Tectonomagmatic Evolution And Mineralization In The Cuoqin Area, Mid-Gangdise, Tibet

The Gangdise tectonic belt, located between two giant suture zones of the Yarlung Zangbo and Bangong-Nujiang, is an important part of the Tethys tectonic domain. Since Mesozoic, it has undergone multi-cycle tectonomagmatic evolution and formed a presently complex tectonic framework. The tectonomagmatic evolution and mineralization of the Gangdise belt have been the focus for long-term scientific debates. Among different opinions, the most popular one is that the temporal and spatial distribution and evolution of the Gangdise plutonic-volcanic belt are controlled by the northward subduction of the Yarlung Zangbo oceanic crust and the southward subduction of the Bangong-Nujiang oceanic crust. Based on the regional geologic survey on the scale of 1/250 000, coupled with geological, geochemical and geophysical investigations in some key regions, this dissertation summarized the tectonomagmatic evolution and mineralization of the mid-Gangdise area.With respect to tectonic evolution, the Gangdise belt has experienced a multi-stage evolutional history since Mesozoic, including oceanic crust subduction, arc-continent collision, intracontinental subduction and collision, and strike-slip and block uplift. During this evolution, seven second-order tectonic units were formed; from north to south are the Mingqianri Cretaceous residual sea basin, the Arsuo tectonic melange zone, the Taricuo-Wenbu Yenshan magmatic arc belt, the Cuoqin-Bangduo late Paleozoic composite back-arc basin, the Jiangrang-Geerdi faulted uplift, the Gangdise-Chazi Himalayan magmatic arc belt, and the Xigaze-Anba fore-arc basin. These units comprise important parts of a poly-arc-basin system and exhibit evolutional features of Mesozoic to Cenozoic arc-basin systems. Mosaic pattern of these tectonic units delineates the lithosphere coupling processes of the Gangdise tectonic belt under mechanisms such as back-arc basin attenuation and arc-continent collision.Mesozoic to Cenozoic magmatic activities in the Cuoqin area of the Gangdise belt were intensive and display temporal cycling and spatial zoning. Magmatic intrusion took place mainly during the Yenshan and Himalayan epochs and is dominated by intermediate to acidic rocks; basic to ultra-basic intrusive rocks are only locally observed. The basic to ultra-basic rocks are distributed along suture zones, whereas the intermediate to acidic intrusives occur mainly to the south and north of the Arsuo tectonic melange zone and the Angren ophiolitic melange zone. These intrusive rocks are the products of the closure of the Yarlung Zangbo and Banggonghu-Nujiang oceanic basins and may represent three magma-induced thermal disturbance events of plate subduction, collision, and post-collision. The magmatic intrusion formed the Daxiong-Bangduo, the Jiangrang, and the Bumusongrong intrusive zones. Volcanic rocks are characterized by wide distribution, complex lithology and lithofacies, and various eruptive forms. They are typically layer- or lens-like in shape and strike parallel to the principal structural lineaments in the region. Horizons of the volcanic rocks mainly include the Zenong (J3-K1z) and Linzizong (E1-2l) Groups; volcanic rocks of the Duoni (K1d) , Langshan (K1l) ,Jingzhushan (K2j) , Rigongla (E3r) and Yulin (Ny) Formations and Quaternary are only locally exposed. The most intensive volcanic activity occurred during the late Cretaceous to Eocene, which formed the Gangdise plutonic-volcanic arc and the Cuoqin composite back-arc basin. The volcanic rocks evolved from low-K to high-K in composition with time and migrated spatially from north to south. They all belong to the calc-alkaline island arc series and are closely related to the evolution of the arc-basin systems of the Gangdise tectonic belt.Based on studies of petrology, litho-geochemistry, tectonic setting, petrogenesis and magmatic evolution, the present dissertation summarized the general evolutionary regularity of the magmatic rocks in time and space. The magmatic rock assemblages are divided into the inter-arc spreading basin t...