Evolution Of Zhikong-Songduo Ocean And Its Implications For Mineralization Of The Nabuding Lead-Zinc In Medro Gongkar,Tibet

Mozhu Gongka county is located in the south foot of Nyenchen Tanglha Mountains,in the central and southern part of Gangdise-Nyenchen Tanglha block,and junction of the Gangdese continental margin volcano-magma arc and the Nianqing Tanggula arc back fault.It is of great significance to study the evolution of Zhikong-Songduo Ocean to constitute the structure of multiterrane-archipelago arc of Tibet plateau and to establish a new subduction system of Paleotethys plate in Lhasa block.Nabuding lead-zinc deposit with certain mineralization potential in the Gangdise metallogenic belt,as a low level of research,its implications of mineralization and evolution of Zhikong-Songduo Ocean study can help to improve and rich regional metallogenic theory.In this paper,petrography,tectonic geology,zircon chronology,petrogeochemistry and other methods combined with previous data,identification the Zhikong-Songduo Oceanic plate stratigraphic unit,divides the Zhikong-Songduo Ocean plate belt,identifies the dual metamorphic belt,study the tectonic evolution of Zhikong-Songduo Ocean and its implications for mineralization of the Nabuding Lead-Zinc.This paper reported discoveries of the ocean plate stratigraphy including the ocean island,seamount,island arc,oceanic basin,and ophiolitic melange belt,which are exposed at the Tangjia-Songduo area.Research on their rock assemblage,metamorphism,petrogeochemistry,formation age,tectonic setting,and divides the Zhikong-Songduo Ocean plate belt.Based on the evidence of ocean plate evolution,it be divided into five stages: initial extension,expansion,southward subduction,trench-arc-basin mode,closure and continental collision.The complete evolutionary history of opening,subduction and closing of Zhikong-Songduo Ocean is constructed.The dating of zircon U-Pb chronology of the migmatites formed by local remelting of high-pressure and ultrahigh-pressure metamorphic rocks shows that the peaking metamorphic age of the Zhikong-Songduo Ocean plate is 251.0±1.1Ma.It represents the subduction and closure of ocean basin and continental collision.The age of plate's reentry and retrograde metamorphism was 243.2±1.5Ma.Thus,the complete evolution of Zhikong-Songduo Ocean wasrestrained chronologically.In Zhikong-Songduo Ocean of the tectonic evolution,Zhikong-Songduo Ocean has been nature in the early permain,the mantle thermal plume upwelling has led to the development of oceanic island in the ocean basin,its including basalt and overlying carbonate cap,the early Permian oceanic island site provides an adequate source of calcium carbonate for the mineralization of the Nbuding Lead-Zinc deposit.