Constraints On The Evolution Of Bangong-Nujiang Collision Zone By The Characteristics Of Metal Element Geochemical Anomalies And Lithogeochemistry In Xiongmei Area

Bangong Co-Nujiang collision zone is located in the central part of the Tibetan Plateau,which is an ideal site to study the opening and closing of ocean basins and continental collisions.The Lhasa terrane and the Qiangtang terrane assembled along the Bangong Co-Nujiang suture zone and formed the Bangong Co-Nujiang collision zone.Large areas of magmatic rocks are exposed in these two terranes,which can be used as lithoprobes and windows to explore the deep earth and trace the oceanic slab subduction,Lhasa-Qiangtang terrane collision,and the mechanism of post-collisional tectonic evolution.However,although many domestic and foreign scholars have carried out a lot of research and made many innovative achievements in the Bangong Co-Nujiang collision zone in recent years.There are still many differences on the genetic mechanism and deep dynamics process of magmatic rocks exposed in Lhasa and Qiangtang terranes,which hinder our understanding of the Bangong Co-Nujiang oceanic slab subduction and the detailed tectonic evolution of subsequent continent-continent collision.Bangong Co-Nujiang collision zone is the oldest one and a famous polymetallic metallogenic belt in the Tibet Plateau.The study area is located in the middle of this belt,Xiongmei area of Shenzha County in northern Lhasa terrane.Magmatic rocks show multistage and multiplicity,exposed widely in study area,which can provide the most direct data sources for the geological and structural evolution of the Bangong Co-Nujiang collision zone during the Early-Late Cretaceous.Our team carried out the project of “Four 1:50000 mineral geological survey in Xiongmei area,Shenzha County,Tibet” in Xiongmei area,and obtained the geochemical anomaly maps of ore-forming elements in the study area.Geochemical anomalies are commonly used for delineating the anomaly extension of metallogenic elements in a region,and then providing information for geological exploration,which is widely used in prospecting.In this study,through the preliminary comparative analysis of geochemical anomalies and magmatism,we found that there is a close relationship between them.Therefore,on the one hand,this study carried out research on the rocks,stratums,structures and other aspects of the study area,and collected previous research results to further summarize the characteristics of magmatism in the study area;On the other hand,according to the data obtained from the project,we delineated the geochemical anomaly areas of 6 ore-forming elements in the study area.Based on the comparative analysis of the above two research results,we found that the geochemical anomalies in the study area are coupled with the Early-Late Cretaceous magmatism.Considering that the mineralization of ore-forming elements is often caused by the corresponding magmatism,and the magmatism is produced in a specific tectonic environment.Therefore,in combination with the regionally geological evolution history,we try to constrain the evolution history of the Bangong Co-Nujiang collisional belt during Cretaceous by using the coupling of geochemical anomalies of ore-forming elements and magmatism.Our research results indicate that the geochemical anomalies of metallogenic elements in the study area are coupled with Cretaceous magmatism,Cu-Mo mineralization were caused by Early Cretaceous magmatism,and Cu-Mo-W-Sn mineralization were caused by Late Cretaceous magmatism.In addition,from Jurassic to Cretaceous,the Bangong Co-Nujiang oceanic slab subducted southward under the Lhasa terrane and underwent slab roll-back,break-off,and delamination of thickened lithosphere.