The Geochemical Characteristics And Geological Significance Of Mantle Peridotite In Doma,Tibet

The Doma area is located in the middle of the Bangong Lake-Nujiang suture zone.Through field geological surveys,there are two types of mantle peridotite in the ultrabasic end numbers of the ophiolite in the area,and the mantle peridotite was used as the bottom component of the ophiolite is generally considered to be an important carrier for understanding the deep information of the upper mantle.The study of its rock and geochemical characteristics can deepen the research on the tectonic background of ophiolite.Therefore,this paper use the Doma mantle peridotite as the object of the study was to conduct research on petrology,mineralogy,and geochemistry,and then to explore the petrogenesis of the mantle peridotite and its tectonic significance,and to provide further constraints for the tectonic evolution of the Banggong Lake-Nujiang Neo-Tethys.The Doma mantle peridotites have different degrees of serpentinization and are mainly composed of strong serpentinized peridotites and serpentinites.Relevant studies have shown that the serpentinized mantle peridotites still retains the most geochemical characteristics of the primary rocks,and then can use the geochemical characteristics of the rock to analyze the formation and evolution history of the rock.Based on the Yb-Ti diagram and the partial melting of heavy rare earths,the primary rocks of the strong serpentinized peridotite was experienced 17%~20% partial melting process,while the primary rocks of the serpentinites was experienced more than 25% of the partial melting process.Based on the total rock geochemical element contents,it was found that the two mantle peridotites are enriched with large ionic lithophile elements(Cs,Ba,U,Pb,Sr),light rare earth elements(LREE),and high field strength elements(Zr,Nb,Hf).The appearance of this phenomenon is explained by the fact that the primary rock was subjected to a partial melting process and was then subjected to the metasomatism of the fluid/melt of the subduction zone.According to this study,in the MgO-related diagram and the Yb-related diagram,it can be clearly distinguished that the strong serpentinized peridotites in the Doma area have the characteristics of the Abyssal peridotites(MOR type)and suffered from the deformation of the subduction zone in the later period.Their primary rock were the subduction-related peridotites.The serpentinites in the Doma area have obvious features of the mantle wedge peridotites,and the spinel composition diagram shows that the primary rocks were mantle wedge peridotites with fore-arc setting.The serpentinization occurred in both of them and eventually remained in the suture zone due to the closure of the ocean.It was a rock record of the subduction evolution stage in the Neo-Tethys Ocean of Bangong Lake-Nujiang.According to previous studies on the Banggong Lake-Nujiang suture zone ophiolites,it was found that the suture zone has universal experienced the intra-oceanic subduction(~187Ma-163Ma)in the Early-Mid Jurassic.This study shows that the mantle peridotites in the Doma area may be formed within the oceanic subduction background of the same period,providing new constraints and data support for the tectonic evolution of the Bangong Lake-Nujiang suture zone.