The discovery of Longyasongduo eclogite from Gongbujiangda County, Tibet, and its significance

Located in the central part of Gangdise plate, the Tangjia-Sumdo eclogite-bearing metamorphic belt played an important role in the evolution of the Paleo Tethys Ocean. However, the exposed scale of eclogites is still unclear. In this study, the authors found a new site of eclogite in Longyasongdo area. The detailed field survey and petrographic and mineralogical study show that the lithology of Longyasongduo eclogite includes rutile eclogite and quartz eclogite. The eclogite is in the form of lens. The surrounding rock of Longyasongduo eclogite is mainly greenschist, with a small part being muscovite quartz schist. The general mineral assemblage of eclogite is garnet+omphagite+phengite+amphibole+rutile+quartz, with minor sphene and ilmenite. The analysis of the EMPA composition profile of the garnet shows typical growth zoning, with Xpyr and Xalm increasing from core to rim but Xspe showing a tendency of decrease. Meanwhile, according to the discovery of garnet amphibolite from the edge of eclogite, it is inferred that Longyasongduo eclogite might have undergone retrograde process. The discovery of Longyasongduo eclogite is of great importance for the study of the tectonic evolution of the Tangjia-Sumdo ophiolite belt.