The discovery of Early Paleozoic eclogite in the upper reaches of Langmuri in eastern East Kunlun Mountains and its significance

Eclogite was recognized recently in the upper reaches of Langmuri in eastern East Kunlun Mountains. In the field, the eclogite occurs in lenticular and massive forms and exhibits fault contact with surrounding rocks. The ecologite-bearing metamorphic zone is 1~3km in width. The lenticular eclogite is distributed in metamorphic rocks of Paleoproterozoic Baishahe Formation and Neoproterozoic granite gneiss.The eclogite facies rock association is composed of eclogite and pomegranate amphibolite, and the eclogite facies mineral assemblage consists of eclogite+omphacite+rutile+quartz. According to eclogite-clinopyroxene mineral temperature and pressure gauge, the temperature and pressure conditions of eclogite rock are estimated as follows: T=650~750℃, p=1.8~2.0GPa, falling into the C-type eclogite zone in garnet Alm+Spess-Pyr-Gross triangular diagram. Zircons in the eclogite CL images show that most zircons have the fan zoning or "fir leaves" structure, with a few weak band structures. Th/U ratios of 31 zircon samples are relatively low (0.06~0.135). The LA-ICP-MS zircon U-Pb ages can be divided into two kinds: a kind of concordant age is 431.9±2.3Ma, representing the eclogite facies metamorphic peak age; the other concordant age is 487±5.9Ma. Original rock might have resulted from the deterioration that occurred under the influence of tectonic events during the subduction process. In consideration of regional ophiolite and tectonic magmatic events, the authors hold that the peak of high-pressure metamorphism in the study area occurred in late Early Silurian in the East Kunlun subduction-collision environment. Combined with the same type of eclogites found in adjacent areas, the authors restored a Palaeozoic high-pressure metamorphic belt in East Kunlun region.