Geochronological evidence of Indosinian (high-pressure) metamorphic event and its tectonic significance in Taxkorgan area of the Western Kunlun Mountains, NW China

Abstract

The CL images, LA-ICP-MS in situ trace elements analysis, and U-Pb dating for zircons indicate that the metamorphic ages of the sillimanite-garnet-biotite gneiss and the garnet-amphibole gneiss from eastern Taxkorgan of the Western Kunlun Mountains are 220±2 and 220±3 Ma respectively, and their protolith ages are younger than 253±2 and 480±8 Ma respectively. Two samples were collected at the same outcrops with HP mafic granulite and HP pelitic granulite. Mineral assemblage of the sillimanite-garnet-biotite gneiss (Grt+Sill+Per+Q) is consistent with that of HP pelitic granulite at early high amphibolite- granulite facies stage. Mineral assemblage of the garnet-amphibole gneiss (Grt+Amp+Pl+Q) is consistent with retro-metamorphic assemblage of HP mafic granulite at amphibolite facies stage. The dating results suggest that these HP granulites underwent peak metamorphism at 220±2 to 253±2 Ma. Thus, the Kangxiwar tectonic zone was probably formed by subduction and collision of the Paleo-Tethys Ocean during Indosinian. Protolith ages of the two samples, together with previously published U-Pb zircon dating age, suggest that the sillimanite-garnet schist-quartzite unit is a late Paleozoic unit, not a part of the Paleoproterozoic Bulunkuole Group.