Geochronological Evidence Of Indosinian Metamorphic Event And Its Tectonic Significance In Kangxiwar Tectonic Zone Of Western Kunlun, NW China

The CL image, LA-ICP-MS in situ trace elements analysis and U-Pb dating for zircons indicate that the metamorphic ages of sillimanite-garnet-biotite gneiss, biotite-plagioclase-amphibole gneiss and garnet-amphibole gneiss from eastern Taxkorgan of the Western Kunlun are (220±2) Ma, (221±3) Ma and (220±3) Ma respectively. The protolith ages of sillimanite-garnet-biotite gneiss and biotite-plagioclase-amphibole gneiss are about Permian. And The protolith age of garnet-amphibole gneiss is smaller than (480±8) Ma respectively. The samples were collected on 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+P1+Q) is consistent with retro-metamorphic assemblage of HP mafic granulite at amphibolite facies stage. The dating results suggest these HP granulites underwent peak metamorphism at (220±2) Ma to (253±2) Ma. Thus, the Kangxiwar suture was probably formed by subduction and collision of the Paleo-Tethys Ocean during Indosinian. Protolith ages of the three samples together with previously published U-Pb zircon dating age, suggest the sillimanite-garnet schist-quartzite unit is a late Paleozoic unit, not a part of the Paleoproterozoic Bulunkuole Group.