Multi-stage Crustal Melting from Late Permian Back-Arc Extension Through Middle Triassic Continental Collision to Late Triassic Post-Collisional Extension in the East Kunlun Orogen

The East Kunlun Orogen is an important part of the East Tethys region and has received significant attention with regards to the evolution of the Tethys Ocean. This contribution presents geochronological, whole-rock major and trace element geochemical, and Sr-Nd-Hf isotopic data of magmatic rocks within the Kengdenongshe polymetallic deposit in the eastern part of the East Kunlun Orogen. Here, we report zircon U-Pb ages of ca. 257 Ma and ca. 211 Ma for granite porphyry intrusions, and ca. 240 Ma for the rhyolitic tuff. These rocks are characterized by high SiO2 variable Al2O3 and K2O, low Na2O, MgO and CaO contents, and high A/CNK ratios, which is typical of S-type granitic rocks. They exhibit large-ion lithophile element enrichment, depletion of high field strength elements, have low (La/Yb)(N) ratios, and negative Eu anomalies. They also display variable (Sr-87/Sr-86), ratios (0.709981 to 0.720907), negative epsilon(Nd) (t) values (-8.7 to -5.5), and a wide (enriched) zircon EH( (t) range (-10.1 to-0.8). The geochemical and isotope data indicate magma derivation through dehydration melting of heterogeneous crustal sources including clay-poor meta-sedimentary rocks and amphibolite, which are both parts of the East Kunlun Orogen basement. These results provide evidence for the evolution of the Paleo-Tethys Ocean in the East Kunlun Orogen including Late Permian (266-255 Ma) back-arc extension, Late Permian to Middle Triassic (255-240 Ma) subduction, Middle Triassic (240-225 Ma) continental collision, and Late Triassic (<225 Ma) post-collisional extension. This study further suggests that the 257 Ma and 211 Ma granite porphyries are related to the asthenosphere upwelling in a back-arc basin and post-collision extensional setting, respectively. The 240 Ma rhyolitic tuff is linked to anatexis associated with crustal thickening during continental collision. (C) 2020 Elsevier B.V. All rights reserved.