Petrogenesis and tectonic implications of Late Triassic granitoids in the Alananshan,East Kunlun belt:evidence from geochemistry,geochronology,and zircon Hf isotopic compositions

The Qimantag in the East Kunlun Orogenic Belt has widespread Triassic magmatic rocks that have received scant attention,with an unresolved issue relating to its petrogenesis and geodynamics.In this paper,we used zircon U-Pb-Hf isotopes and whole-rock geochemistry to trace the petrogenesis and tectonic settings of the moyite and monzogranite from the Qimantag Alananshan,East Kunlun.The moyite and monzogranite are silicic(SiO_(2-)~69.9-76.41%),highly alkali(Na_(2)O+K_(2)O~7.29 to8.96 wt.%),with Mg^(#)about 10.4-30.34,indicative of a high-K calc-alkaline rock series.The rare earth element patterns diagram is right-leaning,with a negative Eu anomaly(δEu=0.31-0.68).They are enriched in Rb,K,and light rare earth elements but depleted in Nb,Ta,and Ti,with abundant amphibole,typical of I-type granites.U-Pb on zircon constrained the emplacement of the moyite at 223.9±2.6 Ma and monzogranite at 226.9±2.9 Ma.TheεHf(t)values range from-2.8 to+0.1 except for one outlier value of-7.0,corresponding two-stage model age of 1249-1437 Ma.Our combined geochemical and isotopic results indicate that the moyite and monzogranite were derived from partial melting of the lower thicken crust with the contribution from the older basement materials.These rocks formed in a post-collision setting that is transitional between compressive collision and extension orogeny.