Age and lithogenesis of Keri syenogranite from eastern part of East Kunlun Orogenic Belt: Constraint on the Middle Triassic tectonic evolution of East Kunlun

The Keri pluton located in the north tectonic belt of the eastern part of East Kunlun Orogenic Belt, is mainly syenogranite contained with mafic microgranular enclaves (MMEs). The LA-ICP-MS zircon U-Pb chronology of host rock and MMEs yield an age of 231.58 +/- 0. 49Ma and 232.6 +/- 2. 3Ma respectively. Keri pluton is weakly peraluminous I-type granite, and belongs to middle-K calcalkaline series. Keri pluton are high in SiO2 (72. 06% similar to 74. 49%), Na2O/K2O (1. 00 similar to 1. 35) and Nb/Ta (15. 4 -27. 9), and relatively low in Mg# (14 similar to 31) and Rb/Ba (0. 10 -0. 46). The rocks generally have a similar variation trend, such as systematic enrichment of LILE and depletion of HFSE. Keri pluton is a result of partial melting of the middle-lower crust, due to the underplating of the mafic melt caused by the plate break -off after the collision between Bayan Har block and East Kunlun block. The MMEs is similar to its host rock in crystallizing age, but the size is relatively finer. The MMEs contain a few phenocrys captured from the host rock, and some acicular apatites. Above evidences suggest the MMEs is the result of the rapid condensation of mafic melt after infusing into the host rock. Due to the fractional crystallization, the concentration gradient differences between the relic melt and MMEs lead to the element diffusion, cause the interchange of material in them. The influence to the granitoid melts by the Late Palozoic-Early Mesozoic mantle -derived magma of East Kunlun is a continuous process, which was from the mantle melting with fluid metasomatism in early subduction stage to the large-scale plate break -off in late subduction atage, from the continuous influence of plate break -off in syncollision stage to delamination of thicken crust in post -collision stage. The influence degrees and features of mantle -derived magma were different in the different geodynamic system of the process. The age and lithogenesis of Keri pluton indicate a syn-collision stage in 232Ma of East Kunlun.