Petrogenesis of the Buziwandaban pluton in western Kunlun： Constraints from LA-ICP-MS zircon U-Pb geochronology and geochemical characteristics
Qiao Gengbiao1，Wang Ping2，Zhao Xiaojian1
1. Xi′an Center，China Geological Survey，Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits，MLR，Xi′an 710054；2. Petroleum Exploration and Development Research Institute of PetroChina Changqing Oilfield Company，Xi′an 710086
The Buziwandaban pluton is located in the intermediate acidic magmatic rocks belt of the western Kunlun area of Xinjiang. The pluton is composed mainly of the inequigranular quartz diorite and monzogranite. Combined with the cathodolumine scence（CL）images and element U and Th features of zircon， this study yielded an age of 225.5±2.3 Ma（n=18，MSWD=1.6）for the pluton using the LA-ICP-MS zircon U-Pb dating， indicating the Late Triassic（T3）. Both of quartz diorite and monzogranite have accessory minerals such as amphibole and sphene. The geochemical analysis show that the pluton is characterized by SiO2=61.41％～73.01％，total alkali（Na2O+K2O）=6.64％～8.25％，and aluminum index A/CNK=0.98～1.04，indicating a transitional composition between metaluminous and peraluminous. The pluton is enriched in LREE，depleted in HREE（LREE/HREE=5.85～20.42，（La/Yb）N=6.38～43.73），with negative Eu anomaly（δEu=0.53～0.85）. While the trace elements are characterized by Rb，Th，K，LREE enriched，and Ba，Sr，Ti，Nb，Zr depleted. All the features suggest a high K calcic-alkaline I type granite. According to the magma origin and formation research，the Buziwandaban pluton was derived from partial melting of the lower continental crust being intermingled with partial mantle source under the condition of temperature ca. 707～718℃. Based on comprehensive analysis of the genetic type of the pluton and evolution of regional tectonic environment，we suggested that when the paleo-Tethys ocean was gradually evolved from subduction toward north to the complete closure in the Late Middle Triassic，and the Buziwandaban pluton was formed just after this tectonic transfrom. That is to say，Buziwandaban pluton was formed in post-collisional tectonic setting in the Early Late Triassic.
Qiao Gengbiao,Wang Ping,Zhao Xiaojian. Petrogenesis of the Buziwandaban pluton in western Kunlun： Constraints from LA-ICP-MS zircon U-Pb geochronology and geochemical characteristics[J]. Chinese Journal of Geology, 2016, 51(4): 1114-1136.