Zircon U-Pb Dating and Geochemical Characteristics of Granite Porphyry in Zhanhongshan Area, East Kunlun

Based on the field investigation of granite porphyry in Zhanhongshan area of East Kunlun, zircon U-Pb dating and geochemical study show that the granite porphyry has a diagenetic age of (243.4 ±1.5) Ma (MSWD=0.99), belonging to the Middle Triassic. The geochemical characteristics of the rocks show that the SiO₂ ranges from 73.82% to 75.65%, K₂O/Na₂O=0.61-0.95, relatively rich in sodium, poor in MnO (0.05%~0.06%), P₂O₅ (0.05%) and TiO₂ (0.17%~0.2%). The A/CNK value is 1~1.09, with an average of 1.053. Al₂O₃ is between 12.02%~13.12%. The values of δ are 1.61~1.89. TFeO/MgO is 2.44~2.54 and DI is 91.2~92.64. All these show that it is a highly fractionated I-type granite of peraluminous and calc-alkaline series. The total REE content of the rocks is low (∑REE=134.89×10^-6~165.65×10^-6), LREE/HREE=7.99~8.85, (La/Yb)_N=9.9~11.21. The fractionation of LREE and HREE is obvious, showing a right dipping curve of LREE enrichment and HREE depletion.δEu is 0.58~0.66. The rocks are characterized by a relative enrichment of large ion lithophiles of Rb, Ba and high field strength elements of U, Th, Pb, whereas a depletion of K, P and Ti. Combined with the diagenetic age, geochemical characteristics and regional tectonic evolution,the authors hold that the rocks formed in the collision environment of the northward subduction of the PaleoTethys ocean.