Geochemical and zircon U-Pb dating characteristics and significance of the Tuluyin granites in the east of East Kunlun orogenic belt

Magmatism is regarded as the deep response to the subduction and collision and also a petroprobe to explore the deep process. The Tuluyin area lies in the east of East Kunlun orogenic belt (EKOB), close to the south of the middle fault of EKOB. Based on detailed field investigation, the authors studied the petrology, geochemistry and geochronology of Tuluyin granitoids. Geochemical composition shows that Tuluyin granitoids are lithologically dominated by granodiorite. The SiO₂ varies from 68.49% to 70.87%. The total alkali content is in the range of 5.94%~7.16%, and the K₂O/Na₂O ratios vary from 0.34 to 0.57. Mg^# values are medium in granitoids (35.92-41.86). The A/CNK values (1-1.07) are lower than 1.1, showing that they belong to slightlyperaluminous calc-alkaline I-type granites. The rocks are enriched in light RRE (LRRE) with a flat heavy RRE (HRRE) pattern. There are no or weak negative Eu anomalies. The ratios of (La/Yb)_N are in the range of 4.17-9.14, with the total REE content varying from 118.91×10^-6 to 143.97×10^-6. The rocks are enriched in large ion lithophile elements (Rb, Th, Ba) and depleted in high field strength elements (Nb, Ta, P, Ti). LA-ICP-MS zircon U-Pb dating shows a crystallization age of 245 Ma, identical with the age of Xiadeboli and Aikengdelesite granitoids, suggesting that they all belong to the Early Indosinian period. Geochemical characteristics indicate that these rocks were derived from partial melting of the crust, with the addition of mass and heat flow from the mantle. Based on the existing geochronologic, geochemical and geological data, the authors hold that Tuluyin granitoids were formed under a background of the Anyemaqen-Paleo-Tethys Oceanic crust subducted into EKOB.