Geochronology, geochemistry and petrogenesis of the Datonggou granitic plutons in the middle section of Altun Mountains

The Datonggou granitic plutons, outcropped in the middle part of Altun Mountains, are principally composed of monzonite granite. The LA-ICP-MS zircon U-Pb isotopic dating indicates that the Datonggou monzonite granite was emplaced at (353.7±1.1) Ma. They have high-K cal-alkaline and strong peraluminous features (SiO₂=74.5%-76.2%, Al₂O₃=12.62%-14.15%, (Na₂O + K₂O)=7.71%-8.29%, K₂O/Na₂O=0.9-1.22, A/CNK=1.0-1.19). The Datonggou granitic plutons are rich in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Ba, Nb, Sr, P, Ti anomaly. REE distribution patterns show strong negative anomaly of Eu (δEu=0.03-0.59) and distinct enrichment of LREE relative to HREE. The geochemical characteristics of trace elements indicate that the rocks were formed by partial melting of variable hybrid sandstone and variable mudstone from the upper crust. The partially melting temperature calculated by whole rock Zr thermometer is 722-745℃ and pressure is 0.8-1.6 GPa. Combined with the data from the Altun Mountains, it is held that the Datonggou granitic plutons in middle Altun Mountains might be related to the delamination of deep blocks under the Altun orogen.