Petrogenesis and Geological Implications of Bashenerxi Monzogranite from East Kunlun Orogen Belt

The Bashenerxi granitic complex intruded at the junction of East Kunlun and South Altyn orogenic belt. In this paper, the hornblende monzogranite and the gray monzonitic granite are both derived from the porphyritic monzogranite unit in the Bashenerxi intrusion. Zircon LA–ICP–MS geochronology shows that the diagenetic ages are (452.8±3.1) Ma and (454.2±4.8) Ma, respectively. A group of age (758±15) Ma is concentrated in the core of zircon. The content of SiO₂ is between 71.97% and 74.12%, A/CNK =1.02～1.07, K₂O = 4.80%～5.79%, and Na₂O =2.83%～3.13%, which belongs to high–silica, high–potassium and peraluminous granites. The distribution pattern of rare earth elements is characterized by “gull type” distribution with strong negative europium anomaly (δEu=0. 31～0.44), enrichment of large ion lithophile elements Rb, K, U, Pb and high field strength elements Zr, Hf, Nb, Ta, and loss of Sr, P, Ti. Zirconium saturation thermometer show that the magma origin temperature was about 800 ℃, and the melting pressure was about 0.8～1.0 GPa. The samples are characterized by peraluminous, alkali rich, relatively poor in sodium, high in potassium and low in calcium. and they are strongly depleted in Ba, Sr, Ti, P and Eu, according this characterized, rock was judged to be S–type granite. The epsilon ε_Hf（t）value of the rocks is 0.86～−8.65. The age of the two–stage Hf model (t_DM²) = 1280～1784 Ma, mainly derived from the Paleo–Mesoproterozoic accretive crust. Based on the regional tectonic evolution and tectonic discrimination, it is considered that the rocks were formed after the Altyn deep subduction continental crust plate was broken off, and the regional tectonic background changed from compression to extension.