Geochemistry and SHRIMP zircon U-Pb age of post-collisional granites in the Southwest Tianshan orogenic belt of China: Examples from the Heiyingshan and Laohutai plutons

The Heiyingshan granite and the Laohutai granite plutons exposed in the Southwest Tianshan resemble A-type granites geochemically. Analysis shows that the both are ferron calc-alkalic peraluminous or ferron alkali-calcic peraluminous with a relatively high concentration of SiO2 (> 70%), high alkali contents (Na2O + K2O = 7.14%-8.56%; K2O > N2O; A/CNK = 0.99-1.20), and pronounced negative anomales in Eu, Ba, Sr, P and Ti. A SHRIMP zircon U-Pb age of 285 +/- 4 Ma was obtained for the Helyingshan hornblende biotite granite intrusion. The geochemical and age dating data reported in this paper indicate that these granites were formed during the post-collisional crustal extension of the Southwest Tianshan orogenic belt, in agreement with the published data for the granites in the South Tianshan.