Petrogenesis of Lincang granites in Sanjiang area of western Yunnan Province: Constraints from geochemistry, zircon U-Pb geochronology and Hf isotope

The Lincang granites in southern Lancangjiang zone of Sanjiang area, located in the west of Yunnan Province, are mainly composed of biotitic monzogranites. The SiO2 and Al2O3 of the granites range 66. 84% similar to 73. 99% and 12. 94% similar to 15. 23%, averagely 69. 72% and 14. 44% respectively. The K2O/Na2O ratio is high, ranging 1. 42 similar to 30. 1, with average of 8. 66. A/CNK varies from 1. 06 to 8. 59, averagely 2. 61, and mostly > 1. 1. So Lincang granites are high-K calc-alkaline and peraluminous to strongly peraluminous series. Lincang granites are also enriched in LILEs and Pb, but strongly depleted in HFSEs. The REE content is between 198. 2 x 10(-6) and 359. 2 x 10(-6) (average 252. 5 x 10(-6)), with (La/Yb)(N) ratios of 7. 87 similar to 17. 62 (average 11. 19) and delta Eu of 0. 34 similar to 0. 57 (average 0. 48). The intrusion is remarkably characterized by enriched LREE and depleted HREE. The chondrite-normalized REE patterns show strong negative Eu anomalies. The zircon U-Pb ages of the two samples are 219. 19 +/- 0. 99Ma and 219. 69 +/- 0. 67Ma, belonging to Late Triassic. The SiO2-P2O5, SiO2-Zr, K2O-Na2O relationship and ACF plot indicate that the Lincang granites are S type granites, which mainly derive from clay-poor psammite. Lincang granites can be dropped into the group of post-collisional granites in the Rb-Y + Nd discrimination diagram. In addition, Lincang granites have the features of low-Sr and high-Yb in the Sr-Yb discrimination diagram, which is in accordance with the granites in southeastern China. Lincang granites have homogeneous zircon Hf isotopic composition. Their zircons have negative epsilon(Hf) (t) values (- 14 similar to - 11) and old Hf isotope crust model ages (1. 95 similar to 2. 15Ga), suggesting that Lincang granites were formed by partial melting of old crust. Therefore, we consider that Lincang granites were formed in post-collisional stage between the Burma-Thai-Malaysia and Simao block in the Late Triassic.