LA-ICP-MS Zircon U-Pb ages and Hf isotope compositions of zircons from lower Cretaceous diorite-dykes in Lianghe area, western Yunnan, and their geological implications

This paper has reported zircons LA-ICP-MS U-Pb data of granodiorite and diorite from early Cretaceous diorite stock in Lianghe, with 206Pb/238U ages being 118.7Ma±1.5Ma and 119.8Ma±1.0Ma respectively, indicating that they were emplaced at about the same time with Early Cretaceous granite. A magmatic zircon sample of the diorite gave a 206Pb/238U age of ca. 140Ma, implying an earlier Early Cretaceous magmatic event; two inherited zircon samples recorded Indo-China magmatism with 206Pb/238U ages being 208.2Ma±6.7Ma and 221.9Ma±2.4Ma. The granodiorite and diorite show similar whole rock εNd(t) values of -8.03 and -7.70, but they have different heterogeneous Hf isotopic compositions of zircons, with variable εHf(t) values being -5.60~-3.28 and -6.73~-3.09 respectively, indicating that they were generated by mixing of crystalline basement-derived felsic melts with mantle-derived basaltic magma. Different Hf isotopic compositions between Lianghe granite and Northern Gangdise Belt granites suggest that the contribution of the mantle-derived magma to granitic rock was less in Lianghe than in Northern Gangdise Belt in early Cretaceous. The granodiorite and diorite were probably produced from a crustal thickening setting.