Magma mixing of granites at Lianghe:In-situ zircon analysis for trace elements, U-Pb ages and Hf isotopes

作者：CONG Feng LIN ShiLiang ZOU GuangFu LI ZaiHui XIE Tao PENG ZhiMin & LIANG Ting Chengdu Center of China Geological Survey Chengdu China; State Key Laboratory of Geological Processes; Mineral Resources China University of Geosciences Wuhan China

来源：Science China Earth Sciences, 2011, (09): 1346-1359.

• Lianghe
• zircon
• trace element
• U-Pb age
• Hf isotope
• magma mixing

In this paper, we report an integrated study of trace element, U-Pb age and Hf isotopic composition of zircons from alkali feldspar granites, granodiorites and diorite enclaves in a recently discovered ring complex at Lianghe in western Yunnan, Chi na. The granitoids showed identical U-Pb ages of 127, 115 and 122 Ma, from felsic to mafic, but had different zircon trace el ements and Hf isotopic compositions. Trace element content decreased with a gradual increase in εHf(t) values of ?9.1 to ?5.4, ?4.5 to 0, and 3.6 to 6.2, respectively. Results indicate that changes in zircon trace elements generally correlate with changes in Hf isotope signatures within single samples and among various granitoids. These relationships reflect the mixing of felsic and mafic magmas. Evidence indicates that depleted mantle-derived mafic magma underplating caused ancient crustal melting, and then formed large-scale granites in Lianghe during the Early Cretaceous. These granodiorites were formed mainly by the mix ing of mafic magma and granitic magma.