Mantle Input to the Crust in Southern Gangdese, Tibet, during the Cenozoic: Zircon Hf Isotopic Evidence  

作　　者：莫宣学 董国臣 赵志丹 朱弟成 周肃 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources,School of the Earth Sciences and Resources,China University of Geosciences

出　　处：《Journal of China University of Geosciences》2009年第2期241-249,共9页中国地质大学学报（英文版）

基　　金：supported by the National Basic Research Program of China (Nos. 2009CB421002, 2002CB412600);the Na-tional Natural Science Foundation of China (Nos. 40873023, 40830317, 40672044, 40503005, 40572048, 40473020);111 Project (No. B07011);China Geological Survey (No. 1212010610104)

摘　　要：The Quxu （曲水） complex is a typical intrusive among the Gangdese batholiths. Two sets of samples collected from the Mianjiang （棉将） and Niedang （聂当） villages in Quxu County, including gabbro, mafic micro-enclaves （MME）, and granodiorites in each set, were well dated in a previous SHRIMP zircon U-Pb analysis （47-51 Ma）. In this article, the same zircons of the 6 samples were applied for LA ICP-MS Hf isotopic analysis. The total of 6 samples yields 176Hf/177Hf ratio ranging from 0.282 921 to 0.283 159, corresponding to εHf（t） values of 6.3-14.7. Their Hf depleted-mantle modal ages （TDM） are in the range of 137-555 Ma, and the zircon Hf isotope crustal model ages （TDMC） range from 178 to 718 Ma. The mantle-like high and positive Era（t） values in these samples suggest a mantledominated input of the juvenile source regions from which the batholith originated. The large variations in εHf（t） values, up to 5-ε unit among zircons within a single rock and up to 15-ε unit among zircons from the 6 samples, further suggest the presence of a magma mixing event during the time of magma generation. We suggest that the crustal end-member involved in the magma mixing is likely from the ancient basement within the Lhasa terrane itself. The zircon Hf isotopic compositions further suggest that magma mixing and magma underplating at about 50 Ma may have played an important role in creating the crust of the southern Tibetan plateau.The Quxu （曲水） complex is a typical intrusive among the Gangdese batholiths. Two sets of samples collected from the Mianjiang （棉将） and Niedang （聂当） villages in Quxu County, including gabbro, mafic micro-enclaves （MME）, and granodiorites in each set, were well dated in a previous SHRIMP zircon U-Pb analysis （47-51 Ma）. In this article, the same zircons of the 6 samples were applied for LA ICP-MS Hf isotopic analysis. The total of 6 samples yields 176Hf/177Hf ratio ranging from 0.282 921 to 0.283 159, corresponding to εHf（t） values of 6.3-14.7. Their Hf depleted-mantle modal ages （TDM） are in the range of 137-555 Ma, and the zircon Hf isotope crustal model ages （TDMC） range from 178 to 718 Ma. The mantle-like high and positive Era（t） values in these samples suggest a mantledominated input of the juvenile source regions from which the batholith originated. The large variations in εHf（t） values, up to 5-ε unit among zircons within a single rock and up to 15-ε unit among zircons from the 6 samples, further suggest the presence of a magma mixing event during the time of magma generation. We suggest that the crustal end-member involved in the magma mixing is likely from the ancient basement within the Lhasa terrane itself. The zircon Hf isotopic compositions further suggest that magma mixing and magma underplating at about 50 Ma may have played an important role in creating the crust of the southern Tibetan plateau.

关 键 词：Tibetan plateau Gangdese batholith Quxu complex GABBRO MME granodiorite zircon Hf isotope magma mixing crustal thickening. 

分 类 号：P597.3[天文地球—地球化学]