Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China  

作　　者：QIU Zhili WU Fuyuan YU Qingyuan XIE Liewen YANG Shufeng 

机构地区：[1]Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China [2]State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China [3]Department of Geosciences, Sun Yat-sen University, Guangzhou 510275, China

出　　处：《Chinese Science Bulletin》2005年第22期2602-2611,共10页

基　　金：This work was supported by the National Natural Science Foundation of China (Grants Nos. 49602025, 40325006 and 40025209);“Excellent Youth”of Chinese Academy of Sciences, and Natural Science Foundation of Guangdong (Grant No. 011143).

摘　　要：Cenozoic basalts are widely distributed in east- ern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the sub- continental lithospheric mantle (SCLM) and petrogenetically related to mantle metasomatism induced by addition of crustal materials. Using the Laser Ablation Multiple Collec- tor Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS), zircon megacrysts from the Cenozoic ba- salts at Changle in Shandong, Mingxi in Fujian, and Penglai in Hainan provinces have been used for Hf isotopic analyses. The data indicate that there is no significant deviation for the different zircon grains in each locale, except those from Penglai. The obtained 176Hf /177Hf ratios are 0.28302 — 0.28308 for Changle, 0.28297—0.28300 for Mingxi, and 0.28288—0.28293 for Penglai, with corresponding εHf values of 8.7—10.8, 7.0—7.9, and 3.9—5.7, respectively. These data display that there existed some regional heterogeneity, but the Hf model ages clustere in the Phanerozoic. Therefore, it is inferred that metasomatism of the lithospheric mantle be- neath eastern China took place in the Phanerozoic, most probably in the Mesozoic-Cenozoic. However, the formation time of the lithospheric mantle is not clearly constrained based on the present Hf isotopic data.Cenozoic basalts are widely distributed in eastern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the subcontinental lithospheric mantle （SCLM） and petrogenetically related to mantle metasomatism induced by addition of crustal materials. Using the Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry （LA-MC-ICPMS）, zircon megacrysts from the Cenozoic basalts at Changle in Shandong, Mingxi in Fujian, and Penglai in Hainan provinces have been used for Hf isotopic analyses. The data indicate that there is no significant deviation for the different zircon grains in each locale, except those from Penglai. The obtained ^176Hf /^177Hf ratios are 0.28302- 0.28308 for Changle, 0.28297-0.28300 for Mingxi, and 0.28288-0.28293 for Penglai, with corresponding ear values of 8.7-10.8, 7.0-7.9, and 3.9-5.7, respectively. These data display that there existed some regional heterogeneity, but the Hf model ages clustere in the Phanerozoic. Therefore, it is inferred that metasomatism of the lithospheric mantle beneath eastern China took place in the Phanerozoic, most probably in the Mesozoic-Cenozoic. However, the formation time of the iithospheric mantle is not clearly constrained based on the present Hf isotopic data.

关 键 词：HF同位素 锆石 新生代时期 玄武岩 

分 类 号：P588.145[天文地球—岩石学]