Paleoproterozoic reworking of ancient crust in the Cathaysia Block,South China:Evidence from zircon trace elements,U-Pb and Lu-Hf isotopes  

作　　者：LIU Rui ZHOU Han Wen ZHANG Li ZHONG ZengQiu ZENG Wen XIANG Hua JIN Song LU Xin Qian LI ChunZhong 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences (Wuhan), Wuhan 430074, China [2]State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China [3]The 7th Geological Team of Zhejiang Province, Lishui 323000, China

出　　处：《Chinese Science Bulletin》2009年第9期1543-1554,共12页

基　　金：Supported by National Natural Science Foundation of China (Grant No. 40873004);Special Funds for National Scientific Research of Commonweal Industries;the Ministry of Land and Resources of China (Grant No. 2008110015);Opening Foun-dation of State Key Laboratory of Continental Dynamics;Northwest University (Grant No. 06LCD12);the Project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)

摘　　要：A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean 207Pb/206Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t) values of -15.6 to -10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Pa-leoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent.A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios （〉0.1）. The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean ^207pb/^206pb age of 1860±13 Ma （MSWD=0.084）, representing the formation age of the granite. The magmatic zircons had negative εHf（t） values of -15.6 to -10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Paleoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent.

关 键 词：微量元素 铪同位素 古元古代 锆石 改造 地壳 中国 Pb 

分 类 号：P534.3[天文地球—古生物学与地层学] Q581[天文地球—地质学]