U-Pb zircon geochronology and Hf isotope study of metamorphosed basic-ultrabasic rocks from metamorphic basement in southwestern Zhejiang:The response of the Cathaysia Block to Indosinian orogenic event  

作　　者：XIANG Hua ZHANG Li ZHOU HanWen ZHONG ZengQiu ZENG Wen LIU Rui JIN Song 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources,Faculty of Earth Sciences,China University of Geosciences,Wuhan 430074,China [2]State Key Laboratory of Continental Dynamics,Northwest University,Xi’an 710069,China

出　　处：《Science China Earth Sciences》2008年第6期788-800,共13页中国科学（地球科学英文版）

基　　金：the National Natural Science Foundation of China (Grant No. 40372094);the Opening Foundation of State Key Laboratory of Continental Dy-namics, Northwest University (Grant No. 06LCD12);the project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)

摘　　要：A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geothermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the metamorphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and metamorphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The ε Hf (t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (T DM2 LC ) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recycling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260–230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720°C, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study provided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.A combined study using LA-ICP-MS U-Pb dating, Hf isotopes, trace elements and the Ti-in-zircon geo-thermometer was carried out on zircons from the metamorphosed basic-ultrabasic rocks in the meta-morphic basement of the Cathaysia Block, southwestern Zhejiang Province. The formation and meta-morphic ages of the rocks from the metamorphic basement of the Cathaysia Block were determined based on zircon U-Pb geochronology. The age for the magmatic crystalline zircons from the protolith is about 1.85 Ga. The εHf(t) values of the older zircons were from ?7 to ?3, with two-stage model Hf ages (TDM2LC) of about 2.9 to 3.4 Ga, indicating that the source material was derived from anatexis and recy-cling of the Archean crust. The newly formed metamorphic zircons yielded U-Pb ages of 260―230 Ma. The metamorphic temperature calculated using the Ti-in-zircon geothermometer ranged from 610 to 720℃, consistent with the results from petrographic observations, indicating that the Cathaysia Block experienced an amphibolite facies metamorphism during the Indosinian. Results from this study pro-vided an important timeframe for the tectonic evolution in South China and the Southeast Asia during the Late Permian and Early Triassic times.

关 键 词：U-Pb dating Hf isotopes Ti-in-zircon GEOTHERMOMETER INDOSINIAN orogenics SOUTHWESTERN ZHEJIANG Province 

分 类 号：P597[天文地球—地球化学]