Hf isotopes of the 3.8 Ga zircons in eastern Hebei Province, China: Implications for early crustal evolution of the North China Craton  

作　　者：WU Fuyuan YANG Jinhui LIU Xiaoming LI Tiesheng XIE Liewen YANG Yueheng 

机构地区：[1]tate Key Laboratory of Tectonic Evolution, Institute of Geology and Geophysics, Chinese Academy Of Sciences, Beijing 100029, China [2]Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China

出　　处：《Chinese Science Bulletin》2005年第21期2473-2480,共8页

基　　金：supported by the National Natural Science Foundation of China(Grant No.40325006);the“Outstanding Youth Project”of CAS;Key Laboratory of Continental Dynamics,Department of Geology.Northwest University.

摘　　要：Zircon U-Pb dating indicates that the fuchsite quartzite in eastern Hebei Province was derived from weathering and erosion of the 3.6-3.8 Ga granitic rocks. In-situ zircon Hf analyses show that the Lu-Hf isotopic system remained closed during later thermal disturbances. Zircons with concordant ages have Hf isotopic model ages of about 3.8 Ga, suggesting a recycling of this ancient crust. The ～3.8 Ga zircons have similar Hf isotopic compositions to those of chondrite, indicating that their source rocks (granitic rocks) were derived from partial melting of the juvenile crust which originated from a mantle without significant crust-mantle differentiation. Therefore, it is proposed that there was no large-scale crustal growth before ～3.8 Ga in eastern Hebei Province. Considering zircon Hf isotopic data from other areas, it is concluded that the most ancient crust in the North China Craton probably formed at about 4.0 Ga, and the possibility to find crust older than 4.0 Ga is very limited.Zircon U-Pb dating indicates that the fuchsite quartzite in eastern Hebei Province was derived from weathering and erosion of the 3.6-3.8 Ga granitic rocks. In-situ zircon Hf analyses show that the Lu-Hf isotopic system remained closed during later thermal disturbances. Zircons with concordant ages have Hf isotopic model ages of about 3.8 Ga, suggesting a recycling of this ancient crust. The -3.8 Ga zircons have similar Hf isotopic compositions to those of chondrite, indicating that their source rocks （granitic rocks） were derived from partial melting of the juvenile crust which originated from a mantle without significant crust-mantle differentiation. Therefore, it is proposed that there was no large-scale crustal growth before -3.8 Ga in eastern Hebei Province. Considering zircon Hf isotopic data from other areas, it is concluded that the most ancient crust in the North China Craton probably formed at about 4.0 Ga, and the possibility to find crust older than 4.0 Ga is very limited.

关 键 词：锆石 同位素 地壳进化 中国 地质构造 

分 类 号：P54[天文地球—构造地质学]