Formation age and tectonic environment of the Gantaohe Group,North China Craton:Geology,geochemistry,SHRIMP zircon geochronology and Hf-Nd isotopic systematics  

作　　者：XIE HangQiang LIU DunYi YIN XiaoYan ZHOU HongYing YANG ChongHui DU LiLin WAN YuSheng 

机构地区：[1]Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China [2]Beijing SHRIMP Center, Chinese Academy of Geological Sciences, Beijing 100037, China [3]Chinese Academy of Geological Sciences, Beijing 100037, China [4]Tianjin Institute of Geology and Mineral Resources, China Geological Survey, Tianjin 200170, China

出　　处：《Chinese Science Bulletin》2012年第36期4735-4745,共11页

基　　金：supported by the China Geological Survey(1212010811033);the National Basic Research Program of China(2012CB416601)

摘　　要：The Gantaohe Group is an important early Precambrian unit in the Trans-North China Orogen,North China Craton,and is mainly composed of greenschist-facies metabasalt,meta-sandstone and dolomitic marble.We report whole-rock geochemical compositions and SHRIMP zircon ages as well as LA-ICP-MS Hf-in-zircon isotopeic analyses for metabasalts from the Gantaohe Group.SHRIMP dating yielded a weighted mean 207Pb/206Pb age of 2087±16 Ma(MSWD=1.3) for magmatic zircons,but there are also abundant ca.2.5 Ga inherited zircon xenocrysts.The magmatic zircons shows a large Hf(t) variation in Hf(t) from 7.17 to +0.45,suggesting an isotopically highly heterogeneous source for the metabasalt.Chemically all samples show no distinct Zr or Hf anomalies,and some samples show no Nd or Ta anomalies in a primitive mantle-normalized trace element variation diagram,and their whole-rock Nd(t) values range from 4.0 to 0.8.We suggest that the basalt is formed by partial melting of a depleted mantle source,followed by significant crustal contamination.Field observations,the presence of abundant inherited zircon,as well as isotope and trace elements geochemistry support formation of the Gantaohe Group on top of a continental basement.These data and the regional geology lead us to conclude that the Trans-North China Orogen constituted an intracontinental rift during the Paleoproterozoic that was connected to the Eastern Block since the end of the Archean.The Gantaohe Group is an important early Precambrian unit in the Trans-North China Orogen, North China Craton, and is mainly composed of greenschist-facies metabasalt, meta-sandstone and dolomitic marble.

关 键 词：微量元素地球化学 SHRIMP锆石年龄 锆石年代学 ND同位素 中国北方 构造环境 形成时代 板块 

分 类 号：P54[天文地球—构造地质学] P597.3[天文地球—地质学]