Geological significance of the former Xiong'er Volcanic Belt on the southwestern margin of the North China Craton  

作　　者：Guanxu CHEN Jinhai LUO Huan XU Jia YOU Yifei LI Zichen CHE 

机构地区：[1]State Key Laboratory of Continental Dynamics (Northwest University),Department of Geology,Northwest University,Xi'an 710069,China

出　　处：《Frontiers of Earth Science》2019年第1期191-208,共18页地球科学前沿（英文版）

基　　金：the National Natural Science Foundation of China (Grant No.41421002);MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University.

摘　　要：The rock association of low-grade metasedimentary rocks and greenschists located within the Meso- Cenozoic Liupanshan Fault system on the southwestern margin of the North China Craton (NCC)is regarded as part of the Paleoproterozoic Xiong'er Group.These low- grade rocks are separated by normal faults,with the greenschist located in the hanging wails.Zircon LA-ICP- MS U-Pb ages of the greenschists range from 2455 to 423 Ma,suggesting that they are not Paleoproterozoic in age. The protolith ages (206-194 Ma)of the greenschists were determined by LA-ICP-MS U-Pb dating of zircons from two siltstone inteflayers.The petrology and geochemistry of the greenschists reveal that their protolith was continental tholeiitic basalt that formed in an extensional environment such as a continental rift.Thus,it is proposed that the protolith of the greenschists was a mafic volcanic rock of Late Triassic-Early Jurassic age and was metamorphosed during the Jurassic due to tectonism within the Liupanshan tectonic belt.These results show that the greenschists should be reclassified and removed from the Xiong'er Group,and explains why they differ so much from those of typical Xiong'er Group successions in other areas.The formation of the mafic volcanic rocks under conditions of continental rifting differs from that of coeval granitic rocks in the western Qinling Orogen,where the extension occurred during a post-collisional stage in the Late Triassic,which further suggests that the southwestern margin of the NCC became an extensional setting after the Late Triassic.

关 键 词：southwestern MARGIN of the NCC PALEOPROTEROZOIC Xiong'er Group GREENSCHIST DETRITAL zircon U-Pb geochronology Late TRIASSIC to Early Jurassic 

分 类 号：P[天文地球]