U–Pb Zircon Geochronology and Geochemistry of the Neoproterozoic Liujiaping Group Volcanics in the Northwest Margin of the Yangtze Block:Implications For the Breakup of the Rodinia Supercontinent  

作　　者：LI Zuochen PEI Xianzhi LI Ruibao PEI Lei LIU Chengjun CHEN Youxin XU Tong YANG Jie WEI Bo 

机构地区：[1]Key Laboratory of Western China's Mineral Resources and Geological Engineering,Ministry of Education,Faculty of Earth Science and Resources,Chang'an University [2]Faculty of Earth Science and Mineral Resources,China University of Geosciences

出　　处：《Acta Geologica Sinica(English Edition)》2015年第4期1213-1225,共13页地质学报（英文版）

基　　金：supported financially by the Specialized Research Fund for the Doctoral Program of Higher Education (No.20110205110004);the National Nature Sciences Foundation of China (Nos.41472191,41172186,40972136,and 40572121);the Fundamental Research Funds for the Central Universities (Nos.CHD2011TD020,CHD2009JC046,2013G1271092,and 2013G1271091)

摘　　要：Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U-Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios （0.43-1.18）, indicating an igneous origin. Geochronological results of LA-ICP-MS U-Pb dating of the Liujiaping Group zircons yield an age of 809 - 11 Ma （MSWD = 2.2）, implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in AI, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations （96.04-265.48 ppm） and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduetion and arc-continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U-Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios （0.43-1.18）, indicating an igneous origin. Geochronological results of LA-ICP-MS U-Pb dating of the Liujiaping Group zircons yield an age of 809 - 11 Ma （MSWD = 2.2）, implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in AI, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations （96.04-265.48 ppm） and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduetion and arc-continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.

关 键 词：GEOCHEMISTRY zircon LA-ICP-MS U-Pb age late Precambrian TECTONICS Shaanxiprovince 

分 类 号：P588.14[天文地球—岩石学] P597.3[天文地球—地质学]