SHRIMP Age and Geochemistry of the Bikou Volcanic Terrane:Implications for Neoproterozoic Tectonics on the Northern Margin of the Yangtze Craton  

作　　者：YANQuanren WANGZongqi A.D.HANSON P.A.DRUSCHKE YANZhen LIUDunyi JIANPing SONGBiao WANGTao JIANGChunfa 

机构地区：[1]InstituteofGeology,ChineseAcademyofGeologicalSciences,Beijing100037 [2]DepartmentofGeosciences,UniversityofNevada,LasVegas,LasVegas,NV89154-4010,USA [3]InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing100029

出　　处：《Acta Geologica Sinica(English Edition)》2003年第4期479-490,共12页地质学报（英文版）

基　　金：supports from the National Natural Science Foundation of China(grants 40172071 and 40211120151 to Yan Quanren);the Ministry of Science and Technology of the People’s Republic of China(grant 2202CB412608 to Wang Zongqi);the China Geological Survey(grant DKD2001002 to Wang Zongqi);the University of Nevada Las Vegas(to Hanson);and the Geological Society of America(to Druschke)are gratefully appreciated.

摘　　要：The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.The Bikou volcanic terrane is predominated by subalkaline tholeiitic lavas. Rock samples display lower initial ratios of Sr and Nd, 0.701248-0.704413 and 0.511080-0.512341 respectively. 207Pb and 208Pb are significantly enriched in the lavas. Most samples have positive εNd, which indicates that the magma was derived from EM-type mantle source, while a few samples with negative εNd indicate that there was contamination in the magma evolution. Magma differentiation is demonstrated by variations of LREE and LILE from depletion to enrichment. Additionally, normalized REE patterns and trace elements showed that lavas from the Bikou volcanic terrane have similar characteristics to those of basalts in arc settings caused by subduction and collision. Analyses showed that the Bikou volcanic terrane is a volcanic arc. New evidence proved that the Hengdan Group, north of the Bikou arc, is a turbidite terrane filling a forearc basin. Consequently, the Bikou volcanic terrane and the Hengdan turbidite terrane construct an arc-basin system. New SHRIMP ages showed that this arc-basin system developed on the northern margin of the Yangtze craton in the Neoproterozoic (846-776 Ma), and this arc-basin system is in agreement with the tectonic processes of Rodinia in the Neoproterzoic.

关 键 词：GEOCHEMISTRY Sr-Nd-Pb isotopes SHRIMP ages Bikou Volcanic Terrane southwestern Qinling Mts. Yangtze Craton RODINIA 

分 类 号：P317[天文地球—固体地球物理学] P59[天文地球—地球物理学]