Geochemical Characteristics and Implications of Eclogite Gravels from Mesozoic Strata at the Northern Margin of Dabie Orogenic Belt  

作　　者：李双应 岳书仓 王道轩 刘因 李任伟 孟庆任 金福全 

机构地区：[1]College of Natural Resources and Environmental Science, Hefei University of Technology, Hefei 230009, China [2]Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

出　　处：《Chinese Journal Of Geochemistry》2004年第2期124-134,共11页中国地球化学学报

基　　金：ThisresearchprojectwasfinanciallysupportedbytheStateKeyBasicResearchDevelopmentProgramofChina (GrantNo.G1 9990 75 5 0 7)

摘　　要：The eclogite gravels, which were found in the Mesozoic Fenghuangtai and Maotanchang formations on the northern margin of the Dabie orogenic belt, are rich in K-2O (1.21%), ∑REE (278μg/g), and LILE (such as Rb, Ba, K, Th, etc.), with high (La/Yb)-N ratios (14.4), on the basis of the analyses of major elements, rare-earth elements (REE) and trace elements. Their enrichment in LILE, notable Nb-Ta depletion through, and depletion in HFSE relative to REE in comparison with the primitive mantle and N-MORB indicate that the protoliths of the eclogite gravels were formed in an island-arc setting. According to the Th-Hf-Ta discrimination diagram, the protoliths of the eclogite gravels are characterized by volcanic arc basalts. Trace element data indicate that the subducted marine sediments were assimilated in the magma chamber, resulting in the enrichment of LILE in the protoliths. Therefore, the protoliths of the eclogite gravels are considered to have been formed in an inland-arc setting, indicating that there had developed a paleo-inland arc before Triassic collision between the North and South China blocks in the Dabie orogenic belt. There is a marked difference between the eclogite gravels and the eclogites developed along the Dabie orogenic belt, solely based on their geochemical data, especially REE. Therefore, the eclogite gravels may not be derived from eclogite terrains preserved in the Dabie orogenic belt.The eclogite gravels, which were found in the Mesozoic Fenghuangtai and Maotanchang formations on the northern margin of the Dabie orogenic belt, are rich in K-2O (1.21%), ∑REE (278μg/g), and LILE (such as Rb, Ba, K, Th, etc.), with high (La/Yb)-N ratios (14.4), on the basis of the analyses of major elements, rare-earth elements (REE) and trace elements. Their enrichment in LILE, notable Nb-Ta depletion through, and depletion in HFSE relative to REE in comparison with the primitive mantle and N-MORB indicate that the protoliths of the eclogite gravels were formed in an island-arc setting. According to the Th-Hf-Ta discrimination diagram, the protoliths of the eclogite gravels are characterized by volcanic arc basalts. Trace element data indicate that the subducted marine sediments were assimilated in the magma chamber, resulting in the enrichment of LILE in the protoliths. Therefore, the protoliths of the eclogite gravels are considered to have been formed in an inland-arc setting, indicating that there had developed a paleo-inland arc before Triassic collision between the North and South China blocks in the Dabie orogenic belt. There is a marked difference between the eclogite gravels and the eclogites developed along the Dabie orogenic belt, solely based on their geochemical data, especially REE. Therefore, the eclogite gravels may not be derived from eclogite terrains preserved in the Dabie orogenic belt.

关 键 词：砂砾层 地球化学 中生代 造山带 凤凰石 榴辉岩 

分 类 号：P595[天文地球—地球化学]