Calcium isotope fractionation and its controlling factors over authigenic carbonates in the cold seeps of the northern South China Sea

作     者：WANG ShuHong YAN Wen MAGALHAES H Vitor CHEN Zhong PINHEIRO M Luis GUSSONE Nikolaus 

作者机构：CAS Key Laboratory of Marginal Sea GeologySouth China Sea Institute of OceanologyChinese Academy of SciencesGuangzhou 510301China Centre for Environmental and Marine Studies(CESAM)and Geosciences DepartmentUniversity of AveiroAveiro 3810-193Portugal Institut fiir MineralogieUniversitgit MiinsterMiinster 48149Germany 

出 版 物：《Chinese Science Bulletin》 (Chinese Science Bulletin)

年 卷 期：2012年第57卷第11期

页      面：1325-1332页

核心收录：

学科分类：070902[理学-地球化学] 081803[工学-地质工程] 0709[理学-地质学] 07[理学] 08[工学] 0818[工学-地质资源与地质工程] 

基　　金：supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-GJ03-01) the National Natural Science Foundation of China (40706022, U0733003 and 41176052) the National Basic Research Program of China (2009CB219502-4) the Knowledge Innovation Program of South China Sea Institute of Oceanology, Chinese Academy of Sciences (LYQY200806) 

主　　题：氧同位素分馏 碳酸盐岩 控制因素 南海北部 冷泉 中国 碳稳定同位素 X射线衍射分析 

摘      要：In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxygen as well as the mineral composition of authigenic carbonates were used to investigate control calcium isotope fractionation. The δ44/40Ca ratios of the southwestern Dongsha area samples ranged from 1.21‰ to 1.52‰ and the ratio of the Baiyun Sag sample was 1.55‰ of the SRM915a isotope standard. X-ray diffraction analysis showed that the carbonate samples consisted of dolomite, calcite and aragonite, with small amounts of high-Mg calcite and siderite. The δ13C values of the carbonates of the southwestern Dongsha area varied between δ49.21‰ and δ16.86‰ of the Vienna PeeDee Belemnite (VPDB) standard and the δ18O values ranged from 2.25‰ to 3.72‰ VPDB. The δ13C value of the Baiyun Sag sample was 2.36‰ VPDB and the δ18O value was 0.44‰ VPDB. The δ13C values of the carbonates of the southwestern Dongsha area revealed there is methane seeping into this area, with a variable contribution of methane-derived carbon. The sampled carbonates covered a range of δ13C values suggesting a dominant methane carbon source for the light samples and mixtures of δ13C values for the heavier samples, with possibly an organic or seawater carbon source. The δ18O values indicated that there is enrichment in 18O, which is related to the larger oxygen isotope fractionation in dolomite compared to calcite. The results of the Baiyun Sag sample exhibited normal seawater carbon and oxygen isotopic values, indicating that this sample is not related to methane seepage but instead to precipitation from seawater. The relatively high δ44/40Ca values indicated either precipitation at comparatively high rates in pore-water regimes with high alkalinity, or precipitation from an evolved heavy fluid with high degrees of Ca consumption (Raleigh type fractionation). The dolomite samples from the