南海西沙西南海底麻坑区天然气水合物发育的孔隙水地球化学证据  

Gas hydrate occurrences inferred from pore water geochemistry in the pockmark field in the southwestern Xisha Uplift, South China Sea

作　　者：陈琳莹 罗敏[1] 

机构地区：[1]上海海洋大学海洋科学学院上海深渊科学工程技术研究中心,上海201306 [2]青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室,山东青岛266071

出　　处：《地球化学》2017年第6期557-566,共10页Geochimica

基　　金：广州海洋地质调查局外协项目(GZH201100305-06-07);海洋矿产资源评价与探测技术功能实验室开放基金项目(KC201704)

摘　　要：南海西沙西南海底广泛发育规模巨大的海底麻坑,麻坑内GC14柱样5.7 m到6.7 m深度孔隙水中Cl^-浓度降低,同时伴随δ^(18)O值升高,显示有天然气水合物的发育。同时,孔隙水中的Cl^-,Na^+和K^+浓度主要沿着海水稀释线分布,排除了黏土矿物脱水引起Cl^-浓度降低和δ^(18)O值升高的可能性。根据Cl-浓度和δ^(18)O值异常估算的水合物饱和度分别为6%~10%和7%~15%。由此可以推断,西沙西南麻坑区可能是具有良好水合物勘探前景的海域。Mega-pockmarks are widely scattered throughout the southwestern Xisha Uplift, northern South China Sea （SCS）. Pore water collected from a gravity-core inside of a mega-pockmark exhibited a decrease in the Cl- concentration concomitant with an increase in the δ18O value at the interval of 5.7-6.7 m below the seafloor, suggesting a possible gas hydrate occurrence. The Cl-, Na＋, and K＋ concentrations cluster mainly along the seawater freshening line without a distinct Na＋ enrichment and K＋ depletion. The gas hydrate contents were estimated to be between 6%-10%, and 7%-15%, respectively, according to the Cl- concentration offsets and the δ18O values obtained from the baselines. The southwestern Xisha Uplift pockmark field is likely to be a good prospective area for the occurrence of gas hydrates in the shallow sediments.

关 键 词：天然气水合物 孔隙水 氯离子 Δ18O 西沙西南 

分 类 号：P592[天文地球—地球化学] P67[天文地球—地质学]