南海北部水合物区HD109站位沉积物及孔隙水特征对甲烷渗漏的响应:来自元素和钡同位素的记录  

Response of sediment and pore water characteristics to methane seep events at station HD109 in gas hydrate area of the northern South China Sea:Evidences from elemental and barium isotope records

作　　者：朱碧[1] 艾鑫宇 葛璐[1] 杨涛[2] ZHU Bi;AI Xinyu;GE Lu;YANG Tao(Institute of Earth's Critical Zone,School of Earth Sciences and Engineering,Hohai University,Nanjing,Jiangsu 211106,China;State Key Laboratory for Mineral Deposits Research,Nanjing University,Nanjing,Jiangsu 210023,China)

机构地区：[1]河海大学地球科学与工程学院地球关键带研究所,江苏南京211106 [2]南京大学内生金属成矿机制研究国家重点实验室,江苏南京210023

出　　处：《地质学报》2024年第9期2607-2618,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41873011)资助的成果。

摘　　要：甲烷渗漏活动及甲烷厌氧氧化作用(AOM)不仅导致特定自生矿物的形成,更会引起沉积物-孔隙水体系中元素和同位素组成的变化。本研究对南海北部水合物赋存区HD109站位开展了沉积物-孔隙水的Ba同位素及微量元素特征研究,综合分析了沉积物-孔隙水的氧化还原敏感元素(Mo、U)、Ba及Ba同位素特征对古今硫酸盐-甲烷转换带(SMTZ)及甲烷渗漏事件的指示。HD109站位孔隙水元素变化特征显示了清晰的地球化学分带,由上至下包括Fe-Mn还原带、硫酸盐还原带和硫酸盐-甲烷过渡带。沉积物Ba元素特征显示现今SMTZ上方有较为明显的钡峰(Ba/Al高值)发育,沉积物浅部Mo、U富集层位及相邻层位Ba/Al值特征综合指示了浅部古钡峰及古SMTZ的存在,代表沉积历史上甲烷渗漏通量较高事件。孔隙水δ^(138/134)Ba值普遍高于海洋颗粒钡及碎屑钡的δ^(138/134)Ba值,反映了沉积物中成岩重晶石溶解的贡献,其中,现代钡峰附近孔隙水具有明显的δ^(138/134)Ba峰值,显示孔隙水δ^(138/134)Ba对自生重晶石沉淀过程有较显著的响应。Methane seeps and methane anaerobic oxidation(AOM)not only lead to the precipitation of authigenic minerals but also impact the elemental and isotopic compositions of sediment-pore water systems.This study investigated the Ba isotopes and trace element characteristics of sediments and pore waters at station HD109 in the northern South China Sea gas hydrate area.The research aimed to explore the utility of integrating redox-sensitive elements(Mo,U),Ba,and Ba isotopes to trace the sulfatemethane transition zone(SMTZ)and methane seep events in both ancient and modern settings.The elemental variations in pore water at station HD109 show a clear geochemical zonation,encompassing the Fe-Mn reduction zone,the sulfate reduction zone,and the sulfate-methane transition zone in an ascending sequence.The Ba characteristics of sediments indicate a prominent barium front above the SMTZ.The interval with Mo and U enrichment at shallow depths,coupled with the Ba/Al characteristics in adjacent intervals,suggests the presence of a past barium front and a past SMTZ,representing periods of more intense methane seeping during sedimentation.Compared to particulate and detrital Ba,pore waters generally display higher δ^(138/134)Ba values,suggesting the dissolution of diagenetic barite in sediments.Porewater near the current barium front has even higher δ^(138/134)Ba values,indicating a significant response to the precipitation of authigenic barite.

关 键 词：甲烷渗漏 Ba同位素 硫酸盐-甲烷转换带 南海北部 

分 类 号：P618.13[天文地球—矿床学]