南海东北陆坡烟囱状冷泉碳酸盐岩生长剖面的碳、氧同位素特征与生长模式  

Carbon and Oxygen Isotope Characteristics of the Growth Profile of a Seep Carbonate Chimney from the Northeastern Slope of the South China Sea and Its Formation Model

作　　者：陈选博[1,2] 韩喜球[1,2] 

机构地区：[1]国家海洋局海底科学重点实验室,杭州310012 [2]国家海洋局第二海洋研究所,杭州310012

出　　处：《沉积学报》2013年第1期50-55,共6页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(批准号:40976040);973项目(2009CB21950607);浙江省杰出青年基金项目(R5110215)联合资助

摘　　要：对SO177航次采集自南海东沙东北古冷泉活动区的烟囱状碳酸盐岩样品(TVG14-C1-1)进行解剖研究,探讨烟囱样品的形成机理。我们首先对烟囱样品的横截面进行高分辨率精细取样并进行碳、氧同位素分析,在充分了解其矿物组成特征的前提下,利用碳酸盐岩—水体系氧同位素分馏方程计算古冷泉流体的氧同位素组成并定量分析流体的端元成分和相对贡献,然后根据它们在烟囱生长剖面上的变化特征,为碳酸盐质烟囱建立生长模式。分析表明,该样品横截面的δ13C值在-50.136‰～-43.923‰之间变化,δ18O值在2.762‰～4.848‰之间变化,由中心向外,碳氧同位素呈反向协同变化趋势,δ13C逐渐升高而δ18O逐步降低。结合该样品的年龄和古海水的氧同位素组成,计算得到形成该样品的冷泉流体的δ18O在1.2‰～2.3‰V-SMOW之间变化,较冰期海水的更富18O。认为在形成烟囱的不同阶段,水合物分解产生的富18O流体与同期海水发生了不同程度的混合,烟囱中心部位水合物分解水的相对贡献高达53.6%,而烟囱外层,水合物分解水的贡献低至6.1‰。通过综合研究,提出了烟囱样品的生长模式。This chimney（TVG14-C1-1 ） was collected by SO177 cruise in 2004 from the northeastern Dongsha, South China Sea. It is composed of Mg-calcite. Author did high resolution sampling on a cross section of the chimney to an- alyze their C-and O-isotope compositions. Based on their mineral composition, we used carbonate-water fractionation equation to calculate the δ^18O of the precipitating fluid and discussed the fluid sources. We showed that the δ^13C of the chimney varied from -50.14%o to -43.92%0, and δ^18O from 2.76%0 to 4.85%0. From the inner to the outer, the δ^13C increased gradually while 8180 was decreaseing. The equilibrium ~180 of the precipitating fluid were in the range of 1.2%0- 2.3%oV-SMOW, which were significantly heavier than the modern seawater or glacial water. It is suggested that the water released from gas hydrate dissociation were responsible for the 180 enrichment. According to the two end - member mixing model, it was calculated that the precipitating fluid consisted of 53.6% gas hydrate wa- ter and 46.4% seawater during the precipitation stage of the inner layer. It got diluted gradually when it diffused into the sediments to form the outer layer, where the contribution of gas hydrate water decreased to 6.1%. Based on the growth structure and the variation of carbon and oxygen isotope composition, a growth model of the seep carbonate chimney was proposed.

关 键 词：南海东北陆坡 烟囱状冷泉碳酸盐岩 碳 氧稳定同位素 冷泉流体来源 生长模式 

分 类 号：P736.21[天文地球—海洋地质]