冲绳海槽中部Jade热液活动区中块状硫化物的稀土元素地球化学特征

用ICP－MS对冲绳海槽Jade热液活动区中6个块状硫化物样品进行了稀土元素分析。除一个样品表现出极微弱的正Eu异常外(δEu=1.09)，其他样品均表现出负Eu异常(δEu=0.58-0.71)和LREE相对富集((La/Yb)N=1.29-47.87)的球粒陨石标准化配分模式。块状硫化物样品之间稀土元素组成的变化是由于热液流体－岩石的相互作用以及海水和热液流体不同程度混合的结果，与深海沉积物，火山岩和海水稀土元素配分模式对比，表明块状硫休物的REE部分来自沉积物和火山岩，海水的混合作用对块状硫化物的REE配分模式具有一定的影响。海底热液硫化物稀土元素组成的变化可以一定程度的反映在出热液流体的演化特征。     

冲绳海槽Jade热液活动区块状硫化物的铅同位素组成及其地质意义

新测行Ｊａｄｅ热液活动区中５件块状硫化物样品的铅同位素组成,具有较小的变化范围,表现出较均一的铅同位素组成特征。在Ｐｂ－Ｐｂ图解上,块状硫化物的铅同位素数据构成线形排列,与该区沉积物和蚀变火山岩的铅同位素组成一致,而与该区新鲜火山岩相比具较高的放射成因铅,证实了该区海底块状硫化物中的铅是由沉积物长英质火山岩来源铅共同构成的混合铅。不同热液活动区铅同位素组成对比研究表明,地质－构造环境的不同是导致各     

冲绳海槽构造演化及其与岩浆、热液和沉积作用的关系：研究进展与展望

冲绳海槽是西太平洋沟-弧-盆体系中典型的弧后盆地。其独特的大地构造位置,岩浆、热液活动与沉积记录一直是学术界研究的热点。基于前人的研究成果,本文综述了冲绳海槽的构造活动对岩浆、热液与沉积的控制作用。菲律宾海板块的俯冲导致了冲绳海槽的形成,并发生了弧岩浆、弧后岩浆和斜切弧后岩浆作用,这三种岩浆作用导致了热液活动在平面分布上的三种不同分区。岩浆的发育和菲律宾海板块俯冲造成的断裂系统为冲绳海槽热液的发育分别提供了热源和通道。在~416 ka发生的浙闽隆起带沉降,导致了冲绳海槽北部的沉积物由粗变细。最后针对冲绳海槽的研究现状,文章对未来的进一步研究作了展望。     

冲绳海槽中部热液活动与IODP331航次初步成果

伊平屋北部热液区（IheyaNoAhhydrothermalfield）位于冲绳海槽中部地区。综合大洋钻探计划（IODP）331航次于2010年9月1日至10月4日在该区钻探了5个站位（C0013-C0017）：C0016站位位于NoahBigChimney（NBC）地区活跃的热液烟囱和硫化物-硫酸盐丘状体上;在C00...     

冲绳海槽地质构造对热液活动的控制机理

海底热液活动一直是当代海洋科学研究的重要前沿领域之一,了解地质构造对海底热液活动的控制作用对于认识热液系统的形成机理及寻找海底硫化物资源具有重要的指示意义。总结了冲绳海槽中部和南部地形与断裂构造、地壳结构、重磁场、热流及岩浆活动等方面的地质构造特征以及海槽热液区分布和热液产物的基本特征。通过比较冲绳海槽与马努斯海盆、马里亚纳海槽、北斐济海盆、劳海盆等基底和扩张阶段不同的弧后盆地构造特征的差异,归纳了冲绳海槽地质构造的特殊性,包括过渡性地壳性质、低扩张程度、高热流值、巨厚沉积层及双峰式火山作用等。冲绳海槽热液活动受到断裂构造、岩浆活动、扩张速率等构造因素的控制,同时受到基岩类型和沉积物盖层等地质条件的影响。海槽中部和南部平行和垂直盆地走向的两组断裂带为流体循环提供了通道,大规模的岩浆活动则为热液系统提供了充足的热量。此外,海槽内广泛分布的酸性火山岩和较厚的沉积盖层与流体相互作用,使得热液产物富含有机质、二氧化碳以及Ag和Au等金属元素。根据冲绳海槽的扩张速率和地质构造特征,推测冲绳海槽仍具有发现新热液区的潜力,其中部和南部两组断裂交汇的部位、轴部火山、受海脊俯冲影响的区域以及靠近岛弧一侧...     

冲绳海槽浮岩研究

目前国内外对冲绳海槽槽底火山岩的研究尚处在初级阶段。笔者对槽底八个样点的浮岩进行了系统的矿物岩石学研究。本文首次对酸性浮岩的中、基性火山岩包体进行了研究,揭示了酸性浮岩下部有相当面积的玄武岩及安山岩存在的事实。旨次提出海槽浮岩具有由基性→酸性较完整的火山活动旋回的认识。提出酸性浮岩是基性熔浆演化到后期的产物的观点,从而解释了存在多年的关于冲绳海槽构造问题争议中的焦点问题之一——“冲绳海槽既为弧后盆地,何以有大量酸性火山岩分布”的质疑。提出冲绳海槽浮岩属于岛弧火山岩的观点,对冲绳海槽构造的科学认识起了一定的积极作用。     

冲绳海槽南奄西热水活动区热水沉积成矿作用

冲绳海槽南奄西热水活动区位于奄美大岛西约１４０ｋｍ的南奄西海丘西坡（２８°２３′～２５５′Ｎ,１２７°３７５～３９５′Ｅ）。１９８６年在该处发现有热水活动的征兆［１］,１９９１年６月发现热水温度达２７０℃的活烟囱［２］。１９９２年６月在此采得温...     

大洋钻探与冲绳海槽

在多次赴冲绳海槽地球物理调查的基础上，综合国内外的调查研究成果，对冲绳海槽地质构造学研究的历史、已查明了地球物理场特征，海底构造特征和需要进一步探讨了问题作了系统的总结，阐明了ＯＤＰ在冲绳海槽钻探的重要意义。     

冲绳海槽北部现代沉积物地球化学研究

本文对冲绳海槽北部现代海底表层沉积物的沉积物地球化学特征进行了系统的分析，探讨了分别代表陆源，火山源和生物源沉积物的地球化学指标。结果表明，ＳｉＯ２主要富集于东海外陆架与陆架坡折带，基本上反映了陆源碎屑沉积或东海陆架外缘的残留砂沉积；Ａｌ２Ｏ３和Ｎａ２Ｏ的含量分布与玻屑砂或火山玻璃的含量有关；ＣａＯ或ＣａＣＯ３代表了生物沉积组份的多寡。     

冲绳海槽岩浆活动研究进展及思考

冲绳海槽以其特有的构造地质环境吸引着众多地质学者的关注。针对冲绳海槽地区岩浆作用过程的研究是其中的核心内容之一。本文综述了近年来冲绳海槽岩浆源区物质特征、岩浆形成演化过程及其控制机制等方面研究取得的主要成果,并在此基础上指出了目前冲绳海槽岩浆活动研究工作中存在的科学问题,提出利用铀系不平衡方法研究冲绳海槽岩浆活动的新思路,同时探讨了今后一段时间内的研究方向应该集中在以下四个方面: ①菲律宾板块俯冲的脱水过程对冲绳海槽岩浆活动的作用;②俯冲过程中深海沉积物对冲绳海槽岩浆的贡献;③冲绳海槽岩浆熔融的控制因素;④冲绳海槽火山活动和海底热液活动的成因关系。     

《变质作用与大陆动力学学术讨论会》在北京召开

冲绳海槽火山岩目前发现有玄武岩、玄武安山岩、安山岩、粗面安山岩、粗面英安岩、英安岩和流纹岩。研究表明,冲绳海槽火山岩均属亚碱性系列,基性岩具有拉斑玄武岩系列和钙碱性系列的过渡性,中、酸性岩多属钙碱性系列;岩石形成于上新世以来,大部分都是富集型地幔玄武质岩浆在分离结晶不同阶段的产物。岩石在分离结晶演化趋势上的一致性和在岩石化学指数变异关系上的多样性是原来快速上升未发生混染的岩浆在断裂构造隔离下分枝独立演化的结果。     

Geologic Control on Hydrothermal Activities in the Okinawa Trough

Revealing the controlling effect of geological structure on seafloor hydrothermal activities is of great significance in understanding the formation mechanism of hydrothermal system and searching for seafloor sulfide resources. This article summarized the topography and faults, crustal structure, gravity and magnetic field, heat flow and magmatism in the middle and southern Okinawa Trough, as well as the general characteristics of hydrothermal field distributions and hydrothermal products. By comparing the Okinawa Trough with the Manus Basin, Mariana Trough, North Fiji Basin and Lau Basin with different rock basements and extension stages, we generalized some specific geological characteristics of the Okinawa Trough, including the transitional crustal nature, low extension degree, high heat flow value, extremely thick sediments, and bimodal volcanism. The hydrothermal activities in the Okinawa Trough are controlled by fault structures, magmatism, and spreading rate, and at the same time, are affected by basement rock types and sediment covers. In the middle and southern parts of the trough, two group of faults that are parallel and perpendicular to the strike of the back-arc basin promote the fluid circulation, and large-scale magmatic activity provides sufficient heat for the hydrothermal system. In addition, the interaction of fluids with the widespread silicic volcanic rocks and thick sediments leads to the enrichment of organic matter, CO ₂, and metals such as Ag and Au in the hydrothermal products. According to the extension rate and geological features of the Okinawa Trough, we believe that the Okinawa Trough has potential to have new hydrothermal fields discovered and we speculate that new hydrothermal fields most possibly exist in the regions influenced by ridge subduction as well as the neo-volcanic zones closed to the island arc.     

Mercury Anomaly in the Okinawa Trough Sediments—An Indicator of Modern Seafloor Hydrothermal Activity

The Okinawa Trough is located between the shelf-sea area of the East China Sea and the deep-sea area of western Pacific Ocean. More than 60 chemical elements in the sediments from the shelf area of the East China Sea, the Okinawa Trough and western Pacific Ocean were determined by advanced techniques including neutron activation analysis, X-ray fluorescence spectrometry, atomic fluorescence spectrometry and atomic absorption spectrometry. Quantitative comparisons of the element abundances of the sediments were made in terms of the enrichment coefficients (K) of the elements.K > 1.5 indicates enrichment (K = 1.5–2, weak enrichment; K = 2–4, strong enrichment) andK > 4, anomalous enrichment. The results show that the Okinawa Trough sediments are characterized by Hg anomaly and the enrichment of such elements as Au, Ag, Se, Te, Sb, Cd, Mn, Mo, etc. Detailed studies show that the excess Hg comes from hydrothermal solutions rather than from the continent, sea water, marine organisms, cosmic dust or volcanic rocks. Attributed to modern hydrothermal activities on the sea floor, Hg anomaly can be used as a geochemical indicator of modern seafloor hydrothermal activity. This project was granted by the National Natural Science Foundation of China.     

Distribution Patterns of Ag in Hydrothermal Precipitates from the Okinawa Trough

The Okinawa Trough is characterized by enrichment of Ag in hydrothermal precipitates; however, the distribution of this enrichment remains poorly constrained. This study presents the results of a field-emission scanning electron microscopy and electron-microprobe analysis based mineralogical and geochemical investigation of the spatial distribution of Ag within Ag-rich sulfide samples from the Okinawa Trough. The tetrahedrite, covellite, and galena in these samples contain high concentrations of...     

Submarine hydrothermal mineralization in the Okinawa Trough, SW of Japan: an overview

The Okinawa Trough is a heavily sedimented, rifted back-arc basin formed in an intracontinental rift zone. Submarine hydrothermal activity is located within the six back-arc rifts located in the middle and southern Okinawa Trough and its distribution is controlled principally by tectonic factors. Subduction of the Daito and Gagua Ridges beneath the Ryukyu Arc has resulted in fracturing of the brittle lithosphere beneath the Okinawa Trough. Hydrothermal activity is strongest in the volcanic arc-rift migration phenomenon (VAMP) area plus the JADE site and Southernmost Part of the Okinawa Trough (SPOT) area which form the prolongation of these two ridges. These areas are characterized by extremely high heat flow locally. Submarine hydrothermal fluids from the Okinawa Trough tend to be strongly influenced by interaction of the hydrothermal fluids with organic matter in the sediment resulting in high alkalinity and NH₄⁺ concentrations of the fluids. The fluids also contain high concentrations of CO₂ of magmatic origin. Submarine hydrothermal mineralization in the trough is diverse. The CLAM site consists principally of carbonate chimneys. Interaction of the hydrothermal fluid with organic matter in the sediment is particularly strong at this site. This is most probably a sediment-hosted deposit in which sulphide minerals have deposited within the sediment column leaving ‘spent ore-fluids’ to emerge at the seafloor. The JADE site consists of active and inactive sulphide–sulphate chimneys and mounds. The Zn–Pb-rich sulphides at this site contain the highest concentrations of Pb, Ag and Au so far recorded in submarine hydrothermal sulphide deposits. At Minami-Ensei Knoll and Hatoma Knoll, active and inactive chimneys consist principally of anhydrite and barite as a result of phase separation of the hydrothermal fluids beneath the seafloor. An intense black smoker has recently been discovered at Yonaguni Knoll in the SPOT area. If it is confirmed that sulphide mineralization is dominant at this site, this could be a highly prospective area. The most prospective areas for economic-grade minerals in the Okinawa Trough appear to be the JADE site and the SPOT area.     

冲绳海槽中部和南部玄武岩的区域性差异及其成因研究

本文从岩石学和岩石化学角度出发 ,对冲绳海槽中部和南部玄武岩样品进行了对比研究。结果表明中部和南部玄武岩均系亚碱性玄武岩 ,其中前者兼具钙碱性系列和拉斑玄武岩系列两种性质 ,后者则主要属拉斑玄武岩系列。根据岩石化学特征命名 ,中部样品主体为石英拉斑玄武岩 ,南部样品则为橄榄拉斑玄武岩。两区海槽玄武岩岩浆均由下伏地幔岩部分熔融而成 ,但源区地幔性质不均一 ,岩浆演化程度各异。中部样品源区地幔性质为过渡型 ,结晶分异程度较高 ;南部样品源于近亏损或富集型的地幔 ,结晶分异程度较弱 ;另外两区玄武岩样品均受到了不同程度的陆壳物质混染。中、南部海槽玄武岩在岩石学、岩石化学方面的差异与源区地幔性质不均一和岩浆演化程度各异有直接关系。海槽玄武岩构造环境属于过渡洋中脊玄武岩 (张性 )与岛弧玄武岩 (压性 )之间 ,代表的仍是海槽早期的岩浆活动。