西南印度洋中脊表层沉积物中硫化物矿物学特征与地质意义

利用电子探针以及扫描电镜和能谱仪相结合的方法对西南印度洋中脊表层沉积物进行了矿物学研究,结果表明:该区沉积物中含有黄铁矿、闪锌矿、黄铜矿以及等轴方黄铜矿等硫化物颗粒,硫化物颗粒多呈自形-半自形,保存完好。其中黄铁矿晶体呈立方体及立方体-八面体聚形形态,闪锌矿与黄铜矿晶体中常见溶蚀孔洞,而等轴方黄铜矿中出现固溶体分解结构。硫化物类型、颗粒结构和微量元素组成指示49.6°E热液区附近沉积物中的硫化物至少属于两个热液成矿阶段的产物,早期为中温成矿阶段,后期经历了高温富Fe流体的改造;50.5°E热液区附近沉积物中出现了高温硫化物组合。     

西南印度洋超慢速扩张脊热液区多金属硫化物纳米矿物学特征初步研究

<正>现代海底"黑烟囱"及其多金属硫化物矿床是一种正在形成的矿床,是研究热液成矿的"天然实验室",具有十分重要的科学意义和经济价值,也因此备受科研学者的青睐(Herzig&Hannington,1995)。在这个"天然实验室"中,海底热液活动既有正在形成大量的贱金属(Cu、Fe、Zn)硫化物矿床,也有金、银等贵金属元素的明显富集     

西南印度洋脊49.6°E热液区多金属硫化物硫同位素组成特征研究

同位素地球化学特征是海底多金属硫化物成矿作用研究的重要内容之一,是成矿物质来源及成矿介质的性质与条件是探讨矿床成因与时空分布规律的关键所在。在海底多金属硫化物成矿过程中,同位素的分馏机制与示踪特性可有效指示成矿元素的物质来源与迁移演化过程及成矿环境的物理化学变化。     

西南印度洋超慢速扩张脊热液区多金属硫化物Fe-Cu-Zn同位素组成特征初步研究

<正>海底热液硫化物是一种重要的海底矿产资源,并在全球范围内的大洋中脊、海山及弧后盆地有较为广泛的分布,具有重要的经济价值和战略意义,其中西南印度洋中脊(SWIR)热液体系更因其超慢速的扩张速率而在全球大洋中脊系统中独具特色,且研究程度较低(陶春辉等,2011)。而同位素地球化学对于解释海底多金属硫     

中印度洋脊热液活动区多金属硫化物Fe-Cu-Zn同位素组成特征的初步研究

<正>近十多年来,随着非传统稳定同位素分析测试技术的迅猛发展,铁、铜、锌等过渡族金属元素的同位素体系已广泛应用于海洋科学、矿床学、环境地球化学等诸多地学研究领域(Maréchal et al.,1999;Zhu et al.,2000;蒋少涌,2003;王跃和朱祥坤,2010a,b,2012),尤其是为判别指示含Fe-Cu-Zn多金属硫化物矿床的物质来源提     

北大西洋中脊海底多金属硫化物资源预测

海底热液多金属硫化物是继大洋铁锰结核和富钴结壳之后发现的叉一巨大具有开发远景的海底矿产资源,具有巨大的潜在经济价值和良好的开发前景。通过综合分析国内外海底矿产资源特征,总结海底多金属硫化物资源的找矿标志,初步建立了海底多金属硫化物资源的描述性找矿模型,并开展了北大西洋中脊海底多金属硫化物资源预测工作。证据权预测结果表明海底多金属硫化物的分布与水深地形、地球物理、海底扩张速率、沉积物厚度、海底火山地震等标志有很大的关系。预测结果与已有热液点具有较好的叠合度,预测方法、预测模型具有可信度及可操作性,对海底多金属硫化物资源调查和评价具有重要的指导意义。     

中印度洋脊Edmond热液区多金属硫化物中超显微金银矿物的发现及其成矿意义

<正>迄今为止,前人已在位于大洋中脊、海山以及弧后盆地热液活动区的部分块状硫化物矿床中发现有大量自然金、银金矿和自然银产出(Hannington et al.,1986,1991,1995;Herzig et al.,1993;Murphy&Meyer,1998;Moss&Scott,2001;Petersen et al.,2002)。但总体而言,Au-Ag系列独立矿物在大多数沿快速-中速扩张洋脊分布、以MORB为容矿基岩的多金属硫化物矿床中     

慢速-超慢速扩张西南印度洋中脊研究进展

西南印度洋中脊具有慢速—超慢速扩张速率和斜向扩张的特征,是全球洋中脊系统研究的热点之一,也是研究海底构造环境、热液活动、地幔深部过程及其动力学机制的重要区域。在前人工作的基础上较为详细地介绍了西南印度洋中脊的研究历史、地形划分、扩张速率及其构造特征,归纳了西南印度洋中脊热液活动及岩石地球化学特征,探讨了超慢速扩张洋脊和超镁铁质岩系热液系统的特殊性,并认为超慢速扩张洋脊广泛暴露的地幔岩及其蛇纹石化作用、超镁铁质岩系热液系统以及热液硫化物成矿作用是西南印度洋中脊今后研究的重要内容。     

西南印度洋中脊钙质沉积物地球化学及矿物学特征

深海沉积物研究能够为海底资源开发利用提供丰富的信息,对推动沉积学发展具有重要的理论意义。以中国大洋科考20航次西南印度洋中脊附近的钙质沉积物为研究对象,选取了10个沉积物样品进行了X射线衍射物相分析、扫描电镜分析、碳氧同位素及微量元素测试。结果表明,研究区钙质沉积物矿物组成主要为方解石,黏土矿物含量较低。方解石以钙质超微化石颗石藻及有孔虫的形态存在,碳氧同位素特征显示超微化石生活在正常的近表层海水环境中,死亡后埋藏环境稳定。稀土元素具有总量低、轻重稀土元素分异明显、Eu中等负异常、Ce中等负异常的特征。微量元素中富亲石元素、贫亲铁元素,亲生物元素Sr、Ba含量远高于其他元素。微量元素特征及Ceanom值说明沉积环境偏氧化。沉积物中大量的生物成因方解石及地球化学特征反映了研究区物源以生物源为主、含有少量陆源及幔源物质的特点。     

Sheltered coastal environments as archives of paleo-tsunami deposits: Observations from the 2004 Indian Ocean tsunami

The 2004 earthquake left several traces of coseismic land deformation and tsunami deposits, both on the islands along the plate boundary and distant shores of the Indian Ocean rim countries. Researchers are now exploring these sites to develop a chronology of past events. Where the coastal regions are also inundated by storm surges, there is an additional challenge to discriminate between the deposits formed by these two processes. Paleo-tsunami research relies largely on finding deposits where preservation potential is high and storm surge origin can be excluded. During the past decade of our work along the Andaman and Nicobar Islands and the east coast of India, we have observed that the 2004 tsunami deposits are best preserved in lagoons, inland streams and also on elevated terraces. Chronological evidence for older events obtained from such sites is better correlated with those from Thailand, Sri Lanka and Indonesia, reiterating their usefulness in tsunami geology studies.     

西南印度洋洋盆演化和岩浆地球化学印迹

西南印度洋中脊（SWIR）平均扩张速率约为14 mm/yr,是全球洋中脊系统的重要组成端元,因其具有慢速-超慢速扩张特征,引起全球科学家的广泛关注。基于前人对SWIR的综合研究成果,从构造和岩浆作用两个角度出发,系统地回顾了SWIR的形成和演化历史,探讨了岩浆的分布特征和地幔不均一性成因。SWIR的形成始于冈瓦纳大陆的裂解,中段洋脊区域（26~42°E）是印度洋最早开启的窗口,历经多次洋脊跃迁和扩展作用形成了斜向扩张展布,多分段的构造格局。地幔热点在冈瓦纳大陆裂解过程中扮演了关键角色,并对SWIR的洋底地貌和岩浆作用具有显著影响,其中Bouvet和 Marion热点在SWIR的西段和中段岩浆均留下了地球化学印迹。SWIR西段岩浆除却Bouvet热点影响之外表现出与大西洋-太平洋型玄武岩相似的同位素地球化学特征。在SWIR中段,39~41°E附近的岩浆具有显著的DUPAL异常特征,与冈瓦纳大陆的初始形成、裂解紧密相关。受俯冲改造的中—新元古代的造山带岩石圈地幔拆沉是造成SWIR中段地幔不均一性的重要根源。在SWIR东段,46~52°E区域内的局部岩浆组成异常,推测具有大陆地壳物质混染的成因。而在Melville转换断层以东,洋脊形成时间最晚,玄武岩的地幔源区受到了富集组分的交代作用,其同位素组成与相邻的中印度洋中脊（CIR）和东南印度洋中脊（SEIR）地幔源区具有亲缘性。     

On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall

The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June–September) monsoon rainfall at sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used. The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan, and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events. The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming that strong IOD events indeed affect the Indian summer monsoon.

Seamounts in the Central Indian Ocean Basin: indicators of the Indian plate movement

The study of seamount parameters in the tectonically most-complicated and least-understood Indian Ocean assumes importance since their properties vary as a function of tectonic setting, physics of lithosphere, conduit geometry and chemical composition of magma. More than 100 such seamounts ranging in summit height (h) from 300 to 2870 m, are indentified in the oceanic crust between Indian continent and Mid-Indian Ridge (MIR) and South-East Indian Ridge (SEIR). Most of the minor seamounts (h > 1000) are found in the southern part of the study area. Major seamounts (h < 1000 m) are roughly distributed in two groups—the northern group on Cretaceous Oceanic Crust and southern group on Pliocene-Miocene Oceanic Crust. On an average northern group seamounts (SM 1 to 6) are taller, wider and flatter than those from the southern group. These seamounts appear to be the result of continuous growth from tapped, moving magma chamber while stress depleted magma and inconsistent Indian Plate movement during Mid-Tertiary are attributed to the origin of southern group of smaller seamounts. Distribution and morphology of seamounts as a whole indicate their formation either from Reunion hotspot or from two separate hotspots in the geological past.     

Petrological Characteristics and Genesis of the Central Indian Ocean Basin Basalts

The Central Indian Ocean Basin (CIOB) basalts are plagioclase-rich, while olivine and pyroxene are very few. The analyses of 41 samples reveal high FeOT (~10–18 wt%) and TiO2 (~1.4–2.7 wt%) indicating a ferrobasaltic composition. The basalts have high incompatible elements (Zr 63–228 ppm; Nb ~1–5 ppm; Ba ~15–78 ppm; La ~3–16 ppm), a similar U/Pb (0.02–0.4) ratio as the normal mid-oceanic basalt (0.16±0.07) but the Ba/Nb (12.5–53) ratio is much larger than that of the normal mid-oceanic ridge basalt (~5.7) and Primitive Mantle (9.56). Interestingly almost all of the basalts have a significant negative Eu anomaly (Eu/Eu*=0.78–1.00) that may have been a result of the removal of feldspar and pyroxene during crystal fractionation. These compositional variations suggest that the basalts were derived through fractional crystallization together with low partial melting of a shallow seated magma.     

North Indian Ocean warming and sea level rise in an OGCM

The variability in the long-term temperature and sea level over the north Indian Ocean during the period 1958–2000 has been investigated using an Ocean General Circulation Model, Modular Ocean Model version 4. The model simulated fields are compared with the sea level observations from tide-gauges, Topex/Poseidon (T/P) satellite, in situ temperature profile observations from WHOI moored buoy and sea surface temperature (SST) observations from DS1, DS3 and DS4 moored buoys. It is seen that the long (6–8 years) warming episodes in the SST over the north Indian Ocean are followed by short episodes (2–3 years) of cooling. The model temperature and sea level anomaly over the north Indian Ocean show an increasing trend in the study period. The model thermocline heat content per unit area shows a linear increasing trend (from 1958–2000) at the rate of 0.0018 × 10¹¹ J/m² per year for north Indian Ocean. North Indian Ocean sea level anomaly (thermosteric component) also shows a linear increasing trend of 0.31 mm/year during 1958–2000.     

Entrainment of circumpolar water in the Indian Ocean region of the Antarctic

The net influx of the circumpolar water on the western (approximately along 10°E) and eastern (approximately 115°E) boundaries of the Indian Ocean, adopting the method of Montgomery and Stroup is computed on bivariate distribution of potential thermosteric anomaly and salinity to identify the characteristics of the flux. The zonal flux at both the boundaries indicates an alternate strong easterly and westerly flow between 36°S and 45°S, south of which the flow is mainly easterly but weak up to 56°S. At the western boundary the easterly flow is 146 Sv and westerly is 98.07 Sv, while at the eastern boundary (115°E) the corresponding fluxes are 123.46 Sv and 27.20 Sv respectively, indicating a net outflux of 48.33 Sv. This water should have been accounted by the melting of ice and influx of the Equatorial Pacific Ocean Water.     

The biogeochemical distribution of trace elements in the Indian Ocean

The present review deals with the distributions of dissolved trace metals in the Indian Ocean in relation with biological, chemical and hydrographic processes. The literature data-base is extremely limited and almost no information is available on particle processes and input and output processes of trace metals in the Indian Ocean basin and therefore much research is needed to expand our understanding of the marine chemistries of most trace metals. An area of special interest for future research is the Arabian Sea. The local conditions (upwelling induced productivity, restricted bottom water circulation and suboxic intermediate waters) create a natural laboratory for studying trace metal chemistry.     

Geochemistry and mineralogy of REY-rich mud in the eastern Indian Ocean

Deep-sea sediments in parts of the Pacific Ocean were recently found to contain remarkably high concentrations of rare-earth elements and yttrium (REY) of possible economic significance. Here we report similar REY-rich mud in a core section from Deep Sea Drilling Project Site 213 in the eastern Indian Ocean. The sediments consist mainly of siliceous ooze, with subordinate zeolitic clay that contains relatively high REY concentrations. The maximum and average total REY (ΣREY) contents of this material are 1113 and 629 ppm, respectively, which are comparable to those reported from the Pacific Ocean. The REY-rich mud at Site 213 shows enrichment in heavy rare-earth elements, negative Ce anomalies, and relatively low Fe₂O₃/ΣREY ratios, similar to those in the Pacific Ocean. In addition, the major-element composition of the Indian Ocean REY-rich mud indicates slight enrichment in lithogenic components, which probably reflects a contribution from southern African eolian dust. A volcaniclastic component from neighboring mid-ocean ridges or intraplate volcanoes is also apparent. Elemental compositions and X-ray diffraction patterns for bulk sediment, and microscopic observation and elemental mapping of a polished thin section, demonstrate the presence of phillipsite and biogenic apatite, such as fish debris, in the REY-rich mud. The strong correlation between total REY content and apatite abundance implies that apatite plays an important role as a host phase of REY in the present deep-sea sediment column. However, positive correlations between ΣREY and elements not present in apatite (e.g., Fe₂O₃, MnO, and TiO₂) imply that the REY-rich mud is not formed by a simple mixture of REY-enriched apatite and other components.     

Review of the Tropical Gyre in the Indian Ocean with Its Impact on Heat and Salt Transport and Regional Climate Modes

Due to the IO monsoon impact, the tropical IO circulation has significant seasonal variation, especially in the northern IO. However, in mean-state, a relatively closed current loop is established by eastward current along the equator and westward current south of equator, which is regarded as Tropical Gyre in the Indian Ocean. Based on this circulation system, relevant studies were reviewed. Its impact on heat and salt transports and regional climate changes were discussed.