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31.
A diverse assemblage of small mafic and ultramafic xenolithsoccurs in alkalic lava from Davidson and Pioneer seamounts locatedat the continental margin of central California. Based on mineralcompositions and textures, they form three groups: (1) mantlexenoliths of lherzolite, pyroxenite, and dunite with olivineof >Fo90; (2) ocean crust xenoliths of dunite with olivine<Fo90, troctolite, pyroxene-gabbro, and anorthosite withlow-K2O plagioclase; (3) cumulates of seamount magmas of alkalicgabbro with primary amphibole and biotite and anorthosites withhigh-K2O plagioclase. The alkalic cumulates are geneticallyrelated to, but more evolved than, their host lavas and probablycrystallized at the margins of magma reservoirs. Modeling andcomparison with experimentally derived phases suggest an originat moderate pressures (0·5–0·9 GPa). Thehigh volatile contents of the alkalic host lavas may have pressurizedthe magma chambers and helped to propel the xenolith-bearinglavas directly from deep storage at the base of the lithosphereto the eruption site on the ocean floor, entraining fragmentsof the upper mantle and ocean crust cumulates from the underlyingabandoned spreading center. KEY WORDS: basaltic magmatism; continental margin seamounts; geothermobarometry; mineral chemistry; xenoliths 相似文献
32.
大洋海山及其生态环境特征研究进展 总被引：1，自引：0，他引：1
海山作为深海大洋独特地貌,尽管其研究可追溯到100多年前,但对大洋海山的形成、地质特征、动力学特性、生态环境等方面了解甚少。随着人们认识海洋程度的提升,特别是回声探测、无人潜水器和卫星技术等技术的应用,对大洋海山的系统探索已取得了前所未有的进展,大洋海山研究已成为当代人们所渴求探索的领域之一。本文对大洋海山的研究历程、分类、生物群落特征、水文环境特征以及维持海山区高生物量的机制进行了总结。目前全球海山主要有两种分类方式,其分类一是基于构造特征,可将海山分为板块内海山、大洋中脊海山和岛弧海山;二是基于山顶到海表面的距离,可将海山分为浅海山、中等深度海山和深海山。海山为生物提供了独特的栖息地,形成了高生物量、高生物多样性和高生物独有性等三种主要的生物群落特征,使海山成为世界海洋渔业的重点海域和生态环境研究的热点区域之一。海山突出的地形对大洋环流造成阻隔,因而在海山周围形成了其独特的水文环境,其中海山环流和上升流是其两种典型代表,这些独特的水文环境特征对生物群落的组成和分布具有重要影响。海山区的高生物量主要通过上升流输送、地形诱捕和海流水平输送三种机制维持,三种机制对支撑海山生态系统的物质循环和能量流动至关重要。 相似文献
33.
R. T. Cox 《Tectonophysics》1999,310(1-4):69-79
Bathymetry and the geoid anomaly of the northern flank of the Hawaiian swell is broader and higher than the southern flank, and it is characterized by higher heat flow than the axis or southern flank. It is here proposed that the northern flank of the Hawaiian swell has been augmented by heat conducted from the hotspot conduit into the upper mantle then transported northward of the volcanic axis by flow in the upper mantle (325°) that is more northerly than Pacific plate motion (292°). By assuming that the deep upper mantle is decoupled from the Pacific plate and is flowing at 325° to the northwest, changes in direction and rate of volcanic propagation and in geochemistry along individual volcanic segments of the Hawaiian volcanic chain can be interpreted in terms of tank experiment results showing that a volcanic hotspot conduit breaks into diapirs when tilted by mantle flow. Hawaiian volcanoes are aligned in en-echelon segments, and the Hawaiian Islands are the two most recent segments. For an individual segment, older northwestern volcanoes are aligned nearly parallel to the 292° plate motion direction, and they propagated to the southeast at approximately the same rate as the 92 km/m.y. speed of northwestward plate motion. In contrast, the alignment of the younger southeastern volcanoes is close to 325°, and they show a conspicuous acceleration in propagation of volcanism marked by out-of-sequence eruptions. Within the model proposed here, diapirs rise from instability nodes that develop along the tilted conduit of a mantle hotspot plume as it is sheared in the direction of deep upper-mantle flow and each diapir gives rise to a single volcanic center. As tilting progresses, diapirs form at lower levels along the conduit in more upstream positions of the mantle flow zone, rise sequentially into the decoupled lithosphere, erupt sequentially, and are translated in the direction of plate motion (older, northwestern Hawaiian Islands). Eventually, flow in the highly tilted conduit is impeded to the degree that the remaining upstream conduit breaks into a number of diapirs that rise together into the lithosphere. These late diapirs, translated as a group aligned in the direction of horizontal mantle flow, erupt over a relatively short time span and show out-of-sequence volcanism (younger, southeastern Hawaiian Islands). At this stage, a new cycle of rising and tilting will initiate the next en-echelon segment. 相似文献
34.
The Philippine Basin,surrounded by a series of oceanic trenches,is an independent deep ocean basin in the West Pacific Ocean.Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges,namely,the West Philippine Basin,the Shikoku and Parece Vela Basins and the Mariana Trough.This paper,through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies,suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature,and therefore,the entire basin is of the nature of oceanic crust.The basin has developed a series of special geomorphic units with different shapes.The KPR runs through the entire Philippine Basin.From the view of geomorphologic features,the KPR is a discontinuous seamount chain (chain-shaped seamounts) and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc.At the positions of 25 N,24 N,23 N and 18 N,obvious discontinuity is shown,which belongs to natural topographic discontinuity.Therefore,the KPR is topographically discontinuous. 相似文献
35.
The Hawaiian–Emperor Seamount chain records the motion of the Pacific Plate relative to the Hawaiian mantle hotspot for 80 m.y. A notable feature of the chain is the pronounced bend at its middle. This bend had been widely credited to a change in plate motion, but recent research suggests a change in hotspot motion as an alternative. Existing paleomagnetic data from the Emperor Chain suggest that the hotspot moved south during the Late Cretaceous and Early Tertiary, but reached its current latitude by the age of the bend. Thus, data from area of the bend are important for understanding changes in plume latitude. In this study, we analyze the magnetic anomalies of five seamounts (Annei, Daikakuji-W, Daikakuji- E, Abbott, and Colahan) in the region of the bend. These particular seamounts were chosen because they have been recently surveyed to collect multibeam bathymetry and magnetic data positioned with GPS navigation. Inversions of the magnetic and bathymetric data were performed to determine the mean magnetization of each seamount and from these results, paleomagnetic poles and paleolatitudes were calculated. Three of the five seamounts have reversed magnetic polarities (two are normal) and four contain a small volume of magnetic polarity opposite to the main body, consistent with formation during the Early Cenozoic, a time of geomagnetic field reversals. Although magnetization inhomogene ties can degrade the accuracy of paleomagnetic poles calculated from such models, the seamounts give results consistent with one another and with other Pacific paleomagnetic data of approximately the same age. Seamount paleolatitudes range from 13.7 to 23.7, with an average of 19.4 ± 7.4 (2σ). These values are indistinguishable from the present-day paleolatitude of the Hawaiian hotspot. Together with other paleomagnetic and geologic evidence, these data imply that the Hawaiian hotspot has moved little in latitude during the past 45 m.y. 相似文献
36.
K. V. L. N. S. Sarma M. V. Ramana V. Subrahmanyam K. S. Krishna T. Ramprasad Maria Desa 《Marine Georesources & Geotechnology》2013,31(1):41-51
Study of bathymetric data for the distal Bengal Fan reveals the presence of positive topographic features resembling seamounts. These features exhibit a relief of about 800 m above the surrounding seafloor at 4,400 m and are associated with large‐amplitude magnetic and gravity anomalies. Magnetic model studies suggest that one of the seamounts evolved along with the oceanic crust represented by the magnetic isochron A32 (～ 72 My), while the other seamount was emplaced over the Cretaceous Quiet Zone Crust with reversed polarity. The seamounts studied provide an environment for possible locations of polymetallic encrustations. Morphology of the seamounts depends on several factors, including physical and chemical composition of the magma, eruption style, sediment thickness, maturity of underlying crust, and time of origin. Studying the seamounts together with integrated geophysical and physical data gave useful indications of their evolution and the existence of possible mineral deposits. 相似文献
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38.
麦哲伦海山区MD、ME、MF海山富钴结壳特征 总被引：10，自引：0，他引：10
麦哲化海山区MD、ME、MF海山具有三层构造的结壳特征，研究表明，结壳可分为上部较致密层、中部疏松层、下部致密层。致密层构造单一，含很少脉石矿物；疏松层构造杂乱，含有大量脉石矿物；较致密层介于两者之间，壳层矿物有锰相矿物（主要为水羟锰矿）、铁相矿物和次要矿物（粘土矿物、钙十字沸石、石英、方解石、磷灰石等）。不同壳层地球化学特征具有明显差异性，Ce异常表明在结壳从下层到上层的生长过程中，环境的氧化性逐渐减弱，结壳^10Be测年结果表明，疏松层的生长速率最大，其次为致密层，较致密层的生长速率最小。推测区的最老的结壳的生长年代为中新世晚期，在4Ma以前，区内水动力条件很弱，氧化性较强；4－3．1MaBP水动力条件较强，氧化性较弱；2．6MaBP以来，水动力条件为强－弱波动期，氧化性较弱。 相似文献
39.
HE Gaowen MA Weilin SONG Chengbing YANG Shengxiong ZHU Benduo YAO Huiqiang JIANG Xunxiong CHENG Yongshou 《海洋学报(英文版)》2011,30(3):63-75
In 2001, the International Seabed Authority (ISBA) initiated the consideration relating to the Regulations for Prospecting and Exploration for Hydrothermal Polymetallic Sulphides and Cobalt-rich Ferromanganese Crusts in the Area at its 7th session. Since then, the consideration of the Regulations has been mainly focused on the size of areas to be allocated for exploration and exploitation of the crusts. This paper, based on the investigation data and the analysis of the distribution characteristics of the crusts, suggests a model for determining the size of areas for exploration and exploitation of the crusts, taking into account various factors such as production scale, crust thickness and grade, mineable area proportion, recovery efficiency, exploration venture, and so on. Through the modeling, the paper suggests that the exploration area (the area covered by each application for approval of a plan of work for exploration of cobalt-rich crusts) shall be 4 856 km2 and the exploitation area (the mine site area) shall be 1 214 km2, for 20 years of 1 million wet tonnes annual production. 相似文献
40.
通过大洋一号船DY105--12 /14 航次采集的结壳样品,对中太平洋CL、CM2、CM3、CX、CQ、 CA、CB 海山结壳的主要成壳元素Mn、Fe、Co、Ni、Cu 的含量进行了测试统计,并与邻区的麦哲伦海山、马绍尔群岛、夏威夷群岛和莱恩群岛进行了对比,中太平洋各海山以及不同区域海山结壳的主成分之间存在一些差异,这主要与各海山结壳的物质来源、成壳环境和成壳时代的差异有关。不同形态类型的结壳主成分具有一定的差别,其主要原因可能是生长机制和形成环境不同造成的。 相似文献