洋中脊-地幔柱、地幔柱-海沟与海沟-洋中脊相互作用

由热点假说的提出发展到静态地幔柱学说和动态地幔柱模式,到现在研究较多的大型火成岩省、脊-柱相互作用和脊-沟相互作用,海底构造研究取得了巨大进步。柱-脊相互作用可导致洋中脊的分段、跃迁与石化过程,反之,洋中脊的变化也可导致地幔柱的形态与直径等发生变化。洋中脊与地幔柱相遇可以出现不同的柱-脊相互作用。地幔柱除可以出现在离散型板块边缘外,还可以随板块迁移进入俯冲带,并出现柱-沟相互作用。地幔柱在俯冲带出现的位置不同,因而其对俯冲过程的影响和作用效果也相应不同,目前提出了6种地幔柱与海沟或俯冲带相互作用的可能模式。脊-柱相互作用和脊-沟相互作用对传统的板块俯冲作用过程是个重要突破。     

地幔柱理论不能解释Austral岛南部板块间的火山作用

人们早已认识到,南太平洋ＣｏｏｋＡｕｓｔｒａｌ火山链的特征很难用地幔柱理论加以解释,地幔柱理论是指板内火山活动受控于板块漂移作用,板块漂移发生在炽热的幔源物质上涌形成的狭窄而稳定的地幔柱之上。如果所有火山活动都与目前位于有火山活动的迈克唐纳海山中的...     

使用地震波反映地球的内部结构

在地球内部产生的地震波提供了帮助我们更好地认识驱动板块运动的地幔对流方式的图案。海底扩张的发现和板块构造理论被接受以后的四十年，重要的盲点在于我们对驱动板块运动的地幔对流的方式以及导致地震、海啸和火山爆发等的原因知之甚少，目前仍然有许多激烈的争论。海洋岩石圈向下嵌入内陆板块，在板块汇聚边界处达到了地球的地幔底部了吗？细热的地幔柱上升通过板块中部“热点”火山下面的地幔了吗？     

科拉半岛碳酸盐中的重氮——深地幔的一个可能指

为了理解古今地幔动力学及地幔与地壳的相互作用,必须确定地幔的结构和组成。一些学者认为,在大部分的地球历史时期内,部分地幔已经从地幔对流圈中分离出来,而仅在地幔柱中保存有原始成分。支持这种观点的证据主要来自于稀有气体,因为地幔柱衍生的岩浆其放射成因同位素与原生同位素的比率通常低于洋中脊玄武岩（ＭＯＲＢｓ）。不同意见来自于地球物理、实验及地球化学证据,这些证据认为,部分俯冲板块沉入６７０ｋｍ深的地震不连续面以下,意味着地球存在全球性扰动。浅地幔的Ｎ同位素组成相对于空气组成的千分比偏差（以δ１５Ｎ表示）大约为…     

北部湾玄武岩地幔源区性质的地球化学示踪及其构造环境

北部湾发育一系列上新世玄武岩，其全岩K—Ar年龄为5．9—2．4Ma，是伴随北部湾盆地拉张而形成的一次较大规模的岩浆活动。岩石化学和微量元素地球化学研究表明，该玄武岩属于碱性玄武岩系，具有OIB型微量元素配分模式，形成于较均一的地幔源区，具有以EM2型地幔端元为主、混有HIMU和EMl型端元的地幔源区性质，形成于地幔柱或地幔热点的构造环境。北部湾盆地与红河剪切断裂带具有相同的地幔源区，而与受太平洋板块影响的地幔源区差别较大。玄武岩形成和北部湾盆地拉张主要受印度板块向欧亚板块俯冲导致的红河断裂带大规模剪切走滑控制，5Ma左右红河断裂带由左行走滑剪切转变为右行走滑剪切的构造性质转换可能是导致地幔异常扰动和岩浆活动的地球动力学机制。     

南海形成演化探究

通过分析前人对南海的研究,对南海扩张期次、扩张脊结构、动力来源等几个关键研究问题进行探讨。认为应将南海放入到欧亚板块、印度一澳大利亚板块和太平洋板块三大板块相互作用的统一构造应力场中进行研究。利用FLAC软件,首次对南海及邻区进行数值模拟分析,并进一步探讨了南海的形成演化机制,认为南海的打开和扩张是印度板块与欧亚板块的碰撞、地幔柱上涌以及太平洋板块向欧亚板块的俯冲共同作用的结果。     

构造地质过程对冲绳海槽热液活动及成矿作用的控制研究综述

在对冲绳海槽及邻区构造地质学和热液地质学调查研究成果进行全面总结的基础上,将深部地球动力学机制、冲绳海槽形成演化、岩浆作用过程、热液系统结构、流体循环模式和成矿作用特征等多方面的问题,纳入到统一的框架下,探讨了冲绳海槽构造地质过程对热液活动和成矿作用的控制机理。分析认为,区域中尺度地幔流引起了东亚大陆边缘岩石圈向东的蠕散,并驱动了菲律宾海板块沿琉球海沟向欧亚板块之下的俯冲。在弧后小尺度地幔对流、岩石圈减薄、板片反卷和俯冲后退的共同作用下,冲绳海槽发生弧后张裂。张裂作用在岩石圈内形成了网状破裂系统,为岛弧和弧后岩浆上涌提供了通道,并且引起了不同来源岩浆的干扰和混合。侵位到地壳浅部的岩浆为热液活动提供了热源和主要成矿物质来源,是影响热液活动分布的主要因素。沉积层覆盖改变了流体的浅部循环结构和原始流体成分。热液区内普遍存在的流体相分离过程,导致了广域成矿作用的发生。     

基于接收函数法的阿拉斯加中南部地幔转换带特征研究

太平洋板块向北美板块俯冲,在北美洲阿拉斯加大陆边缘形成了碰撞造山带和俯冲构造带,前人对该区域阿拉斯加俯冲带地幔转换带的研究存在分歧,一种观点认为太平洋板块俯冲至阿拉斯加中南部下方的地幔转换带内部,引起地幔转换带增厚,另一种观点则认为地幔转换带增厚是由于库拉板块残留造成的。因此,研究阿拉斯加俯冲带区域地幔转换带的精确成像对于厘清太平洋板块俯冲机制和俯冲过程具有重要意义。本文利用美国地震联合学会（IRIS）在阿拉斯加区域布设的USArray部分固定台站接收到远震事件的波形资料,采用天然地震P波接收函数与共转换点道集叠加的方法,反演得到了阿拉斯加山脉和育空高原410 km、660 km间断面和地幔转换带的厚度结构。结果表明：由于太平洋板块俯冲至地幔转换带内部,使得410 km间断面在阿拉斯加山脉东部和育空高原与阿拉斯加山脉交界处的弧形区域出现了抬升现象,抬升幅度为0～20 km,进而导致在该区域出现不同程度的地幔转换带增厚的现象,验证了第一种观点。另外,该地区地幔转换带结构显示,660 km间断面在阿拉斯加山脉东部以及阿拉斯加山脉与育空高原交界的东部出现下沉现象,故此推测阿拉斯加中南部部分区...     

南海海盆及其周缘岩浆岩地球化学特征对岩浆过程及地幔结构的指示意义

本文通过对昆嵩高原,三水盆地以及玳瑁海山岩浆岩的地球化学研究来揭示南海海盆以及周边地区的岩浆过程以及地幔源区的性质。昆嵩,三水及玳瑁海山玄武质岩浆的地球化学特征均反应这些岩浆并非来源于一个起源于核幔边界的深部地幔柱,而是来源于较浅的岩浆源区,例如岩石圈下地幔或者软流圈地幔。此外,南海海盆岩浆岩的地幔源区较昆嵩高原和三水盆地岩浆岩的地幔源区更加亏损并且表现出较低的地幔温度。这些差异可能表明三水盆地内的岩浆活动被南海的开张所抑制,而之后又在昆嵩高原复苏。研究区的地幔表现出不均一性,其中的富集地幔端元表现出EM2的特征。这个EM2富集端员是由于伴随着大陆沉积物的中生代古南海板块俯冲到研究区地幔中所形成的。     

地幔柱中原始惰性气体的特性

惰性气体在解译地球的分异过程时是重要的示踪剂。它们证明了经强烈去气的浅地幔以及去气较轻的深部地幔的存在 ,而这二者间通过地幔柱相联。二者均包含不能由大气或地壳次生的原生Ｈｅ和太阳Ｎｅ。它们还获得了不同程度的放射成因、核成因及裂变成因同位素（４Ｈｅ ,２１Ｎｅ ,４０Ａｒ ,１２９Ｘｅ ,１３１ ,１３２ ,１３４ ,１３６Ｘｅ） ,这些同位素形成于早期地幔大量去气之后。浅地幔作为洋中脊玄武岩（ＭＯＲＢ）的源区 ,其元素及同位素组成已较好地建立 ,而关于深地幔柱惰性气体的特性仍存争论。夏威夷与冰岛地幔柱玄武岩中均包含大…     

Formation of seep bubble plumes in the Coal Oil Point seep field

The fate of marine seep gases (transport to the atmosphere or dissolution, and either bacterial oxidation or diffusion to the atmosphere) is intimately connected with bubble and bubble-plume processes, which are strongly size-dependent. Based on measurements with a video bubble measurement system in the Coal Oil Point seep field in the Santa Barbara Channel, California, which recorded the bubble-emission size distribution (Φ) for a range of seep vents, three distinct plume types were identified, termed minor, major, and mixed. Minor plumes generally emitted bubbles with a lower emission flux, Q, and had narrow, peaked Φ that were well described by a Gaussian function. Major plumes showed broad Φ spanning very small to very large bubbles, and were well described by a power law function. Mixed plumes showed characteristics of both major and minor plume classes, i.e., they were described by a combination of Gaussian and power law functions, albeit poorly. To understand the underlying formation mechanism, laboratory bubble plumes were created from fixed capillary tubes, and by percolating air through sediment beds of four different grain sizes for a range of Q. Capillary tubes produced a Φ that was Gaussian for low Q. The peak radius of the Gaussian function describing Φ increased with capillary diameter. At high Q, they produced a broad distribution, which was primarily described by a power law. Sediment-bed bubble plumes were mixed plumes for low Q, and major plumes for high Q. For low-Q sediment-bed Φ, the peak radius decreased with increasing grain size. For high Q, sediment-bed Φ exhibited a decreased sensitivity to grain size, and Φ tended toward a power law, similar to that for major seep plumes.     

Spatial scales and evolution of stormwater plumes in Santa Monica Bay

Rainfall during winter storms produces extensive turbid, freshwater plumes in the coastal waters of the Southern California Bight. When the plumes result from urban runoff they contain toxic pollutants along with pathogenic bacteria and viruses, often resulting in closure of public beaches. We examined the spatial structure and evolution of stormwater plumes in Santa Monica Bay in 1996. The plumes resulted from freshwater discharge from the Ballona Creek and Malibu Creek watersheds which supply approximately 60% of the freshwater runoff to Santa Monica Bay. The spatial scales of the plumes were determined using shipboard measurements of water properties obtained from towyo transects and surface underway sampling. Salinity maps showed that the plumes typically extended 4-7 km offshore, consistent with scaling by the internal Rossby radius of deformation. Plumes extended along shore 10 km or more. Generally the plumes occupied the upper 10 m of the water column. The persistence time of a plume offshore of Ballona Creek was about three days based on a sequence of surveys in March 1996 following rainfall of about 21 mm. Limited comparison of plumes from Ballona Creek, which drains a developed watershed, and Malibu Creek, which drains a rural watershed, suggested that Malibu Creek required greater rainfall to produce an offshore plume. A stormwater plume offshore of Malibu Creek was observed on both sides of the creek mouth, possibly due to freshwater discharge from smaller surrounding watersheds or advection of freshwater discharges from the east and south. Plumes offshore of Ballona Creek mainly resulted from the creek itself and usually extended northward from the creek mouth, consistent with the wind forcing and the Coriolis acceleration.     

Upwelling plumes in sagami bay and adjacent water around the Izu Islands,Japan

Water plumes, 20 km long or less, identified by low temperature, high salinity and high nutrient concentrations, were observed on the eastern side of Izu Islands where the Kuroshio Current or its branch flowed eastward. The T-S diagrams and the vertical profiles of oceanographic variables indicated that the water plumes resulted from the upwelling of subsurface water. A newly formed plume, characterized by a sharp temperature front and high nutrient concentrations, contained less chlorophyll than did old plumes. It is suggested that the upwelling plumes are maintained for a period long enough to allow luxuriant growth of phytoplankton.     

Chemical variations of hydrothermal particles in the 1996 Gorda Ridge Event and chronic plumes

In response to the 1996 magmatic intrusion on the Gorda Ridge near 42.68°N, 126.78°W in late February, we conducted three cruises to the region in March, April, and June. On all three cruises particulate samples were collected, along with CTD/nephelometer data and total dissolved Fe and Mn samples. During each cruise, we collected samples from large oblate spheroid-shaped event plumes. These event plumes had long axis diameters of about 10–15 km and ranged in depth from about 1800 to 2700 m. A strong linear correlation between nephelometer voltage and particulate Fe allowed us to estimate the total amount of particulate Fe in the event plumes at approximately 20×10⁶ moles of Fe, or 28% of the Fe in the 1986 megaplume on the Cleft Segment of the Juan de Fuca Ridge. We observed significant decreases in particulate Cu and Zn concentrations (>100% decrease in Cu/Fe and Zn/Fe ratios) between the Gorda Ridge event plumes. These results suggest that each of the two event plumes originated from a chemically distinct source fluid. Fe ferrihydrite particles maintained a constant ratio of coprecipitated oxyanion species in the two event plumes. Based upon the chemical inventories for particulate Fe, P, and V, we suggest that event plumes might play a small role in the geochemical budgets for these elements.     

Supply and precipitation of hydrothermal iron in the rift valley of the Mid-Atlantic Ridge at 26° and 29° N

This publication considers the probing data on aquatic anomalies (hydrothermal plumes) in the areas of 26° and 29° N of the Mid-Atlantic Ridge (MAR). The mass of the hydrothermal iron supply and the intensity of the iron sedimentation onto the bottom were estimated by means of sediment traps. It was found that the plume of the TAG hydrothermal vent 6 km³ in volume contained about 67 t of suspended Fe; the plume of the Broken Spur field (up to 8.24 km³ in volume) contained 23.5 t or less because of the lower concentration. The data on the sedimentary matter fluxes showed that 0.3–0.5% of the hydrothermal iron was precipitated immediately from a plume of neutral buoyancy onto the bottom; the bulk of the iron was dissipated into the environment. From the dimensions of the plumes, the flow dynamics, the iron concentrations in the plumes, and the amounts of iron supplied by hydrothermal vents, it was found that the resident time of the plumes considered was from 5 to 10 days.     

现代海底热液柱中锰元素的分析及其地球化学

研究锰在热液中的地球化学性质对于更好地了解热液在海洋中的循环过程和扩散情况很有意义,虽然影响热液中锰的地球化学性质的因素很多,但锰确实是示踪热液活动的最敏感、最有效的元素之一。主要总结了现代海底热液柱中锰元素的分析方法进展,同时对热液柱中锰元素的地球化学特征进行了研究。     

冷泉活动区气泡羽状流数值模拟的进一步研究

以南海气泡羽状流赋存特征为参考,本文继续研究冷泉活动区气泡羽状流的地震响应。为使羽状流建模方案更合理,根据水中气泡在上升过程时其半径的变化情况,修改原建模方案,重新建立了羽状流水体模型。通过正演模拟得到了羽状流炮集地震记录,单炮记录上显示出明显的散射波场特征和模型的周期特点。通过叠前深度偏移处理炮集地震记录,得到边界收敛效果较好的成像剖面,且成像精度较高。以上研究又一次奠定了羽状流地震响应进一步研究的基础,也逐步探索出更适合羽状流地震资料的处理方法,为识别羽状流提供了理论指导。     

Transparent exopolymer particles (TEP) as a component of hydrothermal plume particle dynamics

Transparent exopolymer particles (TEP) have recently been recognized as a class of sticky particles that often stimulate macroaggregate formation. Until now, TEP studies were focused on surface waters, particularly in association with diatom blooms. This is the first report of TEP concentrations in an open ocean deep-sea hydrothermal plume environment. The occurrence of TEP in deep water demonstrates its existence in an environment that is devoid of growing phytoplankton, the organisms generally regarded as TEP's primary source. The main objective of this study was to investigate the presence and potential abundance of TEP within hydrothermal plumes over the Juan de Fuca Ridge. Samples for TEP and bacteria were collected from CTD-rosette casts through hydrothermal plumes over the Juan de Fuca Ridge during the summers of 1999 and 2000. Concentrations of TEP and bacteria within the hydrothermal plumes were significantly greater than in background seawater. TEP number and volume concentrations reported here are low compared to reported values for shallow environments, but are substantially higher than published reports of TEP in other deep water environments. Ratios of TEP anomalies to temperature anomalies (a conservative hydrothermal tracer) increased with distance from the apparent plume source, suggesting that TEP are produced within the aging hydrothermal plumes. Potential TEP sources associated with hydrothermal plumes are discussed. TEP in hydrothermal plumes could stimulate in situ aggregate formation, support populations of attached bacteria, and serve as a potential food source to zooplankton.     

The nature and origin of light hydrocarbon gases associated with mineralization in the Northern Pennines

Earlier studies have shown the occurrence of anomalous amounts of methane in rocks associated with lead/zinc mineralization in a number of deposits in the British Isles and Europe. This has led to speculation that the gas may have originated either as a consequence of reactions involved in the mineralization process or as a result of maturation of the organic matter in the sediment or from a deep source. New data are presented showing the distribution of light hydrocarbon gases from fluid inclusions in minerals from the North and South Pennine Orefields which differ from those observed in the host rocks. Possible sources for the gases in the host rocks and the minerals are examined. Based on the close correlation between the distribution of the gases in the carbonate rocks of Northern England and the conodont colour alteration index map for the area, it is suggested that the anomalous amounts of methane gas in the Northern Pennine host rocks are the result of maturation prior to mineralization. The distribution of gases in the fluid inclusions in the minerals serves as a distinguishing feature, and two assemblages are recognized from the South Pennine Orefield, both of which are distinct from that of the Northern Pennines. It is concluded that these gases, trapped at the time of mineralization, originate as a consequence of reactions which occurred during mineral deposition.