印度洋Carlsberg洋脊玄武岩岩石地球化学特征及其地质意义

本文对采自印度洋Carlsberg脊14个站位的新鲜玄武岩样品进行了常量和微量元素组成分析,旨在研究岩浆源区地幔的性质以及岩浆作用过程。研究结果表明:该区玄武岩为典型的源于亏损型地幔的大洋中脊玄武岩,不同样品经历了不同程度的结晶分异作用,演化过程主要受控于橄榄石的结晶分异作用,部分样品中有单斜辉石结晶分异作用的影响,斜长石的结晶分异作用不显著;玄武岩岩浆来源于亏损型尖晶石二辉橄榄岩地幔的熔融,主微量元素组成中尚未见到富集型组分混入的证据;源区地幔不同比例的熔融作用及其后岩浆演化过程的差异是造成不同样品间地球化学性质差异的主要原因,彼此独立的局部岩浆作用过程是岩浆作用差异的主控制因素。Carlsberg脊玄武岩整体与全球标准大洋中脊玄武岩(N-MORB)平均组分相近,不同脊段间岩浆源区地幔的组成、熔融程度(比例)和熔融深度等无明显差异,这种特征向南直到CIR的北段。     

大西洋中脊玄武岩岩浆源区性质、潜在温度及其指示意义

洋中脊玄武岩（MORB）的微量元素成分和同位素比值具有变化范围大的特点,这些变化很难简单地用地幔部分熔融和结晶分异等岩浆演化过程来解释。传统观点认为洋中脊玄武岩的地球化学成分的多样性是由其下部地幔成分的大尺度不均一性决定的。这种地幔不均一性则是外来物质的加入造成的,如再循环的地壳物质、下大陆岩石圈、交代的岩石圈和外地核等成分加入到上地幔中。在本研究中,我们对大西洋洋中脊的玄武岩展开研究工作,评估了玄武岩源区的温压条件并综合对比了微量元素和同位素比值。靠近地幔柱的洋中脊玄武岩的地球化学和同位素成分具有较大的变化。地幔柱对洋中脊地区的影响范围可以达到1400公里,但并不是每个地幔柱都能够影响其周围1400km范围内的所有洋中脊脊段。未受地幔柱影响的洋中脊玄武岩成分和地幔潜在温度均没有异常表现。我们认为上述现象是由于地幔柱柱头形状不同造成的。地幔柱的流动形状可以分为管状和饼状两种,饼状地幔柱影响其周围的地幔是没有方向性的,而管状地幔柱对其周围地幔的影响在方向上具有选择性。沿着大西洋中脊的玄武岩的元素和同位素比值变化较大,暗示其源区具有较高的不均一性。我们认为该地区地幔不均一性主要是由于上地幔中加入了俯冲板片和拆沉下地壳造成的。另外,地幔柱的活动也不容忽视,它们影响了其周围部分洋脊段的成分变化。     

西太平洋板内玄武岩的同位素地球化学特征

西太平洋板内玄武岩主要是南太平洋中生代板内岩浆作用的产物。对西太平洋板内玄武岩和南太平洋板内玄武岩的对比研究有助于进一步揭示南太平洋超级地幔柱的性质及其时空演化规律。本文收集整理了西太平洋板内玄武岩的Sr,Nd,Pb同位素数据,并与南太平洋板内玄武岩对比。得到如下认识:(1)西太平洋板内玄武岩同位素组成极不均一,覆盖了所有的富集地幔端元,但主要表现为HIMU和EM-1两端元的混合特征;(2)与南太平洋板内玄武岩相比,西太平洋板内玄武岩的同位素组成的极端程度相对偏低,可能是其地幔源区各组分间混合更均匀的结果;(3)自约120 Ma以来,由于HIMU组分在西太平洋板内玄武岩中持续存在,而EM-1和EM-2型组分表现为断续出现,这可能暗示HIMU端元与两种富集端元在深部地幔中所处的空间不同。     

大洋地幔化学组成不均一性成因研究回顾及展望

认识地幔组成不均一性及其成因对于揭示固体地球的演化规律具有重要意义。简要论述了全球典型大洋玄武岩(洋岛/海山玄武岩(OIB)、洋中脊玄武岩(MORB))源区组成不均一性的化学特征及成因,并分析了国内外对地幔组成不均一性的认识不足之处和原因。30多年以来,玄武岩地球化学研究主要围绕地幔组成端元成分差异性及其成因,包括HIMU(‘μ’=~(238)U/~(204)Pb)、EMI和EMII及FOZO(同位素组成介于HIMU和MORB之间)富集端元,以及DMM亏损地幔端元(包括印度洋型(Indian-type MORB)和太平洋型(Pacific-type MORB)。富集地幔端元通常被认为与板块构造导致的地球化学循环有关,然而,这些端元的成因存在多解性。尽管过去常将亏损地幔作为一个地幔端元,但全球主要地幔库的亏损端元之间的同位素差别也是长期演化的结果,地幔亏损端元组成差异的研究也是至关重要的。地幔端元成因的多解性主要是由于对板块构造导致物质循环的关键环节了解不够,以及对地球早期熔融导致的上地幔亏损过程的认识不足。在总结研究现状和科学问题的基础上,本文指出地幔不均一性成因研究的潜力方向和方法:(1)深化对玄武质洋壳深部地幔压力下的物理化学相变研究,认识再循环洋壳重返浅部地幔的基本理论前提;(2)利用年轻的大陆裂张海盆玄武岩,有效检验大陆富集物质是否拆离进入地幔软流圈;(3)碳酸岩熔体来源及其对碱性玄武岩富集端元组成的贡献;(4)板块俯冲进入地幔过程中化学分异过程。     

东太平洋海隆1.5°N～1.5°S和南大西洋中脊13.2°S玄武岩物质组成

对东太平洋海隆(EPRⅠ区和Ⅱ区)和南大西洋中脊(SMAR)6个站位新鲜的玄武岩样品进行了岩石学及地球化学研究。结果显示,EPR玄武岩样品可分为辉石玄武岩、气孔玄武岩和玻基玄武岩3种类型,SMAR玄武岩样品主要为辉石玄武岩。EPR和SMAR玄武岩样品的标准矿物组合相同,均出现了石英和紫苏辉石标准矿物,为典型的拉斑玄武岩。EPRⅠ区和SMAR玄武岩表现出轻稀土富集的配分模式,可能受到了富集地幔源区(EMORB)的影响,其玄武岩可能形成于未经历早期熔融事件的富集地幔或部分熔融程度相对较低。EPRⅡ区玄武岩为正常型洋中脊玄武岩(N-MORB),其源区为经历了早期熔融事件的、亏损洋中脊地幔源区(DMM),且源岩部分熔融程度较高。EPRⅠ区与Ⅱ区不同的幔源特征说明东太平洋海隆地幔源区存在不均一性。     

东太平洋海隆近赤道区玄武岩岩石地球化学与地幔源区特征

本文对东太平洋海隆赤道地区北部和南部的9件玄武岩样品进行了详细的岩相学和主量、微量元素及Sr-Nd-Pb同位素分析研究,结果表明:MgO含量为7.32%~10.22%,Na_2O为3.03%~3.59%,K_2O为0.23%~0.57%,CaO为10.96%~12.39%,Al_2O_3为11.40%~13.76%,该区玄武岩均属于亚碱性玄武岩,具有MORB型的稀土及微量元素特点,原始岩浆均经历了橄榄石和斜长石的分离结晶。轻重稀土元素含量均较低,LREE/HREE比值为0.61~0.97,(La/Yb)N比值为0.72~1.76,(La/Sm)N比值为0.60~1.30,(Gd/Yb)N为0.99~1.16。Sr-Nd-Pb同位素特征更接近NMORB,其中,87Sr/86Sr和143 Nd/144 Nd比值更接近DM源区,而Pb的三种同位素比值要明显高于DM源区,更为接近EM源区。研究表明岩浆起源于尖晶石橄榄岩区,来源于较为亏损的地幔,NEPR玄武岩可能混有HIMU源区,SEPR玄武岩除了混合有HIMU成分外,可能还有少量的EMⅡ成分。     

DSDP/ODP 504B孔上洋壳Nd和Pb同位素变化

低 8 6Sr/ 87Sr和高 14 3 Nd/ 14 4 Nd比值作为洋中脊玄武岩 ( MORB)的特征 ,表明偏离原先亏损的不相容元素的源区。同其它火山环境中的岩浆岩相比较 ,MORB具有相当均一的成分 ,然而在区域和局部范围内同位素和微量元素地球化学的变化较小但很明显。在许多地方 ,区域地球化学变化明显与地幔羽的影响有关。接近洋脊的海山和沿扩张脊的局部地球化学变化表明MORB幔源在较小区域也是不均匀的 ,洋脊表层取样只提供了局部地球化学变化的有限信息。因此 ,我们研究科斯塔里卡断裂南侧DSDP/ ODP50 4B孔新鲜玄武岩剖面是为了阐明太平洋洋壳…     

印度洋亚丁-欧文-卡尔斯伯格脊三联点邻近洋脊的玄武岩地球化学特征及其地幔源区性质

本文研究了亚丁-欧文-卡尔斯伯格脊(AOC)三联点邻近洋脊的玄武岩样品在主量、微量元素和Pb-Sr-Nd同位素特征上的差异和联系并分析其原因。结果表明,AOC附近卡尔斯伯格脊和希巴洋脊的玄武岩均为正常型洋脊玄武岩(N-MORB),起源自亏损地幔,其中卡尔斯伯格脊的样品较希巴洋脊样品更亏损;欧文洋脊玄武岩样品为洋岛玄武岩(OIB)特征,其地幔源区可能有残余陆块物质的混染;亚丁洋脊玄武岩样品类型包括N-MORB、E-MORB和可能的大陆玄武岩,与洋壳形成过程中大陆岩石圈物质的贡献程度有关。除了卡尔斯伯格脊外,阿法热点对各洋脊的岩浆均有一定程度的影响。     

西南印度洋中脊玄武岩地球化学特征及其对岩浆过程的指示意义

对采自西南印度洋中脊(SWIR)50°E附近5个站位的玄武岩样品进行了岩石学和元素地球化学研究.样品主量元素、TAS分类图解和AFM图解显示,SWIR研究区样品类型主要为低钾拉斑玄武岩.相对原始地幔SWIR区玄武岩具有Ba、Nb、Sr负异常,K表现为正异常.稀土元素分配模式均为左倾型,具有轻微的Eu、Ce正异常;SWI...     

太平洋、印度洋中脊型地幔在两个时间段的位置——来自澳大利亚新生代玄武岩Pb、Sr和Nd同位素证据

弄清不同化学成分的软流圈库及其分布有利于了解大规模地幔对流模式及全球范围地幔化学域如Ｄｕｐａｌ异常（主要位于印度洋的一种地幔域,为Ｐｂ、Ｓｒ同位素异常的大洋玄武岩）、印度洋中脊玄武岩（ＭＯＲＢ）型地幔和冈瓦纳岩石圈地幔等的成因和物源。印度洋ＭＯＲＢ在...     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

A Review of Some Environmental Issues Affecting Marine Mining

This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.