首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 61 毫秒
1.
冲绳海槽岩浆源的三分量混合模型   总被引:1,自引:0,他引:1  
综合分析了冲绳海槽玄武岩中微量元素的地球化学特征,发现最少要求三分量混合作用来解释其岩浆源成分,并通过最大方差因子分析估算了3个分量的贡献比例。亏损型地幔是海槽岩浆源的主体,但其中舍有富集型地幔的成分,尤其是海槽中部玄武岩岩浆源中这种富集型地幔成分的特征表现得更为明显。俯冲组分是岩浆源中的另一个主要成分,贡献量为20%左右,是造成海槽区玄武岩中Pb强烈富集的重要原因。  相似文献   

2.
马里亚纳海槽热液区岩石矿物学和岩石化学特征研究   总被引:5,自引:0,他引:5  
马里亚纳海槽中央轴裂谷中的小扩张脊部位,广布火山喷发的玄武岩体,海底热液硫化物就是从这些岩体的裂隙中喷溢堆积起来的。利用我国“大洋一号”船拖网所获岩样进行了矿物学和岩石化学特征研究,认定为高铝低钾的大洋底玄武岩或拉斑玄武岩系列和钙-碱玄武岩。为进一步弄清马里亚钠海槽区热液活动岩石学条件和探讨海槽区热液物质来源提供科学证据。  相似文献   

3.
马里亚纳海槽中央轴裂谷中的小扩张脊部位 ,广布火山喷发的玄武岩体 ,海底热液硫化物就是从这些岩体的裂隙中喷溢堆积起来的。利用我国“大洋一号”船拖网所获岩样进行了矿物学和岩石化学特征研究 ,认定为高铝低钾的大洋底玄武岩或拉斑玄武岩系列和钙 -碱玄武岩。为进一步弄清马里亚纳海槽区热液活动岩石学条件和探讨海槽区热液物质来源提供科学证据  相似文献   

4.
马里亚纳海槽作为正在活动的典型弧后盆地,是研究俯冲作用对岩浆作用和壳幔动力学影响的理想场所。通过对采自该海槽中南部的样品进行系统的岩石地球化学特征对比与研究,并结合前人已发表的岩石地球化学数据,探讨了马里亚纳海槽中南部的地幔富集(亏损)程度、地幔熔融程度、地幔熔融深度以及俯冲物质的加入程度。结果表明:(1)马里亚纳海槽中南部主要发育一套中低钾钙碱性系列玄武岩、玄武质安山岩;(2)海底岩石富集了大离子亲石元素、轻稀土元素,亏损高场强元素、重稀土元素;(3)将马里亚纳海槽沿扩张中心分为三段,对每段地幔熔融的程度和深度进行计算并且消除地幔不均一性的影响,发现在15°N和18°N附近二者呈现负相关关系,其余地区则呈现正相关关系,证明海槽存在两种地幔熔融模式;(4)微量元素比值显示海槽受多种俯冲组分影响,并且马里亚纳海槽南部的南段可能存在另一个富水熔体端元,可能是导致海槽扩张速率较快的原因。对俯冲物质的加入程度进行计算,发现靠近15°N与18°N俯冲组分的影响变弱,这进一步表明,马里亚纳海槽火山岩的变化可能是由于类似N-MORB的地幔源区与类似岛弧的地幔源区混合造成的;俯冲物质是控制地幔熔融程度...  相似文献   

5.
通过对马里亚纳海槽两沉积岩芯中主要化学元素的因子分析,其结果表明,化学元素的共生组合和含量变化,与火山碎屑矿物以及大部分由海底玄武岩和玄武质火山玻璃蚀而成的粘土矿物密切相关。岩芯的化学成分主要来自火山喷发物,因此,元素的地球化学特征反映了该区火山作用的影响。  相似文献   

6.
冲绳海槽是新月形的弧后扩张盆地,强烈的构造活动和广泛的火山作用是海槽重要的特征。本文作者主要借助对海槽火山岩的常量元素、微量元素、Sr-Nd 同位素和年龄数据分析,结合火山的时空分布及相关构造地质条件,揭示了海槽火山作用的演化过程及其与本地区构造活动的关系,以便更好地了解海槽和沟-弧-盆体系的形成演化历史。作者通过研究得出:①海槽的火山岩石地球化学特征表明岩石属钙碱性系列,主要包括玄武岩、玄武质安山岩和流纹岩,岩石组成具双峰结构。②在海槽的不同区段内,火山作用具有一定的差异。海槽不同区段内火山带岩浆源区深度的差异,是造成海槽不同区段火山活动性质变化的原因,而岩浆源深度受俯冲带形态和地壳厚度控制。海槽北、中段火山岩以流纹岩和安山岩为主,流纹岩分布在海槽盆地内,形成时代较新( <1Ma),安山岩大部分分布在岛弧火山带中,形成时代是中、晚中新世。海槽南段火山岩由玄武岩和玄武质安山岩组成,从老到新分布在琉球火山弧(大约13Ma)、台北火山带(3Ma~现代)和南段中央凹陷(晚第四纪)中。③琉球火山弧形成于中、晚中新世(17~6Ma)。但大约12Ma发生的吕宋弧与欧亚板块的碰撞作用改变了本地区的动力条件,而宫古断裂对此次改变起了阻断作用,使海槽南段的张裂要晚于北、中段。另外,中新世琉球岛弧南段的形成确定了海槽南段的弧后盆地性质。 冲绳海槽是年轻的弧后盆地,其岩浆、构造活动发育。对海槽岩浆作用的研究可上溯至20世纪50年代,但由于海水及恶劣气候等条件的制约,几十年来对海槽研究程度仍很有限,且在不同区段有很大差异。特别是对区内岩浆作用的研究,极大地受到样品采集偶然性的限制。作者收集前人资料综合对比海槽不同区段内火山活动的异同,了解海槽火山活动研究中的成就与问题, 为进一步开展此项研究打下基础。  相似文献   

7.
马里亚纳海槽玄武岩岩石学   总被引:3,自引:0,他引:3  
马里亚纳海槽岩石学的研究表明本区岩石属基性的玄武岩,又细分为洋底玄武岩(OFB)和钙碱玄武岩(CAB)。微量元素相对球粒陨石标准化数值特征:除了Sc、Ti,V外,其它过渡元素都有亏损,Cr、Ni出现了明显负异常,Ti相对较富集,稀土元素(REE)表现富集型的型式;同位素测试结果,εNd(0)=6.9。可以认为这些玄武岩是上幔岩的局部熔融形成的岩浆沿着扩张中心喷溢到海底,而形成的新生洋壳。  相似文献   

8.
冲绳海槽沉积物稀土和微量元素的某些地球化学特征   总被引:12,自引:4,他引:8  
吴明清 《海洋学报》1991,13(1):75-81
本文采用等离子体光谱和原子吸收光谱,分别测定了冲绳海槽表层沉积物的15个稀土元素和12个微量元素(其中U、Th、Sc采用化学法)的含量,在此基础上讨论了这些元素的地球化学特征.研究结果表明,随着样品的分布由西向东,Li、Rb、Cu、Ni、V、Cr、Zn等微量元素的含量呈现由低变高、再由高变到低的峰形变化趋势,从属于元素的粒度控制规律;而Th、Sc、稀土等则呈现逐渐降低的单一变化趋势,表明这些元素可能主要赋存于陆源碎屑矿物中.此外,冲绳海槽沉积物的球粒陨石标准化稀土元素分布模式类似于陆壳物质,而在页岩标准化稀土元素分布模式图上,海槽底部及东坡的样品呈现铈的明显亏损,反映了海水独特的稀土配分特点.  相似文献   

9.
马里亚纳海槽热液活动区玄武岩的岩石地球化学特征   总被引:6,自引:0,他引:6  
对拖网采自马里亚纳海槽热液活动区 (18°N附近 )的 8个玄武质岩石样品进行岩石地球化学初步研究。岩石富集 L IL E和 L REE,稀土分布型式呈右倾图式 ,L a N=10 .6 8~ 2 2 .6 4 ,(L a/Yb) N=1.6 1~ 2 .4 7,并略显 Eu正异常。在相对于原始地幔的标准化微量元素分布图中 ,7个样品具较明显的 Nb亏损和 Zr、Hf富集 ,而 1个样品不具 Nb的亏损 ;HFSE/HFSE、L IL E/HFSE、L IL E/L IL E等微量元素比值大都在 N- MORB和 EMI2个地幔端员组分间变化。这表明岩浆起源于受俯冲组分改造或影响的上地幔 ,且地幔源区存在明显的化学不均一性。与冲绳海槽玄武岩相比 ,马里亚纳海槽玄武岩的 Nb亏损明显减弱 ,暗示俯冲组分对地幔源区的影响程度也随之减弱 ,这反映出处于弧后张裂阶段的冲绳海槽与处于从弧后张裂向海底扩张过渡阶段的马里亚纳海槽 ,在岩浆起源及其动力学背景存在明显差异  相似文献   

10.
1992年5月-19926月对绳海槽热液活动区进行调查采样,对拖网采到的新鲜的玄武岩样品做了斑晶矿物学及岩石化学研究。结果表明,冲绳海槽玄武岩的斑晶矿物主要由橄榄石、单斜辉石、斜方辉石和斜长石组成,副矿物有铬铁尖晶石和磁铁矿,因而将样品定为橄榄玄武岩。  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
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。  相似文献   

14.
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.  相似文献   

15.
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.  相似文献   

16.
《海洋学报(英文版)》2014,(8):F0003-F0003
<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology,  相似文献   

17.
18.
This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried out by IFREMER on 19 cores extracted at different depths (from 27 m to 1300 m) (Cochonat, Bourillet, and Savoye, 1993; Mulder et al., 1994). Many scenarios were proposed in order to explain the cause of the Nice slope failure (Habib, 1994). In this article, two of those scenarios were tested. Simulation results are presented and discussed.  相似文献   

19.
20.
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.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号