The smectite to chlorite transition in a fossil seamount hydrothermal system: the Basement Complex of La Palma, Canary Islands   总被引：3，自引：0，他引：3  

P. SCHIFFMAN  H. STAUDIGEL 《Journal of Metamorphic Geology》1995,13(4):487-498

Abstract The hydrothermal metamorphism of a sequence of Pliocene-aged seamount extrusive and volcanoclastic rocks on La Palma includes a relatively complete low-P-T facies series encompassing the zeolite, prehnite-pumpellyite, and greenschist facies. The observed mineral zonations imply metamorphic gradients of 200–300° C km^-1. The transition from smectite to chlorite in the La Palma seamount series is characterized by discontinuous steps between discrete smectite, corrensite and chlorite, which occur ubiquitously as vesicles and, to a much lesser extent, vein in-fillings. Trioctahedral smectites [(Mg/(Fe + Mg) = 0.4–0.75] occur with palagonite and Na-Ca zeolites such as analcime and a thompsonite/natrolite solid solution. Corrensite [(Mg/(Fe + Mg) = 0.5–0.65] first appears at stratigraphic depths closely corresponding to the disappearance of analcime and first appearance of pumpellyite. Discrete chlorite [(Mg/(Fe + Mg) = 0.4–0.6] becomes the dominant layer silicate mineral coincident with the appearance of epidote and andraditic garnet. Within the stratigraphic section there is some overlap in the distribution of the three discrete layer silicate phases, although random interstratifications of these phases have not been observed. Although smectite occurs as both low- and high-charge forms, the La Palma corrensite is a compositionally restricted, 1:1 mixture of low-charge, trioctahedral smectite and chlorite. Electron microprobe analyses of coarse-grained corrensite yield structural formulae close to ideal values based on 50 negative charge recalculations. Calcium (average 0.20 cations/formula unit) is the dominant interlayer cation, with lesser Mg, K and Na. The absence of randomly interlayered chlorite/smectite in the La Palma seamount series may reflect high, time-integrated fluid fluxes through the seamount sequence. This is consistent with the ubiquity of high-variance metamorphic mineral assemblages and the general absence of relict igneous minerals in these samples.  相似文献   

A Study on the Forming Conditions of Basalts in Seamounts of the South China Sea   总被引：2，自引：0，他引：2  

Li Zhaolin  Qiu Zhili  Qin Shecai  Pang Xuebin  Liang Dehua  Teng Yunye  Li Yang 《中国地球化学学报》1994,13(2):107-117

Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are mainly amorphous melt inclusions, which reflects that the volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions have been discovered for the first time in alkali basalts and mantle-derived xenoliths. indicating a process of differentiation between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this nonhomogeneous system. Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ∼ 1185 °C; the Xianbei seamount alkali basalt 960 ∼ 1200 °C; tholeiitic basalt 1040 ∼ 1230 °C; the Daimao seamount tholeiitic basalt 1245 ∼ 1280 °C; and the Jianfeng seamount trachyandestic pumice 880 ∼ 1140 °C. Equilibrium pressures of alkali basalts in the Zhongnan and Xianbei seamounts are 13.57 and 8.8 × 10⁸ Pa, respectively. Pyroxene equilibrium temperatures of mantle xenoliths from the Xianbei seamount were estimated at 1073 ∼ 1121 °C, and pressures at (15.58 ∼ 22.47)×10⁸Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts. This project was financially supported by the National Natural Science Foundation of China and Guangzhou Marine Geology Survey.  相似文献   

Platinum‐Group Element Results for Two Cobalt‐Rich Seamount Crust Ultra‐Fine Reference Materials: MCPt‐1and MCPt‐2     

Yimin Wang  Xiaohong Wang  Wenjun Qu  Yushu Gao  Tiexin Gu  Xingtao Fan  S.I. Andreev  Xuefa Shi 《Geostandards and Geoanalytical Research》2011,35(3):341-352

Two Co‐rich seamount crust reference materials, MCPt‐1 and MCPt‐2, were prepared using ultra‐fine particle size milling technique and characterised for the platinum‐group elements (PGEs). The raw material for these two reference materials was collected separately from the Magellan seamounts of the western Pacific Ocean and the seamounts of the central Pacific Ocean by Russian and Chinese scientists. First, they were ground by ball mill to a ?200 mesh powder, then further processed by ultra‐fine jet mill and well‐mixed. The particle size distributions of the samples were tested by a laser particle analyser; the average particle size was 1.8 and 1.5 μm (equal to about 2000 mesh) respectively. The homogeneity of six major and minor elements in these two materials was tested at the milligram level of sampling mass by high‐precision wavelength dispersive X‐ray fluorescence (XRF) spectrometry and at the microgram level of sampling mass by electron probe microanalyser. The homogeneity of more than forty trace elements, including Pt, was tested at the microgram level of sampling mass by LA‐ICP‐MS. Except for Rh, all PGEs were determined by isotope dilution‐ICP‐MS. Platinum in MCPt‐1 and MCPt‐2 was characterised as certified values, whereas the other five PGEs in MCPt‐1 and MCPt‐2 were reported as reference values. In addition, the information values of sixty‐two major, minor and trace elements were obtained by XRF, ICP‐AES and ICP‐MS. The minimum sampling mass for the determination of PGEs was 1 g, while the minimum sampling mass for the determination of the other elements was 2–5 mg.  相似文献   

Precise location of unsurveyed seamounts in the Austral archipelago area using SEASAT data   总被引：1，自引：0，他引：1  

N. Baudry  M. Diament  Y. Albouy 《Geophysical Journal International》1987,89(3):869-888

Summary. SEASAT altimetric geoid data are used to detect uncharted sea-mounts in the Austral archipelago area. The various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location. These parameters are the shape of the seamount, its density, the crustal model, the effective elastic thickness of the lithosphere and the distance between the seamount and sub-satellite tracks, respectively. The results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks, it is possible to locate it with good confidence and to give an estimation of its height. If the correct elastic thickness is assumed, the precision on the located is order 15 km. Ten previously unsurveyed seamounts have been located in the Austral archipelago. It appears that they are emplaced along two well-defined azimuths (N 110°E and N 150°E) and that two parallel distinct volcanic chains form the Austral archipelago.  相似文献   

造山带中古海山残片的识别——以拉脊山缝合带青沙山和东沟地质填图为例     

付长垒  闫臻  王秉璋  牛漫兰 《地质通报》2021,(1)

造山带内海山/洋岛残片的识别是确定古缝合带和古洋盆存在的直接地质证据。祁连造山带被普遍认为是原特提斯洋盆俯冲和闭合的产物,然而南祁连地区是否存在古洋盆长期存在争议。通过对拉脊山关键地段早古生代岩石开展大比例尺地质填图和室内综合研究,在青沙山和东沟地区识别出连续的由洋岛型枕状玄武岩、火山碎屑岩、泥岩、凝灰岩和灰岩组成的火山-沉积组合序列,它们分别呈构造窗和构造残片产出,是拉脊山增生杂岩的重要组成部分,代表中寒武世—早奥陶世原特提斯洋内海山残片。这些海山残片的识别不仅表明拉脊山地区存在早古生代洋盆和缝合带,同时为造山带古洋盆构造演化研究提供了新思路。  相似文献   

鳞侧尖柳珊瑚Paracis squamata(Nutting,1910)(八放珊瑚亚纲:丛柳珊瑚科)的形态学和系统发育研究     

孙梦岩  詹子锋  徐雨  徐奎栋 《海洋科学》2022,46(8):48-56

2014年自雅浦海沟附近的一座海山通过水下无人遥控潜水器获得3株八放珊瑚样本,通过对其珊瑚虫和骨片观察,并结合线粒体错配修复蛋白基因(mtMutS)的测序分析,进行了分类学和系统发育研究。结果显示,3株八放珊瑚均为鳞侧尖柳珊瑚Paracis squamata (Nutting,1910)。该物种主要特征为具有鳞片状的萼部骨片和无规则板状的共肉组织外层骨片。在基于mtMutS基因构建的系统发育树中,鳞侧尖柳珊瑚与侧尖柳珊瑚未定种(Paracis sp.)以高置信度聚在一起,侧尖柳珊瑚属(Paracis)和鳞尖柳珊瑚属(Lepidomuricea)以高支持率形成姐妹枝。本文对鳞侧尖柳珊瑚的形态学特征进行了全面研究,首次描述了共肉组织内层骨片的特征,揭示侧尖柳珊瑚属与鳞尖柳珊瑚属具有较近的亲缘关系。  相似文献   

海山的倾斜俯冲对上覆板块变形的影响     

李付成  孙珍  张云帆  徐子英  谢辉 《地球物理学进展》2012,27(4):1406-1415

伴随洋壳的俯冲,驼伏其上的海山会导致上覆板块的强烈变形.为解释该构造变形特征,本文运用物理模拟实验的方法,着重分析海山的斜向俯冲对上覆板块变形的影响,并将模拟结果与正向俯冲过程进行对比.实验结果显示:海山开始进入俯冲,前缘楔体的增生会被阻止,同时楔体被抬升并出现脱顶构造,未被海山破坏的楔体会出现后冲断层的激活,后冲断层轴平行于海山的俯冲方向.海山进一步俯冲,突起项部发育一系列张扭性质的微断裂和走滑性质的共轭断裂,尾随突起之后的楔体由于重力会产生正断层系统.比起正向俯冲,斜向俯冲过程中所产生的后逆冲体、海山两侧的叠瓦状逆冲推覆构造都出现不对称分布,断裂和微断裂束的走向不规则散开,后冲断层的轴向及海山俯冲过后在楔体上产生的凹槽的轨迹都不断斜向迁移,且凹槽两侧的地势不一致等.最后利用文中的物理模拟结果,很好的解释了马尼拉海沟中段俯冲构造的构造特征,同时对其他俯冲大陆边缘的构造解释具有指导意义.  相似文献   

陈蔡早古生代俯冲增生杂岩对华夏与扬子地块拼合过程的指示意义     

赵希林  姜杨  邢光福  于胜尧  彭银彪  黄文成  王存智  靳国栋 《吉林大学学报(地球科学版)》2018,48(4):1135-1153

华夏地块与扬子地块的拼合时限与方式长期存在争议。本文对出露于浙江诸暨一带的原"陈蔡岩群"进行了详细的露头尺度解剖。野外地质调查表明,原"陈蔡岩群"主要由不同性质的外来岩块与基质组成。其中：代表外来岩块的大理岩及斜长角闪岩的变质年龄分别为（424.7±2.9）和（420.6±1.8）Ma,成岩年龄分别为（479.2±9.5）~（424.7±2.9）Ma和（507.7±7.8）~（420.6±1.8）Ma,斜长角闪岩原岩为具OIB（洋岛玄武岩）特征的碱性玄武岩,大理岩的原岩为海相碳酸盐岩,二者共同构成了洋岛海山组合。代表原地岩块的变长石石英砂岩主要物源区为3 620~1 530 Ma形成于活动大陆边缘和大陆岛弧环境下的古老地壳物质;与之构造混杂接触的斜长角闪岩变质年龄为（438.0±2.5）Ma,其原岩分别为形成于消减带岛弧环境的岛弧拉斑玄武岩、形成于俯冲环境下的富Nb玄武岩和洋岛海山环境下的具OIB特征的碱性玄武岩类。代表基质的含榴黑云斜长片麻岩LA-MC-ICP-MS锆石U-Pb年龄测试结果表明,其变质年龄为（441.0±3.0）Ma,碎屑²⁰⁶Pb/²³⁸U年龄多数为840~780 Ma,反映其物源主要来自于新元古代,且最年轻的沉积年龄限定在598 Ma,说明片麻岩原岩可能为早古生代沉积地层。陈蔡地区该套岩石组合的发现表明,原"陈蔡岩群"的构造属性应为早古生代俯冲增生杂岩。结合测区及龙游地区新发现的加里东期麻粒岩和退变榴闪岩,提出扬子与华夏两大地块碰撞于445~420 Ma。  相似文献   

软体动物腹足纲分类学研究进展——从近海到深海   总被引：2，自引：0，他引：2  

张素萍  张树乾 《海洋科学集刊》2017,(52):1-10

随着科学技术的不断进步和研究的不断深入,我国关于海洋的研究已由浅海逐步向深海发展,不断取得新的发现和认知。自2014年4月起,中国科学院海洋研究所依托先进的"科学"号海洋科学综合考察船,搭载"发现"号水下机器人（remotelyoperated vehicle,ROV）,先后对冲绳海槽热液区、南海冷泉区、雅浦海山区以及马努斯热液区等深海区域进行了综合性科学考查,采集到了大量深海腹足纲（Gastropoda）标本,其中有一些为未经发现和描述的新种,极大地推动了我国关于深海软体动物物种多样性研究,实现了深海环境和软体动物资源的新认知。本文对近年来从深海采集到的腹足类标本进行了整理分类,对其中的11属13种进行描述,并对深海特殊环境中腹足纲物种多样性进行了总结,对中国软体动物腹足纲从近海至深海的分类现状进行研究论述。  相似文献   

珍贝—黄岩海山链热-重力均衡动态调节机制          下载免费PDF全文

于磊  张健  陈石  董淼  徐长仪 《地震学报》2015,37(4):565-574

珍贝—黄岩海山链作为我国南海的残留扩张中心, 对其研究具有重要的科学意义. 本文运用均衡学方法, 通过重力异常数据反演了过珍贝—黄岩海山链剖面的地壳界面变化, 同时计算了岩石圈热结构状态, 在此基础上建立了珍贝—黄岩海山链的岩石圈地温结构模型. 通过均衡分析方法, 对剖面上测点的海底地形数据进行了热均衡和重力均衡分析, 得到了热均衡和重力均衡形变量. 结果表明, 在珍贝—黄岩海山链高热流区域, 热均衡作用可以产生最大约0.55 km的形变, 其重力均衡形变范围为0.77—1.89 km. 热均衡通过改变海底地形和地壳物质密度不断作用于重力均衡, 重力又反过来作用于热均衡, 形成了热均衡-重力均衡动态调节机制.   相似文献