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1.
西北印度洋中脊玄武岩源区地幔特征 总被引：1，自引：0，他引：1
利用全球岩石地球化学数据库(Pet DB)中有关卡尔斯伯格洋脊(CR)、北中印度洋脊(NCIR)及南中印度洋脊(SCIR)玄武岩的微量元素及同位素组成数据,分析了玄武岩的元素地球化学特征及其沿脊轴的变化,旨在探讨玄武岩源区地幔的(不)均一性及岩浆作用过程的差异。初步研究结果表明:CR、NCIR及SCIR玄武岩组成相近,仅在个别脊段表现有微量稀土元素和同位素组成上的差异,玄武岩整体与N-MORB组成特征相近,与先前通常认为的典型印度洋中脊玄武岩不同。玄武质岩浆主要源自尖晶石二辉橄榄岩地幔的熔融,岩浆源区主要由两个地幔端元构成,即以亏损型地幔(DMM)为主(69%),其次为富集型地幔(EMⅡ,27%)。富集组分可能源自古老陆壳物质的混染。自CR经NCIR到SCIR整个印度洋中脊西北分支玄武岩的Sr、Nd及Pb同位素组成表现出均一性,表明岩浆源区地幔组成相近。在SCIR 19°S附近脊段岩浆源区地幔存在有不均一性,有EMⅡ型地幔端元混入的迹象。在CR 3.5°N附近脊段,玄武岩明显富集K、Ba、La及U等微量元素,但由于缺少同位素数据,源区地幔特征有待进一步研究。在上述研究成果的基础上,提出了该区大比例尺的调查填图及密集采样和精细室内分析是CR深入研究的基础,同时加强Sr、Nd、Pb及Re、Os、Be等同位素分析测试,可提供揭示CR地幔不均一性的可靠依据,而厘清印度洋型地幔对CR的影响程度则有助于深入认识地幔不均一性的成因及地幔动力学过程。 相似文献
2.
《海洋地质与第四纪地质》2014,(5)
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。 相似文献
3.
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
4.
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。 相似文献
5.
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。 相似文献
6.
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
7.
《海洋地质与第四纪地质》2017,(1)
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。 相似文献
8.
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;SWIR区玄武岩都起源于上地幔,SWIR玄武岩则明显向EMⅡ端元偏移。SWIR玄武岩地幔源区相对最为富集,可能为DM和EMⅡ的混合源区,存在少量的陆壳成分。研究区玄武质岩浆起源深度为尖晶石橄榄岩区域处于中度还原环境下,经历了明显的橄榄石+单斜辉石+斜长石的分离结晶。 相似文献
9.
西太平洋俯冲带是世界上最典型、最活跃的俯冲带,分布众多的海沟-岛弧-弧后盆地（沟弧盆）系统。马里亚纳俯冲带是典型的洋-洋俯冲带,而马里亚纳海槽作为马里亚纳俯冲带的重要构造单元,是研究不受陆壳物质影响的俯冲作用的理想区域。前人对马里亚纳海槽岩浆地幔源区性状、俯冲组分的影响、岩浆演化等进行了详细研究。结果表明：（1）马里亚纳海槽岩浆源区主要为亏损地幔,岩性主要为橄榄岩,且不同区段具有不一致的地幔部分熔融程度;（2）不同区段受到来自蚀变洋壳及沉积物的俯冲组分的影响程度也不同,并由此影响了不同区段的地幔熔融程度和初始岩浆成分;（3）俯冲组分的影响自中段向南北两段逐渐加强,中段主要受到来自沉积物熔体的影响,南、北段受到板片释放的含水流体的影响则更为明显;（4）不同区段甚至同一区段的岩浆在演化过程中,经历了橄榄石、辉石、斜长石等斑晶矿物的差异性分离结晶过程,这也很好地解释了该区丰富的岩石类型和玄武质岩石的不同矿物组合特征。以上研究很好地促进了对马里亚纳海槽岩浆作用过程的认识,也深化了对俯冲带构造-岩浆作用的理解。 相似文献
10.
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
11.
We present new major element, ICP-MS trace element, and Sr–Nd–Pb isotope data of basalts from four locations along the Carlsberg Ridge (CR), northern Indian Ocean. The basalts are low-K tholeiites with 7.52–9.51 wt% MgO, 49.40–50.60 wt% SiO2, 0.09–0.27 wt% K2O, 2.55–2.90 wt% Na2O, and 0.60–0.68 Mg#. Trace element contents of the basalts show characteristics similar to those of average normal MORB, such as LREE depleted patterns with (La/Sm)N ratio of 0.55–0.69; however, some samples are enriched in large-ion lithophile elements such as K and Rb, suggesting probable modification of the mantle source. Poor correlations between the compatible elements [e.g. Ni, Cr, and Sr (related to olivine, clinopyroxene and plagioclase, respectively)] and the incompatible elements (e.g. Zr and Y), and positive correlations in the Zr versus Zr/Y and Nb versus Nb/Y plots suggest a magmatic evolution controlled mainly by mantle melting rather than fractional crystallization. Our results extend the CR basalt range to higher radiogenic Pb isotopes and lower 143Nd/144Nd. These basalts and basalts from the northern Indian Ocean Ridge show lower 143Nd/144Nd and higher 87Sr/86Sr values than those of the depleted mantle (DM), defining a trend towards pelagic sediment composition. The Pb isotopic ratios of basalts from CR 3–4°N lie along the compositional mixing lines between the DM and the upper continental crust. However, the low radiogenic Pb of basalts from CR 9–10°N lie on the mixing line between the DM and lower continental crust. Since the Pb isotopic ratio of MORB would decrease if the source mantle was contaminated by continental lithospheric mantle, we suggest that CR contains continental lithospheric material, resulting in heterogeneous mantle beneath different ridge segments. The continental lithospheric material was introduced into the asthenosphere before or during the breakup of the Gondwana. These results support the long-term preservation of continental material in the oceanic mantle which would significantly influence the isotopic anomaly of the Indian Ocean MORB. 相似文献
12.
白垩纪以来太平洋上地幔组成和温度变化 总被引：1，自引：0，他引：1
张国良 《海洋学报(英文版)》2016,35(4):19-25
The geological evolution of the Earth during the mid-Cretaceous were shown to be anomalous, e.g., the pause of the geomagnetic field, the global sea level rise, and increased intra-plate volcanic activities, which could be attributed to deep mantle processes. As the anomalous volcanic activities occurred mainly in the Cretaceous Pacific, here we use basalt chemical compositions from the oceanic drilling(DSDP/ODP/IODP) sites to investigate their mantle sources and melting conditions. Based on locations relative to the Pacific plateaus, we classified these sites as oceanic plateau basalts, normal mid-ocean ridge basalts, and near-plateau seafloor basalts. This study shows that those normal mid-ocean ridge basalts formed during mid-Cretaceous are broadly similar in average Na8, La/Sm and Sm/Yb ratios and Sr-Nd isotopic compositions to modern Pacific spreading ridge(the East Pacific Rise). The Ontong Java plateau(125–90 Ma) basalts have distinctly lower Na8 and143Nd/144 Nd, and higher La/Sm and 87Sr/86 Sr than normal seafloor basalts, whereas those for the near-plateau seafloor basalts are similar to the plateau basalts, indicating influences from the Ontong Java mantle source. The super mantle plume activity that might have formed the Ontong Java plateau influenced the mantle source of the simultaneously formed large areas of seafloor basalts. Based on the chemical data from normal seafloor basalts, I propose that the mantle compositions and melting conditions of the normal mid-ocean ridges during the Cretaceous are similar to the fast spreading East Pacific Rise. Slight variations of mid-Cretaceous normal seafloor basalts in melting conditions could be related to the local mantle source and spreading rate. 相似文献
13.
对采自太平洋洋中脊(277组)、印度洋洋中脊(159组)、马里亚纳海槽(53组)、马里亚纳岛弧(39组)、中南劳海盆(72组)共600组玄武岩数据进行了独立成分分析,从Sr-Nd-Pb五维同位素比值空间提取出占样本方差99%的3个独立成分(IC1,IC2,IC3),并利用这3个独立成分(ICs)与微量元素比值之间的相关性来讨论独立成分的起源。分析结果表明:IC1可以将马里亚纳海槽玄武岩与太平洋洋中脊及马里亚纳岛弧玄武岩区分,并且IC1值与(La/Sm)N比值呈正相关。IC2可以将马里亚纳海槽和马里亚纳岛弧玄武岩区分,而且IC2值与Ba/Th比值呈正相关;IC3可以将弧后盆地和洋中脊玄武岩区分,同时IC3值与Th/Nb呈负相关。分析独立成分的统计特征和微量元素比值特征可知,IC1与印度洋型MORB地幔的富集组分相关,IC2与太平洋板块俯冲产生的含水流体相关,IC3与再循环俯冲沉积物熔体相关。根据ICs地理分布特点,我们认为:1)马里亚纳海槽北部比南部受到更多印度洋型MORB地幔富集组分的影响,表明印度洋型MORB地幔可能从北部置换太平洋型MORB地幔;2)海槽北部地幔源区则是受到再循环沉积物熔体的影响较大,而中部和南部地幔源区可能受到更多俯冲流体的影响。 相似文献
14.
超慢速扩张洋中脊具有不同于其他扩张速率洋中脊的特征，表现为剧烈变化的洋壳厚度和典型的非岩浆段。本文对前人研究的洋中脊岩浆形成关键因素和迁移聚集模式进行综合分析，结合实际地球物理和地球化学的观测数据，探讨了超慢速扩张洋中脊岩浆从地幔源区形成、迁移汇聚、形成洋壳的整个地质过程，进一步指出了影响洋壳结构的关键控制因素。研究结果表明，超慢速扩张洋中脊沿轴洋壳厚度的变化受岩浆补给量和迁移汇聚的共同制约。其中，岩浆补给量受控于洋中脊的地幔潜热、地幔成分和扩张速率的变化；岩浆迁移和汇聚过程则与超慢速扩张洋中脊密集的分段特征和阻渗层的空间结构密切相关。 相似文献
15.
西南印度洋中脊是典型的慢速扩张洋中脊之一。对采自西南印度洋中脊50°E附近的7件玄武岩和蛇纹石化橄榄岩样品所作的分析表明,基性玄武岩类SiO2含量为43.72%～48.40%,TiO2含量较少,为1.14%～1.52%;MgO含量为5.96%～10.98%;TFe2O3含量为4.55%～5.2%;Mg#值为0.53～0.64,里特曼指数σ为2.34～20.10。微量元素Zr/Nb和Y/Nb比值为显示N-MORB的性质,但是其他微量元素的比值(Ba/Nb,Ba/Th,La/Nb,Nb/U,Nb/Pb)均不显示正常洋中脊玄武岩的特征,微量元素原始地幔标准化蛛网图显示强烈富集K和Pb,亏损Nb,稀土元素显示较为平缓的分配模式。超基性蛇纹石化橄榄岩的主量元素特征为SiO2为38.91～45.49;TiO2含量为0.02～0.28;MgO含量很高,为36.87～40.61,TFe2O3含量为2.82～3.91,Mg#值为0.92～0.94。微量元素中Ni,Cr的含量很高,原始地幔标准化蛛网图显示橄榄岩强烈富集K和Pb,Ba,Th,La,Ce,Ti中等程度富集,而亏损Nb,Sr。稀土元素总量较低,标准化曲线显示轻稀土元素富集模式。结合地球化学特征及前人研究资料分析认为,西南印度洋中脊的基性岩和超基性岩属同源性质,其原始地幔物质可能为部分正常洋中脊亏损地幔混染了陆壳或远洋沉积物的结果。 相似文献
16.
Ling Chen Limei Tang Jichao Yang Xiaohu Li Wei Wang Fengyou Chu Jie Zhang 《海洋学报(英文版)》2021,40(11):147-161
We present major and trace element data of lava recovered from the northern Yap Trench in the western Pacific and discuss their petrogenesis and tectonic implications within the framework of interactions between the Caroline Ridge and Yap Trench. Rocks were collected from both landward and seaward trench slopes and exhibited geochemical characteristics similar to backarc basin basalt (BABB) and mid-ocean ridge basalt (MORB), including high Fe content, tholeiitic affinity, high TiO2 value at a given FeOT/MgO ratio, Ti/V ratio between 20 and 50, low Ba/Nb ratio and Th/Nb ratio, and trace element patterns commonly displayed by BABB and MORB, which are distinct from arc lava. These rocks seem to have been generated during mantle upwelling and decompression melting at a spreading center. However, compared with typical forearc lava produced by seafloor spreading in the Mariana forearc region, such as the early Eocene forearc basalts and late Neogene forearc lava in the southernmost Mariana Trench, the Yap Trench lava is derived from a more fertile mantle and feature a more minor subduction component; thus, they cannot be the products of forearc mantle decompression melting. We suggest that the landward slope lava represents backarc basin crust that was overthrust onto the forearc lithosphere during the collision of the Caroline Ridge with the Yap Trench (20–25 Ma), which played a key role in the evolution of the Yap subduction system. Moreover, the seaward slope lava represents the subduction plate crust that accreted onto the deep trench during the collision. This collision event resulted in the cessation of Yap Arc magmatism; thus, the Yap Trench volcanic rocks (<25 Ma) previously suggested to be arc magma products may actually represent the nascent island arc lava with a lower subduction component than in the mature Mariana Arc lava. 相似文献
17.
冲绳海槽中部伊平屋脊火山岩地球化学和Sr-Nd-Pb同位素组成：对岩石成因和地幔源区的指示 总被引：1，自引：0，他引：1
As an active back-arc basin, the Okinawa Trough is located in the southeastern region of the East China Sea shelf and is strongly influenced by the subduction of the Philippine Sea Plate. Major element, trace element and Sr-NdPb isotopic composition data are presented for volcanic rocks from the Iheya Ridge(IR), the middle Okinawa Trough. The IR rocks record large variations in major elements and range from basalts to rhyolites. Similar trace element distribution characteristics together with small variations in ~(87)Sr/~(86)Sr(0.703 862–0.704 884), ~(144)Nd/~(143)Nd(0.512 763–0.512 880) and Pb isotopic ratios, demonstrate that the IR rocks are derived from a similar magma source. The fractional crystallization of olivine, clinopyroxene, plagioclase, and amphibole, as well as accessory minerals, can reasonably explain the compositional variations of these IR rocks. The simulations suggest that approximately 60% and 75% fractionation of an evolved basaltic magma can produce trace element compositions similar to those of the intermediate rocks and acid rocks, respectively. The analysis of their Sr-Nd-Pb isotopic content ratios suggest that the source of the rocks from the IR is close to the depleted mantle(DM) but extends to the enriched mantle(EMII), indicating that the mantle source of these rocks is a mixture between the DM and EMII end members. The simulations show that the source of the IR volcanic rocks can be best interpreted as the result of the mixing of approximately 0.8%–2.0% subduction sediment components and 98.0%–99.2% mantlederived melts. 相似文献
18.
Pb and other ore metals in modern seafloor tectonic environments: Evidence from melt inclusions 总被引：1，自引：0，他引：1
Many modern seafloor tectonic environments are host to hydrothermal systems and associated polymetallic sulfide deposits. Metal transport and precipitation are controlled by magmatic processes such as pre-eruptive degassing and the hydrothermal cycle. The original availability of Pb and other ore metals in a given setting is dependent on concentrations in the original magmatic source or additional enrichment processes. We have examined the Pb budget of melt inclusions from nine modern seafloor settings representing back-arcs, mid-ocean ridges and seamounts. Melt inclusions provide information on the characteristics of parental magmas, including insights into metal budgets. Trace element data in melt inclusions hosted in plagioclase, olivine and pyroxene were obtained by laser-ablation inductively-coupled mass-spectrometry.Results from back-arcs emphasize the impact of slab-subduction and dehydration processes on the chemical characteristics of generated magmas. Volatile- and fluid-mobile element-rich melt inclusions at Manus basin and Okinawa trough reflect a robust contribution of elements from the subducting slab as evidenced by relatively low Ce/Pb ratios. At Bransfield strait, on the other hand, melt inclusions are volatile poor, and fluid-mobile element ratios are similar to mid-ocean ridge values indicating little or no contribution from the slab. High Cu concentrations at Manus basin and Okinawa trough can be explained by fluxing of ferric iron from the subducting slab benefiting the production of sulfate over sulfide.Metal budgets for seamounts located on and nearby the axis of mid-ocean ridge segments appear to be independent of any input of mantle plume material. Results from the southern Explorer ridge (strong lower mantle influence, transitional- and enriched-MORBs), Pito and Axial seamounts (moderate lower mantle influence, transitional-MORBs) and a Foundation near-ridge seamount (little to no mantle influence, normal-MORB) show that, despite similar tectonic environments and varying contributions of mantle plume material, Cu, Zn and Pb values do not vary significantly between the enriched and non-enriched magma components of a given setting. 相似文献