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1.
Ferromanganese(Fe-Mn) crusts are potential archives of the Cu and Zn isotope compositions of seawater through time. In this study, the Cu and Zn isotopes of the top surface of 28 Fe-Mn crusts and 2 Fe-Mn nodules were analysed by MC-ICP-MS using combined sample-standard bracketing for mass bias correction. The Zn isotope compositions of the top surface of Fe-Mn crusts are in the range of 0.71‰ to 1.08‰, with a mean δ~(66) Zn value of 0.94‰±0.21‰(2 SD, n=28). The δ~(65) Cu values of the top surface of Fe-Mn crusts range from 0.33‰ to0.73‰, with a mean value of 0.58‰±0.20‰(2 SD, n=28). The Cu isotope compositions of Fe-Mn crusts are isotopically lighter than that of dissolved Cu in deep seawater(0.58‰ vs. 0.9‰). In contrast, the δ~(66) Zn values of Fe-Mn crusts appear to be isotopically heavy compared to deep seawater(0.94‰±0.21‰ vs. 0.51‰±0.14‰). The isotope fractionation between Fe-Mn crusts and seawater is attributed to equilibrium partitioning between the sorption to crusts and the organic-ligand-bound Cu and Zn in seawater. The Cu and Zn isotopes in the top surface of Fe-Mn crusts are not a direct reflection of the Cu and Zn isotopes, but a function of Cu and Zn isotopes in modern seawater. This study proposes that Fe-Mn crusts have the potential to be archives for paleoceanography through Cu and Zn isotope analysis. 相似文献
2.
ZHONG Yi CHEN Zhong GONZALEZ Francisco Javier ZHENG Xufeng LI Gang LUO Yun MO Aibin XU Antao WANG Shuhong 《海洋学报(英文版)》2018,37(7):41-54
Ferromanganese nodules and crusts contain relatively high concentration of rare earth elements(REE) and yttrium(REY),with a growing interest in exploitation as an alternative to land-based REY resources.On the basis of comprehensive geochemical approach,the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed.The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity.Total REY contents range from 69.1×10~(–6) to 2 919.4×10~(–6),with an average value of 1 459.5×10~(–6).Especially,the enrichment rate of Ce content is high,accounting for almost 60% of the total REY.This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts.Moreover,the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin.Finally,Light REE(LREE) and heavy REE(HREE) oxides of the ferromanganese deposits in the study area can be classified into four grades: non-enriched type,weakly enriched type,enriched type,and extremely enriched type.According to the classification criteria of rare earth resources,the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals. 相似文献
3.
Adsorption kinetics of the interaction between Pt, Pd and Rh(defined here as platinum group elements, PGEs)ions and macromolecular organic compounds(MOCs, 10 kDa), including humic acid, carrageenan and bovine serum albumin, and different cutoff fractions of natural organic matter(1 kDa and 3 kDa) obtained from seawater using centrifugal ultrafiltration devices were investigated. For a given element, all the adsorption kinetics did not reach equilibrium except the interaction between Pt and 1 kDa cutoff, and between Pd and humic acid.For all the tested MOCs, the adsorption kinetics could be divided into two stages, a rapid adsorption process in the first 8 h and the desorption stage after the first 8 h until the equilibrium. The change trend of partition coefficient(log_(10)K_d) values with experiment time was consistent with that of the kinetic curves. However, in the interaction between PGE ions and natural dissolved organic matter(NDOM), an obvious difference in the change trends of log_(10)K_d and kinetic curves was observed. It indicated that the partition behavior of PGE ions interacting with NDOM in seawater was a combined effect of different organic constituents. The adsorption and log_(10)K_d of PGEs in the 1 kDa NDOM fraction were higher and more stable than those in the 3 kDa NDOM fraction. The results also indicated that the 1–3 kDa NDOM may dominate the interaction between PGEs ions and NDOM. Moreover, no kinetic model could perfectly simulate the adsorption process. It indicated that the colloidal struction and morphology of MOCs or NDOM in seawater might be inhomogeneous. Hence, the interaction between PGE ions and organic matter in seawater was a complicated process and needs further research. 相似文献
4.
Serpentinites, which contain up to 13 wt% of water, are important reservoirs for chemical recycling in subduction zones. In the past two decades, forearc mantle serpentinites were identified in different locations around the world. Here, we present petrology and whole rock chemistry of ultramafic and mafic rocks dredged from the Hahajima Seamount, which is located 24–40 km west to the junction of the Izu-Bonin Trench and the Mariana Trench. Nearly all the collected samples are extensively hydrated, and olivine grains in ultramafic rocks are replaced by serpentine minerals, with only one sample preserving remaining trace of orthopyroxene. Our new results show that the Hahajima serpentinized peridotite samples are all MgO-rich(~42 wt%), but have low contents in Al_2O_3, CaO, rare earth and high field strength elements, which is consistent with the overall depleted character of their mantle protoliths. Model calculations indicate that these Hahajima peridotite samples were derived from 10%–25% partial melting of the presumed fertile mantle source, which is generally lower than those of peridotites from Torishima Forearc Seamount, Conical Seamount and South Chamorro Seamount(mostly25%). All the serpentinites from these four forearc seamounts show strong enrichment in fluid-mobile and lithophile elements(Li, Sr, Pb and U). In details, Hahajima Seamount serpentinites do not have obvious enrichment in Cs and Rb, and display remarkably high abundances of U. These observations indicate that the serpentinization of Hahajima peridotites occurred by addition of seawater or low temperature seawater-derived hydrothermal fluid, without or with little contribution from slab-derived fluids. The geochemical signature of serpentinites from Hahajima Seamount could be interpreted as the result of the combination of extensive partial melting and subsequent percolation of seawater through the mantle wedge. 相似文献
5.
Rare earth elements-rich phase and enriching mechanism in sediments from CC area, the Pacific Ocean 总被引:1,自引:0,他引:1
Compared to North American shale composition (NASC),REE contents of sediments from the CC area in the Pacific Ocean are obviously high except that cerium has equal content to that of NASC.Three-valence rare earth elements were completely enriched in phosphate-phase and cerium in iron-phase.Rare earth elements in the sediments were originally derived from seawater.During lithigenic and minerogenic processes of metalliferous nodules,three-valence rare earth elements in sediments mobilized and incorporated into sediments as authigenous biogenic-apatite,while cerium had change from Ce3+ to Ce4+ and directly precipitated from seawater and entered metalliferous nodules and caused Ceanomalies in REE pattern in sediments. 相似文献
6.
The contents of Fe, Mn, Cu, Co, Ni, Pb and Zn in the seaiment associated with manganese nodules from the Northern Central Pacific Ocean and in their acid-soluble fractions were determined and correlations among the elements and between the trace metals and environmental parameters were discussed. It has been found that the contents of Mn, Cu and Ni in the sediment are one order of magnitude higher than those in the common sediment. As shown in the manganese nodules, they may mainly derive from seabed. The contents of all trace metals in the sediment are obviously governed by Fe-and Mn-oxides, organic matter, seawater depth, particle size and Eh. Multi-element correlation equations were developed for all trace metals. The trace metals in acid-soluble fraction of the sediment were also much higher than ihose of common sediment and negatively correlated with water depth, implying the possible influence of carbonate speciation. 相似文献
7.
In the present paper, iodine(I), iron(Fe), manganese(Mn), cobalt(Co), phosphorus(P) and calcium(Ca)contents in three ferromanganese crusts from the Pacific Ocean are measured by spectrophotometric method and inductively coupled plasma atomic emission spectrometers(ICP-AES) to investigate the contents and distribution of iodine in ferromanganese crusts. The results show that iodine contents in three crusts vary between 27.1 and 836 mg/kg, with an average of 172 mg/kg, and the profile of iodine in the three crusts all exhibits a two-stage distribution zone: a young non-phosphatized zone and an old phosphatized zone that is rich in I, P and Ca. The iodine content ratios of old to young zone in MP5D44, CXD62–1 and CXD08–1 are 2.3, 3.4 and 13.7, respectively.The boundary depths of two-stage zone in MP5D44, CXD62–1 and CXD08–1 locate at 4.0 cm, 2.5 cm and 3.75 cm,respectively, and the time of iodine mutation in three crusts ranges from 17–37 Ma derived from 129 I dating and Co empirical formula, which is consistent with the times of Cenozoic phosphatization events. The present study shows that the intensity of phosphatization is the main responsible for the distribution pattern of iodine in the crusts on the basis of the correlation analysis. Consequently, iodine is a sensitive indicator for phosphatization. 相似文献
8.
On the basis of the satellite maps of sea level anomaly(MSLA) data and in situ tidal gauge sea level data,correlation analysis and empirical mode decomposition(EMD) are employed to investigate the applicability of MSLA data,sea level correlation,long-term sea level variability(SLV) trend,sea level rise(SLR) rate and its geographic distribution in the South China Sea(SCS).The findings show that for Dongfang Station,Haikou Station,Shanwei Station and Zhapo Station,the minimum correlation coefficient between the closest MSLA grid point and tidal station is 0.61.This suggests that the satellite altimeter MSLA data are effective to observe the coastal SLV in the SCS.On the monthly scale,coastal SLV in the western and northern part of SCS are highly associated with coastal currents.On the seasonal scale,SLV of the coastal area in the western part of the SCS is still strongly influenced by the coastal current system in summer and winter.The Pacific change can affect the SCS mainly in winter rather than summer and the affected area mostly concentrated in the northeastern and eastern parts of the SCS.Overall,the average SLR in the SCS is 90.8 mm with a rising rate of(5.0±0.4) mm/a during1993–2010.The SLR rate from the southern Luzon Strait through the Huangyan Seamount area to the Xisha Islands area is higher than that of other areas of the SCS. 相似文献
9.
Si-Fe-Mn-oxyhydroxides dredged at the PACMANUS(Papua New Guinea–Australia–Canada–Manus)hydrothermal field, Eastern Manus Basin, have 87Sr/86Sr=0.708 079–0.708 581; εNd=5.149 833–6.534 826;208Pb/204Pb=38.245–38.440; 207Pb/204Pb=15.503–15.560; 206Pb/204Pb=18.682–18.783. 87Sr/86 Sr isotope ratios are relatively homogeneous and close to the value of the surrounding seawater(0.709 16). The content of Sr in the samples contributed by seawater was estimated to be 76.7%–83.1% of total amount. The mixing temperature of hydrothermal fluids and seawater were ranging from 53.2°C to 72.2°C and the hydrothermal activities were unstable when the samples precipitated. The εNd values of all the samples are positive, which differ from the values of ferromanganese nodules(crusts) with hydrogenic origin. Nd was mainly derived from substrate rocks leached by hydrothermal circulation and preserved the hydrothermal signature. Pb isotopic compositions of most samples show minor variability except Sample #9–2 that has relatively high values of Pb isotopes. The Pb may be derived from the Eastern Manus Basin rocks leached by the hydrothermal fluid. The slightly lower 208Pb/204 Pb and207Pb/204 Pb values of the samples indicated that the hydrothermal circulation in PACMANUS was not entire and sufficient, or that hydrothermal circulation had transient changes in the past. Si-Fe-Mn-oxyhydroxides in the samples preserved the heterogeneities of local rocks. 相似文献
10.
The contents of Mn, Fe, Cu, Co, Ni, Pb and Zn in manganese nodules and associated pelagic sediment from the Northern Central Pacific have been measured, and the correlations between the elements of the nodules and between the chemical composition and the sedimentary environments have been analyzed. It has been found that Cu, Ni and Zn are preferentially enriched in the Mn-oxide phases while Co and Pb in the Fe-oxide phases of the nodules. The elements within the same phase are positively correlated and the elements within different phases are negatively correlated. It is concluded that the elements in the Fe-oxide phase may have directly deposited from seawater while Mn-oxide phase elements are mainly derived from interstitial waters. 相似文献
11.
全球三大洋海山钴结壳资源量估算 总被引:8,自引:0,他引:8
钴结壳具有Co、Ni、Cu和Mn及其他金属的潜在矿产资源和储存在结壳层中古环境信息的双重意义。与深海多金属结核和热液硫化物矿床相比,具有较高Co、Ni和Pt含量的海山钴结壳有可能成为商业勘探的潜在目标。为合理地估算出全球三大洋海山钴结壳资源量,基于我国西太平洋海山钴结壳拖网采样调查资料和对太平洋海山钴结壳资源分布规律和钴结壳矿区圈定参数指标的深入研究,按海山不同高度、不同洋壳年龄赋予不同结壳厚度,进而计算出全球三大洋海山钴结壳分布面积为3 039 452.14km2和干结壳资源量为(1 081.166 1~2 162.332 2)×108 t。太平洋海山钴结壳分布面积为2 123 087.12km2和干结壳资源量为(513.244~1 026.488)×108 t,大西洋海山钴结壳分布面积为512 509.74km2和干结壳资源量为(116.503 2~233.006 4)×108 t,印度洋海山钴结壳分布面积为403 855.28km2和干结壳资源量为(81.484 9~162.969 8)×108 t。三大洋海山钴结壳的Mn、Co、Ni和Cu金属量分别为(138.848 0~277.696 0)×108 t,(3.967 6~7.935 2)×108 t、(2.793 6~5.587 2)×108 t和(0.825 1~1.650 2)×108 t。根据钴结壳的Co含量、Co通量和厚度相关分析,所赋予的钴结壳厚度占理论推测厚度的6.10%~12.20%,这与Ku等得出"钴结壳生长时间约占其整个生命史4%"的认识非常相近。三大洋海山钴结壳实测厚度与赋值厚度对比分析表明,太平洋海山钴结壳赋值厚度平均值为1.87cm,实测厚度平均值为1.77cm,相对误差为5.35%,大西洋和印度洋相对误差分别为18.18%和23.23%。研究数据表明按海山高度和洋壳年龄所赋的钴结壳厚度基本合理,估算出的钴结壳资源量基本可靠。本文首次估算出三大洋海山钴结壳资源量,为整个海盆和三大洋海山钴结壳资源量估算提供了新方法。 相似文献
12.
太平洋海山富钴结壳中铂族元素赋存状态与富集机理 总被引:2,自引:1,他引:1
通过选择性化学提取法,对太平洋采薇海山富钴结壳样品中铂族元素进行分级提取实验,利用电感耦合等离子体质谱仪(ICP-MS)测定了铂族元素含量。赋存状态结果显示,富钴结壳中铂族元素在各个化学相态中富集比例从大到小依次为:铁氧化物相、残渣态、锰氧化物相、碳酸盐相、吸附态,未磷酸盐化新壳层和磷酸盐化老壳层中铂族元素都主要赋存于铁氧化物相中,其富集比例为59.26%~82.19%,残渣态中磷酸盐对铂族元素具有一定的富集能力,其富集比例为17.23%~35.37%。不同类型地质体中铂族元素的赋存状态结果,也证实了富钴结壳和海山结核中铂族元素富集主要受到铁氧化物相和残渣态的影响。太平洋海山富钴结壳中铂族元素的富集机理推测为铁氧/氢氧化物胶体粒子的吸附作用,使海水中PtC l24-离子被吸附到铁氧化物相中,从而使富钴结壳中铂族元素富集。 相似文献
13.
南海多金属结壳(核)铁锰矿物/海水界面效应与成矿元素的富集 总被引:1,自引:0,他引:1
海底铁锰结壳和结核是重要的海底矿产资源,蕴含着丰富的金属元素并且具有巨大的经济价值。本文主要以南海多金属结壳(核)为研究对象,采用X射线粉晶衍射(XRD)、激光拉曼光谱、红外光谱分析(FTIR)以及X射线光电子能谱对铁锰矿物的矿物学和谱学特征进行了系统的分析和研究。粉晶衍射和拉曼光谱分析结果表明,南海多金属结壳的矿物组成为水羟锰矿、石英和长石,结核的矿物组成为钡镁锰矿、水羟锰矿、石英和长石,铁相矿物均为无定形铁氧化物/氢氧化物,并且锰相矿物和铁相矿物的结晶程度均较差。红外光谱分析结果显示多金属结核和结壳中的铁锰矿物具有大量表面羟基,这些含质子表面羟基官能团,可为海水中各成矿元素的络合提供丰富的活性位点。XPS分析表明多金属结核和结壳中铁锰矿物表面以Fe、Mn和O元素为主,其中Fe呈正三价态,Mn以正四、正三价为主,可能还含有少部分正二价态。对比南海多金属结壳(核)与太平海山结壳,南海多金属结壳(核)具有更为显著的表面羟基氧(-OH)含量,而太平洋海山结壳则以晶格氧(O2-)为主,表明太平洋海山结壳铁锰矿物结晶程度较南海多金属结壳(核)高。综合研究表明,在海底铁锰结壳和结核中(氢)氧化锰/铁矿物与海水之间界面效应对金属离子的富集机理主要有:(1)金属离子与矿物表面羟基进行络合反应,形成以配位键相连的羟基络合物,或与表面的质子交换生成稳定的内层络合物;(2)矿物的带电表面与金属离子通过静电作用形成双电层,生成外层络合物;(3)金属离子与矿物结构中的Mn、Fe离子同晶置换而成为结构阳离子。 相似文献
14.
西太平洋麦哲伦海山区是全球重要的铁锰结壳资源分布区,具有丰富的稀土元素资源潜力。本文对采自麦哲伦海山区Kocebu海山的11个铁锰结壳表层样(<1 mm)进行稀土元素地球化学研究,探讨其含量特征、成因和影响稀土元素富集的环境因素。结果表明:Kocebu海山铁锰结壳表层样品ΣREY(Rare earth elements and yttrium)平均含量为1 366 mg/kg,低于前人在麦哲伦海山区其他海山以及邻近的马尔库斯–威克海山区的分析结果;样品轻稀土富集和Ce正异常(平均值为1.45)特征以及稀土元素成因图解、配分曲线和分配系数曲线等均表明该海山结壳属于水成成因;海水中稀土元素含量和溶解氧含量是控制结壳生长的关键环境参数,二者在Kocebu海山所在海区的浅水环境中含量较低;结壳ΣREY含量偏低与采样点水深较浅导致的海水稀土元素含量和溶解氧含量较低密切相关,受碎屑矿物的稀释作用影响较小。在开展铁锰结壳地球化学特征研究和资源勘探评价时应充分考虑采样水深的分布范围,局部水深样品的分析结果可能导致研究结果出现较大偏差。 相似文献
15.
Abstract The morphological features associated with Co-rich manganese deposits, the size variations of nodules, and the occurrence of different substrates have been analyzed, to evaluate the influence of various seabed slope angles on the distribution of these features. The coverage and size of the crusts depend on their surface morphology and seabed topography, resulting in cobble-type, lineated, or step-like outcrops. Small nodules (1–4 cm in diameter) dominate all seabed slopes, with a few locations having nodules ranging from 1 to 8 or 1 to 10 cm. Sediments invariably occur as substrates for nodules and as cover for crusts, their coverage being inversely proportional to that of the nodules and crust outcrops. Steeper seafloor areas have large crust outcrops exposed with no or few nodules and sediments associated with them. The intermediate slopes have a combination of nodules, sediments, and crusts in various proportions, depending on topography and gradient. Large-scale nodule occurrences, followed by sediment fields and crust outcrops on seabed slopes of < 3°, 3–7°, and > 15°, respectively, represent typical morphological distribution zones of the Co-rich manganese deposits on a seamount in the central Pacific Ocean. A transition zone between nodule-dominated fields and large crust outcrops occurs for slopes from 7° to 15°. This detailed study on distribution of Co-rich deposits gives a better understanding for purposes of their exploitation. 相似文献
16.
为探讨富钴结壳铂族元素的来源,以西太平洋采薇海山群富钴结壳样品为研究对象,利用X射线衍射法、等离子体发射光谱法和质谱法,对富钴结壳样品进行了矿物组成、主量元素和铂族元素含量分析。研究表明,富钴结壳的主要结晶矿物为水羟锰矿,次要矿物有石英、斜长石、钾长石和碳氟磷灰石,同时含有大量非晶态铁氧/氢氧化物。富钴结壳中Mn和Fe含量最高,且明显富集铂族元素,铂族总量为142~1 352 ng/g,其中Pt为114~1 268 ng/g,占铂族总量的80%以上。老壳层的铂族元素含量高于新壳层,老壳层发生了磷酸盐化作用。富钴结壳的铂族元素之间发生了分异作用,Pd组(PPGE)含量高于Ir组(IPGE)。铂族元素配分模式显示Pt正异常和Pd负异常,具有Pt富集而Pd亏损特征,推测富钴结壳的铂族元素来源于洋壳蚀变过程中海山玄武岩和海水之间的水−岩反应。富钴结壳的铂族元素与CaO、P2O5、Ba和Cu正相关,推测铂族元素赋存于磷酸盐矿物相中。富钴结壳生长剖面从上到下,由新到老,铂族元素含量呈逐渐增加趋势,海水氧化性环境和高海洋生产力可增进磷酸盐化作用,从而进一步促进了铂族元素的富集。该研究对于揭示富钴结壳铂族元素的来源具有一定的参考价值。 相似文献
17.
Andrea Koschinsky Marc Van Gerven Peter Halbach 《Marine Georesources & Geotechnology》2013,31(4):375-391
Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hydrogenetic crusts from a central Pacific seamount revealed lower concentration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly increased terrigenous input of Fe, Pb, Al, and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crust ages average at 10 My. The old phosphatized crust generation that started to grow about 20 My ago on the Pacific seamounts is not pronounced at the Tropic Seamount. The typical hydrographic and morphological parameters for hyrogenetic crust growth have also been found at the Tropic Seamount, which implies that the Tropic Seamount crusts have developed according to the hydrogenetic growth model. There are no indications of hydrothermal influence. 相似文献
18.
利用等离子体发射光谱法、等离子体质谱法以及相态分析手段,对太平洋徐福海山富钴结壳稀土和铂族元素地球化学特征、赋存状态及富集机制进行研究。结果表明,富钴结壳稀土和铂族元素明显富集,其稀土总量为1 842~2 854 μg/g,铂族总量为144~1 180 ng/g,老壳层中稀土和铂族元素含量明显高于新壳层,这可能与老壳层发生磷酸盐化作用有关。轻稀土元素含量明显高于重稀土元素含量,呈现Ce正异常而Eu无异常,具有明显Ce富集特征。铂族元素之间发生了明显分异作用,PPGE含量明显高于IPGE,表现出明显Pt正异常而Pd负异常,具有明显Pt富集而Pd亏损特征。稀土元素赋存状态显示,新壳层中稀土元素主要赋存于铁氧化物相,其富集比例为65.40%~70.05%,老壳层中稀土元素主要赋存于残渣态,富集比例为62.27%~65.77%,这可能与残渣态中磷酸盐有关。铂族元素赋存状态显示,新壳层和老壳层中铂族元素都主要赋存于铁氧化物相,其富集比例为63.66%~69.51%,残渣态(29.20%~34.68%)对铂族元素也有一定的富集能力。富钴结壳稀土和铂族元素的富集推测为铁氧化物胶体粒子的吸附作用,受海水氧化性环境影响,可溶性Ce3+和Pt2+分别被氧化成不溶性Ce4+和Pt4+,沉淀被吸附到铁氧化物相中,从而造成富钴结壳稀土和铂族元素的富集。 相似文献
19.
西太平洋Lamont海山中新世以来富钴结壳成矿环境的演化 总被引:5,自引:0,他引:5
分析了西太平洋Lamont海山12个站位33个富钴结壳样品的主元素和稀土元素,结果表明,该海山富钴结壳成因类型属于水成成因,并且在形成过程中基本未受到磷酸盐化作用的影响。Lamont海山的一个富钴结壳样品剖面的电子探针数据显示,该海山富钴结壳的成矿环境在新第三纪以来至少存在2个演化阶段:第1阶段,23~15 Ma,富钴结壳中Mn相对富集,成矿环境以富氧贫硅为特征;第2阶段,15~0 Ma,富钴结壳中Fe相对富集,成矿环境以贫氧富硅为特征。成矿环境的氧化能力总体上呈现下降的趋势。联系新生代世界大洋,尤其是西太平洋的地质演化背景,认为引起成矿环境演变的原因主要是西太平洋大洋板块的WNW向漂移和新第三纪以来全球水道开合,造成了Lamont海山所处海区最低含氧带逐渐减薄。 相似文献
20.
The Magellan seamounts began forming as large submarine shield volcanoes south of the equator during the Cretaceous. These
volcanoes formed as a cluster on the small Pacific plate in a period when tectonic stress was absent. Thermal subsidence of
the seafloor led to sinking of these volcanoes and the formation of guyots as the seamounts crossed the equatorial South Pacific
(10–0°S) sequentially and ocean surface temperatures became too high for calcareous organisms to survive. Guyot formation
was completed between about 59 and 45 Ma and the guyots became phosphatized at about 39–34 and 27–21 Ma. Ferromanganese crusts
began formation as proto-crusts on the seamounts and guyots of the Magellan Seamount cluster towards the end of the Cretaceous
up to 55 Ma after the formation of the seamounts themselves. The chemical composition of these crusts evolved over time in
a series of steps in response to changes in global climate and ocean circulation. The great thickness of these crusts (up
to 15–20 cm) reflects their very long period of growth. The high Co contents of the outer parts of the crusts are a consequence
of the increasing deep circulation of the ocean and the resulting deepening of the oxygen minimum zone with time. Growth of
the Co-rich Mn crusts in the Magellan Seamount cluster can be considered to be the culmination of a long journey through time. 相似文献