太平洋铁锰结壳的锶同位素地球化学研究

本文研究中太平洋的翰斯顿岛卡林海山铁锰结壳ＲＤ４－２和东太平洋海盆铁锰结壳５４０５的锶同位素组成特征，并利用铁锰结壳的锶同位素组成与大洋海水锶同位素演化标准曲线对比，推断出结壳生长起始年龄、接三元混合模式，计算玄武质组分和硅铝质组分对锶同位素的贡献。     

太平洋结核结壳中的锶铅同位素关系研究

依据多金属结核、铁锰结壳的记录 ,研究了太平洋海水结核结壳中锶、铅同位素的关系 ,结果表明 ,太平洋海水中锶同位素与铅同位素无明显的相关性。作者认为这是由于太平洋海水中锶、铅的滞留时间相差很大 ,达 4个数量级 ,锶同位素记录了 10 0 0 0 0 a至百万年时间尺度上全球性大洋范围内海水物质来源的变化 ,而铅同位素能在较小的时间尺度上反映局部的大洋海水物质来源的信号 ,是高分辨率的物源示踪剂     

铁锰结壳的铪（Hf）同位素地层学

海水的放射成因同位素组成随时间的变化具有提供大陆风化作用、洋底热液活动、大洋环流的变化以及其与构造和气候事件有关系的信息的潜力。所有主要洋盆中铁锰结壳的Ｓｒ、Ｎｄ和Ｐｂ同位素记录已用来研究海水的长期变化。由于分析困难 ,直到现在Ｈｆ同位素也没有引起人们的关注。在此 ,我们提供了挖掘自中太平洋海山的两个铁锰结壳的第一个高分辨率和精确的Ｈｆ同位素剖面 ,试图限定Ｈｆ同位素在中太平洋深水中的演化。目前海水中的Ｈｆ同位素组成还不得不直接测定 ,但是可以预料 ,由于以下原因Ｈｆ比Ｎｄ同位素组成更加易变。第一 ,由地幔…     

富Co铁锰结壳铂族元素与铼-锇同位素组成及其意义

用ICP－MS测定了太平洋富Co铁锰结壳铂族元素和铼－锇同位素组成。富Co铁锰结壳不仅异常富集铂族元素，而且铂族元素及其它亲铁元素的配发与陨石特征非常相似。铁锰结壳的铼－锇同位素组成明显有别于大陆地壳岩石，和K－T界线沉积物相似，接近陨石值。世界大洋范围内的富Co铁锰结壳均产于远离海底构造热液活动区，几乎不可能受到地幔源热液作用的直接影响。因此，富Co铁锰结壳中的铂族元素可能部分来源于地外物质。     

上新世/更新世之交太平洋经向翻转流演化

随着北半球冰盖的发育,全球气候环境发生了显著变化。太平洋经向翻转流（PMOC）对全球海洋热量分配和大气CO₂在深海的封存起举足轻重的作用,但是关于PMOC与北半球冰盖的形成之间的关系还欠缺研究。本文收集了太平洋海山富钴结壳的Nd同位素记录,通过对比不同区域Nd同位素记录的演化特征,分析风尘输入、水团演化等因素对Nd同位素记录的影响,探讨了太平洋经向翻转流演化及其与全球气候变化之间的关系,认为北太平洋深层水下沉的停滞和亚洲风尘输入增加可能是导致深层水Nd同位素从距今3～4 Ma开始降低的原因。同时,因北太平洋深层水下沉停滞,PMOC改组,使得更多的CO₂在深水封存,从而对全球气候变冷和北半球冰盖形成产生了积极的贡献。     

多金属结核,铁锰结壳的同位素地球化学研究

本文介绍国家大洋专项“八·五”重点项目“深海地质研究”中一级专题“东太平洋海盆多金属结核同位素地球化学研究”（ＤＹ８５－０２－０３－０４）所取得的成果，总结了多金属结核Ｓｒ、Ｐｂ、Ｏ、Ｓｉ、Ｃ同位素地球化学特征，并探讨了铁锰结壳Ｓｒ、Ｐｂ同位素组成特征及其古环境意义．     

80 Ma以来海水Os同位素组成曲线的精细特征:中、西太平洋多金属结壳的记录

80 Ma以来的海水Os同位素标准曲线具有K/T（白垩纪/第三纪）界线低值、E/O（始新世/渐新世）界线低值和中新世“挠曲”3个特征形态，这可以解释为陨击事件或超基性岩风化事件造成的陆、幔源物质供给关系的变化。将海水Os同位素标准曲线与多金属结壳Os同位素组成曲线进行对比，根据形态和取值的贴合程度可以为结壳进行年代厘定。由于取样精度的限制和生长间断的广泛存在，仅以此3个特征比对曲线存在不确定性。本研究综合对比中、西太平洋6块结壳的Os同位素组成曲线，总结出了4种记录在结壳中的海水Os同位素曲线的特征规律：K/T界线之前的“早期异常（波动）”；E/O界线之后曲线上升过程中的“小停顿”；E/O界线之后曲线上升过程末尾的“异常偏高点”；“中新世‘挠曲’错后”至10 Ma左右。这些新的特征形态可作为年代控制点，使得结壳年代框架的厘定可以更准确可靠。这4种特征形态可以初步解释为地质历史时期海洋中、幔源物质的供应关系变化或是看作随着数据的积累而对标准曲线的细化和校正。     

铁锰结壳年代学方法及其应用

铁锰结壳记录了丰富的古海洋和古气候信息,要分析这些信息,必须先确定各壳层的生长年龄。目前主要使用的定年方法有:Be同位素定年、U系同位素定年、Os同位素定年、经验公式法、古地磁地层学方法和古生物地层学方法等。每种定年方法均各有利弊,其中10Be是年龄小于10 Ma结壳的最佳定年方法; U系同位素定年精度高,但定年范围小于0.5 Ma; Os同位素定年时间尺度长,且可以判断沉积间断,但需要有区域的海水Os同位素演化曲线; Co经验公式因为简单易行,是结壳估算年龄最为常用的方法,但该法无法判断沉积间断,在使用时需特别谨慎,应确保经验公式适用于所研究的样品;如果结壳厚度大、生长速率较快且不存在沉积间断,古地磁地层学方法可以快速地进行定年;此外,如果结壳中古生物化石较多,可考虑采用古生物地层学方法。在分析铁锰结壳年代学方法利弊基础上,本文利用U系定年法、古地磁地层学法和经验公式计算法分别对南海铁锰结壳进行定年,通过比较,认为目前铁锰结壳较优的定年方法为古地磁地层学方法。     

中太平洋富钴结壳中生物标志物、有机碳同位素地球化学及其古海洋环境意义

利用2003年大洋DY105-12,14航次在中太平洋海山获取的KXD28富钴结壳样品,采用气相色谱(GC)内标法对该结壳样品的分层样进行了可溶有机质(氯仿沥青“A”)及其族组成(饱和烃、芳烃、非烃)、正构烷烃、类异戊二烯烃的定量分析,并结合总有机碳(TOC)及有机碳同位素(δ¹³C)分析,探讨了结壳样品有机质来源及富钴结壳组成与生长环境之间的关系。结果表明:(1)富钴结壳中有机质生物母源主要为海洋生物和菌藻类,并混有少量陆源物质;有机碳同位素同样也指示了海洋水生生物碳同位素特征;(2)KXD28结壳从底层到最外层有机碳同位素发生了很大变化,结壳中有机碳同位素组成变化与结壳生长过程中的海洋环境气候相符合:富钴结壳生长前期δ¹³C组成由正变负,对应全球气候变冷,南极底层流向太平洋挺进;而富钴结壳生长后期δ¹³C逐渐偏正,与全球气候变暖和南极底层流萎缩相关联。     

太平洋水——沉积物系统氢氧同位素与海洋环境

通过太平洋水、孔隙水和沉积物等的氢氧稳定同位素研究,太平洋不同地区和不同水层所处环境的差异,导致氢氧同位素的组成也不同,海水、孔隙水和沉积物的同位素组成有较大差别。同位素组成表明,大洋底层水反映了南极表层水流的特征,并且受到冰冻效应的影响,故太平洋底层水的来源主要是贫＾１８Ｏ和贫氘的富氧南极流。底层水的氢氧同位素组成表明,中太平洋和东太平洋底部处于富氧环境中,这种环境有利于好气性微生物的发育和繁殖     

Basin-scale seawater lead isotopic character and its geological evolution indicated by Fe-Mn deposits in the SCS

Abstract

The geochemical characteristics and Pb isotope variations in Fe-Mn deposits collected from the South China Sea (SCS) were studied in this paper. The mineralogical and chemical composition data indicate that the deposits are almost all hydrogenetic in origin. Compared with the Fe-Mn deposits in other oceans, the SCS Fe-Mn deposits have a significantly higher Pb content because of higher material supply in addition to a lower growth rate of the deposits. Pb isotope ratios in the surface of the SCS Fe-Mn deposits are relatively uniform, with a characteristic of relatively lower ²⁰⁶Pb/²⁰⁴Pb ratio. The Pb isotopic compositions of the SCS Fe-Mn deposits are controlled by the Pacific Deep Water and local inputs, which include eolian dust from the Asian continent and weathering products from Taiwan, Luzon and SCS submarine volcanic rocks. The continuously increasing ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios along the transect of nodule D581 over the past 3.5?Ma are affected by the stepwise closure of the Luzon Strait that reduced volcanic material supply and the deep current strengthen at the same time.     

First investigations of massive ferromanganese crusts in the NE Atlantic in comparison with hydrogenetic pacific occurrences

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.     

多金属结壳生长间断期与磷酸盐化事件的关系

磷酸盐化的发生会造成多金属结壳主要成矿元素的贫化,总体上抑制结壳的生长。磷酸盐化作用呈幕式在太平洋内发生,已有研究将其发生期次与多金属结壳中的磷酸盐化层位及其P、Ca等元素地球化学特征对应,为结壳的年代厘定提供证据。然而,由于磷酸盐化多次发生且在结壳多个层位中显现,首先需要厘定出较为可靠的多金属结壳年代框架,才能与磷酸盐化事件相互佐证。本研究通过定年范围较大,同时可以识别结壳中存在的生长间断的Co-Os法定年体系,为中、西太平洋6块多金属结壳定年,并参考肉眼识别的磷酸盐化矿化特征和地球化学特征佐证年代框架,同时分析磷酸盐化作用对结壳成矿的影响。39～34 Ma和27～21 Ma的两次大规模磷酸盐化期次全部对应多金属结壳的大规模间断期,而71 Ma、55 Ma和31 Ma等小规模磷酸盐化事件多数可在多金属结壳的层位和地球化学特征中识别,对应P和Ca百分含量的飙升和峰值特征。这一方面证实了磷酸盐化的发生整体抑制了结壳的生长,且具有广泛的影响范围和明确的时代区间,另一方面则佐证了多金属结壳年代框架的准确性。     

LONG-DISTANCE ATMOSPHERIC TRANSPORT OF DUST FROM CHINESE DESERT TO THE NORTH PACIFIC

The Chinese desert is one of the major sources of atmospheric mineral dust transported for a long distance to the North Pacific by the atmospheric circulation. The characteristic of the aerosol in the North Pacific is smilar to that of the aerosol in North China with a considerable concentration of mineral in spring due to the large-scale dust storm occurring in North China. The study of isotope tracer indicates that the concentration of Al is significantly related to 210Pb, suggesting that the mineral aerosol in the North Pacific may origir ate from the desert in Northwest China by using air mass trajectory analysis. About 6-12×106 tons of Chinese desert mineral dust per year would be transported to the North Pacific.     

西太平洋Lamont海山中新世以来富钴结壳成矿环境的演化

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。     

Paleoclimatic changes in southern Africa during the intensification of Northern Hemisphere glaciation: evidence from ODP Leg 175 Site 1085

Pliocene age sediments from Ocean Drilling Program Leg 175, Site 1085-A and B in the Cape Basin were analyzed to investigate the impact of the intensification of Northern Hemisphere glaciation (INHG) on the South Atlantic Benguela Current system from 4 to 2 Ma. Proxies for productivity (concentrations and mass accumulation rates of total organic carbon, carbon to nitrogen ratios, percent calcium carbonate, and percent biogenic silica) as well as weight percent sand (a proxy for preservation or winnowing) peak at 3.2, 3.0, 2.4, and 2.25 Ma. Normative calculations of allied trace and major elemental determinations indicate synchronous increases in productivity peaks, as well as high concentrations and accumulations of terrigenous sediments. Coeval increases in hemipelagic sedimentation and productivity indicators could be the result of enhanced eolian sedimentation resulting from strengthened winds, leading to elevated rates of upwelling and enhanced productivity. However, rapid burial, as indicated by high sedimentation rates, could also enhance preservation. The very high concentrations (>30%) and accumulations (up to 60 g/cm²/kyr) limit the likelihood that eolian sedimentation was the only transport mechanism, invoking an additional fluvial source. Rapid burial by either eolian or fluvial transport links these intervals of enhanced preservation and productivity with continental climate changes resulting from (1) increased winds and/or dust availability due to higher aridity in the Namibia/northern South Africa region; (2) lowered sea-level related to increased ice volume; (3) increased sediment load due to wetter conditions in the continental interior; or (4) some combination. Peaks at 3.2, 2.4 and 2.25 Ma are coincident with maximum precession, suggesting a link between hemipelagic sedimentation and enhanced monsoonal circulation over southern Africa. The Site 1085 sedimentary record during the INHG seems to be controlled by low-latitude processes linked to precession rather than hig-latitude processes.     

晚新生代风尘沉积的稀土元素地球化学特征及其古气候意义

通过西峰巴家咀剖面晚新生代风尘沉积中的红粘土、黄土、古土壤的稀土元素、分布模式、特征参数的研究，并与晚第三纪红色沙漠风成砂、晚第三纪河流相细砂岩、第四纪沙漠风成砂、现代尘暴粉尘、中国黄土以及青藏高原远源西风粉尘进行对比分析，结果表明，晚新生代风尘沉积物均具有轻稀土适度富集、缓右倾斜型、Eu负异常的REE分布模式；晚第三纪红色沙漠是红粘土的主要物源之一；红粘土和典型的风尘物质－现代尘暴粉尘及中国黄土有相似的沙漠物质来源和形成过程，与基岩明显不同，这为红粘土的“风成说”而非“残积说”提供了新的证据。巴家咀红粘土的堆积过程与第四纪黄土相似，东亚季风环流而非西风环流控制着沙漠区粉尘物质的输送。     

晚上新世以来菲律宾海盆XT4孔黏土矿物特征及其古环境意义

菲律宾海是典型风尘汇聚区,菲律宾海远离吕宋岛的深海沉积物是重建构造尺度亚洲风尘演化历史的良好载体。选取菲律宾海盆XT4孔沉积物开展了黏土矿物研究,并结合前人研究成果,在明确该孔黏土矿物来源的基础上,探讨了晚上新世以来亚洲风尘的演化历史及其可能的影响机制。菲律宾海盆XT4孔黏土矿物以伊利石为主,平均含量为39%,蒙脱石含量次之,平均为28%,绿泥石平均含量为18%,高岭石平均含量为15%。XT4孔黏土矿物组成符合亚洲大陆风尘与周边火山岛弧的二端元混合模型特征,其中蒙脱石主要为周边火山岛弧物质贡献,而伊利石、绿泥石和高岭石主要是亚洲风尘贡献。晚上新世以来XT4孔的伊利石/蒙脱石比值表现为阶段性变化,主要反映了北半球高纬冰川的扩张导致亚洲中纬度地区干旱化加剧。此外,东亚夏季风降雨强弱和空间分布的变化也是源区风尘释放的重要环境因子之一。本文结果初步揭示了晚上新世以来中国干旱-半干旱地区的环境演化历程,有助于深入理解多圈层相互作用下的风尘循环及其生物地球化学效应。     

Fine-scale compositional variations in a Co-rich Mn crust from the Marcus-Wake Seamount cluster in the western Pacific based on electron microprobe analysis (EMPA)

The internal structure and composition of a 37-mm-thick Co-rich Mn crust from the Lamont Guyot in the Marcus-Wake Seamount cluster have been studied in detail by means of electron-probe microanalysis (EPMA). 184 point analyses for 16 elements were carried out at an average spacing of 0.20 mm and each point was dated using the Co-geochronometer method. Two types of variation in composition were observed in the crust: long-term trends and short-term erratic variations. The long-term trends were identified using the fifth order polynomial. Mn and Ni were shown to increase in concentration from 23.3 Ma to a maximum at about 20 Ma and then decline steadily to the Present, whereas Fe, P and Si showed the opposite trend. By contrast, Co displayed a double humped pattern with maxima at about 19 Ma and 3.5 Ma and minima at 23.3 Ma, about 11 Ma and at Present. The long-term trends in element concentrations in the crust lead us to suggest that much of the Fe in western Pacific Ocean ferromanganese crusts is aeolian in origin and derived from the deserts of central Asia. Cooling of the Asian mainland at about 20 Ma led to an increase in the flux of Fe to the oceans. This was supplemented by an additional input of Fe into the crusts as a consequence of the dissolution of biogenic CaCO₃ tests at 4.5−10.5 Ma. For the short-term erratic variations, three periods of 0.61, 0.96 and 1.65 m.y. were identified by spectral analysis. The second harmonics of these periods are 1.22, 1.92 and 3.30 m.y., which may correspond to the highest-order periods for eccentricity of 1.31, 2.04 and 3.47 m.y. This suggests the possibility that the high-frequency oscillations of the time series data are linked to climatic changes controlled by the highest-order periods of the Milankovitch cycles.