西太平洋海底海山富钴结壳惰性气体同位素组成及其来源

采用高真空气体质谱系统测定了西太平洋麦哲伦海山富钴结壳不同层圈及其基岩的惰性气体丰度和同位素组成,结果显示:(1)西太平洋富钴结壳主要是水成成因,其中惰性气体来源不同,He 绝大多数来自宇宙尘(IDPs),少量来自陆源风成微粒;Ar 主要来自海水溶解的大气,少量来自陆源风成微粒或沉积岩建造水;Ne 和 Xe 主要来自海水中溶解大气, 少量来自宇宙尘;(2)在具三层结构的结壳中,亮煤层(致密层)的惰性气体同位素相对外层和疏松层有较大的不同,显示大洋磷酸岩化对早期沉积的结壳惰性气体组成有较大的影响,如导致~4He 的升高和~3He/~4He 的显著降低;(3)太平洋富钴结壳玄武岩基岩的~3He/~4He 非常低,为0.0095～0.074Ra,与本区磷块岩基岩(0.087Ra)相似,而远低于正常海底玄武岩的~3He/~4He 比值,显示这些基岩曾与富含放射性成因~4He 和 P 的上升洋流或沉积物中建造水发生过水/岩反应,这个过程将释放出较多的成矿元素,有利于富钴结壳的形成,海底海山玄武岩中较低的 He 同位素组成可作为富钴结壳的找矿标志之一。     

Helium isotopes in ferromanganese crusts from the central Pacific Ocean

Helium isotopes have been measured in samples of two ferromanganese crusts (VA13/2 and CD29-2) from the central Pacific Ocean. With the exception of the deepest part of crust CD29-2 the data can be explained by a mixture of implanted solar- and galactic cosmic ray-produced (GCR) He, in extraterrestrial grains, and radiogenic He in wind-borne continental dust grains. ⁴He concentrations are invariant and require retention of less than 12% of the in situ He produced since crust formation. Loss has occurred by recoil and diffusion. High ⁴He in CD29-2 samples older than 42 Ma are correlated with phosphatization and can be explained by retention of up to 12% of the in situ-produced ⁴He. ³He/⁴He of VA13/2 samples varies from 18.5 to 1852 R_a due almost entirely to variation in the extraterrestrial He contribution. The highest ³He/⁴He is comparable to the highest values measured in interplanetary dust particles (IDPs) and micrometeorites (MMs). Helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in-falling terrestrial and extraterrestrial grains of Fe-Mn crusts. The extraterrestrial ³He concentration of the crusts rules out whole, undegassed 4-40 μm diameter IDPs as the host. Instead it requires that the extraterrestrial He inventory is carried by numerous particles with significantly lower He concentrations, and occasional high concentration GCR-He-bearing particles.     

辽宁宽甸新生代火山岩和地幔包体的稀有气体同位素组成及其演化意义

通过对宽甸新生代碱性玄武岩、地幔包体及辉石巨晶的稀有气体同位素组成的分析，认为不同岩性稀有气体含量的差异反映了岩浆作用过程中轻、重稀有气体的分馏特性，较轻的稀有气体(He、Ne)比较重的稀有气体(Kr、xe)具有更高的活动性和不相容性；该地区上地幔源区具有典型的MORB型源区特征，以辉石巨晶为代表；地幔包体的^3He／^4He值较低，可能是地幔流体交代作用造成的；大陆碱性玄武岩具有与大洋玄武岩截然不同的He同位素组成，反映了大陆区地幔岩浆上升过程中受到了陆壳物质混染。地幔源区^40Ar／^36Ar值为350左右，二辉橄榄岩和碱性火山岩的^40Ar／^36Ar值比大气略高，可能有大气组分的混合。部分样品中有^21Ne、^22Ne、^129Xe、^134Xe和^136Xe相对于大气的过剩现象，是核成因造成的。     

Helium and Argon Isotopic Composition of Cenozoic Alkali Basalts and Mantle-Derived Xenoliths from Kuandian, Liaoning Province, China

The noble gas isotopic composition and content data of 2 alkali basalts, 3 Iherzolite xenoliths and one clinopyroxene megacryst from the Kuandian region have confirmed the occurrence of a fractionation of noble gases during magmatism. Light noble gases such as He and Ne are high in mobility and appear to be incompatible as compared with heavy ones ( such as Kr and Xe). Therefore, light noble gases are abundant in volcanics, especially in the volcanics with bubbles; lherzolite xenoliths have relatively high heavy noble gases. The clinopyroxene megacryst has the lowest abundance of noble gases, probably due to its high P-T origin. Noble gas isotopic composition of the clinopyroxene megacryst reveals that the mantle source beneath the Kuandian area has an MORB-like reservoir with^3 He/^4He ratio of—10 Ra(Ra: atmospheric^3 He/^4He ratio) and^40 Ar/^36 Ar ratio of 345.6. The Iherzolite xenoliths possess moderate^3 He/^4He ratios of 2.59 -4.53 Ra, reflecting the loss of primary helium during rock deformation or metasomatism caused by enriched mantle fluids during the up-lifting. The alkali volcanics have very low^3 He/^4 He ratios(0.47—0.61 Ra),indicating a contribution of radiogenic^4 He, probably having resulted from crust contamination. Most of the samples have excess^21 Ne and^22 Ne as compared with atmospheric neon, but Kr and Xe isotopic compositions are indistinguishable from atmospheric values within uncertainties with only individual samples having excess^129Xe,^134Xeand^136 Xe.     

Effect of Phosphatization on Element Concentration of Cobalt-Rich Ferromanganese Crusts

1 Introduction Co-rich ferromanganese crusts occurring on submarine guyots have received much attention from scientists since the beginning of the 1980’s because they are enriched in Co, Mn, Pt, and rare earth elements (REEs), and have large potential mineral resources, occurring as they do on topographic highs relative to polymetallic nodules in the C-C (Clarion-Clipperton) zone (Halbach et al., 1982, 1989; Hein et al., 1992, 1999; Usui and Someya, 1997; Yamazaki and Sharma, 1998, 2000…     

西太平洋海山玄武岩的岩石学特征及与上覆富钴结壳的关系

通过对西太平洋海山玄武岩和玄武质火山角砾岩的岩石学特征及其气孔充填物成分变化的研究,讨论了海山玄武岩与上覆富钴结壳的关系。富钴结壳的基岩火山岩主要为碱性玄武岩和玄武质火山角砾岩。碱性玄武岩中气孔充填物为S型和C型,S型和C型气孔充填物不共存在同一个气孔中。S型气孔充填物的物质成分富Si、Fe、K、Mg、Al,Co含量一般为0.17%~0.46%,其成分与碱性玄武岩的组成类似,其物质来源可能与碱性玄武岩有关。C型气孔充填物为O、Ca、C及少量Si、Al、Mg、Fe、K等元素,C型气孔充填物可能与海水中物质的沉积有关。由Si、Al、Fe、Mg、K等元素变化曲线反映出的S型气孔充填物沉积过程与富钴结壳早期的沉积过程具有相似的趋势,说明富钴结壳早期沉积物的物质来源可能与碱性玄武岩有关,富钴结壳物质来源可能是碱性玄武岩和海水共同作用的结果。     

利用多波束回波强度进行中太平洋潜鱼海山底质分类

中、西太平洋海山区是富钴结壳的重要富集区,钙质远洋沉积、碳酸盐岩沉积及重力作用引起的滑塌沉积是海山山顶和斜坡的主要沉积类型,它们的空间分布规律对于富钴结壳的分布至关重要.在国内首次利用EM122多波束回波强度资料对中太平洋潜鱼海山进行了底质类型研究,对回波强度资料进行处理和统计分类,并与浅地层剖面和地质取样结果对比,分析得出了4种底质类型,即富钴结壳、钙质远洋沉积、碳酸盐岩基底及碎屑流沉积.这几种底质类型具有不同的回波强度特征,其中富钴结壳区表现为均一的回波强度高值特征;钙质远洋沉积区表现为均一的回波强度低值特征,二者回波强度值相差约20 dB.结果显示潜鱼海山山顶仅局部发育钙质远洋沉积,大部分为碳酸盐岩基底出露区,山顶边缘及侧翼山脊处为主要的富钴结壳分布区.此外,该海山存在3处较大规模的重力滑塌沉积区,主要为碎屑流沉积.      

富钴结壳中贵金属元素的特征

对太平洋CL、CM海山调查时获取9个富钴结壳样品,采用化学处理及ICP-MS法进行分析。对贵金属元素含量分布特征、富集因子、标准化模式以及来源进行探讨和研究。结果表明：海山结壳中贵金属元素Ag、Au、Ru、Rh、Pd、Pt等的平均含量分别为： 1.05×10^-6、2.3×10^-6、15.6×10^-9、22.3×10^-9、2.39×10^-9和432×10^-9。与结核、洋壳及陆地矿石的Pd/（Pt+Pd）、Pt/（Pt+Pd）和Pd/Pt等贵金属元素的比值相比,大洋富钴结壳的 Pd/（Pt+Pd） 比值最低,为0.006;其次是结核,为0.06;洋壳为0.08;陆地矿石的Pd/（Pt+Pd）比值较大,为0.35～0.65。结壳的Pt/（Pt+Pd）比值最高,为0.99;其次是结核,为0.95;洋壳为0.93;陆地矿石的Pt/（Pt+Pd）比值相对较低,为0.33～0.65。统计分析显示了不同区域、不同环境中贵金属元素的特征参数变化,并且说明富钴结壳中富铂、金、钌、铑,而贫钯。贵金属元素标准化显示,海山富钴结壳均存在着Pt、Au正异常和Pd的负异常,其中Au异常幅度与结核的Au异常一致。     

Subduction of solar-type noble gases from extraterrestrial dust: constraints from high-pressure low-temperature metamorphic deep-sea sediments

Solar-type helium (He) and neon (Ne) in the Earths mantle were suggested to be the result of solar-wind loaded extraterrestrial dust that accumulated in deep-sea sediments and was subducted into the Earths mantle. To obtain additional constraints on this hypothesis, we analysed He, Ne and argon (Ar) in high pressure–low temperature metamorphic rocks representing equivalents of former pelagic clays and cherts from Andros (Cyclades, Greece) and Laytonville (California, USA). While the metasediments contain significant amounts of ⁴He, ²¹Ne and ⁴⁰Ar due to U, Th and K decay, no solar-type primordial noble gases were observed. Most of these were obviously lost during metamorphism preceding 30 km subduction depth. We also analysed magnetic fines from two Pacific ODP drillcore samples, which contain solar-type He and Ne dominated by solar energetic particles (SEP). The existing noble gas isotope data of deep-sea floor magnetic fines and interplanetary dust particles demonstrate that a considerable fraction of the extraterrestrial dust reaching the Earth has lost solar wind (SW) ions implanted at low energies, leading to a preferential occurrence of deeply implanted SEP He and Ne, fractionated He/Ne ratios and measurable traces of spallogenic isotopes. This effect is most probably caused by larger particles, as these suffer more severe atmospheric entry heating and surface ablation. Only sufficiently fine-grained dust may retain the original unfractionated solar composition that is characteristic for the Earths mantle He and Ne. Hence, in addition to the problem of metamorphic loss of solar noble gases during subduction, the isotopic and elemental fractionation during atmospheric entry heating is a further restriction for possible subduction hypotheses.     

Ferromanganese crusts as indicators for paleoceanographic events in the NE Atlantic

Hydrogenetic ferromanganese crusts reflect the chemical conditions of the sewater from which they formed. Fine-scale geochemical analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts.¹⁰Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2–5 Ma ago) resulted in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized crust generation might be as old as approximately 30–40 Ma.     

中国富钴结壳合同区海水的稀土元素特征及其意义

通过对西太平洋34件海水样品的稀土元素（REY:REE+Y）测试及其与研究区富钴结壳稀土耦合特征分析,揭示了海水稀土特征及其成因.海水的稀土含量随水深呈现逐渐增加的趋势,∑ REY范围为14.0×10-12~65.5×10-12,平均值为31.9×10-12,其中Y的绝对值（均值为6.0×10-12~24.1×10-12）和相对值（（Y/Ho）_N均值为1.98）均较高,La含量次之（均值为1.8×10-12~11.6×10-12）,Ce含量相对较低（均值为2.4×10-12~8.8×10-12）,δCe范围为0.33~1.03（均值为0.66）,（La/Yb）_N平均值为0.71.海水稀土元素北美页岩标准化后显示左倾模式,具有显著的Ce负异常、Y正异常和无明显的Eu异常特征.研究区普遍发育水成成因的富钴结壳,即其稀土元素和其他组分均源自海水.富钴结壳的稀土含量相对海水富集6~7个数量级,其Ce正异常和Y负异常的稀土模式与海水构成良好的耦合关系,指示富钴结壳类组分对海水稀土清扫具有选择性,是造成海水稀土模式的重要因素.海山上发育的磷块岩以及周围盆地深海泥中的磷酸盐组分,它们具有较高的稀土含量和类似于海水的稀土模式,指示海洋磷酸盐消耗稀土时并未分馏而是继承海水模式.海水独特的稀土模式特征是补给与消耗平衡作用的结果,铁锰氧化物和海洋磷酸盐是两种典型的海洋自生组分,它们对海水稀土特征的形成至关重要.      

70 Ma以来风尘活动在太平洋铁锰结壳中的记录

开展风尘沉积研究对于了解源区气候变化和大气循环过程具有重要意义。利用高分辨率电子探针技术,通过对铁锰结壳中风尘指示因子（Al沉积通量）的年际变化研究,探讨低纬度铁锰结壳中风尘沉积特征。结果显示：在过去近70 Ma中,低纬度铁锰结壳Al沉积通量平均值为300.5  μg/(cm^2·ka),并且记录了南、北半球的不完整风尘史。在晚白垩世－晚中新世期间,M06铁锰结壳位于热带辐合带之南,受南半球风系影响,其Al沉积通量大小反映了环太平洋区域火山活动强度;晚中新世后,受北半球风系控制,M06铁锰结壳Al通量的变化反映了亚洲风尘源区构造和气候的变化。     

Peculiarities of the distribution of rare-earth elements and yttrium in mineral phases of the ferromanganese crusts from the Detroit guyot (Pacific Ocean)

The concentrations of rare-earth elements and yttrium (REY) were first determined in four major mineral fractions of cobalt-rich ferromanganese crusts (CMC) from the Detroit guyot at the northern latitudes of the Pacific Ocean. It was shown that REY in the CMC from these latitudes are mainly adsorbed by the manganese phase unlike the crusts of the equatorial part of the ocean where iron hydroxides are the key REY sorbents from seawater. This is caused by the variations in the hydrochemical characteristics of seawater with the latitude of the CMC formation.     

Planetary and pre-solar noble gases in meteorites

Noble gases are not rare in the Universe, but they are rare in rocks. As a consequence, it has been possible to identify in detailed analyses a variety of components whose existence is barely visible in other elements: radiogenic and cosmogenic gases produced in situ, as well as a variety of “trapped” components – both of solar (solar wind) origin and the “planetary” noble gases. The latter are most abundant in the most primitive chondritic meteorites and are distinct in elemental and isotopic abundance patterns from planetary noble gases sensu strictu, e.g., those in the atmospheres of Earth and Mars, having in common only the strong relative depletion of light relative to heavy elements when compared to the solar abundance pattern. In themselves, the “planetary” noble gases in meteorites constitute again a complex mixture of components including such hosted by pre-solar stardust grains.The pre-solar components bear witness of the processes of nucleosynthesis in stars. In particular, krypton and xenon isotopes in pre-solar silicon carbide and graphite grains keep a record of physical conditions of the slow-neutron capture process (s-process) in asymptotic giant branch (AGB) stars. The more abundant Kr and Xe in the nanodiamonds, on the other hand, show a more enigmatic pattern, which, however, may be related to variants of the other two processes of heavy element nucleosynthesis, the rapid neutron capture process (r-process) and the p-process producing the proton-rich isotopes.“Q-type” noble gases of probably “local” origin dominate the inventory of the heavy noble gases (Ar, Kr, Xe). They are hosted by “phase Q”, a still ill-characterized carbonaceous phase that is concentrated in the acid-insoluble residue left after digestion of the main meteorite minerals in HF and HCl acids. While negligible in planetary-gas-rich primitive meteorites, the fraction carried by “solubles” becomes more important in chondrites of higher petrologic type. While apparently isotopically similar to Q gas, the elemental abundances are somewhat less fractionated relative to the solar pattern, and they deserve further study. Similar “planetary” gases occur in high abundance in the ureilite achondrites, while small amounts of Q-type noble gases may be present in some other achondrites. A “subsolar” component, possibly a mixture of Q and solar noble gases, is found in enstatite chondrites. While no definite mechanism has been identified for the introduction of the planetary noble gases into their meteoritic host phases, there are strong indications that ion implantation has played a major role.The planetary noble gases are concentrated in the meteorite matrix. Ca-Al-rich inclusions (CAIs) are largely planetary-gas-free, however, some trapped gases have been found in chondrules. Micrometeorites (MMs) and interplanetary dust particles (IDPs) often contain abundant solar wind He and Ne, but they are challenging objects for the analysis of the heavier noble gases that are characteristic for the planetary component. The few existing data for Xe point to a Q-like isotopic composition. Isotopically Q-Kr and Q-Xe show a mass dependent fractionation relative to solar wind, with small radiogenic/nuclear additions. They may be closer to “bulk solar” Kr and Xe than Kr and Xe in the solar wind, but for a firm conclusion it is necessary to gain a better understanding of mass fractionation during solar wind acceleration.     

CCSD中HP-UHP岩石稀有气体同位素地球化学及其对板块折返过程的示踪意义

利用高真空气相质谱系统测定了CCSD中HP-UHP变质岩中主要造岩矿物流体包裹体的稀有气体同位素组成,得出其3He/4He为(0.004~0.775)×10-6,相应R/Ra为0.003~0.553,40Ar/36Ar变化较大,为316.2~11358.8,高于大气40Ar/36Ar(295.5);20Ne/22Ne和21Ne/22Ne分别为9.47~12.4和0.026~0.051,而134Xe/132Xe和136Xe/132Xe分别为0.376~0.484和0.324~0.416,均高于其相应大气值。CCSD中HP-UHP岩石主要造岩矿物的He-Ar、Xe和Ne等同位素组成清楚显示其中流体包裹体主要由地壳变质流体和少量大气饱和水组成,而深源地幔流体组分很低,其中He主要来自地壳,Ar主要由壳源放射性成因40Ar*和少量(平均32.6%)大气Ar混合组成,少量Ne和Xe可能来自地幔。CCSD中HP-UHP岩石具有F40Ar相似文献   

Manganese and Molybdenum in Phosphorites from the Ocean

The behavior of molybdenum and manganese is studied in phosphorite samples from shelves, seamounts, and islands of the ocean. In shelf phosphorites, molybdenum and manganese contents are 2–128 and 12–1915 ppm, respectively, while the Mo/Mn ratio ranges from 0.004 to 4.5. Phosphorites from oceanic seamounts impregnated with ferromanganese oxyhydroxides contain 0.84–14.5 ppm of Mo and 0.1–17% of Mn. The Mo/Mn ratio ranges within 0.0008–0.004. Phosphate-bearing ferromanganese crusts overlying the seamount phosphorites contain 54–798 ppm of Mo and 10–20% of Mn; Mo/Mn ratio varies within 0.002–0.005. Corresponding values for most island phosphorites are 0.44–11.2 ppm, 27–287 ppm, and 0.008–0.20, respectively. Phosphorites from reduced environments are characterized by a relative enrichment in Mo and depletion in Mn, whereas the Mo/Mn ratio reaches maximum values. The ratio decreases with transition to suboxic and oxic conditions. Molybdenum content in recent shelf sediments is commonly higher than that in authigenic phosphorites from these sediments. Recent phosphorite nodules from the Namibian shelf become depleted in Mo and Mn during their lithification, but Pliocene–Pleistocene nodules of similar composition and origin from the same region are enriched in Mo and characterized by a variable Mn content. The higher Mo content in phosphate-bearing ferromanganese crusts is a result of coprecipitation of Mo and Mn from seawater. Nonweathered phosphorites on continents and phosphorites from oceanic shelves are largely enriched in Mo with the Mo/Mn ratio ranging from 0.01 to 1.0. This is an evidence of their formation in reducing conditions.     

Noble gases,nitrogen and cosmic ray exposure age of the Sulagiri chondrite

The Sulagiri meteorite fell in India on 12 September 2008,LL6 chondrite class is the largest among all the Indian meteorites.Isotopic compositions of noble gases(He,Ne,Ar,Kr and Xe) and nitrogen in the Sulagiri meteorite and cosmic ray exposure history are discussed.Low cosmogenic(~(22)Ne/~(21)Ne)_c ratio is consistent with irradiation in a large body.Cosmogenic noble gases indicate that Sulagiri has a 4πcosmic-ray exposure(CRE) age of 27.9 ± 3.4 Ma and is a member of the peak of CRE age distribution of IX chondrites.Radiogenic ~4He and ~(40)Ar concentrations in Sulagiri yields the radiogenic ages as 2.29 and4.56 Ca,indicating the loss of He from the meteorite.Xenon and krypton are mixture of Q and spallogenic components.     

Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount,NW Pacific,at water depths of 800–5500 m

Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm²/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.     

麦哲伦海山铁锰结壳中氟的古海洋环境意义

碳氟磷灰石的出现是铁锰结壳磷酸盐化的标志,氟是碳氟磷灰石的主要伴生元素.为了解氟作为铁锰结壳磷酸盐化指标的可行性,采用离子选择电极法测定了西太平洋麦哲伦海山区铁锰结壳中氟的质量分数,探讨了铁锰结壳中氟的分布特征、来源及其对磷酸盐化的指示作用.研究结果表明,铁锰结壳中的氟主要来源于海洋有机质的分解,并富集于受到磷酸盐化作用的结壳层中,以碳氟磷灰石为主要赋存相,氟对铁锰结壳的磷酸盐化作用有较为灵敏的指示作用.     

中太平洋海山多金属结壳的成矿特征

根据我国大洋多金属结壳的调查资料并结合其他相关的研究结果，对中太平洋海山区多金属结壳的类型，产状，成分，结构，分布等成矿特征进行了初步的研究，结果表明，中太平洋海山区富钴结壳广泛发育，但成矿特征较大地受地形，水溶，基岩类型等成矿环境因素的影响与制约。