Pyrite of distinctive isotopic composition from the Hemlo deposit: A potential tool to identify this type of gold mineralization in Archean terrain     

Keiko Hattori  Eion M. Cameron   《Journal of Geochemical Exploration》1987,28(1-3)

Most sulphides from various rock types and mineralization of Archean age exhibit sulphur isotope values (δ³⁴S) near 0‰. This is due to a general absence of conditions suitable for the oxidation-reduction reactions essential for isotopic fractionation. However, some important occurrences of Archean Au mineralization do display significant variations in δ³⁴S). One such occurrence with unusual isotopic compositions is the Hemlo gold deposit: pyrite from the ore typically has δ³⁴S < −6‰ to a minimum value of −17.5‰ The isotopic composition of the pyrite is correlated with the content of Au, indicating that they are genetically related.The sulphur isotope data suggest that sulphur compounds experienced redox reactions in the hydrothermal system at Hemlo and that sulphate was present prior to the Au mineralization. This sulphate may be of exogenic origin from a restricted basin, or of endogenic origin from magmatic-hydrothermal fluids. Other characteristic features of the deposit, such as enrichment in Sb, Tl and Hg, may also be explained by ore deposition under moderately oxidizing conditions.Distinctive δ³⁴S values were also observed in pyrite from Au mineralization at Heron Bay, 30 km west of Hemlo, and from baritic strata 21 to 27 km west and on approximate strike from Hemlo. These occurrences also represent sulphate-bearing hydrothermal systems and, as such, give distant information on the unusual environment of the mineralization at Hemlo. Since the isotopes of sulphur are sensitive to oxidation conditions they may be used to identify hydrothermal activities characteristic of this type of Au mineralization and to explore for other unusual areas of sulphate accumulation in Archean terrains.  相似文献   

Intergranular trace elements in mantle xenoliths from Russian Far East: Example for mantle metasomatism by hydrous melt     

Junji  Yamamoto  Shun'ichi  Nakai  Koshi  Nishimura  Ichiro  Kaneoka  Hiroyuki  Kagi  Keiko  Sato  Tasuku  Okumura  Vladimir S.  Prikhod'ko  Shoji  Arai 《Island Arc》2009,18(1):225-241

Based on both major and trace element chemistry, the occurrence of the intergranular component in mantle-derived xenoliths from far eastern Russia has been constrained. Whole-rock trace element measurements of one xenolith show apparent negative anomalies in Ce, Th, and high field strength elements on normalized trace element patterns. The trace element pattern of the whole rock differs from those of constituent minerals, indicating that the anomalies in the whole rock are attributable to the presence of an intergranular component. That assumption was confirmed using in situ analysis of trace elements in the intergranular substance and melt inclusion using laser ablation inductively coupled plasma–mass spectrometry. Both the intergranular component and the melt inclusions have identical trace element patterns, which mean that these materials are a cognate metasomatizing agent. The anomalies are regarded as mantle metasomatism related to an aqueous fluid. Hydrous minerals were observed on the wall of the melt inclusions using micro-Raman spectroscopy, indicating that the melt inclusions contained a large amount of water. Thus, this study reveals a trace element composition of a hydrous metasomatizing agent in the mantle.  相似文献   

石英摆标定控制电路的分析与研究     

郝长安  倪友忠  蒋建华  陈军  赵伦  杨其明 《地震地磁观测与研究》2008,29(1):85-88

地倾斜观测精度在很大程度上取决于格值标定的准确性,本文通过利用一些简单的控制电路,使得一起标定更加准确。希望对其他有着相同仪器的台站起到一定的参考价值。  相似文献   

Coordinated mineralogical and isotopic analyses of a cosmic symplectite discovered in a comet 81P/Wild 2 sample          下载免费PDF全文

Ann N. Nguyen  Eve L. Berger  Keiko Nakamura‐Messenger  Scott Messenger  Lindsay P. Keller 《Meteoritics & planetary science》2017,52(9):2004-2016

We have discovered in a Stardust mission terminal particle a unique mineralogical assemblage of symplectically intergrown pentlandite ((Fe,Ni)₉S₈) and nanocrystalline maghemite (γ‐Fe₂O₃). Mineralogically similar cosmic symplectites (COS) have only been found in the primitive carbonaceous chondrite Acfer 094 and are believed to have formed by aqueous alteration. The O and S isotopic compositions of the Wild 2 COS are indistinguishable from terrestrial values. The metal and sulfide precursors were thus oxidized by an isotopically equilibrated aqueous reservoir either inside the snow line, in the Wild 2 comet, or in a larger Kuiper Belt object. Close association of the Stardust COS with a Kool mineral assemblage (kosmochloric Ca‐rich pyroxene, FeO‐rich olivine, and albite) that likely originated in the solar nebula suggests the COS precursors also had a nebular origin and were transported from the inner solar system to the comet‐forming region after they were altered.  相似文献   

Spatial distribution of organic matter in the Bells CM2 chondrite using near‐field infrared microspectroscopy     

Yoko KEBUKAWA  Satoru NAKASHIMA  Michio ISHIKAWA  Kento AIZAWA  Tsutomu INOUE  Keiko NAKAMURA‐MESSENGER  Michael E. ZOLENSKY 《Meteoritics & planetary science》2010,45(3):394-405

Abstract– Distributions of organic functional groups as well as inorganic features were analyzed in the Bells (CM2) carbonaceous chondrite using near‐field infrared (NFIR) spectroscopy. NFIR spectroscopy has recently been developed to enable infrared spectral mapping beyond the optical diffraction limit of conventional Fourier transform infrared microspectroscopy. NFIR spectral mapping of the Bells 300 nm thick sections on Al plates for 7.5 × 7.5 μm² areas showed some C‐H‐rich areas which were considered to represent the organic‐rich areas. Heterogeneous distributions of organic matter as well as those of inorganic phases such as silicates (Si‐O) were observed with 1 μm spatial resolution. The NFIR mappings of aliphatic C‐H (2960 and 2930 cm^?1) and structural OH (3650 cm^?1) confirm that organic matter is associated with phyllosilicates as previously suggested. The NFIR mapping method can provide 1 μm spatial distribution of organic functional groups and their association with minerals. High local sensitivity of NFIR enables us to find organic‐rich areas and to characterize them by their aliphatic CH₂/CH₃ ratios. The aliphatic CH₂/CH₃ ratio of Bells is slightly higher than Murchison, similar to Orgueil, and lower than literature values of IDPs and cometary dust particles.  相似文献   

Penetration tracks in aerogel produced by Al2O3 spheres     

Friedrich Hörz  Mark J. Cintala  Thomas H. See  Keiko Nakamura‐Messenger 《Meteoritics & planetary science》2009,44(9):1243-1264

Abstract— We conducted impact experiments into SiO₂‐based aerogel of uniform density (0.02 g cm^?3) with spherical corundum projectiles. The highly refractory nature and mechanical strength of corundum minimizes projectile deformation and continuous mass loss by ablation that might have affected earlier experiments with soda‐lime glass (SLG) impactors into aerogel targets. We find that corundum is a vastly superior penetrator producing tracks a factor of 2.5 longer, yet similar in diameter to those made by SLG. At velocities <4 km s^?1 a cylindrical “cavity” forms, largely by melting of aerogel. The diameter and length of this cavity increase with velocity and impactor size, and its volume dominates total track volume. A continuously tapering, exceptionally long and slender “stylus” emerges from this cavity and makes up some 80–90% of the total track length; this stylus is characterized by solid‐state deformations. Tracks formed below 4 km s^?1 lack the molten cavity and consist only of a stylus. Projectile residues recovered from a track's terminus substantially resemble the initial impactors at V > 4 km s^?1, yet they display two distinct surfaces at higher velocities, such as a blunt, forward face and a well‐preserved, hemispherical trailing side; a pronounced, circumferential ridge of compressed and molten aerogel separates these two surfaces. Stringers and patches of melt flow towards the impactor's rear where they accumulate in a characteristic melt tip. SEM‐EDS analyses indicate the presence of Al in these melts at velocities as low as 5.2 km s^?1, indicating that the melting point of corundum (2054 °C) was exceeded. The thermal model of aerogel impact by Anderson and Cherne (2008) suggests actual aerogel temperatures <5000 K at comparable conditions. We therefore propose that projectile melting occurs predominantly at those surfaces that are in contact with this very hot aerogel, at the expense of viscous heating and associated ablation. Exposure to superheated aerogel may be viewed as extreme form of “flash heating.” This seems consistent with observations from the Stardust mission to comet Wild 2, such as relatively pristine interiors of rather large, terminal particles, yet total melting of most fine‐grained dust components.  相似文献   

Role of the ocean in controlling atmospheric CO2 concentration in the course of global glaciations     

Akira Oka  Eiichi Tajika  Ayako Abe-Ouchi  Keiko Kubota 《Climate Dynamics》2011,37(9-10):1755-1770

Responses of ocean circulation and ocean carbon cycle in the course of a global glaciation from the present Earth conditions are investigated by using a coupled climate-biogeochemical model. We investigate steady states of the climate system under colder conditions induced by a reduction of solar constant from the present condition. A globally ice-covered solution is obtained under the solar constant of 92.2% of the present value. We found that because almost all of sea water reaches the frozen point, the ocean stratification is maintained not by temperature but by salinity just before the global glaciation (at the solar constant of 92.3%). It is demonstrated that the ocean circulation is driven not by the surface cooling but by the surface freshwater forcing associated with formation and melting of sea ice. As a result, the deep ocean is ventilated exclusively by deep water formation in southern high latitudes where sea ice production takes place much more massively than northern high latitudes. We also found that atmospheric CO₂ concentration decreases through the ocean carbon cycle. This reduction is explained primarily by an increase of solubility of CO₂ due to a decrease of sea surface temperature, whereas the export production weakens by 30% just before the global glaciation. In order to investigate the conditions for the atmospheric CO₂ reduction to cause global glaciations, we also conduct a series of simulations in which the total amount of carbon in the atmosphere?Cocean system is reduced from the present condition. Under the present solar constant, the results show that the global glaciation takes place when the total carbon decreases to be 70% of the present-day value. Just before the glaciation, weathering rate becomes very small (almost 10% of the present value) and the organic carbon burial declines due to weakened biological productivity. Therefore, outgoing carbon flux from the atmosphere?Cocean system significantly decreases. This suggests the atmosphere?Cocean system has strong negative feedback loops against decline of the total carbon content. The results obtained here imply that some processes outside the atmosphere?Cocean feedback loops may be required to cause global glaciations.  相似文献   

苏鲁超高压变质带胡家林超镁铁质岩成因及构造意义   总被引：1，自引：1，他引：0  

谢志鹏  王建  HATTORI Keiko  薛传东  钟军伟  王泽利 《岩石学报》2018,34(6):1539-1556

胡家林超镁铁质杂岩体产于苏鲁超高压变质带中部,纯橄岩和(石榴)单斜辉石岩呈不连续透镜体产于蛇纹石化橄榄岩中。纯橄岩遭受了部分蛇纹石化(烧失量=6.6%～13.2%),全岩富集强相容元素(Ni、Cr、Co)和Ir族PGE(IPGE;Ir、Os、Ru)及高IPGE/PPGE值,亏损Al、Ti、V,具高Mg~#橄榄石(Fo=91.7～92.4)和高Cr~#(0.68～0.76)尖晶石。纯橄岩高耐熔地球化学及矿物化学特征和古老的大陆岩石圈地幔相一致,表明其原岩来源于弧前地幔,代表了华北克拉通古老的大陆岩石圈地幔残留。(石榴)单斜辉石岩全岩呈相对低含量的强相容元素(Cr、Ni、Co)和IPGE,高含量的Al、Ti、V和流体迁移元素(Sr、Pb和Ba),球粒陨石标准化REE配分图呈明显"上凸"型,具低Mg~#橄榄石(Fo=76.6～76.8)和低Al_2O_3(2.76%)和高SiO_2(54.56%～56.87%)的单斜辉石。全岩组成和矿物化学表明其原岩为俯冲带内超镁铁质火成堆晶岩,最初岩浆由地幔岩高程度部分熔融的熔体和俯冲带中富H_2O流体和/或熔体构成。(石榴)单斜辉石岩原岩曾被地幔流带入扬子大陆俯冲板片和上覆地幔楔之间的俯冲通道,经历了超高压变质作用和生成大量石榴石。(石榴)单斜辉石岩在折返过程中,与大陆岩石圈地幔楔剥离的蛇纹石化橄榄岩及纯橄岩相结合,形成超镁铁质杂岩体,整体被低密度的俯冲板片(主要由花岗质片麻岩和变质沉积岩组成)裹挟,折返至地壳浅部。  相似文献   

Oceanic tides over the Newfoundland and Scotian Shelves from TOPEX/POSEIDON altimetry     

Guoqi Han  Moto Ikeda  Peter C. Smith 《大气与海洋》2013,51(4):589-604

Abstract

A modified response analysis in the form of an orthotide parametrization is used to derive major semi‐diurnal and diurnal tidal constituents over the Newfoundland and Scotian Shelves from TOPEX/POSEIDON altimeter data. The orthotide formulation simultaneously solves for eight major semi‐diurnal and diurnal constituents, and has an accuracy of better than ～1.5 cm for each constituent. Tidal elevations are derived from the altimeter data on the ascending and descending satellite ground tracks, and interpolated using the method of statistical interpolation. The semi‐diurnal constituents (M₂, S₂ and N₂) compare favourably with available in‐situ observations and a numerical model. The diurnals (K₁ and O₁) are not as accurate as the semi‐diurnals, especially in the nearshore environment. The paper demonstrates the ability of TOPEX/POSEIDON altimetry to provide accurate tidal data over a continental shelf.  相似文献   

Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara   总被引：2，自引：0，他引：2  

Ali Pinar  Keiko Kuge  Yoshimori Honkura 《Geophysical Journal International》2003,153(1):133-145

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