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121.
Molecular-scale mechanisms of distribution and isotopic fractionation of molybdenum between seawater and ferromanganese oxides 总被引:1,自引:0,他引:1
Teruhiko Kashiwabara Yoshio Takahashi Akira Usui 《Geochimica et cosmochimica acta》2011,75(19):5762-5784
The distribution of Mo between seawater and marine ferromanganese oxides has great impacts on concentration and isotopic composition of Mo in modern oxic seawater. To reveal the adsorption chemistry of Mo to ferromanganese oxides, we performed (i) detailed structural analyses of Mo surface complexes on δ-MnO2, ferrihydrite, and hydrogenetic ferromanganese oxides by L3- and K-edge XAFS, and (ii) adsorption experiments of Mo to δ-MnO2 and ferrihydrite over a wide range of pHs, ionic strengths, and Mo concentrations. XAFS analyses revealed that Mo forms distorted octahedral (Oh) inner-sphere complexes on δ-MnO2 whereas it forms a tetrahedral (Td) outer-sphere complex on ferrihydrite. In the hydrogenetic ferromanganese oxides, the dominant host phase of Mo was revealed to be δ-MnO2. These structural information are consistent with the macroscopic behaviors of Mo in adsorption experiments, and Mo concentration in modern oxic seawater can be explained by the equilibrium adsorption reaction on δ-MnO2. In addition, the large isotopic fractionation of Mo between seawater and ferromanganese oxides detected in previous studies can be explained by the structural difference between and adsorbed species on the δ-MnO2 phase in ferromanganese oxides. In contrast, smaller fractionation of Mo isotopes on ferrihydrite is due to little change in the Mo local structures during its adsorption to ferrihydrite.The structures of Mo species adsorbed on crystalline Fe (oxyhydr)oxides, goethite, and hematite were also investigated at pH 8 and I = 0.70 M (NaNO3). Our XAFS analyses revealed that Mo forms inner-sphere complexes on both minerals: Td edge-sharing (46%) and Oh double corner-sharing (54%) for goethite, and Td double corner-sharing (14%) and Oh edge-sharing (86%) for hematite. These structural information, combined with those for amorphous ferrihydrite and δ-MnO2, show the excellent correlation with the magnitude of adsorptive isotopic fractionation of Mo reported in previous studies: the proportion of Oh species or their magnitude of distortion in Mo surface complexes become larger in the order of ferrihydrite < goethite < hematite < δ-MnO2, a trend identical to the magnitude of isotopic fractionation.Based on the comparison with previous reports for Mo surface species on various oxides, the chemical factors that affect Mo surface complex structures were also discussed. The hydrolysis constant of cation in oxides, log KOH (or the acidity of the oxide surfaces, PZC) is well correlated with the mode of attachment (inner- or outer-sphere) of Mo surface complexes. Furthermore, the symmetric change in Mo species from Td to Oh is suggested to be driven by the formation of inner-sphere complexes on specific sites of the oxide surfaces. 相似文献
122.
Itaru Yamashita Adichat Surinkum Yutaka Wada Makoto Fujihara Masao Yokoyama Haider Zaman Yo-ichiro Otofuji 《Journal of Asian Earth Sciences》2011,40(3):784-796
Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α95 = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α95 = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin. 相似文献
123.
124.
选用密集的高精度地震台网Hi-net 2002~2004年记录的836个地震事件的23,895条P波和21,969条S波的到时资料,计算得到了日本西南地区水平分辨率约33 km,垂直分辨率4~15 km的三维地壳P波和S波速度结构,并进一步获得泊松比分布.研究表明,在大山火山下存在显著的低速异常,表明该火山可能是一个潜在的活火山.速度异常图像清楚地显示了菲律宾板块俯冲至西南日本地区下,其上方存在的低速高泊松异常表明可能有流体的存在,分析得出可能来自板块俯冲过程中的脱水作用.并进一步探讨了流体在地震孕育及触发的过程中可能起的重要作用. 相似文献
125.
Strong motion uncertainty determined from observed records by dense network in Japan 总被引:2,自引:1,他引:1
Nobuyuki Morikawa Tatsuo Kanno Akira Narita Hiroyuki Fujiwara Toshihiko Okumura Yoshimitsu Fukushima Aybars Guerpinar 《Journal of Seismology》2008,12(4):529-546
The variation of ground motions at specific stations from events in six narrow areas was inspected by using K-NET and KiK-net
records. A source-area factor for individual observation stations was calculated by averaging ratios between observed values
for horizontal peak acceleration and velocity, as well as acceleration response spectra for 5% damping, and predicted values
using a ground-motion model (usually known as an attenuation relation) by Kanno et al. (Bull Seismol Soc Am, 96:879–897, 2006). Standard deviations between observed and predicted amplitudes after the correction factor are less than 0.2 on the logarithmic
scale and decrease down to around 0.15 in the short-period range. Intra-event standard deviation clearly increases with decreasing
distance due to differing paths around near source area. Standard deviations may increase with amplitude or decrease with
magnitude; however, both amplitude and magnitude of the data are strongly correlated with distance. The standard deviation
calculated in this study is obviously much smaller than that of the original ground-motion model, as epistemic uncertainties
are minimized by grouping ground motions at specific stations. This result indicates that the accuracy of strong ground motion
prediction could be improved if ground-motion models for specified region are determined individually. For this to be possible,
it is necessary to have dense strong-motion networks in high-seismicity regions, such as K-NET and KiK-net. 相似文献
126.
通过分析发生在日本周边深源地震的宽频带波形资料,估计了日本列岛下的660km不连续面(d660)的深度变化。许多宽频带波形记录到了在d660顶部发生反射的sScS的后续波。sScS后续波与sScS间的到时差包含了震中与台站下方的d660深度变化的信息。我们成功地检测到这两种震相并将其分离,到目前为止还没有这方面研究的报道。我们由sScS与其后续波的到时差来求每个震中与记录台站下的d660的深度变化。研究结果显示,西部日本下的d660较深(大于660km),这可能是滞留在地幔转换带中的冷的太平洋板块造成的。在日本中部,d660变深,显然这不是太平洋板块本身造成的,因为日本中部已经位于该滞留板片的东部。日本东北部下的d660变得较浅,这可能是太平洋板片形状变化或下地幔热物质上涌形成局部热异常造成的。 相似文献
127.
Abstract: The sulfur isotopic ratios (δ34 S) of ore minerals from the Toyoha deposit, Hokkaido, one of the largest Pb–Zn–Ag polymetallic vein-type deposits in Japan, were studied. More than 90% of the δ34 S values of the studied sulfide minerals collected from the Toyoha deposit range from +5 to +9%, with an average of approximately +7% irrespective of the mineral species, veins, elevations, depth, mineralization stages and mineral assemblages. Relatively uniform δ34 S values obtained in this study suggest that the reduced aqueous sulfur species predominated over the oxidized sulfur in the ore solution throughout the mineralization stages. Thus, the source of sulfur for the ore sulfides is postulated to be magmatic.
The temperature obtained from the fluid inclusion study and the temperature of the sulfur isotopic geothermometer are not consistent. This suggests that each mineral precipitated under disequilibrated conditions with respect to the sulfur isotope.
The change in redox conditions presumably encountered between the mineralization stages did not account for the isotopic fluctuations since the isotopic exchanges between the oxidized and reduced aqueous sulfurs are much slower than the rate of oxidation of the ore solution. 相似文献
The temperature obtained from the fluid inclusion study and the temperature of the sulfur isotopic geothermometer are not consistent. This suggests that each mineral precipitated under disequilibrated conditions with respect to the sulfur isotope.
The change in redox conditions presumably encountered between the mineralization stages did not account for the isotopic fluctuations since the isotopic exchanges between the oxidized and reduced aqueous sulfurs are much slower than the rate of oxidation of the ore solution. 相似文献
128.
Akira IMAI 《Resource Geology》2000,50(1):1-23
Abstract: The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu‐Au deposit genetically related to a quartz monzonite (“adamellite”) porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore– and alteration–petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post‐ore “granodiorite” porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Sub‐dendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomor‐phic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher XMg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor. Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu‐Fe sul–fides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE‐trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2%) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks. 相似文献
129.
130.
Upper Mantle Velocity Structure Estimated From Ps-Converted Wave Beneath the North-Eastern Japan Arc 总被引:2,自引:0,他引:2
Toru Matsuzawa Norihito Umino Akira Hasegawa Akio Takagi 《Geophysical Journal International》1986,86(3):767-787
Summary. The upper boundary of the descending oceanic plate is located by using PS -waves (converted from P to S at the boundary) in the Tohoku District, the north-eastern part of Honshu, Japan. the observed PS-P time data are well explained by a two-layered oceanic plate model composed of a thin low-velocity upper layer whose thickness is less than 10 km and a thick high-velocity lower layer; the upper and lower layers respectively have 6 per cent lower and 6 per cent higher velocity than the overriding mantle. the estimated location of the upper boundary is just above the upper seismic plane of the double-planed deep seismic zone. This result indicates that events in the upper seismic plane, at least in the depth range from 60 to 150 km, occur within the thin low-velocity layer on the surface of the oceanic plate. 相似文献