The development of Fe-nodules surrounding biological material mediated by microorganisms     

Hidekazu Yoshida  Koshi Yamamoto  Yuki Murakami  Nagayoshi Katsuta  Toru Hayashi  Takeshi Naganuma 《Environmental Geology》2008,55(6):1363-1374

Takashikozo is a phenomenon of Quaternary sediments in Japan. They are cylindrical Fe-oxyhydroxide nodules that form as plaques round plant roots, where Fe is preferentially concentrated to develop a solid wall. Structural features suggest that after the roots have decayed, the central space where the roots were situated acts as a flow path for oxidized water. Analysis of microbial 16S rDNA extracted from the nodules identified iron-oxidizing bacteria encrusted round the roots where they are the likely initiators of nodule formation. Direct microscopic observation revealed an accumulation of Fe-oxyhydroxides that fill the pore spaces and is also likely to be linked with the encrusting microbial colonies. Geological history and nanofossil evidence suggest that these Fe-nodules may have been buried at a depth of up to several tens of meters for at least 10⁵ years in reducing Quaternary sediments. Thus Fe-oxyhydroxide nodules that have formed in a geological environment at the interfaces between water and rock by microbial mediation can persist under reducing conditions. If this is the case, the phenomenon is significant as an analogue of post-closure conditions in radioactive waste repositories, since it could influence nuclide migration.  相似文献   

Back-arc rifting in the Izu-Bonin Island Arc: Structural evolution of Hachijo and Aoga Shima Rifts   总被引：1，自引：0，他引：1  

Adam  Klaus Brian  Taylor Gregory F.  Moore Fumitoshi  Murakami Yukinobu  Okamura 《Island Arc》1992,1(1):16-31

Abstract Multi- and single-channel seismic profiles are used to investigate the structural evolution of back-arc rifting in the intra-oceanic Izu-Bonin Arc. Hachijo and Aoga Shima Rifts, located west of the Izu-Bonin frontal arc, are bounded along-strike by structural and volcanic highs west of Kurose Hole, North Aoga Shima Caldera and Myojin Sho arc volcanoes. Zig-zag and curvilinear faults subdivide the rifts longitudinally into an arc margin (AM), inner rift, outer rift and proto-remnant arc margin (PRA). Hachijo Rift is 65 km long and 20–40 km wide. Aoga Shima Rift is 70 km long and up to 45 km wide. Large-offset border fault zones, with convex and concave dip slopes and uplifted rift flanks, occur along the east (AM) side of the Hachijo Rift and along the west (PRA) side of the Aoga Shima Rift. No cross-rift structures are observed at the transfer zone between these two regions; differential strain may be accommodated by interdigitating rift-parallel faults rather than by strike- or oblique-slip faults. In the Aoga Shima Rift, a 12 km long flank uplift, facing the flank uplift of the PRA, extends northeast from beneath the Myojin Knoll Caldera. Fore-arc sedimentary sequences onlap this uplift creating an unconformity that constrains rift onset to ～1-2Ma. Estimates of extension (～3km) and inferred age suggest that these rifts are in the early syn-rift stage of back-arc formation. A two-stage evolution of early back-arc structural evolution is proposed: initially, half-graben form with synthetically faulted, structural rollovers (ramping side of the half-graben) dipping towards zig-zagging large-offset border fault zones. The half-graben asymmetry alternates sides along-strike. The present ‘full-graben’ stage is dominated by rift-parallel hanging wall collapse and by antithetic faulting that concentrates subsidence in an inner rift. Structurally controlled back-arc magmatism occurs within the rift and PRA during both stages. Significant complications to this simple model occur in the Aoga Shima Rift where the east-dipping half-graben dips away from the flank uplift along the PRA. A linear zone of weakness caused by the greater temperatures and crustal thickness along the arc volcanic line controls the initial locus of rifting. Rifts are better developed between the arc edifices; intrusions may be accommodating extensional strain adjacent to the arc volcanoes. Pre-existing structures have little influence on rift evolution; the rifts cut across large structural and volcanic highs west of the North Aoga Shima Caldera and Aoga Shima. Large, rift-elongate volcanic ridges, usually extruded within the most extended inner rift between arc volcanoes, may be the precursors of sea floor spreading. As extension continues, the fissure ridges may become spreading cells and propagate toward the ends of the rifts (adjacent to the arc volcanoes), eventually coalescing with those in adjacent rift basins to form a continuous spreading centre. Analysis of the rift fault patterns suggests an extension direction of N80°E ± 10° that is orthogonal to the trend of the active volcanic arc (N10°W). The zig-zag pattern of border faults may indicate orthorhombic fault formation in response to this extension. Elongation of arc volcanic constructs may also be developed along one set of the possible orthorhombic orientations. Border fault formation may modify the regional stress field locally within the rift basin resulting in the formation of rift-parallel faults and emplacement of rift-parallel volcanic ridges. The border faults dip 45–55° near the surface and the majority of the basin subsidence is accommodated by only a few of these faults. Distinct border fault reflections decreases dips to only 30° at 2.5 km below the sea floor (possibly flattening to near horizontal at 2.8 km although the overlying rollover geometry shows a deeper detachment) suggesting that these rifting structures may be detached at extremely shallow crustal levels.  相似文献   

The Trobriand Subduction System in the Western Solomon Sea     

J. Lock  H. L. Davies  D. L. Tiffin  F. Murakami  K. Kisimoto 《Geo-Marine Letters》1987,7(3):129-134

A south-dipping Subduction system which underlies the Trobriand Trough and 149° Embayment, on the southern margin of the Solomon Sea, is active or was recently active. Oceanic basement is overlain by 2.5 s, two-way travel time (TWTT), of sediment that shows at least two stages of deformation: early thrusts (inner wall) and normal faults (outer wall), and later normal faults that have elevated the outer trench margin. Thrust anticlines and slope basins are developed on the inner wall. The floor of the Solomon Sea Basin arches upward between the Trobriand Trough and the New Britain Trench to form isolated peaks and ridges in the east (152° Peaks) and an east-west Central Ridge in the west. Structures in the subduction system, and in the Solomon Sea Basin, plunge westward towards the point of collision with the New Britain Trench.  相似文献   

Sea surface temperature observation by Global Imager (GLI)/ADEOS-II: Algorithm and accuracy of the product   总被引：1，自引：0，他引：1  

Futoki Sakaida  Kohtaro Hosoda  Masao Moriyama  Hiroshi Murakami  Akira Mukaida  Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):311-319

A sea surface temperature (SST) retrieval algorithm for Global Imager (GLI) aboard the ADEOS-II satellite has been developed. The algorithm is used to produce the standard SST product in the Japan Aerospace Exploration Agency (JAXA). The algorithm for cloud screening is formed by combinations of various types of tests to detect cloud-contaminated pixels. The combination is changed according to the solar zenith angle, which enables us to detect clouds even in the sun glitter region in daytime. The parameters in the cloud-detection tests have been tuned using the GLI global observations. SST is calculated by the Multi-Channel SST (MCSST) technique from the detected clear pixels. Using drifting buoy measurements, match-up data are produced to derive the coefficients of the MCSST equations and to examine their performance. The bias and RMSE of the GLI SST are 0.03 K and 0.66 K for daytime and, −0.01 K and 0.70 K for nighttime, respectively.  相似文献   

The Hard X-ray Telescope (HXT) for the SOLAR-A mission     

T. Kosugi  K. Makishima  T. Murakami  T. Sakao  T. Dotani  M. Inda  K. Kai  S. Masuda  H. Nakajima  Y. Ogawara  M. Sawa  K. Shibasaki 《Solar physics》1991,136(1):17-36

The Hard X-ray Telescope (HXT) is a Fourier-synthesis imager; a set of spatially-modulated photon count data are taken from 64 independent subcollimators and are Fourier-transformed into an image by using procedures such as the maximum entropy method (MEM) or CLEAN. The HXT takes images of solar flares simultaneously in four energy bands, nominally 15 (or 19)–24, 24–35, 35–57, and 57–100 keV, with an ultimate angular resolution as fine as 5 arc sec and a time resolution 0.5 s. Each subcollimator has a field of view wider than the solar disk. The total effective area of the collimator/detector system reaches 70 cm², about one order of magnitude larger than that of the HINOTORI hard X-ray imager. Thanks to these improvements, HXT will for the first time enable us to take images of flares at photon energies above 30 keV. These higher-energy images will be compared with lower-energy ones, giving clues to the understanding of nonthermal processes in solar flares, i.e., the acceleration and confinement of energetic electrons. It is of particular importance to specify the acceleration site with regard to the magnetic field figuration in a flaring region, which will be achieved by collaborative observations between HXT and the Soft X-ray Telescope on board the same mission.After the launch the name of SOLAR-A has been changed to YOHKOH.  相似文献   

Reply to comment on ‘Yamada H,Nakamura F,Watanabe Y,Murakami M and Nogami T. 2005. Measuring hydraulic permeability in a streambed using the packer test. Hydrological Processes 19: 2507–2524’     

Hiroyuki Yamada  Futoshi Nakamura  Yasuharu Watanabe  Marie Murakami  Takeshi Nogami 《水文研究》2008,22(17):3545-3545

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Dating pseudotachylyte of the Asuke Shear Zone using zircon fission-track and U–Pb methods     

Masaki Murakami  Jan Ko&#x;ler  Hideo Takagi  Takahiro Tagami 《Tectonophysics》2006,424(1-2):99-107

Zircon fission-track (FT) and U–Pb analyses were performed on zircon extracted from a pseudotachylyte zone and surrounding rocks of the Asuke Shear Zone (ASZ), Aichi Prefecture, Japan. The U–Pb ages of all four samples are  67–76 Ma, which is interpreted as the formation age of Ryoke granitic rocks along the ASZ. The mean zircon FT age of host rock is 73 ± 7 (2σ) Ma, suggesting a time of initial cooling through the zircon closure temperature. The pseudotachylyte zone however, yielded a zircon FT age of 53 ± 9 (2σ) Ma, statistically different from the age of the host rock. Zircon FTs showed reduced mean lengths and intermediate ages for samples adjacent to the pseudotachylyte zone. Coupled with the new zircon U–Pb ages and previous heat conduction modeling, the present FT data are best interpreted as reflecting paleothermal effects of the frictional heating of the fault. The age for the pseudotachylyte coincides with the change in direction of rotation of the Pacific plate from NW to N which can be considered to initialize the NNE–SSW trending sinistral–extensional ASZ before the Miocene clockwise rotation of SW Japan. The present study demonstrates that a history of fault motions in seismically active regions can be reconstructed by dating pseudotachylytes using zircon FT thermochronology.  相似文献   

Determination of the oxidation state of radiogenic Pb in natural zircon using X-ray absorption near-edge structure     

Kazuya Tanaka  Yoshio Takahashi  Kenji Horie  Hiroshi Shimizu  Takashi Murakami 《Physics and Chemistry of Minerals》2010,37(4):249-254

We examined the L_III-edge Pb X-ray absorption near-edge structure (XANES) of three natural zircon samples with different amounts of radiation doses (1.9 × 10¹⁵ to 6.8 × 10¹⁵ α-decay events/mg). The results suggest that the oxidation state of radiogenic Pb in the zircon sample with the highest radiation dose is divalent. The XANES spectra of the two other samples with lower radiation doses suggest that radiogenic Pb(II) is present, and further that some Pb may be tetravalent. This is the first work on the determination of the oxidation state of radiogenic Pb in natural zircon using XANES.  相似文献   

The relation between Cu/Au ratio and formation depth of porphyry-style Cu–Au ± Mo deposits     

Hiroyasu Murakami  Jung Hun Seo  Christoph A. Heinrich 《Mineralium Deposita》2010,45(1):11-21

Constraints on gold and copper ore grades in porphyry-style Cu–Au ± Mo deposits are re-examined, with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction. Defining an arbitrary subdivision at a molar Cu/Au ratio of 4.0 × 10⁴, copper–gold deposits have a shallower average depth of formation (2.1 km) compared with the average depth of copper–molybdenum deposits (3.7 km), based on assumed lithostatic fluid pressure from microthermometry. The correlation of Cu/Au ratio with depth is primarily influenced by the variations of total Au grade. Despite local mineralogical controls within some ore deposits, the overall Cu/Au ratio of the deposits does not show a significant correlation with the predominant type of Cu–Fe sulfide, i.e., chalcopyrite or bornite. Primary magma source probably contributes to metal endowment on the province scale and in some individual deposits, but does not explain the broad correlation of metal ratios with the pressure of ore formation. By comparison with published experimental and fluid analytical data, the observed correlation of the Cu/Au ratio with fluid pressure can be explained by dominant transport of Cu and Au in a buoyant S-rich vapor, coexisting with minor brine in two-phase magmatic hydrothermal systems. At relatively shallow depth (approximately <3 km), the solubility of both metals decreases rapidly with decreasing density of the ascending vapor plume, forcing both Cu and Au to be coprecipitated. In contrast, magmatic vapor cooling at deeper levels (approximately >3 km) and greater confining pressure is likely to precipitate copper ± molybdenum only, while sulfur-complexed gold remains dissolved in the relatively dense vapor. Upon cooling, this vapor may ultimately contract to a low-salinity epithermal liquid, which can contribute to the formation of epithermal gold deposits several kilometers above the Au-poor porphyry Cu–(Mo) deposit. These findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator. Low-pressure brine + vapor systems are favorable for coprecipitation of both metals, leading to Au-rich porphyry–copper–gold deposits. Epithermal gold deposits may be associated with such shallow systems, but are likely to derive their ore-forming components from a deeper source, which may include a deeply hidden porphyry–copper ± molybdenum deposit. Exposed high-pressure brine + vapor systems, or stockwork veins containing a single type of intermediate-density inclusions, are more likely to be prospective for porphyry–copper ± molybdenum deposits.  相似文献   

The effect of microorganisms on Fe precipitation rates at neutral pH   总被引：4，自引：0，他引：4  

Takeshi Kasama  Takashi Murakami   《Chemical Geology》2001,180(1-4):117-128

The effect of microorganisms on Fe precipitation rates at neutral pH in the field was examined. The studied area was a cave having Fe-stalactites composed mainly of ferrihydrite and associated microorganisms. The microorganisms were covered with ferrihydrite. Water associated with stalactites was slightly supersaturated with respect to ferrihydrite, and had a dissolved oxygen concentration of 2 ppm, a pH of 6, and an Fe concentration of approximately 14 ppm. Fe precipitation rates were estimated from decreases in Fe concentrations in water during flowing through the Fe-stalactites. The estimated Fe precipitation rate in the field ranges from 6.8×10⁻⁸ to 4.0×10⁻⁷ mol/l/s. These values are in good agreement with bulk estimates of Fe-stalactite growth rates derived from the length increase (1.3 cm) of one formation over 30 days. The estimated Fe precipitation rates are faster by about four orders of magnitude than expected inorganic precipitation rates. On-site Fe precipitation experiments with sterilized and unsterilized Fe-stalactites and without Fe-stalactites indicate that microorganisms are the controlling factor accelerating Fe precipitation rates at neutral pH. These results suggest that microbially accelerated Fe precipitation rates are more likely related to exopolysaccharides and microbial surface properties than metabolic precipitation mechanisms.  相似文献