Measurement of⁵³Mn in deep-sea iron and stony spherules     

Kunihiko Nishiizumi 《Earth and Planetary Science Letters》1983,63(2):223-228

Cosmic-ray-produced⁵³Mn (t_1/2 = 3.7 × 10⁶years) was measured in individual and groups of deep-sea iron and stony spherules by highly sensitive neutron activation analysis. The activities found were less than 20 dpm⁵³Mn/kg Fe (10^?5?10^?6 dpm⁵³Mn/sample) in iron spherules except one iron spherule whose activity was 241 ± 73 dpm⁵³Mn/kg Fe. These low activities may indicate evaporative loss of⁵³Mn due to heating in the earth's atmosphere. On the other hand, all stony spherules contained 200–260 dpm⁵³Mn/kg Fe which is similar to chondritic values. These spherules may be ablation debris from large objects.  相似文献   

Mineralogy and geochemistry of the Au-Ag ore deposits of the South Korean Peninsula     

H. Kaneda  H. Shimazaki  M. S. Lee 《Mineralium Deposita》1986,21(3):234-243

Pyrite and arsenopyrite are the predominant ore minerals in the Korean Au-Ag deposits of this study. The X _Ni ^py , X _Co ^py , X _Ni ^apy , and X _Co ^apy values range between 100 and 3,000 ppm, 200 and 6,000 ppm, 200 and 8,200 ppm, and 100 and 10,200 ppm, respectively. Most X _Ni ^py /X _Co ^py values fall in the field lower than values varying 0.16–1.30. Arsenopyrite also tends to prefer cobalt rather than nickel showing X _Ni ^apy /X _Co ^apy values between 0.20 and 1.40. The concentrations of minor elements in ores and gangue minerals vary 1–55 ppm Au and 1–1,120 ppm Ag for the former and 4–57 ppm Ni and 2–45 ppm Co for the latter. The Au/Ag ratio in ore has a good correlation to the Ni/Co ratio of arsenopyrite to gangue. The (Ni/Co)_py-(Ni/Co)_gangue and (Ni/Co)_apy-(Ni/Co)_gangue diagrams revealed that the values from the Korean Au-Ag deposits plot in the field lower than 900 °C which is the lowermost temperature determined by previous partitioning experiments.  相似文献   

Pre-seismic crustal deformation caused by an underthrusting oceanic plate,in eastern Hokkaido,Japan     

Kunihiko Shimazaki 《Physics of the Earth and Planetary Interiors》1974,8(2):148-157

Eastern Hokkaido is being considered as one of the prime candidates for a future great earthquake in Japan. Geodetic work and seismological data suggest that the continental plate is being compressed and dragged down into the asthenosphere by the underthrusting Pacific plate.A quantitative examination of this idea was carried out by an application of the finite-element method to a static-field problem of crustal deformation. The effect of heterogeneous medium with Poisson's ratio differing from 0.25 is significant. An inverse problem was solved by applying a quadratic programming method to the observed vertical displacement.A model, which assumes a nearly uniform tangential displacement along the interface of the oceanic and continental lithospheres down to a depth of 100 km, explains a gravity-change as well as the general features of crustal deformation observed in eastern Hokkaido. The displacement rate is estimated to be 2.7 cm/year. It indicates that a rebound of the continental lithosphere now brings about a thrust-type earthquake whose reverse slip is comparable to that estimated for great shallow earthquakes along the Kuril trench. A possibility of aseismic rebound is suggested at the lower part of the interface.  相似文献   

Late quaternary uplift in eastern Indonesia     

H.D. Tjia  Shoji Fujii  Kunihiko Kigoshi  Arata Sugimura 《Tectonophysics》1974,23(4):427-433

Radiocarbon dates of fifteen samples representing raised shorelines on various islands of the tectonically mobile region of eastern Indonesia suggest rates of tectonic uplift ranging up to 12.5 mm/year. Low rates of 0.35–1.2 mm/year are from Biak Island and are averages for the last 31,000–36,000 years. The low rates may be explained to indicate subsidence alternating with uplift, both of which occurring under influence of the large Irian fault zone that passes to the immediate south of the island. Very young elevated strandlines (250 years BP) indicate rates of uplift between 8 and 12.5 mm/year which seem to demonstrate the episodic character of vertical diastrophic movements. Intermediate rates of uplift are in the order of 5 mm/year and may represent averages for eastern Indonesia.  相似文献   

Oxygen and carbon isotope zonations of wall rocks around the Kamioka Pb---Zn skarn deposits, central Japan: application to prospecting     

Koh Naito  Yasumasa Fukahori  He Peiming  Wakaba Sakurai  Hidehiko Shimazaki  Yukihiro Matsuhisa 《Journal of Geochemical Exploration》1995,54(3)

Mapping of the oxygen and carbon isotopic composition of hydrothermally altered wall rocks was conducted during blind ore prospecting for Pb---Zn skarn deposits in the Kamioka mining district, central Japan. The wall rocks consist of heterogeneous rock units. Oxygen and carbon isotope ratios were determined for 35 limestones and 33 silicate rocks from the area around the Mozumi deposit (3 km × 3 km) in the Kamioka mining district. The results (δ¹⁸O_spsmow of − 1.1 to + 17.3% and δ¹³C_sppdb of − 5.0 to +4.8% for limestones, and δ¹⁸O_spsmow of −0.8 to + 12.5% for silicate rocks) show isotope zonations of the wall rocks, with lighter isotopic compositions toward the center of mineralization. The isotope zonations likely formed by interaction of thermal waters with the wall rocks during skarn mineralization. The isotopically light zone indicates a higher paleotemperature or higher water-to-rock ratios, and occurs in the footwall of the 7Gohi fault. This structure is spatially related to the distribution of orebodies, indicating that the fault was the main conduit of the ore-forming fluids. The oxygen and carbon isotopic compositions of limestones vary regularly across limestone bodies hosted by the silicate wall rocks, suggesting that the thermal waters were pervasive throughout the wall rocks at the time of mineralization.An isotopically light zone was also found in the southeastern corner of the study area, where significant mineralization had yet to be identified. This suggested an extension of the extinct hydrothermal system to this area, and the possibility of hidden orebodies underneath. Recent drilling in this area has intercepted a zone 45 m thick with a grade of 13.4% Zn, 0.03% Pb and 8 g per metric ton at about 380 m depth.  相似文献   

Oxygen isotope study of the Kamioka Zn-Pb skarn deposits,Central Japan     

H. Shimazaki  M. Kusakabe 《Mineralium Deposita》1990,25(3):221-229

The Kamioka Zn-Pb deposits consist of clinopyroxene-rich skarns replacing limestone lenses in Hida gneissose rocks. Paleozoic metabasite, early Jurassic Funatsu granitic rocks and late Cretaceous porphyritic dikes and stocks, are the known igneous rocks in the mining area. Oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits (Table 1), and some minerals and rocks from the major rock units around the deposits (Table 2), have been analyzed. The estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits, range as low as -4 to +3 (SMOW). These values are considerably lower than expected from magmatic waters, and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn- and ore-forming fluids. The data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin, promoted by a hidden batholithic intrusion at the time of the late Cretaceous.  相似文献   

Biomass estimation of Sonneratia caseolaris (l.) Engler at a coastal area of Hai Phong city (Vietnam) using ALOS-2 PALSAR imagery and GIS-based multi-layer perceptron neural networks     

Tien Dat Pham  Kunihiko Yoshino  Dieu Tien Bui 《地理信息系统科学与遥感》2017,54(3):329-353

This study tested the use of machine learning techniques for the estimation of above-ground biomass (AGB) of Sonneratia caseolaris in a coastal area of Hai Phong city, Vietnam. We employed a GIS database and multi-layer perceptron neural networks (MLPNN) to build and verify an AGB model, drawing upon data from a survey of 1508 mangrove trees in 18 sampling plots and ALOS-2 PALSAR imagery. We assessed the model’s performance using root-mean-square error, mean absolute error, coefficient of determination (R²), and leave-one-out cross-validation. We also compared the model’s usability with four machine learning techniques: support vector regression, radial basis function neural networks, Gaussian process, and random forest. The MLPNN model performed well and outperformed the machine learning techniques. The MLPNN model-estimated AGB ranged between 2.78 and 298.95 Mg ha^?1 (average = 55.8 Mg ha^?1); below-ground biomass ranged between 4.06 and 436.47 Mg ha^?1 (average = 81.47 Mg ha^?1), and total carbon stock ranged between 3.22 and 345.65 Mg C ha^?1 (average = 64.52 Mg C ha^?1). We conclude that ALOS-2 PALSAR data can be accurately used with MLPNN models for estimating mangrove forest biomass in tropical areas.  相似文献   

The sensitivity of hillslope bedrock erosion to precipitation     

Justine J. Owen  Ronald Amundson  William E. Dietrich  Kunihiko Nishiizumi  Brad Sutter  Guillermo Chong 《地球表面变化过程与地形》2011,36(1):117-135

Decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem. Hillslope erosion rates are well known to respond to changes in hillslope boundary conditions (e.g. channel incision rates) through their dependence on soil thickness, and precipitation is an important control on soil formation. Surprisingly though, compilations of hillslope denudation rates suggest little precipitation sensitivity. To isolate the effects of precipitation and boundary condition, we measured rates of soil production from bedrock and described soils on hillslopes along a semi‐arid to hyperarid precipitation gradient in northern Chile. In each climate zone, hillslopes with contrasting boundary conditions (actively incising channels versus non‐eroding landforms) were studied. Channel incision rates, which ultimately drive hillslope erosion, varied with precipitation rather than tectonic setting throughout the study area. These precipitation‐dependent incision rates are mirrored on the hillslopes, where erosion shifts from relatively fast and biologically‐driven to extremely slow and salt‐driven as precipitation decreases. Contrary to studies in humid regions, bedrock erosion rates increase with precipitation following a power law, from ～1 m Ma^?1 in the hyperarid region to ～40 m Ma^?1 in the semi‐arid region. The effect of boundary condition on soil thickness was observed in all climate zones (thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels), but the difference in bedrock erosion rates between the hillslopes within a climate region (slower erosion rates on hillslopes with stable boundaries) decreased as precipitation decreased. The biotic‐abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness. Our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta     

Matthias M. M. MEIER  Kees C. WELTEN  Marc W. CAFFEE  Jon M. FRIEDRICH  Peter JENNISKENS  Kunihiko NISHIIZUMI  Muawia H. SHADDAD  Rainer WIELER 《Meteoritics & planetary science》2012,47(6):1075-1086

Abstract– We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (¹⁰Be, ²⁶Al, ³⁶Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm^?2, consistent with the preatmospheric size of asteroid 2008 TC₃ that produced the Almahata Sitta strewn field; (2) both have, within error, a ²¹Ne/²⁶Al‐based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 10–20 Ma, visible only in cosmogenic ³⁸Ar. We also discuss the approximately 3.8 Ga (⁴He) and approximately 4.6 Ga (⁴⁰Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC₃ is derived has not experienced a large break‐up event in the last 3.8 Ga.  相似文献   

Detection of Aseismic Slip on an Inland Fault by Crustal Movement and Groundwater Observations: A Case Study on the Yamasaki Fault, Japan     

Yuichi Kitagawa  Naoji Koizumi  Ryu Ohtani  Kunihiko Watanabe  Satoshi Itaba 《Pure and Applied Geophysics》2006,163(4):657-673

To understand the detailed process of fault activity, aseismic slip may play a crucial role. Aseismic slip of inland faults in Japan is not well known, except for that related to the Atotsugawa fault. To know whether aseismic slip does not occur, or is merely not detected, is an important question. The National Institute of Advanced Industrial Science and Technology constructed an observation site near Yasutomi fault, a part of the Yamasaki fault system, and has collected data on the crustal strain field, groundwater pressures, and crustal movement using GPS. In a departure from the long-term trend, a transient change of the crustal strain field lasting a few months was recorded. It indicated the possibility of an aseismic slip event. Furthermore, analyses of data from the extensometers at Yasutomi and Osawa observation vaults of Kyoto University, as well as GPS data from the Geographical Survey Institute (GEONET), revealed unsteady crustal strain changes. All data could be explained by local, left-lateral, aseismic slip of the order of 1 mm in the shallow part of the Yasutomi fault.  相似文献