Chemical characteristics of the Cretaceous-Tertiary boundary layer at Gubbio, Italy   总被引：2，自引：0，他引：2  

Mitsuru Ebihara  Tsutomu Miura 《Geochimica et cosmochimica acta》1996,60(24):5133-5144

Platinum metals (Pd, Ir, Pt) and Au were determined by radiochemical neutron activation analysis (RNAA) on Cretaceous-Tertiary (K---T) boundary samples collected at Gubbio, Italy. In addition, about thirty elements were determined by instrumental NAA (INAA) for both the Cretaceous and the Tertiary layer samples, as well as the boundary clay samples. Iridium and other Pt metals were observed to be similarly enriched, relative to CI-chondrite, in the boundary layers, i.e., they occur in chondritic ratios. On the other hand, correlations among the metals are not very good, suggesting that Pt metals were not incorporated into clay materials in a single phase, but rather, they behaved separately according to their own solution chemistries. In the Gubbio section, the chemical composition does not change so much across the K---T boundary layer, except for Ir (and possibly other Pt group elements) and is very similar to that of the “North American shale composite (NASC)”. Arsenic and Sb were observed not to be anomalously enriched in the Gubbio K---T boundary layers. This implies that their abundances cannot be a clue in elucidating an event which must have happened at the K---T boundary period. NASC-normalized REE abundance patterns for the boundary samples show characteristic features due to some REE precipitation out of seawater. REE abundances are not variable among the Cretaceous, the Tertiary, and the boundary samples, suggesting that conditions for precipitation and sedimentation were similar across the K---T boundary at Gubbio.  相似文献   

A trachyte–syenite core within a basaltic nest: filtering of primitive injections by a multi-stage magma plumbing system (Oki-Dōzen,south-west Japan)     

Marco Brenna  Setsuya Nakada  Daisuke Miura  Kiyoshi Toshida  Hisatoshi Ito  Natsumi Hokanishi  Shun’ichi Nakai 《Contributions to Mineralogy and Petrology》2015,169(2):1-21

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FE analysis of grid reinforced embankment system on soft Bangkok clay     

D. T. BergadoJ. C. ChaiN. Miura 《Computers and Geotechnics》1995,17(4):447-471

The behavior of a reinforced embankment on soft Bangkok clay has been analyzed by plane strain finite element method. The finite element analysis considers the selection of proper soil/reinforcement properties according to the relative displacement pattern of upper and lower interface elements. The large deformation phenomenon is simulated by updating the node coordinates, including those of the embankment elements above the current construction level, which ensures that the applied fill thickness simulates the actual field value. A full scale test reinforced embankment with a vertical face (wall) on Bangkok clay has been analyzed by the proposed finite element method, and the numerical results are compared with the field data. The response of a reinforced embankment on soft ground is principally controlled by the interaction between the reinforced soil mass and soft ground and the interaction between the grid reinforcement and the backfill soil. The tension in reinforcement and lateral displacement of the wall face varied during consolidation of foundation soil. The maximum tension force occurred in the reinforcement layer placed at the base of reinforced mass, due to bending of the reinforced mass resulting from differential settlements. It is considered necessary to account for the permeability variation of the soft ground foundation in the finite element analysis.  相似文献   

Shear moduli of volcanic soils   总被引：1，自引：0，他引：1  

T. Sahaphol  S. Miura 《Soil Dynamics and Earthquake Engineering》2005,25(2):819

The shear modulus of soils is one of the important parameters in small strain level geotechnical problems (i.e. the study of earthquake effects and soil–structure interaction). In this paper, the shear moduli of crushable volcanic soils at small strain level were investigated in bender element and cyclic undrained triaxial tests. Comparison of results shows that the shear moduli from bender element tests agree well with those determined in cyclic triaxial tests. The influence of particle breakage, effective confining pressure, consolidation time, void ratio and fines content on the shear modulus are also discussed. In the present study, empirical equations for evaluating the shear modulus of granular materials with particle breakage are proposed based on the test results.  相似文献   

Structural characteristics controlling the seismicity crustal structure of southern Japan Trench fore-arc region, revealed by ocean bottom seismographic data     

Seiichi Miura  Shuichi Kodaira  Ayako Nakanishi  Tetsuro Tsuru  Narumi Takahashi  Naoshi Hirata  Yoshiyuki Kaneda 《Tectonophysics》2003,363(1-2):79-102

The Japan Trench is a plate convergent zone where the Pacific Plate is subducting below the Japanese islands. Many earthquakes occur associated with plate convergence, and the hypocenter distribution is variable along the Japan Trench. In order to investigate the detailed structure in the southern Japan Trench and to understand the variation of seismicity around the Japan Trench, a wide-angle seismic survey was conducted in the southern Japan Trench fore-arc region in 1998. Ocean bottom seismometers (15) were deployed on two seismic lines: one parallel to the trench axis and one perpendicular. Velocity structures along two seismic lines were determined by velocity modeling of travel time ray-tracing method. Results from the experiment show that the island arc Moho is 18–20 km in depth and consists of four layers: Tertiary and Cretaceous sedimentary rocks, island arc upper and lower crust. The uppermost mantle of the island arc (mantle wedge) extends to 110 km landward of the trench axis. The P-wave velocity of the mantle wedge is laterally heterogeneous: 7.4 km/s at the tip of the mantle wedge and 7.9 km/s below the coastline. An interplate layer is constrained in the subducting oceanic crust. The thickness of the interplate layer is about 1 km for a velocity of 4 km/s. Interplate layer at the plate boundary may cause weak interplate coupling and low seismicity near the trench axis. Low P-wave velocity mantle wedge is also consistent with weak interplate coupling. Thick interplate layer and heterogeneous P-wave velocity of mantle wedge may be associated with the variation of seismic activity.  相似文献   

The occurrence of chlorine in serpentine minerals     

Y. Miura  J. Rucklidge  G. L. Nord Jr. 《Contributions to Mineralogy and Petrology》1981,76(1):17-23

Partially serpentinized dunites containing small amounts of Chlorine (< 0.5%) from Dumont, Quebec, and Horoman, Hokkaido, Japan, and one containing less than 0.05% Chlorine from Higashi-Akaishi-Yama, Ehime, Japan have been examined using the electron probe microanalyzer and scanning transmission electron microscope with X-ray analytical capabilities. Chlorine was found together with Si, Mg, Ca and Fe in the serpentine minerals of the Dumont and Hokkaido dunites but not in the Ehime dunite. Chlorine is found associated only with the most finely crystalline facies of the serpentine (grain size less than 10 nm). The Ehime dunite contained no such fine grained serpentine, and was thus effectively chlorine-free, as are the coarser grained serpentines of the other samples. The finegrained chlorine-bearing serpentine also has a much higher concentration of Fe, and can contain smaller amounts of Ca, Ni and Mn than the coarse-grained variety as well as minute awaruite (FeNi₃) grains. This fine-grained serpentine probably represents an early stage in the transformation of olivine to serpentine, with chlorine from hydrothermal solutions assisting the necessary chemical changes. The Cl increases the reaction rate by lowering the activation barrier to reaction by the introduction of reaction steps.On leave of absence from Department of Mineralogical Sciences and Geology, Yamaguchi University, Yamaguchi 753, Japan  相似文献   

A methodology for locating strong motion arrays     

F. E. Udwadia  H. Miura 《地震工程与结构动力学》1980,8(5):439-453

This paper investigates a methodology for locating strong motion accelerographs in a seismically active region. Starting with the probability density of earthquakes in a given region, the paper attempts, within the framework of optimization theory, to formulate the following two questions: (1) given N accelerographs, where should they be located in a seismically active zone, and (2) having fixed these N accelerographs, where should the next M be located? Three different cost functions are presented. Some closed form solutions are illustrated for problems when N and M are small. For larger arrays, numerical optimization is resorted to. To demonstrate the methodology, a region with J faults, with given spatial locations is selected. An efficient algorithm for optimization is utilized and the technique illustrated. Good agreement with closed form solutions obtained in some simple cases is indicated. Specific application of the method to the placing of twenty strong motion instruments in a seismically active area has been carried out, and the patterns of sensor location, for each of the cost functions, illustrated.  相似文献   

Kaolin deposits at Melthonnakkal and Pallipuram within Trivandrum block, southern India     

M. Nakagawa  M. Santosh  S. Yoshikura  M. Miura  T. Fukuda  A. Harada 《Gondwana Research》2006,9(4):530-538

The kaolin deposits at Melthonnakkal and Pallipuram mines form part of the Warkalli Formation belonging to the Tertiary sequence in southern Kerala and occur at the boundary between the Tertiary sequence and Precambrian granulite facies metapelites (khondalites). The sedimentary clays are composed mainly of kaolinite, quartz and gibbsite. XRD and SEM studies have revealed that kaolinite is well-crystallized variety and the platy crystals are scarcely broken in the sedimentary clays. These sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites, and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock. Besides, the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by Quaternary tropical weathering processes.  相似文献   

Japan Trench and tectonics of the Japanese Island Arcs     

Nobuaki Niitsuma 《Island Arc》2004,13(1):306-317

Abstract Seven chronostratigraphic stages were established based on the correlation of magneto‐biostratigraphic marker horizons within the Deep Sea Drilling Project and Ocean Drilling Program cores from the forearc of the Japan Trench. Because the stages are coeval with changes in the rate of sedimentation, lithofacies, magnetic intensity and composition of fossil assemblages, they probably reflect the tectonic situation in the Japan Trench forearc and also in the arc–trench system. The stages correlate to the tectonic events of the Japanese Island Arcs; for example, evolution of the Boso triple junction, initiation of Philippine Sea Plate subduction and the Japan Sea opening.  相似文献   

Soil erosion and overland flow in Japanese cypress plantations: spatio-temporal variations and a sampling strategy     

Takanori Sato  Nobuaki Tanaka  Anand Nainar  Koichiro Kuraji  Mie Gomyo  Haruhiko Suzuki 《水文科学杂志》2020,65(13):2322-2335

ABSTRACT

Many studies have focused on soil erosion in unmanaged Japanese cypress plantations because the sparse understory vegetation and litter covering the forest ground enhance soil erosion. In this study, soil erosion, litter, and overland flow measurements were conducted over 14 months to identify the spatio-temporal variation and examine the optimal sample size. Fifteen traps (each 0.25 m wide) were installed in line along the bottom of a 15-m-wide slope. Soil erosion and overland flow had large spatial variations as compared to litter. The temporal coefficient of variation of soil erosion and overland flow was highest during dry seasons, while smaller during wet seasons. The random sampling analysis showed that the rate of decrease in spatio-temporal variation became moderate as the sample size increased beyond six. This result indicated that the optimal sample size was five, the total width of which was equivalent to about 8% of the monitored slope width.  相似文献