Acoustic properties of deformed rocks in the Nobeoka thrust,in the Shimanto Belt,Kyushu, Southwest Japan          下载免费PDF全文

Yoshitaka Hashimoto  Shogo Abe  Hiroki Tano  Gaku Kimura  Asuka Yamaguchi  Rina Fukuchi  Jun Kameda  Yohei Hamada  Yujin Kitamura  Koichiro Fujimoto  Mio Eida 《Island Arc》2017,26(4)

Laboratory measurements for compressional and shear wave velocities (Vp and Vs, respectively) and porosity were conducted with core samples from the Nobeoka Thrust Drilling Project (NOBELL) under controlled effective pressure (5–65 MPa at 5 MPa intervals) and wet conditions. Samples were classified according to deformation texture as phyllite, foliated cataclasite, or non‐foliated cataclasite. Measured values of Vp, Vs, and porosity are within a range of 5.17–5.57 km/s, 2.60–2.71 km/s, and 2.75–3.10 %, respectively, for phyllite; 4.89–5.23 km/s, 2.46–2.57 km/s, and 3.58–4.53 %, respectively, for foliated cataclasite; and 4.90–5.32 km/s, 2.51–2.63 km/s, and 3.79–4.60 %, respectively, for non‐foliated cataclasite, which are all consistent with the previous laboratory experiments conducted with outcrop samples under dry conditions. However, our results also indicate higher Vp and Vs and lower porosity than those measured by the previous studies that adopted the wire‐line logging methods. The variations in Vp, Vs, and porosity are controlled by deformation structure and are greater for phyllite and foliated cataclasite than for non‐foliated cataclasite.  相似文献   

Element transport by dehydration of subducted sediments: Implication for arc and ocean island magmatism   总被引：5，自引：0，他引：5  

Yoshitaka Aizawa  Yoshiyuki Tatsumi  & Hirohisa Yamada 《Island Arc》1999,8(1):38-46

High-pressure experiments on a natural pelite have been conducted at 2–11-GPa pressures in order to evaluate contributions of subducted sediments to arc and ocean island magmatism. Obtained phase relations suggest that, at least in modern subduction zones, subsolidus dehydration of chlorite and phengitic muscovite in the subducted sediments, rather than partial melting, is a predominant process in overprinting sediment components onto the magma source region. Trace element compositions of sediment-derived fluids are estimated based on dehydration experiments at 5.5 GPa and 900/1300°C. Pb is effectively transported by fluids relative to other elements. This results in the Pb enrichment for arc basalts by fluids, generated by the dehydration of subducted sediments, together with altered mid-ocean ridge basalt (MORB), and complementary depletion of Pb in subducted sediments. Inferred arc magma compositions obtained by model calculations based on the present experimental results agree well with a natural primitive arc basalt composition. A large increase in the U/Pb ratio in the subducted sediments at deeper levels than major dehydration depths results in a high Pb isotopic ratio through radioactive decay after long periods of isolation. Combined with other isotopic ratios such as Sr and Nd, it is possible to produce the EM II source, one of the enriched geochemical reservoirs for ocean island basalt magmas, by mixing of a small amount of subducted sediments with depleted or primitive mantle.  相似文献   

Effect of Anisotropy on the Long-Term Strength of Granite     

Yoshitaka Nara 《Rock Mechanics and Rock Engineering》2015,48(3):959-969

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CaPtO3 as a novel post-perovskite oxide     

Kenya Ohgushi  Yoshitaka Matsushita  Nobuyoshi Miyajima  Yoshio Katsuya  Masahiko Tanaka  Fujio Izumi  Hirotada Gotou  Yutaka Ueda  Takehiko Yagi 《Physics and Chemistry of Minerals》2008,35(4):189-195

Structural, morphological, magnetic, and thermal properties have been investigated for a novel post-perovskite oxide CaPtO₃ synthesized under high pressure. By comparing obtained structural parameters with those for known post-perovskite compounds, we argue that the chemical bond has a strong covalent character. Precise measurements of the Langevin susceptibility χ ₀ = −9.6 × 10⁻⁵ emu/mol and Debye temperature θ ∼ 470 K provide a good opportunity to confirm the reliability of first-principle calculations on predicting physical properties of the Earth’s D” layer.  相似文献   

Spatiotemporal dynamics of forest net primary production in China over the past two decades     

Quan Wang  Ping Zhao  Hai Ren  Yoshitaka Kakubari 《Global and Planetary Change》2008,61(3-4):267-274

Forest ecosystems play an important role in global carbon cycle regulation. Clarifying the dynamics and mechanism of carbon sink is of both scientific and political importance. In this paper, we have investigated the spatiotemporal change of forest net primary production (NPP) in China for recent two decades based on the geographically weighted regression (GWR) with a cumulative remote sensing index, the maximum normalized difference vegetation index (NDVI_max). GWR is a recently developed regression method with special emphasis on spatial non-stationarity. Outputs of forest NPP at three different stages was generated by the GWR model with NDVI_max for the 1980s, early and late 1990s which were consequently analyzed. Our results indicated a wave-like pattern of change in forest NPP in the three stages with a trough-like depression for the early 1990s. The average forest NPP increased by about 0.72% from the 1980s to the late 1990s. A continuously increasing trend at a pace of 0.07% and 0.22% yr^− 1 was observed in the tropical and subtropical zones from the 1980s to late 1990s respectively, while a continuously decreasing trend (− 0.05% yr^− 1) was noted for the temperate zone. From forest type perspective, only the deciduous broadleaf forests exhibited a continuously decreasing trend of 0.18% yr^− 1. The complex spatiotemporal patterns revealed by this study suggest the need for further research in this direction in order to build in-depth insights into the revealed complexities.  相似文献   

Fourth‐ to third‐order cycles in the Hakobuchi Formation: Shallow‐marine Campanian final deposition of the Yezo Group,Nakagawa area,northern Hokkaido,Japan     

Hisao Ando  Yoshitaka Tamura  Daisuke Takamatsu 《Island Arc》2010,19(4):567-589

The Yezo Group has a wide longitudinal distribution across Hokkaido, northern Japan. It represents a Cretaceous (Early Aptian–Late Maastrichtian) and Late Paleocene forearc basin‐fill along the eastern margin of the paleo‐Asian continent. In the Nakagawa area of northern Hokkaido, the uppermost part of the Yezo Group consists of the Hakobuchi Formation. Along the western margin of the Yezo basin, 24 sedimentary facies (F) represent 6 facies associations (FA), suggesting prevailing storm‐dominated inner shelf to shoreface environments, subordinately associated with shoreface sand ridges, outer shelf, estuary and fluvial environments. The stacking patterns, thickness and facies trends of these associations allow the discrimination of six depositional sequences (DS). Inoceramids Sphenoceramus schmidti and Inoceramus balticus, and the ammonite Metaplacenticeras subtilistriatum, provide late Early to Late Campanian age constraints to this approximately 370‐m thick final stage of deposition and uplift of the Yezo forearc basin. Six shallow‐marine to subordinately non‐marine sandstone‐dominated depositional sequences include four 10 to 110‐m thick upward‐coarsening regressive successions (FS1), occasionally associated with thin, less than 10‐m thick, upward‐fining transgressive successions (FS2). The lower DS1–3, middle DS4–5 and upper DS6 represent three depositional sequential sets (DSS1–3). These eastward prograding and westward retrograding recurring shallow‐marine depositional systems may reflect third‐ and fourth‐order relative sealevel changes, in terms of sequence stratigraphy.  相似文献   

Tectonic incorporation of the upper part of oceanic crust to overriding plate of a convergent margin: An example from the Cretaceous–early Tertiary Mugi Mélange, the Shimanto Belt, Japan     

Eisei Ikesawa  Gaku Kimura  Katsushi Sato  Kotoe Ikehara-Ohmori  Yujin Kitamura  Asuka Yamaguchi  Kohtaro Ujiie  Yoshitaka Hashimoto   《Tectonophysics》2005,401(3-4):217-230

A tectonic mélange exposed on land is examined to reveal relationships between mélange formation, underplating, and deformation mechanisms, focusing on the deformation of basaltic rocks. The studied Mugi Mélange of the Shimanto Belt is composed of a shale matrix surrounding various blocks of sandstone, pelagic sediments, and basalts. The mélange was formed during Late Cretaceous to early Tertiary times in a subduction zone under P–T conditions of 150–200 °C and 6–7 km depth as estimated from vitrinite reflectance and quartz veins fluid inclusions. The mélange represents a range of deformation mechanisms; pressure solution with micro-scale cataclasis in the shale matrix, brittle tension cracking in the blocks, and ubiquitous strong cataclasis in the basal portion of basaltic layers. The cataclastic deformation in the basalts suggests a breakage of a topographic high in the seismogenic depth.  相似文献   

Geochemical and Microbiological Analysis of Sambe Hot Springs,Shimane Prefecture,Japan     

Keiko Sasaki  Yoshitaka Uejima  Atsushi Sakamoto  Qianqian Yu  Junichiro Ishibashi  Naoko Okibe  Tsuyoshi Hirajima 《Resource Geology》2013,63(2):155-165

Microbiological contribution to the formation of the manganese deposits in Sambe hot springs, Shimane, was investigated in combination with water chemistry, characterization of sediments and microbial community structure. Analysis of bacterial and fungal community structure based on DNA extracted from a Mn‐oxidizing enrichment culture indicated close matches with Pseudomonas putida, Phoma sp. and Plectosphaerella cucumerina, all Mn‐oxidizing microorganisms. These sediments were poorly crystalline and formed at neutral pH values, which is characteristic of biogenic precipitates. The EPMA results demonstrated a positive correlation between Mn and Ba contents in well‐crystalline Mn oxide grains. Substantial Ba contents were observed inside Mn oxide grains. These findings indicated that Ba contents in sediments are influenced by not only aqueous Ba²⁺ concentrations but also crystallinity of biogenic birnessite. Barium would be incorporated in birnessite during biomineralization.  相似文献   

天然硅藻土的应力水平与孔隙空间分布的关系   总被引：4，自引：1，他引：3  

洪振舜  立石义孝  邓永锋 《岩土力学》2004,25(7):1023-1026

采用压汞法研究了不同固结压力作用下具有强结构性的天然沉积硅藻土的微观孔隙入口孔径分布与应力水平的关系。研究结果表明：当应力水平小于固结屈服应力时,具有强结构性的天然沉积硅藻土的微观孔隙入口孔径分布几乎与应力水平无关,而当外加应力水平达到固结屈服压力时,虽然总体孔隙空间体积几乎与天然沉积状态时一样,但其微观孔隙入口孔径分布则发生显著变化。在屈服后阶段,随着应力水平的增大硅藻土的孔隙空间体积逐渐减少,最大孔隙变小,整体孔隙空间的孔径趋于均匀。并对微观结构变化与宏观力学特性的内在联系也进行了初步探讨。  相似文献   

Temporal stress variations along a seismogenic megasplay fault in the subduction zone: An example from the Nobeoka Thrust,southwestern Japan          下载免费PDF全文

Ryoji Kawasaki  Yoshitaka Hashimoto  Makoto Otsubo  Asuka Yamaguchi  Yujin Kitamura  Jun Kameda  Yohei Hamada  Rina Fukuchi  Gaku Kimura 《Island Arc》2017,26(3)

The Nobeoka Thrust, an ancient megasplay fault in the Shimanto Belt, southwestern Japan, contains fault rocks from the seismogenic zone, providing an accessible analog of active megasplay faults in deep subduction settings. In this study, the paleostress along the Nobeoka Thrust was analyzed using multiple inversion techniques, including k‐means clustering of fault datasets acquired from drillcores that intersected the thrust. The six resultant stress orientation clusters can be divided into two general groups: stress solutions with north–south‐trending σ₁ axes, and those with east–west‐trending σ₁ axes. These groups are characterized by the temporal changes for the orientations of the σ₁ and σ₃ principal stress axes that involve alternation between horizontal and vertical. The findings are probably due to a change in stress state before and after earthquakes that occurred on the fault; similar changes have been observed in active tectonic settings, such as the 2011 Tohoku‐Oki earthquake (Japan).  相似文献