Large-amplitude internal waves observed in the Kruzenshtern Strait of the Kuril Island Chain and possible water transport and mixing     

Tomohiro Nakamura  Yasuhiro Kawasaki  Tokihiro Kono  Toshiyuki Awaji 《Continental Shelf Research》2010

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Influence of shear angle on hangingwall deformation during tectonic inversion     

Yasuhiro Yamada  Ken McClay 《Island Arc》2010,19(3):546-559

Tectonic inversion is a common phenomenon in island arc settings, especially in back‐arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault‐related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep‐sided half‐graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn‐extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5° during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.  相似文献   

Monitoring heat losses using Landsat ETM+ thermal infrared data — a case study at Kuju fumarolic area in Japan     

Md. Bodruddoza Mia  Yasuhiro Fujimitsu 《Acta Geophysica》2013,61(5):1262-1278

To monitor heat losses using Landsat 7 thermal infrared data from 2002 to 2010 within the active fumarolic region of Kuju volcano in Japan, we used the Stefan-Boltzmann equation for radiative heat flux (RHF) estimation. Heat discharge rate (HDR) was calculated by using the relationship coefficient of RHF and HDR, obtained from two previous studies. The highest total RHF was found to be about 57.7 MW in 2002 and the lowest was about 21.1 MW in 2010. We found the highest HDR, of about 384.5 MW, in 2002 and the lowest, of about 140.8 MW, in 2010. The RHF anomalous areas were showing a declining trend during our study period. The relationship between the land surface temperature (LST) above ambient and RHF was, as expected, in a strong correlation for each result during our study period. Overall, our study was able to delineate the declining trend of heat losses that supports a previous study of similar declining trend of HDR using steam maximum diameter method from the active fumarolic region of Kuju volcano.  相似文献   

Mapping hydrothermal altered mineral deposits using Landsat 7 ETM+ image in and around Kuju volcano, Kyushu, Japan     

MD. Bodruddoza Mia  Yasuhiro Fujimitsu 《Journal of Earth System Science》2012,121(4):1049-1057

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The early Miocene (~25 Ma) volcanism in the northern Kyushu-Palau Ridge,enriched mantle source injection during rifting prior to the Shikoku backarc basin opening   总被引：2，自引：1，他引：1  

Satoru Haraguchi  Teruaki Ishii  Jun-Ichi Kimura  Yasuhiro Kato 《Contributions to Mineralogy and Petrology》2012,163(3):483-504

The northern Kyushu-Palau Ridge (KPR), remnant conjugate arc of the Izu-Ogasawara (Bonin)-Mariana (IBM) active arc, is dominated by basalt-andesite except for the Komahashi-Daini Seamount where acidic plutonic rocks of 38 Ma were recovered. These mafic to intermediate volcanics are produced by the rifting volcanism in the proto-IBM arc associated with spreading of the Shikoku Basin. The HFSE and HREE contents and ratios of these volcanics indicate enriched source mantle composition compared to recent volcanic front. The LILE ratios exhibit similar characteristics to reararc volcanism of the recent Izu arc, and some enriched volcanics exhibit high abundance of sediment melt inputs. Based on these observations and compilations of the published data set, the replacement event of the wedge mantle under the IBM arc occurred two times. The first event occurred between 45 and 38 Ma, with Pacific type mantle being replaced by depleted Indian type mantle. The second event occurred between 36 and 25 Ma, enriched mantle flowed from reararc side. The slab component during the proto-IBM arc rifting was a similar characteristic to recent reararc volcanism of the Izu arc, and sediment melt added in a local area.  相似文献   

A new U–Pb zircon age dating and palynological data from a Lower Permian section of the southernmost Paraná Basin,Brazil: Biochronostratigraphical and geochronological implications for Gondwanan correlations     

Ana Luisa Outa Mori  Paulo Alves de Souza  Juliana Charão Marques  Ricardo da Cunha Lopes 《Gondwana Research》2012,21(2-3):654-669

Index species useful for correlations with the International Stratigraphical Column are rare or absent in the Pennsylvanian–Permian strata of the Paraná Basin in Brazil, preventing accuracy in geochronologic assignments. Besides, absolute datings are very scarce in comparison with other Gondwana basins. This paper presents palynological data from an outcrop on the surroundings of the Candiota coal mine, southmost Brazil, from several levels of the Rio Bonito and Palermo formations. The presence of certain index species of spore–pollen allowed the recognition of two Permian palynozones: the Vittatina costabilis and the Lueckisporites virkkiae zones. Furthermore, U–Pb in zircons from a volcaniclastic level interbedded in the coal strata of the former unit was analyzed through LA-MC-ICP-MS method, providing a new absolute age dating of 281.4 ± 3.4 Ma (Cisuralian, Early Permian). This dating is assumed as the oldest occurrence of the L. virkkiae Zone in Paraná Basin, which contains index species that are widespread in other Gondwana basins. A well distributed surface boundary occurs in this section also, allowing local and regional correlations. These new biostratigraphical and geochronological data are integrated, in order to offer a deep analysis on the stratigraphical significance for correlations across the Occidental Gondwana.  相似文献   

Explosive volcanic eruptions triggered by cosmic rays: Volcano as a bubble chamber     

Toshikazu Ebisuzaki  Hiroko Miyahara  Ryuho Kataoka  Tatsuhiko Sato  Yasuhiro Ishimine 《Gondwana Research》2011,19(4):1054-1061

Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm^?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H₂O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions.  相似文献   

Editorial     

Brian Horsfield  Ralf Littke  James J. Mori  G. S. Lynn Soreghan 《International Journal of Earth Sciences》2015,104(6):1497-1498

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Phase relations of iron and iron–nickel alloys up to 300 GPa: Implications for composition and structure of the Earth's inner core     

Yasuhiro Kuwayama  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi 《Earth and Planetary Science Letters》2008,273(3-4):379-385

We have investigated the phase relations of iron and iron–nickel alloys with 18 to 50 wt.% Ni up to over 300 GPa using a laser-heated diamond-anvil cell. The synchrotron X-ray diffraction measurements show the wide stability of hcp-iron up to 301 GPa and 2000 K and 319 GPa and 300 K without phase transition to dhcp, orthorhombic, or bcc phases. On the other hand, the incorporation of nickel has a remarkable effect on expanding the stability field of fcc phase. The geometry of the temperature–composition phase diagram of iron–nickel alloys suggests that the hcp–fcc–liquid triple point is located at 10 to 20 wt.% Ni at the pressure of the inner core boundary. The fcc phase could crystallize depending on the nickel and silicon contents in the Earth's core, both of which are fcc stabilizer.  相似文献   

Possible magma intrusion revealed by temporal gravity, ground deformation and ground temperature observations at Mount Komagatake (Hokkaido) during the 1996–1998 crisis     

Philippe Jousset  Hitoshi Mori  Hiromu Okada 《Geophysical Journal International》2000,143(3):557-574

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