Reconstruction of paleotemperatures in the Northwest Pacific over the past 3000 years from δO values of the micro-bivalvia Carditella iejimensis found in a submarine cave     

Nagisa Yamamoto  Akihisa Kitamura  Tomohisa Irino  Tomoki Kase  Syu-ichi Ohashi 《Global and Planetary Change》2008,62(1-2):97-106

We measured the δ¹⁸O values of the whole shells of the cavernicolous micro-bivalvia Carditella iejimensis obtained from sediments within a submarine cave (31 m water depth) at Ie Island (Okinawa Island, Japan) in the subtropical Northwest Pacific. Our results show no significant millennial-scale trend in the δ¹⁸O record, implying that both springtime temperature and the δ¹⁸O of sea water at 30 m depth around the Okinawa Islands have been stable for the past 3000 years at values similar to those of today. Moreover, we found one exceptionally light δ¹⁸O value from specimens spanning the past 250 years. The δ¹⁸O-derived temperature represents a departure of 2.1 °C from the average value for the past 250 years, being equal to the departure recorded during unusually high temperatures in the spring of 1998. This finding may imply that such high springtime sea surface temperature has been a rare event over the past 3000 years.  相似文献   

Complex organic molecules in an early stage of protostellar evolution     

Nami Sakai  Takeshi Sakai  Satoshi Yamamoto 《Astrophysics and Space Science》2008,313(1-3):153-157

We have detected the rotational lines of HCOOCH₃ toward a Class 0 low-mass protostar, NGC1333 IRAS4B, which is reported to be extremely young according to the dynamical age of the molecular outflow (a few 100 yr). This suggests that the complex organic molecules appear from the very early stage of protostellar evolution. On the other hand, the complex organic molecules are not detected in a more evolved protostar, L1527. We have also found a similar trend in a massive star forming region, NGC2264. The HCOOCH₃ emission is almost absent toward IRS1, whereas it is concentrated near MMS3, which is younger than IRS1. In addition, the HCOOCH₃ intensity peak is slightly shifted from the dust emission peak, as is seen in the Orion KL Compact Ridge, giving an important clue to solve its origin.  相似文献   

Constraining tephra dispersion and deposition from three subplinian explosions in 2011 at Shinmoedake volcano,Kyushu, Japan     

Fukashi Maeno  Masashi Nagai  Setsuya Nakada  Rose E. Burden  Samantha Engwell  Yuki Suzuki  Takayuki Kaneko 《Bulletin of Volcanology》2014,76(6):1-16

Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?10⁶ m³ for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?10⁶ m³ for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?10⁶ kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations.  相似文献   

Evaluation of a curve-fitting method for diffuse reflectance spectra in the UV–Visible–NIR wavelength region     

M. Miyamoto  T. Arai  M. Komatsu  A. Yamamoto  T. Mikouchi 《Polar Science》2009,3(2):110-116

The Modified Gaussian Method (MGM) proposed by Sunshine et al. [Sunshine, J.M., Pieters, C.M., Pratt, S.F., 1990. Deconvolution of mineral absorption bands: an improved approach. Journal of Geophysical Research 95, 6955–6966.] is generally used to decompose spectra in the UV–Visible–NIR wavelength region into the characteristic absorption bands of minerals. Here, we compare the optimized results obtained using different curve-fitting methods for this spectrum. The result obtained using the Gaussian function for the absorption band shows a better fit than that obtained using the Lorentzian function. The background continuum of a quadratic polynomial for the wavenumber provides a better result than does the linear function for the wavenumber. We successfully decomposed the spectra of ordinary chondrites and eucrites into the absorption bands of olivine and pyroxene. The wavelength positions of these absorption bands are broadly consistent with the Fe contents of olivine and pyroxene. Although the present results are derived from a limited number of spectra, they are of use in terms of the decomposition of diffuse reflectance spectra.  相似文献   

Formation of chaotic rock units during primary accretion processes: Examples from the Miura–Boso accretionary complex, central Japan     

Yuzuru  Yamamoto  Manami  Nidaira  Yasufumi  Ohta  Yujiro  Ogawa 《Island Arc》2009,18(3):496-512

Chaotic rock units exposed in the upper part of the accretionary complex preserve detailed tectonic information related to the periods before, during, and immediately after accretion. Based on the detailed survey in the upper Miocene Miura–Boso accretionary complex, central Japan, three types of chaotic rock units were identified on the basis of the grain sizes and characteristics of blocks and surrounding matrices. The chaotic rock units composed of silt matrices and sandy to pebbly blocks (Type 3) formed by gravity-driven slumping upon the seafloor. The slumping occurred contemporaneously with deposition of the Misaki and Nishizaki Formations within the Izu–Bonin forearc. Vertical variations in the direction of slump vergence represent successive changes from an initially flat seabed to tilting to the northwest and finally to the southeast. Slumping with a northwest vergence indicates landward tilting of the seafloor immediately prior to accretion, whereas vergence to the southeast reflects oceanward tectonic tilting that occurred once the sediments had crossed the deformation front. Other chaotic rock units that have matrices abundant in sand and pebbles (Types 1, 2) formed as a result of subsurface liquefaction and injection associated with large earthquakes that occurred during and after accretion of the sediments. These chaotic rock units are useful in examining surface/subsurface changes such as tectonic tilting of the seafloor and earthquake events during the initial accretion process.  相似文献   

Unconformity between a Late Miocene–Pliocene accretionary prism (Nishizaki Formation) and Pliocene trench‐slope sediments (Kagamigaura Formation), central Japan     

Yuzuru Yamamoto  Shun Chiyonobu  Toshiyuki Kurihara  Asuka Yamaguchi  Shoko Hina  Mari Hamahashi  Hugues Raimbourg  Romain Augier  Leslie Gadenne 《Island Arc》2012,21(4):231-234

  相似文献   

Probing the lower ionospheric perturbations associated with earthquakes by means of subionospheric VLF/LF propagation          下载免费PDF全文

Masashi Hayakawa 《地震科学（英文版）》2011,24(6):609-637

There have been reports for many years that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes (EQs) attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we present a possible use of VLF/LF (very low frequency (3–30 kHz)/low frequency (30–300 kHz)) radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies (ionospheric perturbations) and EQs (especially with large magnitude and with shallow depth), medium-distance (6-8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (the effect of atmospheric gravity waves, the effect of Earth's tides, etc.), and the mechanism of lithosphere-atmosphere-ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetic study.  相似文献   

导电薄层下三维岩脉的CSAMT响应分析   总被引：3，自引：2，他引：1       下载免费PDF全文

王若  Masashi Endo  底青云  王妙月 《地球物理学报》2010,53(3):677-684

为了研究探测3D导电岩脉状目标体的可控源音频电磁法（CSAMT）的最佳观测装置,我们用压缩积分方程法数值模拟了赋存于导电薄层下的3D导电岩脉的电磁场响应.计算结果表明,最有效的源的位置是把发射源沿岩脉的走向放置.相对于其他几种装置,这种观测装置得到的异常场与主场的比值最大.利用这种最佳的观测装置,通过将异常场E_ya 和 H_xa与噪音作对比,研究了当岩脉的埋深和高度发生变化时岩脉的可探测性问题.当岩脉的顶部埋深增加时,导电岩脉的可探测性降低.岩脉高度的变化对异常场幅值的影响要小于岩脉顶部埋深所产生的影响.所以通常情况下,即便应用了最有效的CSAMT装置,也很难探测到岩脉的高度,应用钻孔中的探测可能会解决这个问题.  相似文献   

Duplex of metamorphic units including ultramafic rocks in the central region of Tokunoshima,Southwest Japan          下载免费PDF全文

Shuro Ueda  Hiroshi Yamamoto  Masaru Terabayashi 《Island Arc》2017,26(4)

Geological observations in the central part of Tokunoshima in the Amami Islands, Southwest Japan, reveal that discrete layers of serpentinite, dioritic gneiss, and amphibolite are intercalated into pelitic schist and these rock bodies form a northwest‐dipping tectonic stack. A subhorizontal psammitic schist layer overlies them. These rocks underwent ductile deformation that is denoted by penetrative foliation and mineral lineation. Microstructures of the sheared metamorphic rocks and serpentinite indicate top‐to‐the‐east, ‐southeast or ‐south (hanging‐wall up) displacements. The en echelon array of rock bodies is interpreted as a duplex with the psammitic schist layer on its top and the pelitic schist layer on its bottom. It is inferred that the serpentinite‐bearing duplex was formed due to the tectonic erosion and the subsequent accretionary growth operated in a Cretaceous or older subduction zone. Tokunoshima has been considered to belong to the Shimanto Belt. However, regional low‐pressure and high‐temperature type amphibolite‐facies metamorphism and related ductile deformation have not been recognized in the other areas of the Shimanto Belt. There is no metamorphic rock occurrence comparable to that of Tokunoshima in the neighboring islands. The metamorphic rocks in Tokunoshima can be correlated to any of low‐pressure/temperature type metamorphic regions in Kyushu.  相似文献   

Late Cretaceous uplift history of the Cretaceous volcanic arc in Southwest Japan: Provenance analysis of the Yuasa–Aridagawa basin based on U–Pb zircon ages          下载免费PDF全文

Ryosuke Shunori  Makoto Takeuchi  Koshi Yamamoto 《Island Arc》2018,27(4)

The Ryoke Metamorphic complex has undergone low‐P/T metamorphism and was intruded by granitic magmas around 100 Ma. Subsequently, the belt was uplifted and exposed by the time deposition of the Izumi Group began. The tectonic history of uplift, such as the timing and processes, are poorly known despite being important for understanding the spatiotemporal evolution of the Ryoke Metamorphic Belt. U–Pb zircon ages from sedimentary rocks in the forearc and backarc basins are useful for constraining uplift and magmatism in the provenance. U–Pb dating of detrital zircons from 12 samples (four sandstones and eight granitic clasts) in the Yuasa–Aridagawa basin, a Cretaceous forearc basin in the Chichibu Belt of Southwest Japan, gave mostly ages of 60–110 Ma. Granitic clasts contained in conglomerate suggest that granitic intrusions predate the formation of Coniacian and Maastrichtian conglomerate. Emplacement ages of granitic bodies originated from granitic clasts in Coniacian conglomerate are (110.2 ±1.3) Ma, (106.1 ±1.8) Ma, (101.8+5.8–3.8) Ma, and (95.3 ±1.4) Ma; for granitic clasts in Maastrichtian conglomerate, (89.6 ±1.8) Ma, (87.3+2.4–1.8) Ma, (85.7 ±1.2) Ma, and (82.7 ±1.2) Ma. The results suggest that detrital zircons in the sandstones were mainly derived from volcanic eruptions contemporaneous with depositional age, and plutonic rocks of the Ryoke Metamorphic Belt. Zircon ages of the granitic clast samples also indicate that uplift in the provenance began after Albian and occurred at least during the Coniacian to Maastrichtian. Our results, together with the difference of provenance between backarc and forearc basins suggest that the southern marginal zone of the Ryoke Metamorphic Belt was uplifted and supplied a large amount of clastic materials to the forearc basins during the Late Cretaceous.  相似文献