An experimental study on impact-induced alterations of planetary organic simulants          下载免费PDF全文

Yasuhito Sekine  Kenya Kodama  Takamichi Kobayashi  Seiji Obata  Yu Chang  Nanako O. Ogawa  Yoshinori Takano  Naohiko Ohkouchi  Koichiro Saiki  Toshimori Sekine 《Meteoritics & planetary science》2018,53(6):1267-1282

The present study systematically investigates shock-induced alteration of organic simulants of planetary bodies (OSPBs) as a function of peak shock pressure and temperature by impact experiments. Our results show that the composition and structure of OSPBs are unchanged upon impacts at peak pressures ≤~5 GPa and temperatures ≤~350 °C. On the other hand, these are dramatically changed upon impacts at >7–8 GPa and > ~400 °C, through loss of hydrogen-related bonds and concurrent carbonization, regardless of the initial compositions of OSPBs. Compared with previous results on static heating of organic matter, we suggest that shock-induced alteration cannot be distinguished from static heating only by Raman and infrared spectroscopy. Our experimental results would provide a proxy indicator for assessing degree of shock-induced alteration of organic matter contained in carbonaceous chondrites. We suggest that a remote-sensing signature of the 3.3–3.6 μm absorption due to hydrogen-related bonds on the surface of small bodies would be a promising indicator for the presence of less-thermally-altered (i.e., <350 °C) organic matter there, which will be a target for landing to collect primordial samples in sample-return spacecraft missions, such as Hayabusa2 and OSIRIS-REx.  相似文献   

An extreme flood caused by a heavy snowfall over the Indigirka River basin in Northeastern Siberia     

Shunsuke Tei  Tomoki Morozumi  Shin Nagai  Shinya Takano  Atsuko Sugimoto  Ryo Shingubara  Rong Fan  Alexander Fedorov  Tuyara Gavrilyeva  Nikita Tananaev  Trofim Maximov 《水文研究》2020,34(3):522-537

Flooding is one of the greatest disasters that produces strong effects on the ecosystem and livelihoods of the local population. Flood frequency is expected to increase globally making its risk assessment an urgent issue. In spring-summer 2017, an extreme flooding occurred in the Indigirka River lowland of Northeastern Siberia that inundated a large area. In this study, the extent and climatic drivers of the flooding were determined using the results of field observations, satellite images, and climate reanalysis dataset, and its possible effects on the ecosystem were discussed. In 2017, a significant lowland area of around 16,016 km² was covered with water even in July, which was 5,217 km² (around 4% of the total area) greater than the water-covered area in 2015 when usual hydrological condition in the area was observed. The hydrographic signature obtained for the Indigirka River water level in 2017 was unusual. Although the water level rose sharply at the end of May (which was typical for the Arctic region), it did not fall afterwards and even increased again to an annual daily maximum value in the middle of July. The climate reanalysis dataset obtained for the temporal–spatial variations of snow water equivalent, snowmelt, and runoff over the lowland revealed that a large amount of snowmelt runoff in June and July 2017 produced a large water-covered area and unusually high river water levels that lasted until summer. Snow depth from winter to spring was largest in 2017 over the period from 2009 to 2017, and the surface of the lower reach of the lowland was partially covered with snow even in the end of June due to the extreme snowfall that occurred in October 2016. Such unusual hydrological conditions waterlogged most trees over the lowland, which caused serious ecosystem devastation and changes in the material cycle.  相似文献   

Application of scanning X-ray analytical microscope to the petrographic characterization of a ductile shear zone: an alternative method to image microstructures     

K. Michibayashi  S. Togami  M. Takano  M. Kumazawa  T. Kageyama 《Tectonophysics》1999,310(1-4):55-67

A ductile shear zone within a metasomatic biotite band in the Ryoke granite, Teshima, SW Japan, has been studied using the scanning X-ray analytical microscope (SXAM). This enabled the quantitative distributions of major elements, such as Si, K, Fe, Al and Ca, to be determined within the shear zone. These element maps were processed to transform them into images showing the distribution of minerals such as quartz, biotite, plagioclase and K-feldspar, which form the major minerals within the biotite band and the granite protolith. Mineral profiles based on these mineral maps compared with the simple shear strain profile reveal that the shear zone is most intense where quartz and biotite have been substituted for the primary mineral assemblage of the granite protolith, suggesting that the stresses imposed on the granite caused the shear strain to localize along the biotite band to produce the observed shear zone. It appears that the rheological behavior changed around 50–60% of quartz modal composition.  相似文献   

New heat flow measurements in the Ulleung Basin, East Sea (Sea of Japan): relationship to local BSR depth, and implications for regional heat flow distribution     

Young-Gyun Kim  Sang-Mook Lee  Osamu Matsubayashi 《Geo-Marine Letters》2010,30(6):595-603

In July 2007, new marine heat flow data were collected at ten sites (HF01–10) in the central and southwestern sectors of the Ulleung Basin (East Sea or Sea of Japan) as part of regional gas hydrate research. In addition, cores were collected at five of these sites for laboratory analysis. The results show that the geothermal gradient ranged from 103–137 mK/m, and the in-situ thermal conductivity from 0.82–0.95 W/m·K. Laboratory measurements of thermal conductivity were found to deviate by as much as 40% from the in-situ measurements, despite the precautions taken to preserve the cores. Based on the in-situ conductivity, the heat flow was found to increase with water depth toward the center of the basin, ranging from 84–130 mW/m². Using a simple model, we estimated the heat flow from the depths of the BSR, and compared this with the observed heat flow. In our study area, the two sets of values were quite consistent, the observed heat flows being slightly higher than the BSR-derived ones. The evaluation of regional pre-1994 data revealed that the heat flow varied widely from 51–157 mW/m² in and around the basin. Due to a large scatter in these older data, a clear relationship between heat flow and water depth was not evident, in contrast to what would be expected for a rifted sedimentary basin. This raises the question as to whether the pre-1994 data represent the true background heat flow from the underlying basin crust since the basin opening, and/or whether they contain large measurement errors. In fact, evidence in support of the latter explanation exists. BSRs are generally found in the deep parts of the basin, and vary by only ±15 m in depth below the seafloor. From the average BSR depth, we inferred the background heat flow using a simple model, which in the case of the Ulleung Basin is approximately 120 and 80 mW/m² for 2.5 and 1 km below sea level, respectively.  相似文献   

Did boninite originate from the heterogeneous mantle with recycled ancient slab?          下载免费PDF全文

Susumu Umino  Kyoko Kanayama  Keitaro Kitamura  Akihiro Tamura  Osamu Ishizuka  Ryoko Senda  Shoji Arai 《Island Arc》2018,27(1)

Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T–P conditions and Pb–Hf–Nd–Os isotopic modeling. Primitive melt inclusions in chrome spinel from Ogasawara and Guam islands show severely depleted high‐SiO₂, MgO (high‐silica) and less depleted low‐SiO₂, MgO (low‐silica and ultralow‐silica) boninitic compositions. The genetic conditions of 1 346 °C at 0.58 GPa and 1 292 °C at 0.69 GPa for the low‐ and ultralow‐silica boninite magmas lie on adiabatic melting paths of depleted mid‐ocean ridge basalt mantle with a potential temperature of 1 430 °C in Ogasawara and of 1 370 °C in Guam, respectively. This is consistent with the model that the low‐ and ultralow‐silica boninites were produced by remelting of the residue of the protoarc basalt during the forearc spreading immediately following the subduction initiation. In contrast, the genetic conditions of 1 428 °C and 0.96 GPa for the high‐silica boninite magma is reconciled with the ascent of more depleted harzburgitic source which pre‐existed below the Izu–Ogasawara–Mariana forearc region before the subduction started. Mixing calculations based on the Pb–Nd–Hf isotopic data for the Mariana protoarc basalt and boninites support the above remelting model for the (ultra)low‐silica boninite and the discrete harzburgite source for the high‐silica boninite. Yb–Os isotopic modeling of the high‐Si boninite source indicates 18–30 wt% melting of the primitive upper mantle at 1.5–1.7 Ga, whereas the source mantle of the protoarc basalt, the residue of which became the source of the (ultra)low‐Si boninite, experienced only 3.5–4.0 wt% melt depletion at 3.6–3.1 Ga, much earlier than the average depleted mid‐ocean ridge basalt mantle with similar degrees of melt depletion at 2.6–2.2 Ga.  相似文献   

Seasonal changes in the sediment flux on steep hillslopes in a humid diurnal frost environment          下载免费PDF全文

Fumitoshi Imaizumi  Osamu Suzuki  Asako Togari‐Ohta 《地球表面变化过程与地形》2017,42(3):389-398

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Experiment and Theoretical Study of Earthquake Detection Capability by Means of Microwave Passive Sensors on a Satellite     

Takano  T. Maeda  T. 《Geoscience and Remote Sensing Letters, IEEE》2009,6(1):107-111

This letter presents the possibility of detecting earthquakes (EQs) from microwaves emitted when rock fractures. The method is based on an experiment in which microwave emission was detected from rock fracturing in a laboratory for the first time in the world. First, the method of calibrating emitted microwave power from experimental data is presented. A model of microwave emission and propagation to a satellite is then proposed. An advantage of microwaves is that they penetrate the Earth's ionosphere, unlike radiowaves of frequencies lower than several tens of megahertz. The power received by a satelliteborne receiver is estimated by assuming parameters of a radiometer currently operating in orbit. The result indicates that a satelliteborne receiver can detect microwave signals generated by an EQ. Based on this result, we attempted to detect some features associated with an actual EQ from the data of the Advanced Microwave Scanning Radiometer for Earth Observation System aboard the remote sensing satellite Aqua.  相似文献   

Emplacement processes of proto-arc basalt in the Izu–Bonin–Mariana arc system     

Yuki Kusano  Osamu Ishizuka  Rosemary Hickey-Vargas  Richard J. Arculus 《Island Arc》2021,30(1):e12401

Ascertaining the emplacement mechanism of oceanic basaltic lavas is important in understanding how ocean floor topography is produced and oceanic plates evolve, particularly during the early stages of crustal development of a supra-subduction zone. A detailed study of the volcanic stratigraphy at International Ocean Discovery Program (IODP) Site U1438 in the Amami Sankaku Basin, west of the Kyushu–Palau Ridge, has revealed the development of lava accretion and ridge topography on the Philippine Sea plate at about 49 Ma. Igneous basement rocks penetrated at Site U1438 are the uppermost 150 m of ~6 km-thick oceanic crust, and comprise, in a downhole direction, sheet flows (12.6 m), lobate sheet flows (61.3 m), pillow lavas (50.7 m), and thin sheet flows (25.3 m). The lowermost sheet flows are intercalated with layers of limestone and epiclastic tuff. Lithofacies analysis reveals that the lowermost sheet flows, limestone, and tuff formed on an axial rise, the pillow lavas were emplaced on a ridge slope, and the lobate sheet flows formed off ridge on an abyssal plain. The lithofacies of the basement basalt corresponds to the upper portions of fast-spreading oceanic crust, suggesting that subduction initiation was associated with intermediate to fast rates of seafloor spreading. The surface sheet flows are olivine–clinopyroxene-phyric basalt and differ from the lower basalt flows that contain phenocrysts of olivine and plagioclase, with or without clinopyroxene. The depleted chrome-spinel composition and olivine–clinopyroxene phenocryst assemblage in the surface sheet flows suggests a slight contribution of water for magma generation not present for the lower basalt flows. Considering the lithological difference between the backarc and forearc oceanic crust in the Izu–Bonin–Mariana arc, with sheet flow dominant in the former, seafloor spreading occurred faster in the later stage of subduction initiation.  相似文献   

耦合融雪的分布式流域"降雨-径流"数值模型   总被引：1，自引：0，他引：1       下载免费PDF全文

黄金柏  王斌  桧谷治  山本晋一 《水科学进展》2012,23(2):194-199

针对中国对耦合融雪的"降雨-径流"过程数值计算模型方面的研究较少,本文联合应用能量平衡方程及运动波理论的基础方程式,结合GIS技术构建分布式流域耦合融雪的"降雨-径流"数值计算模型,并应用流域实测资料进行了有效性验证。研究结果表明:在不考虑融雪条件下,实测流量与计算结果之间存在着较大的误差;在考虑融雪条件下,实测流量与计算结果之间的误差在基准允许范围之内(小于3%);在积雪与融雪区,对流域"降雨-径流"过程的数值计算须考虑融雪。该研究为积雪融雪区提供了一种耦合融雪的"降雨-径流"过程数值计算的新方法。  相似文献   

Origin of the Velocity-Strengthening Nature of Granular Friction     

Takahiro Hatano  Osamu Kuwano 《Pure and Applied Geophysics》2013,170(1-2):3-11

A simple theory for a constitutive law for steady state dynamic friction in granular matter is presented. Starting from the energy balance equation together with the kinetics of grains, the energy dissipation rate is estimated, which directly leads to a constitutive law. The result indicates that a system of lower density is stronger than a system of higher density, albeit somewhat counterintuitive. This is a consequence of the fact that the grain rearrangement, which causes energy dissipation, is more frequent in a system of lower density. Thus, the velocity-strengthening nature of granular friction is naturally explained by the negative shear-rate dependence of the density. The present theory also qualitatively explains the experimental observation that a system of smaller layer thickness tends to be velocity-weakening.  相似文献