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111.
Vincent Famin Satoru Nakashima Anne-Marie Boullier Koichiro Fujimoto Tetsuro Hirono 《Earth and Planetary Science Letters》2008,265(3-4):487-497
Fourier transform infrared (FTIR) microanalysis of pseudotachylytes (i.e. friction-induced melts produced by seismic slip) from the Nojima fault (Japan) reveals that earthquakes almost instantaneously expel 99 wt.% of the wall rock CO2 content. Carbon is exsolved because it is supersaturated in the friction melts. By extrapolation to a crustal-scale fault rupture, large events such as the M7.2 Kobe earthquake (1995) may yield a total production of 1.8 to 3.4 × 103 tons CO2 within a few seconds. This extraordinary release of CO2 can cause a flash fluid pressure increase in the fault plane, and therefore enhance earthquake slip or trigger aftershocks; it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes. Because carbon saturation in silicate melts is pressure-dependent, FTIR can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults. 相似文献
112.
Color-change processes of a plinian pumice and experimental constraints of color-change kinetics in air of an obsidian 总被引:1,自引:0,他引:1
Mihoko Moriizumi Satoru Nakashima Satoshi Okumura Yuta Yamanoi 《Bulletin of Volcanology》2009,71(1):1-13
Colors of plinian pumices were measured by spectrocolorimetry, and their quantitative color parameters in the L*a*b* color
space were determined. A series of heating experiments of obsidian was conducted to simulate the color-change processes of
rhyolitic glasses. In these experiments, following three stages of color-change processes were observed. Stage I showed a
rapid b* (yellowishness) increase associated with fast dehydration controlled by water diffusivity (D
water). In stage II, a* (reddishness) increase was accompanied by Fe2+ decrease. Both a* increase and Fe2+ decrease can be simulated by a diffusion model. Obtained diffusivity D
oxidation were about two orders of magnitude smaller than D
water
. The a*-value increase after the oxidation in stage III appeared to be quasi-linear with time, indicating the zeroth order
reaction corresponding to the formation of hematite-like structures in rhyolitic glasses. The diffusion-limited a* increase
model in stage II was applied to a natural plinian pumice fall unit to evaluate time periods of color-change processes through
oxidation by air of fragmented rhyolitic materials. 相似文献
113.
Antidunes and their sedimentary structures can be useful in reconstructing paleo‐hydraulic conditions, especially for large discharge events. However, three‐dimensional (3D) antidunes in sand‐sized sediments have not yet been studied extensively, as compared to either two‐dimensional (2D) antidunes or antidunes in gravel‐sized sediments. In this study, we estimated formative conditions of gravel step‐pool morphologies and applied them to the formation of 3D antidunes over a sand bed. Formative conditions are expressed in terms of a relationship between the water discharge per unit width and the bed slope. Flume experiments demonstrated that 3D mound‐like antidune configurations and their associated internal sedimentary structures could be preserved. Internal sedimentary structures were characterized by shallow lens‐like structures whose bases were erosional. Although gently‐dipping concave‐upward lamination was dominant, convex‐upward lamination was occasionally observed. The dimensions of lenticular lamina‐sets can be used to estimate antidune geometry. Thus if 3D antidunes can be interpreted in the stratigraphic record, it is possible to estimate the paleo‐hydraulic parameters such as water discharge and bed slope more precisely than previously. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
114.
We measured the velocity distributions of impact ejecta with velocities higher than ∼100 m s−1 (high-velocity ejecta) for impacts at variable impact angle α into unconsolidated targets of small soda-lime glass spheres. Polycarbonate projectiles with mass of 0.49 g were accelerated to ∼250 m s−1 by a single-stage light-gas gun. The impact ejecta are detected by thin aluminum foils placed around the targets. We analyzed the holes on the aluminum foils to derive the total number and volume of ejecta that penetrated the aluminum foils. Using the minimum velocity of the ejecta for penetration, determined experimentally, the velocity distributions of the high-velocity ejecta were obtained at α=15°, 30°, 45°, 60°, and 90°. The velocity distribution of the high-velocity ejecta is shown to depend on impact angle. The quantity of the high-velocity ejecta for vertical impact (α=90°) is considerably lower than derived from a power-law relation for the velocity distribution on the low-velocity ejecta (less than 10 m s−1). On the other hand, in oblique impacts, the quantity of the high-velocity ejecta increases with decreasing impact angle, and becomes comparable to those derived from the power-law relation. We attempt to scale the high-velocity ejecta for oblique impacts to a new scaling law, in which the velocity distribution is scaled by the cube of projectile radius (scaled volume) and a horizontal component of impactor velocity (scaled ejection velocity), respectively. The high-velocity ejecta data shows a good correlation between the scaled volume and the scaled ejection velocity. 相似文献
115.
Abstract Arc volcanism of the past 10 my in the northeast Honshu and Izu-Bonin Arcs shows several notable features. In the northeast Honshu Arc, the spatial distribution of volcanism exhibits several clusters elongated nearly perpendicular to the arc and the possible migration of volcanism from the back-arc side to the volcanic front side, at least, during the past 5 my. The pattern of clusters seems to have flip-flopped around 5 Ma. In the Izu-Bonin Arc, there are a series of across-arc seamount chains, in which volcanic activity occurred from ca 17 Ma to ca 3 Ma, similar to the clusters of the northeast Honshu Arc, although the recent active rifting occurs almost parallel to the arc. On the basis of studies of numerical modeling, these features might be explained, at least qualitatively, by the small-scale convection under the island arc. Several inferences can be made from our modeling results for the tectonics of the Izu-Bonin Arc. The angle of dip of subducting plate in the Izu-Bonin Arc might have increased. This can explain the disappearance of volcanism along the seamount chains and the recent along-arc volcanism with narrow rifting. The trend of seamount chains, which is oblique to the arc, might not be their intrinsic feature but rather a result of the lateral movement of the back-arc region after their formation. These inferences can be tested by the future detailed morphological and chronological studies of the Izu-Bonin Arc. 相似文献
116.
This study examined whether heavy oil (HO) increases viral production and how that change may affect the marine bacterial community. The addition of a relatively low concentration (10 μg/mL) of HO to seawater resulted in the highest degree of viral lysis. Although the composition of the bacterial community did not change upon the viral lysis in terms of the taxa present, the relative abundance of the γ-Proteobacteria family Alteromonadaceae decreased (by 10 %) after the HO exposure, implying that the selective lysis by viruses and induced prophages may be responsible for changes in the composition of the bacterial community. 相似文献
117.
Satoru?HaraguchiEmail author Jun-Ichi?Kimura Ryoko?Senda Koichiro?Fujinaga Kentaro?Nakamura Yutaro?Takaya Teruaki?Ishii 《Contributions to Mineralogy and Petrology》2017,172(5):25
An intra-arc rift (IAR) is developed behind the volcanic front in the Izu arc, Japan. Bimodal volcanism, represented by basalt and rhyolite lavas and hydrothermal activity, is active in the IAR. The constituent minerals in the rhyolite lavas are mainly plagioclase and quartz, whereas mafic minerals are rare and are mainly orthopyroxene without any hydrous minerals such as amphibole and biotite. Both the phenocryst and groundmass minerals have felsic affinities with a narrow compositional range. The petrological and bulk chemical characteristics are similar to those of melts from some partial melting experiments that also yield dry rhyolite melts. The hydrous mineral-free narrow mineral compositions and low-Al2O3 affinities of the IAR rhyolites are produced from basaltic middle crust under anhydrous low-temperature melting conditions. The IAR basalt lavas display prominent across-arc variation, with depleted elemental compositions in the volcanic front side and enriched compositions in the rear-arc side. The across-arc variation reflects gradual change in the slab-derived components, as demonstrated by decreasing Ba/Zr and Th/Zr values to the rear-arc side. Rhyolite lavas exhibit different across-arc variations in either the fluid-mobile elements or the immobile elements, such as Nb/Zr, La/Yb, and chondrite-normalized rare earth element patterns, reflecting that the felsic magmas had different source. The preexisting arc crust formed during an earlier stage of arc evolution, most probably during the Oligocene prior to spreading of the Shikoku back-arc basin. The lack of systematic across-arc variation in the IAR rhyolites and their dry/shallow crustal melting origin combines to suggest re-melting of preexisting Oligocene middle crust by heat from the young basaltic magmatism. 相似文献