The relative formation ages of ferromagnesian chondrules inferred from their initial aluminum‐26/aluminum‐27 ratios     

Smail Mostefaoui  Noriko T. Kita  Shigeko Togashi  Shogo Tachibana  Hiroko Nagahara  Yuichi Morishita 《Meteoritics & planetary science》2002,37(3):421-438

Abstract— We performed a systematic high‐precision secondary ion mass spectrometry ²⁶Al‐²⁶Mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite Bishunpur (LL3.1). The chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and/or glass. The chemical compositions of the chondrules vary from FeO‐poor to FeO‐rich. Eight chondrules show resolvable ²⁶Mg excesses with a maximum δ²⁶Mg of ?1% in two chondrules. The initial ²⁶Al/²⁷Al ratios inferred for these chondrules range between (2.28 ± 0.73) × 10^?5 to (0.45 ± 0.21) × 10^?5. Assuming a homogeneous distribution of Al isotopes in the early solar system, this range corresponds to ages relative to CAIs between 0.7 ± 0.2 Ma and 2.4_+0.7^?0.4 Ma. The inferred total span of the chondrule formation ages is at least 1 Ma, which is too long to form chondrules by the X‐wind. The initial ²⁶Al/27Al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine‐rich chondrules formed earlier than pyroxene‐rich chondrules. Though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of Si from earlier generations of chondrules followed by addition of Si to the precursors of later generation chondrules.  相似文献   

Fluid evolution and geobarometry on the Ohtani and Kaneuchi tungsten-quartz vein deposits,Japan: oxygen and carbon isotopic evidence     

Y. Morishita 《Mineralium Deposita》1991,26(1):40-50

The Ohtani and Kaneuchi deposits are tungsten-bearing quartz veins of hypothermal type which are hosted by Cretaceous granodiorite and sedimentary rocks respectively. Oxygen and carbon isotopic compositions were measured on minerals associated with the deposits to determine whether the ore-forming fluids were derived from related igneous bodies. The oxygen isotopic equilibrium temperatures of quartz-muscovite pairs within veins from the Ohtani and Kaneuchi deposits range from 530° to 190°C and from 400° to 300°C, respectively. The equilibrium temperatures of the granodiorite (600°C), greisen (590° to 530°C) and veins in the Ohtani deposit decrease in this order. The calculated oxygen isotopic composition of the Ohtani ore-forming fluid is around 12 (SMOW) above 500°C and lowers successively toward 3 as temperature decreases. The fluid at the earliest stage of mineralization could be in equilibrium with the granodiorite at about 600°C. These lines of evidence suggest that the granodiorite magma played a crucial role in the mineralization. The evolution trend of the Ohtani ore-forming fluid can be explained by a combined process of cooling due to heat conduction, adiabatic expansion and mixing of magmatic water with ground water. Calcites from the deposits have carbon isotopic ratios ranging from -11 to + 2 with the oxygen isotopic ratios in a narrow range. Since the CO₂/CH₄ fugacity ratio of the fluid is estimated to have been near unity, a slight fluctuation in fO₂ caused the large variation in the carbon isotopic composition of calcite. The formation pressures for the Ohtani and Kaneuchi deposits are calculated to be 1.5 kb and 1.4 kb, respectively, on the basis of the difference between the pressure-dependent homogenization temperatures of fluid inclusions and the pressure-independent isotopic equilibrium temperatures. These values are reasonable for the depths in which hypothermal ore deposits have formed.  相似文献   

Distribution depth of the transforming stage larvae of myctophid fishes in the subtropical–tropical waters of the western North Pacific     

Chiyuki Sassa  Kouichi Kawaguchi  Yuichi Hirota  Minoru Ishida 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2181-2193

We describe the day–night vertical distribution patterns of 18 species or types of myctophid fish larvae at the transforming stage based on discrete depth sampling from the surface down to 1000-m depth in the subtropical–tropical western North Pacific. A total of 551 transforming stage larvae were collected at the 19 sampling stations. Except for the Diaphus species and Notolychnus valdiviae, all of the transforming stage larvae (including genera Benthosema, Bolinichthys, Centrobranchus, Ceratoscopelus, Diogenichthys, Hygophum, Lampanyctus, Lobianchia, Myctophum, Symbolophorus, and Triphoturus) were collected in the lower mesopelagic zone from 600- to 900-m depth during both day and night, showing no diel vertical migration (DVM). On the contrary, the Diaphus species and N. valdiviae larvae undergo DVM during the transforming stage, occurring below 200-m layer during the daytime and migrating up to the upper 150-m layer at night, i.e., they show earlier adaptation to juvenile–adult behaviors. Most myctophid fish larvae are known to undertake substantial ontogenetic vertical migration (OVM) from the epipelagic to mesopelagic zones during their early life stage. Although considerable sampling effort was carried out in this study, transforming larvae, except for the above two migratory ones, were not collected in the epipelagic and upper mesopelagic zones, strongly suggesting that their sinking speed would be high. It would be advantageous for survival to spend their highly vulnerable transforming stage in the lower mesopelagic zone, where predation pressures are lower and physical conditions are more stable than in the upper layers.  相似文献   

Medieval coastal inundation revealed by a sand layer on the Ita lowland adjacent to the Suruga Trough,central Japan     

Yuki Sawai  Koichiro Tanigawa  Toru Tamura  Yuichi Namegaya 《Natural Hazards》2016,80(1):505-519

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Characterizing the flush of stream chemical runoff from forested watersheds     

Zhao Zhang  Fulu Tao  Peijun Shi  Wei Xu  Yu Sun  Takehiko Fukushima  Yuichi Onda 《水文研究》2010,24(20):2960-2970

A flush can be defined as stream chemical exhibiting higher concentrations during the prophase of a storm event at an event scale, or exhibiting progressively lower concentrations during several successive storms at a seasonal scale. Investigating the flush characteristics of chemical runoff from forested watersheds is important and helpful to understand the chemical dynamics as well as to design a sampling schedule strategy during storm events. Here, three parameters describing the flush characteristic are quantified and the flush characteristics of chemicals from four Japanese forested watersheds (Mie, Kochi, Nagano and Tokyo) were investigated at both event and seasonal levels. We found that the characteristics of the flush were complicated, and depended on the constituents of the hydrochemistry, climate and runoff quality. Generally, the flush occurs more readily for particulate components than for those in solution; the flush on nitrate‐nitrogen is weaker in regions of nitrogen saturation, such as Nagano and Tokyo, than in Mie and Kochi. Rainfall feature was the main factor controlling the flush of particulate components. However, the source available in a watershed plays a main role on the flushes of dissolve chemicals. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A Paleogene magmatic overprint on Cretaceous seamounts of the western Pacific     

Naoto Hirano  Hirochika Sumino  Taisei Morishita  Shiki Machida  Takaomi Kawano  Kazutaka Yasukawa  Takafumi Hirata  Yasuhiro Kato  Teruaki Ishii 《Island Arc》2021,30(1):e12386

The West Pacific Seamount Province (WPSP) represents a series of short-lived Cretaceous hotspot tracks. However, no intraplate volcanoes in advance of petit-spot volcanism erupted near a trench have been identified after the formation of the WPSP on the western Pacific Plate. This study reports new ages for Paleogene volcanic edifices within the northern WPSP, specifically the Ogasawara Plateau and related ridges, and Minamitorishima Island. These Paleogene ages are the first reported for basaltic rocks on western Pacific seamounts, in an area that has previously only yielded Cretaceous ages. The newly found Paleogene volcanisms overprint the Early–middle Cretaceous volcanic edifices, because the seamount or paleo-island material-covered reefal limestone caps on these edifices are uniformly older than the Paleogene volcanism identified in this study. This study outlines several possible causative factors for the Paleogene volcanism overprinting onto existing Cretaceous seamounts, including volcanism related to lithospheric stress, or a younger hotspot track within the northern part of the WPSP that records magmatism from ~60 Ma.  相似文献   

Sedimentary Features of Tsunami Deposits in Carbonate-Dominated Beach Environments: A Case Study from the 25 October 2010 Mentawai Tsunami     

Purna Sulastya Putra  Yuichi Nishimura  Eko Yulianto 《Pure and Applied Geophysics》2013,170(9-10):1583-1600

This study provides a case history of tsunami deposition in a carbonate-dominated environmental setting. We present the results of a sedimentological investigation conducted on deposits formed by the 25 October 2010 Mentawai Island Tsunami and report on deposits analyzed at three sites on North Pagai Island: Sabeu Gunggung, Macaroni Resort, and Tumalei. The deposits are mainly composed of medium to coarse sand-sized fragments of corals, shells and foraminifera, with thickness ranging from 3 to 26 cm. The deposits consist of two to five layers, with fining-upward trends dominating. Local topography noticeably affects the thickness, number of layers, and distribution of tsunami deposits. The foraminiferal assemblage and diversity vary at each sample point, along transect and between different transects. Based on the foraminiferal content, most of the deposit material likely came from shallower depths. In addition, density distribution of the tsunami deposit material exhibits some degree of variability in terms of the range of densities in each sample and the trend of the overall density along each transect. In contrast to heavy mineral-dominated deposits, the density of carbonate grains as a function of size may be an important consideration when carbonate-dominated deposits are used to interpret hydraulic conditions that created a particular tsunami deposit. Since there are relatively few studies of tsunami deposits in carbonate-dominated environmental settings such as the Mentawai Islands, our study provides a useful case history of tsunami deposition in such an environmental setting.  相似文献   

Without power? Landslide inventories in the face of climate change     

Oliver Korup  Tolga Görüm  Yuichi Hayakawa 《地球表面变化过程与地形》2012,37(1):92-99

Projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides, particularly as a consequence of altered precipitation and temperature regimes. Whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated. We test this notion with simple Monte Carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions. Our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters, critically depending on, among others, the size of the largest of landslides recorded. Conversely, comparable model parameter values may obscure significant, i.e. more than twofold, changes to landslide occurrence, and thus inferred rates of hillslope denudation and sediment delivery to drainage networks. A time series of some of Earth's largest mass movements reveals clustering near and partly before the last glacial‐interglacial transition and a distinct step‐over from white noise to temporal clustering around this period. However, elucidating whether this is a distinct signal of first‐order climate‐change impact on slope stability or simply coincides with a transition from short‐term statistical noise to long‐term steady‐state conditions remains an important research challenge. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Field measurements of absolute gravity in East Antarctica     

Koichiro Doi  Hideaki Hayakawa  Takahito Kazama  Toshihiro Higashi  Shingo Osono  Yoichi Fukuda  Jun Nishijima  Yuichi Aoyama  Junichi Ueda 《极地研究(英文版)》2013,(4):339-343

Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.  相似文献   

Cosmic ray sidereal diurnal variation of galactic origin observed by neutron monitors     

K. Nagashima  Y. Ishida  S. Mori  I. Morishita 《Planetary and Space Science》1983,31(11):1269-1278

We have analyzed the sidereal diurnal variation of cosmic rays, using 620 station-years of neutron monitor data during the period 1958–1979. The sidereal variation averaged over the period for all the stations in the Northern Hemisphere is different from the corresponding variation in the Southern Hemisphere. The difference is statistically significant and can be identified with the spurious sidereal variation produced from the stationary anisotropy of solar origin, responsible for the solar semi-diurnal variation. The variation common to both hemispheres is also exceptionally significant from the statistical point of view and could be regarded as being due to a uni-directional galactic anisotropy. This variation has an amplitude of 0.0204 ± 0.0015% and a phase of 6.8 ± 0.3 h and is clearly different from that ( ～ 0.05%, 0 ～ 3 h) observed in the high rigidity region (500 ～ 10⁴ GV). The physical meaning of the variation is discussed from the standpoint of the heliomagnetospheric modulation of galactic anisotropy.  相似文献