Oxygen and magnesium isotopic compositions of amoeboid olivine aggregates from the Semarkona LL3.0 chondrite     

Shoichi Itoh  Sara S. Russell  Hisayoshi Yurimoto 《Meteoritics & planetary science》2007,42(7-8):1241-1247

Abstract— Amoeboid olivine aggregates (AOAs) in the LL3.0 Semarkona chondrite have been studied by secondary ion mass spectrometry. The AOAs mainly consist of aggregates of olivine grains with interstitial Al‐Ti‐rich diopside and anorthite. Oxygen‐isotopic compositions of all phases are consistently enriched in ¹⁶O, with δ^17,18O = ～?50‰. The initial ²⁶Al/²⁷Al ratios are calculated to be 5.6 ± 0.9 (2σ) × 10^?5. These values are equivalent to those of AOAs and fine‐grained calcium‐aluminum‐rich inclusions (FGIs) from pristine carbonaceous chondrites. This suggests that AOAs in ordinary chondrites formed in the same ¹⁶O‐rich calcium‐aluminum‐rich inclusion (CAI)‐forming region of the solar nebula as AOAs and FGIs in carbonaceous chondrites, and subsequently moved to the accretion region of the ordinary chondrite parent body in the solar nebula.  相似文献   

http://www.sciencedirect.com/science/article/pii/S167498711400070X     

Yingfeng Ji  Shoichi Yoshioka 《地学前缘(英文版)》2015,6(1):61-78

We investigated the relationships among slab geometry,obliquity,and the thermal regime associated with the subduction of oceanic plates using a three-dimensional(3D) parallelepiped thermal convection model.Various models with convex and concave slab shapes were constructed in the numerical simulation,and the temperature and mantle flow distributions were calculated.The results revealed that when the slab dip angle increases,or the obliquity of subduction becomes steeper,the interplate temperature decreases remarkably.Cooler(warmer) zones on the plate interface were identified from the modeling where there was a larger(smaller) subduction angle.Consequently,the interplate temperature distribution is partly controlled by the true subduction angle(TSA),which is a function of the slab dip angle and the obliquity of subduction.The rate of change of the interface temperature for the TSA was10-50 ℃(10°TSA 20°) at depths ranging from(TSA- 10) × 5 km to 60 +(TSA- 10) × 5 km for a flat slab after a subduction history of 7 Myrs.The along-arc slab curvature affects the variation in TSA.The slab radius also appeared to influence the radius of induced mantle flow.  相似文献   

Source parameters controlling the generation and propagation of potential local tsunamis along the Cascadia margin     

Eric Geist  Shoichi Yoshioka 《Natural Hazards》1996,13(2):151-177

The largest uncertainty in assessing hazards from local tsunamis along the Cascadia margin is estimating the possible earthquake source parameters. We investigate which source parameters exert the largest influence on tsunami generation and determine how each parameter affects the amplitude of the local tsunami. The following source parameters were analyzed: (1) type of faulting characteristic of the Cascadia subduction zone, (2) amount of slip during rupture, (3) slip orientation, (4) duration of rupture, (5) physical properties of the accretionary wedge, and (6) influence of secondary faulting. The effect of each of these source parameters on the quasi-static displacement of the ocean floor is determined by using elastic three-dimensional, finite-element models. The propagation of the resulting tsunami is modeled both near the coastline using the two-dimensional (x-t) Peregrine equations that includes the effects of dispersion and near the source using the three-dimensional (x-y-t) linear long-wave equations. The source parameters that have the largest influence on local tsunami excitation are the shallowness of rupture and the amount of slip. In addition, the orientation of slip has a large effect on the directivity of the tsunami, especially for shallow dipping faults, which consequently has a direct influence on the length of coastline inundated by the tsunami. Duration of rupture, physical properties of the accretionary wedge, and secondary faulting all affect the excitation of tsunamis but to a lesser extent than the shallowness of rupture and the amount and orientation of slip. Assessment of the severity of the local tsunami hazard should take into account that relatively large tsunamis can be generated from anomalous tsunami earthquakes that rupture within the accretionary wedge in comparison to interplate thrust earthquakes of similar magnitude.  相似文献   

IV-3 Wave energy absorption of irregular waves     

Shoichi Nakamura  Shigeru Naito 《Ocean Engineering》1985,12(6):577

  相似文献   

Petrography and oxygen isotopic compositions in refractory inclusions from CO chondrites     

Shoichi Itoh  Hideyasu Kojima 《Geochimica et cosmochimica acta》2004,68(1):183-194

Fine-grained Ca-Al-rich inclusions (FGIs) in Yamato-81020 (CO3.0) and Kainsaz (CO3.1-CO3.2) chondrites have been studied by secondary ion mass spectrometry. The FGIs from Yamato-81020 consist of aggregates of hibonite, spinel, melilite, anorthite, diopside and olivine grains with no petrographic evidence of alteration. In contrast, the FGIs from Kainsaz commonly contain alteration products such as nepheline. From replacement textures and chemical compositions of altered and unaltered FGIs, we conclude that the alteration products formed by decomposition of melilite and anorthite. All phases in the Yamato-81020 FGIs are enriched in ¹⁶O, with δ^{17, 18}O = ∼−40‰ except for one FGI that experienced melting. Oxygen isotopic compositions of melilite, anorthite, some spinel and diopside in Kainsaz FGIs changed from δ^{17, 18}O = ∼−40‰ toward 0‰ by aqueous alteration. Alteration products in FGIs are depleted in ¹⁶O relative to primary phases, with δ^{17, 18}O = ∼0‰. These results show that FGIs in CO chondrites commonly had ¹⁶O-rich compositions in the solar nebula. The original ¹⁶O-rich FGIs were modified to ¹⁶O-poor compositions during aqueous alteration in the parent body.  相似文献   

Age of the Taishu Group,southwestern Japan,and implications for the origin and evolution of the Japan Sea     

Takashi Ninomiya  Shoichi Shimoyama  Koichiro Watanabe  Kenji Horie  Daniel J. Dunkley  Kazuyuki Shiraishi 《Island Arc》2014,23(3):206-220

The Taishu Group, a marine formation with a thickness of >5400 m, crops out on Tsushima Island, located in the southwestern Japan Sea. The group, which is generally regarded as early Eocene to early Miocene in age, provides important information about the tectonic setting of the Japan Sea. In this study, we present new SHRIMP U–Pb dates for igneous zircons from the Kunehama Tuff, which is in the basal part of the Taishu Group, and the Oobaura Tuff, which is in the uppermost part of the group. Results show that the Taishu Group was deposited rapidly, during the short interval of 17.9–15.9 Ma (early–middle Miocene), and is equivalent to other early–middle Miocene strata found in the Japan Sea region. Our results provide new constraints on the geological history of the Japan Sea and its islands.  相似文献   

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada     

Kento Motomura  Shoichi Kiyokawa  Minoru Ikehara  Kentaro Tanaka  Yuji Sano 《Island Arc》2020,29(1)

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.  相似文献   

Systematic errors in estimation of insolation by empirical formulas     

Shoichi Kizu 《Journal of Oceanography》1998,54(2):165-177

Systematic errors in the estimation of surface, insolation,Q, by two popular empirical formulas are investigated statistically by using coincident measurements of the global solar radiation and the total cloud cover at JMA observatories over Japan. The results show that Reed’s (1977) widely-accepted formula remarkably overestimatesQ under overcast conditions. The overestimation is particularly evident in the summer months. The formula also overestimatesQ in cloud-free conditions, which may be due to an overestimation of the clear-sky transmittance by Seckel and Beaudry, (1973). By contrast, Kondo and Miura’s (1985) formula underestimatesQ under overcast conditions, whereas it slightly overestimates in partially cloudy conditions. It is shown that these systematic errors can explain some, of the published differences between the estimation ofQ by the two formulas. The users of these formulas should be careful since these cloudiness-dependent errors can contaminate not only the absolute values but also the temporal anomalies or the spatial variability of the insolation, predicted by them. In particular, it can be serious in regions of dense cloud cover such as the northern North Pacific, the northern North Atlantic and the Southern Ocean. It is also shown that the ratio ofQ to the insolation at the top of the atmosphere,Q _TOA, takes on a range of values, particularly under dense cloud cover. This implies an inherent difficulty in estimation ofQ by a simple empirical formula utilizing only readily-available observables such as cloudiness.  相似文献   

Spiral mode of standing accretion shock instability in core-collapse supernovae     

Wakana Iwakami  Naofumi Ohnishi  Kei Kotake  Shoichi Yamada  Keisuke Sawada 《Astrophysics and Space Science》2009,322(1-4):43-47

The study of standing accretion shock instability (SASI) in core-collapse supernova cores has been done with three-dimensional (3D) computer simulations. Rotations with various perturbations were introduced from outer boundary of an initial steady accreting flow. We found that one or two armed spiral accreting flow onto the proto-neutron star (PNS) is formed inside the shock wave depending on perturbations. The linear growth of spiral modes are clearly diagnosed by the mode analysis of the shock surface, and the lower m modes grow quickly in the linear regime.  相似文献   

Evaluation of plastic energy dissipation capacity of steel beams suffering ductile fracture under various loading histories     

Yu Jiao  Satoshi Yamada  Shoichi Kishiki  Yuko Shimada 《地震工程与结构动力学》2011,40(14):1553-1570

The energy dissipation capacity of a structure is a very important index that indicates the structural performance in energy‐based seismic design. This index depends greatly on the structural components that form the whole system. Owing to the wide use of the strong‐column weak‐beam strength hierarchy where steel beams dissipate the majority of earthquake input energy to the structures, it is necessary to evaluate the energy dissipation capacity of the beams. Under cyclic loadings such as seismic effects, the damage of the beams accumulates. Therefore, loading history is known to be the most pivotal factor influencing the deformation capacity and energy dissipation capacity of the beams. Seismic loadings with significantly different characteristics are applied to structural beams during different types of earthquakes and there is no unique appropriate loading protocol that can represent all types of seismic loadings. This paper focuses on the effects of various loading histories on the deformation capacity and energy dissipation capacity of the beams. Cyclic loading tests of steel beams were performed. In addition, some experimental results from published tests were also collected to form a database. This database was used to evaluate the energy dissipation capacity of steel beams suffering from ductile fracture under various loading histories. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献