Carbon isotope fractionation between graphite and diamond during shock experiments     

Teruyuki Maruoka  Christian Koeberl  Jun‐ichi Matsuda  Yasuhiko Syono 《Meteoritics & planetary science》2003,38(8):1255-1262

Abstract— Carbon isotopic compositions were measured for shock‐produced diamond and shocked graphite formed at peak pressures ranging from 37 to 52 GPa. The δ¹³C values of diamonds produced in a sealed container were generally lower than that of the initial graphite. The differences in the carbon isotopic composition between initial graphite and shocked graphite/diamond may reflect kinetic isotopic fractionation during the oxidation of the graphite/diamond and/or analytical artifacts possibly induced by impurities in the samples. The pressure effect on the isotopic fractionations between graphite and diamond can be estimated from the δ¹³C values of impurity‐free diamonds produced using a vented container from which gases, including oxygen, in pore spaces escaped during or after the diamond formation (e.g., 0.039 ± 0.085‰ at a peak pressure of 52 GPa). Any isotopic fractionation induced by shock conversion of graphite to diamond is too small to be detected in natural shock‐induced diamond‐graphite systems related to terrestrial impact cratering processes.  相似文献   

Mean pole,z-term and Kuroshio     

Isao Naito 《Journal of Oceanography》1974,30(4):168-178

Secular variations of the mean pole and the z-term in the latitudinal vatiations are discussed geophysically in relation to oceanic motions on the large scale, particularly, to the variations of the Kuroshio system.It is shown that the large scale meanders of the Kuroshio occurred when the direction of displacement of the mean pole turned to the European continent from the North East Pacific and when the z-term changed from decrease to increase. The libration of the mean pole has connection with the zonal circulation of the oceanic mass and the secular variation of the z-term has connection with that of the meridional circulation. The large abrupt decrease in the z-term during 1955–1959 has close connection with the wellknown abnormal variation of sea surface temperature in the North Pacific during the same period.The structures of occurrence of the Kuroshio meanders in 1934 and 1969 may be different from those in 1953 and 1959, and the Kuroshio meander perhaps occurred after 1916 and existed during 2 or 3 years. Particularly the occurrence of the Kuroshio meander in 1959 may originate in the abrupt southward flow of oceanic mass in the Pacific.Except for some cases great earthquakes with magnitude of nearly 8 occurred near the Japan Trench and the Kurile-Kamchatka Trench about one year before the occurrences of the Kuroshio meander, and in the regions from the Alaska Peninsula to the Japan Islands great earthquakes occurred during the disappearance of the Kuroshio meander with a few exceptions.Existence of dynamical interactions between the ocean and the solid-earth may be suggested.  相似文献   

Anisotropic phase transition of rutile under shock compression     

Keiji Kusaba  Masae Kikuchi  Kiyoto Fukuoka  Yasuhiko Syono 《Physics and Chemistry of Minerals》1988,15(3):238-245

Shock recovery experiments for single crystal and powdered specimens of TiO₂ with the rutile structure were performed in the pressure range up to 72 GPa. Single crystal specimens were shocked parallel to [100], [110] and [001] directions. X-ray powder diffraction analysis showed that the amount of -PbO₂ type TiO₂ produced by shock-loading depended strongly on the shock propagation direction. The maximum yield (about 70%) was observed for shock loading to 36 GPa parallel to the [100] direction. In the [001] shock direction, the yield is much smaller than that of the [100] direction. This anisotropic yield was consistent with the observed anisotropy of the phase transition pressure in shock compression measurements. However, transformation to the -PbO₂ type cannot explain the large volume change observed above about 20 GPa. On the basis of the high pressure behavior of MnF₂, we assumed that the high pressure phase was either fluorite or distorted fluorite type and that the phase conversion to the -PbO₂ type was induced spontaneously in the pressure reduction process.We present a displacive mechanism of phase transition under shock compression from the rutile structure to the fluorite structure, in which the rutile [100] is shown to correspond to the fluorite [001] or [110] and the rutile [001] to the fluorite [110]. Direct evidence is obtained by examining the [100] shocked specimen by high resolution electron microscopy.  相似文献   

Mantle process beneath Philippine Sea back-arc spreading ridges: A synthesis of peridotite petrology and tectonics   总被引：2，自引：0，他引：2  

Yasuhiko  Ohara 《Island Arc》2006,15(1):119-129

Abstract In order to obtain a general view of the mantle process beneath a back‐arc basin spreading ridge, the diversity of peridotite petrology and tectonic occurrences in two back‐arc basin spreading ridges from the Philippine Sea were examined: the Parece Vela Rift and the Mariana Trough. The Parece Vela Basin spreading ridge (Parece Vela Rift) was a physically fast/intermediate‐spreading ridge, although many tectono‐magmatic features resemble those of slow‐ to ultraslow‐spreading ridges. Two unusual features of the Parece Vela Rift further demonstrate the uniqueness of the ridge: full‐axial development of oceanic core complexes and exposure of mantle peridotite at segment midpoints. The Parece Vela Rift yields a lithological assemblage of residual but still fertile lherzolite/harzburgite, plagioclase‐bearing harzburgite and dunite; similar assemblages are reported from the equatorial Mid‐Atlantic Ridge at the Romanche Fracture Zone and the ultraslow‐spreading ridges from the Indian and Arctic Oceans. The tectono‐magmatic characteristics of the Parece Vela Rift suggest that diffuse porous melt flow and pervasive melt–mantle interaction were the important mantle processes there. Globally, this ‘porous melt flow‐type’ mantle process is likely to occur beneath a segment midpoint of the ridge having a thick lithosphere, typically an ultraslow‐spreading ridge. In contrast, the Mariana Trough is a typical slow‐spreading ridge, exposing mantle peridotite at segment ends. The Mariana Trough yields a lithological assemblage of residual harzburgite and veined harzburgite, a common assemblage among the global abyssal peridotite suite. The tectono‐magmatic characteristics of the Mariana Trough suggest that channeled melt/fluid flow and limited melt–mantle interaction are the important mantle processes there, because of the colder wall‐rock peridotite in the segment end. This ‘channeled melt flow‐type’ mantle process is likely to occur in the shallow lithospheric mantle at the segment ends of any spreading ridges.  相似文献   

Diffusive Shock Acceleration of Electrons at an Interplanetary Shock Observed on 21 Feb 1994     

N. Shimada  T. Terasawa  M. Hoshino  T. Naito  H. Matsui  T. Koi  K. Maezawa 《Astrophysics and Space Science》1998,264(1-4):481-488

  相似文献   

对流层平流层气溶胶粒子的形态和化学组成   总被引：13，自引：1，他引：12  

许黎  樊小标  石广玉  岩坂泰信  奥原靖彦  原圭一郎  龚知本  周军 《气象学报》1998,56(5):551-559

分析研究了１９９３年和１９９４年的８月、９月在香河地区上空采集的单个气溶胶粒子的形态及化学元素和化合物的组成。结果表明：１９９３年,在对流层大气中的气溶胶颗粒经常出现不规则形的粒子,可能是土壤粒子;而在平流层大气中的颗粒以具有“卫星”结构的硫酸粒子为主;硫酸铵粒子则经常出现在对流层的中、下部。香河地区上空颗粒物的化学元素组成比较复杂,单一化学元素组成的粒子较少,粒子主要含有Ｓｉ,Ｆｅ,Ａｌ和Ｓ等元素。气溶胶的化合物有硫酸盐、硅酸盐、硝酸盐和磷酸盐等  相似文献   

Impact fragmentation experiments of basalts and pyrophyllites     

Yasuhiko Takagi  Hitoshi Mizutani  Shin-Ichi Kawakami 《Icarus》1984,59(3):462-477

Results of impact fragmentation experiments for basalts and pyrophyllites are reported. Aluminum cylindrical projectiles were impacted on cubic basalt and pyrophyllite targets at velocities of 70 to 990 m/sec. The targets and projectiles were 20 g to 3.3 kg and 2 to 20 g in weight respectively. Weights of the fragments produced by impacts were measured and the size distributions of fragments were examined. Data of the largest fragment mass (m_L) normalized to the original target mass (M_t), m_L/M_t, correlate better with the nondimensional impact stress, P_I, a new scaling parameter introduced by H. Mizutani, Y. Takagi, and S. Kawakami (1984, in preparation) than the conventional projectile's kinetic energy per unit target mass, E/M_t, used in the previous studies. All the m_L/M_t data for basalts obtained in the present study are summarized by m_L/M_t = 2.95 × 10^?2P_I^?1 where P_I = P₀L³/YR³, P₀ = peak shock pressure, L = projectile size, R = target size and Y = material strength of target. For aluminum targets, however, the m_L/M_t is 2.5 orders of magnitude larger than that for brittle targets at impacts with the same P_I. Size distributions of fragments expressed in a log N - log (m/M_t) diagram divided into three regimes bounded by two inflection points. In each regime the curve is expressed by $\text{N (>}\text{m}\text{M}{}_{\mathrm{t}}\text{) = A (}\text{m}\text{M}{}_{\mathrm{t}}\text{)}{}^{\mathrm{?a}}$. The slopes, a, of the log $\text{N -}\text{log}\text{(}\text{m}\text{M}{}_{\mathrm{t}}\text{)}$ curves in the regimes of a large and a medium size range are positively correlated with the nondimensional impact stress, P_I, and expressed as a = C₃ + a₃log P_I. The slopes, a, in the smallest size range are, on the other hand, nearly constant and have values of $\text{0.5}\text{to}\text{0.7 (}\text{1}\text{2}\text{?}\text{2}\text{3}\text{)}$. Present results indicate that the impact fragmentation is scaled well by the new scaling parameter, P_I, of Mizutani, Takagi, and Kawakami and that the present experimental data may shed new light on planetary impact processes.  相似文献   

Searches for very high energy gamma rays from blazars with CANGAROO-III telescope in 2005-2009     

Y. Mizumura  J. Kushida  K. Nishijima  G.V. BicknellR.W. Clay  P.G. EdwardsS. Gunji  S. HaraS. Hayashi  S. KabukiF. Kajino  A. KawachiT. Kifune  R. KiuchiK. Kodani  Y. MatsubaraT. Mizukami  Y. MizumotoM. Mori  H. MuraishiT. Naito  M. OhishiV. Stamatescu  D.L. SwabyT. Tanimori  G. ThorntonF. Tokanai  T. ToyamaS. Yanagita  T. YoshidaT. Yoshikoshi 《Astroparticle Physics》2012,35(9):563-572

We have searched for very high energy (VHE) gamma rays from four blazars using the CANGAROO-III imaging atmospheric Cherenkov telescope. We report the results of the observations of H 2356-309, PKS 2155-304, PKS 0537-441, and 3C 279, performed from 2005 to 2009, applying a new analysis to suppress the effects of the position dependence of Cherenkov images in the field of view. No significant VHE gamma ray emission was detected from any of the four blazars. The GeV gamma-ray spectra of these objects were obtained by analyzing Fermi/LAT archival data. Wide range (radio to VHE gamma-ray bands) spectral energy distributions (SEDs) including CANGAROO-III upper limits, GeV gamma-ray spectra, and archival data, even though they are non-simultaneous, are discussed using a one-zone synchrotron self-Compton (SSC) model in combination with a external Compton (EC) radiation. The HBLs (H 2356-309 and PKS 2155-304) can be explained by a simple SSC model, and PKS 0537-441 and 3C 279 are well modeled by a combination of SSC and EC model. We find a consistency with the blazar sequence in terms of strength of magnetic field and component size.  相似文献   

Adjustment of self-formed bankfull channel geometry of meandering rivers: modelling study     

Kensuke Naito  Gary Parker 《地球表面变化过程与地形》2020,45(13):3313-3322

We consider the evolution of the hydraulic geometry of sand-bed meandering rivers. We study the difference between the timescale of longitudinal river profile adjustment and that of channel width and depth adjustment. We also study the effect of hydrological regime alteration on the evolution of bankfull channel geometry. To achieve this, a previously developed model for the spatiotemporal co-evolution of bankfull channel characteristics, including bankfull discharge, bankfull width, bankfull depth and down-channel bed slope, is used. In our modelling framework, flow variability is considered in terms of a specified flow duration curve. Taking advantage of this unique feature, we identify the flow range responsible for long-term bankfull channel change within the specified flow duration curve. That is, the relative importance of extremely high short-duration flows compared to moderately high longer duration flows is examined. The Minnesota River, MN, USA, an actively meandering sand-bed stream, is selected for a case study. The longitudinal profile of the study reach has been in adjustment toward equilibrium since the end of the last glaciation, while its bankfull cross-section is rapidly widening due to hydrological regime change in the last several decades. We use the model to demonstrate that the timescale for longitudinal channel profile adjustment is much greater than the timescale for cross-sectional profile adjustment due to a lateral channel shift. We also show that hydrological regime shift is responsible for the recent rapid widening of the Minnesota River. Our analysis suggests that increases in the 5–25% exceedance flows play a more significant role in recent bankfull channel enlargement of the Minnesota River than increase in either the 0.1% exceedance flow or the 90% exceedance flow. © 2020 John Wiley & Sons, Ltd.  相似文献   

New insights on the origin of troctolites from the breakaway area of the Godzilla Megamullion (Parece Vela back‐arc basin): The role of melt‐mantle interaction on the composition of the lower crust          下载免费PDF全文

Alessio Sanfilippo  Henry J. B. Dick  Yasuhiko Ohara  Massimo Tiepolo 《Island Arc》2016,25(3):220-234

The troctolites and olivine‐gabbros from the Dive 6 K‐1147 represent the most primitive gabbroic rocks collected at the Godzilla Megamullion, a giant oceanic core complex formed at an extinct spreading segment of the Parece Vela back‐arc basin (Philippine Sea). Previous investigations have shown that these rocks have textural and major elements mineral compositions consistent with a formation through multistage interaction between mantle‐derived melts and a pre‐existing ultramafic matrix. New investigations on trace element mineral compositions basically agree with this hypothesis. Clinopyroxenes and plagioclase have incompatible element signatures similar to that of typical‐MORB. However, the clinopyroxenes show very high Cr contents (similar to those of mantle clinopyroxene) and rim having sharply higher Zr/REE ratios with respect to the core. These features are in contrast with an evolution constrained by fractional crystallization processes, and suggest that the clinopyroxene compositions are controlled by melt‐rock interaction processes. The plagioclase anorthite versus clinopyroxene Mg#[Mg/(Mg + Fe^Tot)] correlation of the Dive 6 K‐1147 rocks shows a trend much steeper than those depicted by other oceanic gabbroic sections. Using a thermodynamic model, we show that this trend is reproducible by fractionation of melts assimilating 1 g of mantle peridotite per 1 °C of cooling. This model predicts the early crystallization of high Mg# clinopyroxene, consistent with our petrological observation. The melt‐peridotite interaction process produces Na‐rich melts causing the crystallization of plagioclase with low anorthite component, typically characterizing the evolved gabbros from Godzilla Megamullion.  相似文献