Volatilization of sodium from silicate melt spheres and its application to the formation of chondrules     

Akira Tsuchiyama  Hiroko Nagahara  Ikuo Kushiro 《Geochimica et cosmochimica acta》1981,45(8):1357-1367

The rates of volatilization of Na from liquid spheres of chondrule compositions have been determined as functions of time, temperature, partial pressure of oxygen, and sizes of the spheres. The Na₂O content in the sphere is uniform in each run. but it decreases with time of the run, indicating that the rate of diffusion of Na in the liquid is greater than that of volatilization, and that the latter is the rate-controlling process. The rate of sodium volatilization becomes greater with increasing temperature and with decreasing P_O2 and size of the spheres. The relation of the Na₂O content in the liquid sphere with time and its size indicate that the amount of Na₂O volatilized from the liquid spheres within unit time is proportional to the surface area of the spheres and the concentration of Na₂O in the liquid. From these relations, the rate of volatilization of sodium can be obtained at constant temperature and P_o2. The rate of volatilization of sodium satisfies the Arrhenius relation within the temperature range from about 1450–1600 C at 10^?9,2 atm p_O2; the activation energy for the sodium volatilization is approximately 100 kcal-mole^?1. The rate is also approximately proportional to within the range of p_O2 from 10^?10.2 to 10^?5.0 atm at about 1500° C. Based on the present results and the Na₂O contents in chondrules. it is suggested that they experienced an instant heating with maximum temperature of 1400–2200° C followed by an immediate cooling.  相似文献   

Estimating groundwater storage changes in the Mississippi River basin (USA) using GRACE   总被引：7，自引：0，他引：7  

Matthew Rodell  Jianli Chen  Hiroko Kato  James S. Famiglietti  Joe Nigro  Clark R. Wilson 《Hydrogeology Journal》2007,15(1):159-166

Based on satellite observations of Earth’s time variable gravity field from the Gravity Recovery and Climate Experiment (GRACE), it is possible to derive variations in terrestrial water storage, which includes groundwater, soil moisture, and snow. Given auxiliary information on the latter two, one can estimate groundwater storage variations. GRACE may be the only hope for groundwater depletion assessments in data-poor regions of the world. In this study, soil moisture and snow were simulated by the Global Land Data Assimilation System (GLDAS) and used to isolate groundwater storage anomalies from GRACE water storage data for the Mississippi River basin and its four major sub-basins. Results were evaluated using water level records from 58 wells set in the unconfined aquifers of the basin. Uncertainty in the technique was also assessed. The GRACE-GLDAS estimates compared favorably with the well based time series for the Mississippi River basin and the two sub-basins that are larger than 900,000 km². The technique performed poorly for the two sub-basins that have areas of approximately 500,000 km². Continuing enhancement of the GRACE processing methods is likely to improve the skill of the technique in the future, while also increasing the temporal resolution.  相似文献   

Geology of the Gorny Altai subduction–accretion complex, southern Siberia: Tectonic evolution of an Ediacaran–Cambrian intra-oceanic arc-trench system   总被引：1，自引：0，他引：1  

Tsutomu Ota  Atsushi Utsunomiya  Yuko Uchio  Yukio Isozaki  Mikhail M. Buslov  Akira Ishikawa  Shigenori Maruyama  Koki Kitajima  Yoshiyuki Kaneko  Hiroshi Yamamoto  Ikuo Katayama   《Journal of Asian Earth Sciences》2007,30(5-6):666-695

The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic–Early Paleozoic age, such as an accretionary complex (AC), high-P/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient subduction–accretion processes. This study investigated the detailed geology of the Upper Neoproterozoic to Lower Paleozoic rocks in a traverse between Gorno-Altaisk city and Lake Teletskoy in the northern part of the region, and in the Kurai to Chagan-Uzun area in the southern part. The tectonic units of the studied areas consist of (1) the Ediacaran (=Vendian)–Early Cambrian AC, (2) ca. 630 Ma HP complex, (3) the Ediacaran–Early Cambrian OP complex, (4) the Cryogenian–Cambrian island arc complex, and (5) the Middle Paleozoic fore-arc sedimentary rocks. The AC consists mostly of paleo-atoll limestone and underlying oceanic island basalt with minor amount of chert and serpentinite. The basaltic lavas show petrochemistry similar to modern oceanic plateau basalt. The 630 Ma HP complex records a maximum peak metamorphism at 660 °C and 2.0 GPa that corresponds to 60 km-deep burial in a subduction zone, and exhumation at ca. 570 Ma. The Cryogenian island arc complex includes boninitic rocks that suggest an incipient stage of arc development. The Upper Neoproterozoic–Lower Paleozoic complexes in the Gorno-Altaisk city to Lake Teletskoy and the Kurai to Chagan-Uzun areas are totally involved in a subhorizontal piled-nappe structure, and overprinted by Late Paleozoic strike-slip faulting. The HP complex occurs as a nappe tectonically sandwiched between the non- to weakly metamorphosed AC and the OP complex. These lithologic assemblages and geologic structure newly documented in the Gorny Altai region are essentially similar to those of the circum-Pacific (Miyashiro-type) orogenic belts, such as the Japan Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient subduction zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran–Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-trench setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.  相似文献   

Volcanic events associated with an enigmatic submarine earthquake     

Hiroko Sugioka  Yoshio Fukao  Toshihiko Kanazawa  & Kenji Kanjo 《Geophysical Journal International》2000,142(2):361-370

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Stable hydrogen isotope measurement of archaeal ether-bound hydrocarbons     

Masanori KanekoFumio Kitajima  Hiroshi Naraoka 《Organic Geochemistry》2011,42(2):166-172

Compound-specific hydrogen isotope analysis of ether-bound isoprenoid hydrocarbons from archaeal membranes has been developed using chemical degradation and gas chromatography/pyrolysis/isotope ratio mass spectrometry. The ether-bound hydrocarbons are quantitatively converted to saturated hydrocarbons by cleavage of ether bonds with HI followed by H₂ reduction in the presence of PtO₂. The δD value of ether-bound hydrocarbon moieties are corrected by way of isotopic mass balance calculation for the hydrogen incorporated during the hydrogenation. The method was successfully applied to determination of the δD values of biphytane moieties in glycerol dialkyl glycerol tetraethers (GDGTs) from a Sulfolobus sp. culture and a marine sediment.  相似文献   

Investigation of cutting methods for small samples of Hayabusa and future sample return missions     

Masayuki Uesugi  Ryo Noguchi  Tooru Matsumoto  Junya Matsuno  Takashi Nagano  Akira Tsuchiyama  Shigenori Harada  Kaori Yokoyama  Yoshiaki Yodo  Noboru Takeda  Toru Yada  Shogo Yakame  Yuzuru Karouji  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Akio Fujimura  Mitsuru Ebihara  Fumio Kitajima  Keisuke Nagao  Tomoki Nakamura  Hiroshi Naraoka  Takaaki Noguchi  Ryuji Okazaki  Hisayoshi Yurimoto 《Meteoritics & planetary science》2014,49(7):1186-1201

We report the investigation of cutting methods for Hayabusa samples. The purpose of our study is to explore the possibility of applying multiple analyses to a single particle effectively. We investigated the cutting performance of a blade dicing saw, laser, focused ion beam (FIB), and physical breaking by microindenter. Cutting performance was examined by estimating the aspect ratio of the cut slit, i.e., depth over width of the slit. We also investigated the possible contamination and sample damage by cutting. The result of the investigation shows that we can cut the samples from <50 μm to 500 μm using those methods with aspect ratios from 10 to 20, although they would introduce some contamination or damage to the samples. Our investigations also provide an important basis for the analysis of samples obtained by future sample return missions.  相似文献   

Anisotropy of Mg isotopic fractionation during evaporation and Mg self-diffusion of forsterite in vacuum     

Maho Yamada  Shogo Tachibana  Hiroko Nagahara  Kazuhito Ozawa 《Planetary and Space Science》2006,54(11):1096-1106

Evaporation of solid materials under low-pressure conditions could play important roles in chemical and isotopic fractionations in the early solar system. We have studied anisotropy of isotopic fractionation of ²⁶Mg and ²⁵Mg during kinetic evaporation of forsterite (Mg₂SiO₄), which is potentially a powerful tool to understand thermal histories of crystals in the early solar system. Ion-microprobe depth profiling revealed that the Mg isotopic zoning profiles of forsterite evaporated at 1500-1700 °C are notably differing along the a-, b-, and c-axes, which can be attributed to anisotropy in self-diffusion coefficient of Mg (D) and an isotopic fractionation factor for evaporation of Mg (α). The D and α were obtained from zoning profiles by applying the diffusion-controlled isotopic fractionation model of Wang et al. [1999. Evaporation of single crystal forsterite: Evaporation kinetics, magnesium isotope fractionation, and implications of mass-dependent isotopic fractionation of a diffusion-controlled reservoir. Geochim. Cosmochim. Acta 63(6), 953-966.].The D is largest and smallest along the a- and c-axes, respectively. The activation energy of 560-670 kJ/mol indicates that Mg diffusion at 1500-1700 °C occurred in the intrinsic diffusion regime.The α seems to be larger along the a- or c-axes than along the b-axis. The α along the a- or c-axes show weak temperature dependence. The α along all the crystallographic orientations is closer to unity than that expected from the kinetic theory of gases. These lines of evidence suggest that surface processes such as breaking of bonds and surface diffusion are responsible for the isotopic fractionation.  相似文献   

Eclogite-facies fluid infiltration: constraints from δ18O zoning in garnet     

Ashley K. Russell  Kouki Kitajima  Ariel Strickland  L. Gordon Medaris Jr.  Daniel J. Schulze  John W. Valley 《Contributions to Mineralogy and Petrology》2013,165(1):103-116

In situ analysis reveals that eclogite-facies garnets are zoned in δ¹⁸O with lower values in the core and rims that are ~1.5 to 2.5 ‰ higher. This pattern is present in 9 out of 12 garnets analyzed by SIMS from four orogenic eclogite terranes, and correlates with an increase in the mole fraction of pyrope and Mg/Fe ratio from core to rim, indicating prograde garnet growth. At the maximum temperatures and the time-scales experienced by these garnets, calculated intragranular diffusion distances for oxygen are small (<5 μm), indicating that δ¹⁸O records primary growth zoning and not diffusive exchange. The oxygen isotope gradients are larger than could form due to temperature changes during closed-system mineral growth. Thus, gradients reflect the compositions of fluids infiltrating during prograde metamorphism. Values of δ¹⁸O in garnet cores range from ?1 to 15 ‰, likely preserving the composition of the eclogite protoliths. Two garnet cores from the Almenningen eclogite in the Western Gneiss Region, Norway, have δ¹⁸O ~?1 ‰ and are the first negative δ¹⁸O eclogites identified in the region. In contrast with orogenic eclogites, seven high δ¹⁸O garnets (>5 ‰) from two kimberlites are homogeneous in δ¹⁸O, possibly due to diffusive exchange, which is possible for prolonged periods at higher mantle temperatures. Homogeneity of δ¹⁸O in garnets outside the normal mantle range (5–6 ‰) may be common in kimberlitic samples.  相似文献   

A rotary-shear low to high-velocity friction apparatus in Beijing to study rock friction at plate to seismic slip rates   总被引：2，自引：0，他引：2  

Shengli Ma  ;Toshihiko Shimamoto  ;Lu Yao  ;Tetsuhiro Togo  ;Hiroko Kitajima 《地震学报(英文版)》2014,(5):469-497

This paper reviews 19 apparatuses having highvelocity capabilities,describes a rotary-shear low to highvelocity friction apparatus installed at Institute of Geology,China Earthquake Administration,and reports results from velocity-jump tests on Pingxi fault gouge to illustrate technical problems in conducting velocity-stepping tests at high velocities.The apparatus is capable of producing plate to seismic velocities（44 mm/a to 2.1 m/s for specimens of 40 mm in diameter）,using a 22 kW servomotor with a gear/belt system having three velocity ranges.A speed range can be changed by 103 or 106by using five electromagnetic clutches without stopping the motor.Two cam clutches allow fivefold velocity steps,and the motor speed can be increased from zero to 1,500 rpm in 0.1-0.2 s by changing the controlling voltage.A unique feature of the apparatus is a large specimen chamber where different specimen assemblies can be installed easily.In addition to a standard specimen assembly for friction experiments,two pressure vessels were made for pore pressures to 70 MPa;one at room temperature and the other at temperatures to 500 °C.Velocity step tests are needed to see if the framework of rate-and-state friction is applicable or not at high velocities.We report results from velocity jump tests from 1.4 mm/s to 1.4 m/s on yellowish gouge from a Pingxi fault zone,located at the northeastern part of the Longmenshan fault system that caused the 2008 Wenchuan earthquake.An instantaneous increase in friction followed by dramatic slip weakening was observed for the yellowish gouge with smooth sliding surfaces of host rock,but no instantaneous response was recognized for the same gouge with roughened sliding surfaces.Instantaneous and transient frictional properties upon velocity steps cannot be separated easily at high velocities,and technical improvements for velocity step tests are suggested.  相似文献   

Silicification of pelitic schist in the Ryoke low-pressure/temperature metamorphic belt, Southwest Japan: Origin of competent layers in the middle crust     

Masaru  Terabayashi  Hiroshi  Yamamoto  Eri  Hiwatashi  Kouki  Kitajima 《Island Arc》2010,19(1):17-29

We propose that competent layers composed of silicified rocks in the Cretaceous Ryoke low-pressure/temperature (low- P/T ) metamorphic belt in the Iwakuni–Yanai area, Southwest Japan, may be an exhumed equivalent of a seismically-reflective bright-layer in the middle crust. Silicified rocks crop out as layers or long lenticular bodies several to fifteen meters in thickness, and they are restricted to the area of greenschist facies conditions within a structural thickness of about one kilometer. The silicified rock layers exhibit a sharp contact with subjacent biotite schist but a gradational contact with overlying pelitic schist. Silicified rock is mainly composed of fine-grained quartz and minor muscovite and biotite, and some colored minerals have been variably decolorized by alteration. This implies that silicification turned the color of pelitic schists to pale gray or milky white. Quartz veins cutting schistosity at high angles were preferentially developed in the silicified rocks, while schistosity-parallel quartz veins, which underwent viscous flow, were observed in the underlying biotite schists. En echelon quartz veins and fishnet-like quartz veins are characteristic of silicified rocks. The modes of occurrence of quartz veins indicate that silicified rocks were competent relative to underlying biotite schist. The combination of contact with high-competence contrast adjacent to low-permeability silicified rocks may be a good reflector of seismic waves. If the silicified rocks were distributed in the middle crust to a considerable extent, they may result in seismic bright-layer reflections.  相似文献