Re-Os isotope systematics and fractionation of siderophile elements in metal phases from CBa chondrites     

Nao Nakanishi  Tetsuya Yokoyama  Satoki Okabayashi  Tomohiro Usui  Hikaru Iwamori 《Meteoritics & planetary science》2018,53(5):1051-1065

We report Os isotope compositions of metal grains in two CB_a chondrites (Bencubbin and Gujba) determined using a micromilling sampling coupled with thermal ionization mass spectrometry, together with the abundances of major and trace siderophile elements obtained by electron probe microanalysis and femtosecond laser ablation inductively coupled plasma–mass spectrometry. The CB_a metal grains presented ¹⁸⁷Os/¹⁸⁸Os ratios akin to carbonaceous chondrites with limited variations (0.1257–0.1270). Most of the CB_a metal grains were scattered along a ¹⁸⁷Re-¹⁸⁷Os reference isochron of IIIAB iron meteorites, indicating that the CB_a metals experienced limited Re-Os fractionation at the time of their formation. The Re/Os ratios of sampling spots for the CB_a metals, recast from the observed ¹⁸⁷Os/¹⁸⁸Os ratios, had a positive correlation with their Os/Ir ratios. In addition, the metal grains showed a positive correlation in a Pd/Fe versus Ni/Fe diagram. These correlations suggest that the CB_a metal grains have formed via equilibrium condensation or evaporation from a gaseous reservoir at ~10⁻⁴ bar with enhanced metal abundances. Compared to the Bencubbin metals, the Gujba metals are characterized by having systematically lower Pd/Fe and Ni/Fe ratios that span subchondritic values. Such a difference was most likely induced by the compositionally heterogeneous impact plume from which the metals were condensed.  相似文献   

The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献   

ESR dating of palaeolithic calcite: A comparison between powder and monocrystal spectra with thermal annealing     

Yuji Yokoyama  Roland Bibron  Concle Leger 《Quaternary Science Reviews》1988,7(3-4)

Evolution of ESR spectra with thermal annealing at different temperatures is studied for a monocrystal calcite taken in the Orgnac III site. Up to 20 ESR lines are recognized from the angular dependence of these lines. These lines are compared with the ESR lines observed for powder and rotating monocrystal calcites.The h1 line (g = 2.0057) and h3 line (g = 2.0007) are isotropic or nearly isotropic and are due to the electrons trapped in the amorphous region formed by fission tracks or alpha-ray recoil nuclei. The h2 line (g = 2.0021) is a composite of several different lines.  相似文献   

Comparison of the high-pressure schist belts of New Caledonia and Sanbagawa,Japan     

R. N. Brothers  K. Yokoyama 《Contributions to Mineralogy and Petrology》1982,79(2):219-229

The high-pressure schist terranes of New Caledonia and Sanbagawa were developed along the oceanic sides of sialic forelands by tectonic burial metamorphism. The parent rocks were chemically similar, as volcanic-sedimentary trough or trench sequences, and metamorphic temperatures in both belts were 250° to 600° C. From phase equilibria curves, total pressures were higher for New Caledonia (6–15 kb) than for Sanbagawa (5–11 kb) and the estimated thermal gradients were 7–10° C/km and 15° C/km respectively.PT paths identify the higher pressure in New Caledonia (P differences 2 kb at 300° C and 4 kb at 550° C) with consequent contrast in progressive regional metamorphic zonation for pelites in the two areas: lawsonite-epidote-omphacite (New Caledonia) and chlorite-garnet-biotite (Sanbagawa). In New Caledonia the Na-amphibole is dominantly glaucophane and Na-pyroxenes associated with quartz are Jadeite (Jd_95–100) and omphacite; in Sanbagawa the amphibole is crossite or riebeckite and the pyroxene is omphacite (Jd₅₀). For both areas, garnet rims show increase in pyrope content with advancing grade, but Sanbagawa garnets are richer in almandine. Progressive assemblages within the two belts can be equated by such reactions as:New Caledonia Sanbagawa glaucophane+paragonite+H₂Oalbite+chlorite+quartz glaucophane+epidote+H₂Oalbite+chlorite+actinolite and the lower pressure Japanese associations appear as retrogressive phases in the New Caledonia epidote and omphacite zones.The contrasts inPT gradient, regional zonation and mineralogy are believed due to differences in the tectonic control of metamorphic burial: for New Caledonia, rapid obduction of an upper sialic plate over an inert oceanic plate and sedimentary trough; and for Sanbagawa, slower subduction of trench sediments beneath a relatively immobile upper plate.  相似文献   

Corrigendum to “Global ice volumes at the Last Glacial Maximum and early Lateglacial” [Earth Planet. Sci. Lett. 181 (2000) 513–527]     

Kurt Lambeck  Yusuke Yokoyama  Paul Johnston  Anthony Purcell 《Earth and Planetary Science Letters》2001,190(3-4):275

  相似文献   

Gravimetric studies of Taal Volcano,philippines     

I. Yokoyama  A. Alcaraz  O. Peña 《Bulletin of Volcanology》1975,39(3):479-489

Taal Volcano is peculiar in its violent explosivity in spite of its low altitude. The surrounding topographies suggest that the origin of Taal Volcano is either a caldera or a graben structure. To confirm the caldera origin one must search for a vast quantity of caldera ejecta balancing with the depression. As a first step, a gravity survey was carried out on and around Taal Volcano, and high gravity anomalies were lound on Volcano Island. The distribution of the gravities may suggest a graben structure overlying a denser layer of igneous material.  相似文献   

Seismological significance of the 1977–1978 eruptions and the magma intrusion process of usu volcano, Hokkaido     

Hm. Okada  H. Watanabe  H. Yamashita  I. Yokoyama 《Journal of Volcanology and Geothermal Research》1981,9(4):311-334

An earthquake swarm, and the major pumice eruptions in August 1977 which followed, marked the start of the dacitic doming activity of Usu volcano in southwestern Hokkaido, Japan. The sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data. The distribution of the abundant hypocenters shows clearly an earthquake-free zone beneath the summit crater. The hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations, considered due to magma intrusion into this earthquake-free zone. The earthquake mechanism solutions are mostly of dip-slip type and are interpreted in terms of the doming deformations. The existence of earthquake families (earthquakes with similar waveforms) is the main cause of the peculiar occurrence of earthquakes in space, time and magnitude. The concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm, and the observed episodic deformations.  相似文献   

Production of radionuclides by cosmic rays at mountain altitudes     

Yuji Yokoyama  Jean-Louis Reyss  François Guichard 《Earth and Planetary Science Letters》1977,36(1):44-50

Production rates of²²Na (T_1/2 = 2.6years) from aluminium by the action of cosmic rays are measured at the Mont Blanc (altitude 4600 m), the Aiguille du Midi (3840 m), and the Col du Lautaret (2070 m). They are2.3 ± 0.5,1.8 ± 0.3,and0.77 ± 0.18 atoms min^?1 kg^?1, respectively, in good agreement with the calculated production rates, 2.4, 1.7 and 0.6 atoms min^?1 kg^?1, respectively, at the three stations.Production rates of²⁴Na (T_1/2 = 15hours) from aluminium and magnesium are also measured at the Aiguille du Midi; the observed rates of3.4 ± 0.4and6.0 ± 1.7 atoms min^?1 kg^?1, respectively, agree well with the theoretically expected rates of 3.7 and 5.6 atoms min^?1 kg^?1.The production rates of³H,⁷Be,¹⁰Be,¹⁴C,²²Na,²⁶Al,³⁶Cl,³⁷Ar,³⁹Ar,⁵³Mn,⁵⁴Mn, and⁵⁵Fe in terrestrial rocks by the action of cosmic rays are calculated in order to show the possibility of applying the measurements of these cosmogenic radionuclides to the earth science.  相似文献   

Trans-Equatorial Loop System Arising from Coronal Hole Boundaries through Interactions between Active Regions and Coronal Holes     

Masaki Yokoyama  Satoshi Masuda 《Solar physics》2010,263(1-2):135-152

It is not clear how trans-equatorial loop systems (TLSs) are formed, although they have been observed often with Yohkoh/SXT. We focus here on a TLS that appeared on 27 May 1998. Yokoyama and Masuda (Solar Phys. 254, 285, 2009) proposed a new scenario for the formation mechanism of the TLS. In this scenario, they pointed out the importance of magnetic interaction between an active region and a coronal hole to make “strong-seed magnetic fields” before a transient (bright and short-lived) trans-equatorial loop was created. The main aims of this study are to verify the scenario and to make the TLS formation mechanism clear, based on observational data. Yohkoh/SXT images, SOHO/MDI magnetograph data, and Kitt Peak coronal-hole maps were mainly used for our analyses. We investigated the TLS in detail from the time that there were no signatures of the TLS to its clear appearance. The following results are obtained: i) an active region emerged in the vicinity of a coronal-hole boundary, ii) the coronal-hole boundary retreated during the period when the active region was developing, iii) temporal variations of soft X-ray intensities were roughly synchronized between the coronal-hole boundary and a trans-equatorial region, and iv) new closed loops were observed in soft X-rays clearly at the coronal-hole boundary. Since i), ii), iii), and iv) are just what we expect in the scenario of YM2009, the scenario found support. We conclude that the TLS was originating with large-scale magnetic fields of the coronal-hole boundary through magnetic reconnection between the active region and a coronal hole.  相似文献   

Dynamics of two satellites in the 2/1 Mean–Motion resonance: application to the case of Enceladus and Dione     

N. CallegariJr.  T. Yokoyama 《Celestial Mechanics and Dynamical Astronomy》2007,98(1):5-30

The dynamics of a pair of satellites similar to Enceladus–Dione is investigated with a two-degrees-of-freedom model written in the domain of the planar general three-body problem. Using surfaces of section and spectral analysis methods, we study the phase space of the system in terms of several parameters, including the most recent data. A detailed study of the main possible regimes of motion is presented, and in particular we show that, besides the two separated resonances, the phase space is replete of secondary resonances.  相似文献