Petrography of Yamato 984028 lherzolitic shergottite and its melt vein: Implications for its shock metamorphism and origin of the vein     

Shin Ozawa  Masaaki Miyahara  Eiji Ohtani  Makoto Kimura  Yoshinori Ito 《Polar Science》2011,4(4):550-557

Yamato 984028 (Y984028) is a newly identified lherzolitic shergottite, recovered from the Yamato Mountains, Antarctica, in 1999. As part of a consortium study, we conducted petrographic observations of Y984028 and its melt vein in order to investigate its shock metamorphism. The rock displays the typical non-poikilitic texture of lherzolitic shergottite, characterized by a framework of olivine, minor pyroxene (pigeonite and augite), and interstitial maskelynite. Shock metamorphic features include irregular fractures in olivine and pyroxene, shock-induced twin-lamellae in pyroxene, and the complete conversion of plagioclase to maskelynite, features consistent with those found in other lherzolitic shergottites. The melt vein is composed of coarse mineral fragments (mainly olivine) entrained in a matrix of fine-grained euhedral olivine (with several modes of compositional zoning) and interstitial glassy material. Some coarse olivine fragments consist of an assemblage of fine-grained euhedral to subhedral olivine crystals, suggesting shock-induced fragmentation, recrystallization, and/or a process of sintering. The implication is that the fine-grained olivine crystals in the matrix of the melt vein represent complicated crystallization environments and histories.  相似文献   

Mineralogical and spectroscopic investigation of the Tagish Lake carbonaceous chondrite by X‐ray diffraction and infrared reflectance spectroscopy     

Matthew R. M. IZAWA  Roberta L. FLEMMING  Penelope L. KING  Ron C. PETERSON  Phil J. A. McCAUSLAND 《Meteoritics & planetary science》2010,45(4):675-698

Abstract– We have carried out a sample‐correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the Tagish Lake C2 chondrite. Rietveld refinement of high‐resolution powder X‐ray diffraction (XRD) data was used to determine quantitative major mineral abundances. Thermal infrared (400–4500 cm⁻¹, 2.2–25.0 μm) spectra of the same samples were obtained using diffuse (biconical) reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results are in good agreement with previous studies of the mineralogy of the Tagish Lake meteorite; we find however that Tagish Lake is more varied in major mineralogy than has previously been reported. In particular, we observed two new distinct lithologies, an inclusion‐poor magnetite‐ and sulfide‐rich lithology, and a carbonate‐rich, siderite‐dominated lithology in addition to the previously documented carbonate‐rich and carbonate‐poor lithologies. Grain density for each Tagish Lake sample was calculated from the measured mineral modal abundances and known mineral densities. For powders from three originally intact inclusion‐rich samples, the calculated grain density is 2.77 ± 0.05 g cm⁻³, in excellent agreement with those reported in the literature for other intact inclusion‐rich Tagish Lake samples. Tagish Lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite‐serpentine content, likely a result of mineral separation in the meltwater holes from which they were collected; the disaggregated samples may not therefore adequately represent bulk samples of the Tagish Lake meteorite. The predominance of very fine‐grained material in the Tagish Lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith. Gypsum and talc have been found by XRD in powders from the inclusion‐rich, intact Tagish Lake samples in this study, and may have been present in the parent body; if present, these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra.  相似文献   

Phase relations in the carbon-saturated C–Mg–Fe–Si–O system and C and Si solubility in liquid Fe at high pressure and temperature: implications for planetary interiors     

Suguru Takahashi  Eiji Ohtani  Hidenori Terasaki  Yoshinori Ito  Yuki Shibazaki  Miho Ishii  Ken-ichi Funakoshi  Yuji Higo 《Physics and Chemistry of Minerals》2013,40(8):647-657

The phase and melting relations of the C-saturated C–Mg–Fe–Si–O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = ?1.7 to ?1.2, where ΔIW is the deviation of the oxygen fugacity (fO₂) from an iron-wüstite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < ?3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe–Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO₂, whereas the solubility of Si decreased with increasing fO₂. The carbon-bearing phases were graphite, Fe₃C, SiC, and Fe alloy melt (Fe–C or Fe–Si–C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < ?6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe–Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth’s core.  相似文献   

QUE 94204: A primitive enstatite achondrite produced by the partial melting of an E chondrite‐like protolith     

Matthew R. M. IZAWA  Roberta L. FLEMMING  Neil R. BANERJEE  Sergei MATVEEV 《Meteoritics & planetary science》2011,46(11):1742-1753

Abstract– Queen Alexandra Range (QUE) 94204, an enstatite achondrite, is a coarse‐grained, highly recrystallized, chondrule‐free and unbrecciated rock dominated (about 70 vol%) by anhedral, equigranular crystals of orthoenstatite of nearly endmember composition (Fs_0.1–0.4, Wo_0.3–0.4) with interstitial plagioclase, kamacite, and troilite. Abundance of approximately 120° triple junctions and the close association of metal–sulfide and plagioclase‐rich melts indicate that QUE 94204 has undergone limited partial melting with inefficient melt extraction. Mineral chemistry indicates a high degree of thermal metamorphism. Kamacite in QUE 94204 contains between 2.09 and 2.55 wt% Si, similar to highly metamorphosed EL chondrites. Plagioclase has between 4.31 and 6.66 wt% CaO, higher than other E chondrites but closer in composition to plagioclase from metamorphosed EL chondrites. QUE 94204 troilite contains up to 2.55 wt% Ti, consistent with extensive thermal metamorphism of an E chondrite‐like precursor. Results presented in this study indicate that QUE 94204 is the result of low degree, (about 5–20 vol%, probably toward the lower end of this range) partial melting of an E chondrite protolith. Textural and chemical evidence suggests that during the metamorphism of QUE 94204, melts formed first at the Fe,Ni‐FeS cotectic near approximately 900 °C, followed by plagioclase‐pyroxene silicate partial melts near approximately 1100 °C. Neither the Fe,Ni‐FeS nor the plagioclase‐pyroxene melts were efficiently segregated or extracted. QUE 94204 belongs to a grouplet of similar “primitive enstatite achondrites” that are analogous to the acapulcoites‐lodranites, but that have resulted from the partial melting of an E chondrite‐like protolith.  相似文献   

A possible substellar companion to the intermediate-mass giant HD 175679     

Liang Wang  Bun＇ei Sato  Gang Zhao  Yu-Juan Liu  Kunio Noguchi  Hirovasu Ando  Hideyuki Izumiura  Eiji Kambe  Masashi Omiya  Hiroki Harakawa  Fan Liu  Xiao-Shu Wu  Yoichi Takeda  Michitoshi Yoshida  Eiichiro Kokubo 《天体物理学报》2012,(1):84-92

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Spatiotemporal characterization of land surface temperature in Mount Kilimanjaro using satellite data     

Eduardo Eiji Maeda  Pekka Hurskainen 《Theoretical and Applied Climatology》2014,118(3):497-509

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How to cut a sediment core for 210Pb geochronology     

Xueqiang Lu  Eiji Matsumoto 《Environmental Geology》2005,47(6):804-810

²¹⁰Pb geochronology is described mathematically, but how to cut a sediment core is not explicit. Thick sectioning may reduce dating reliability; but on the contrary, thin sectioning is time-consuming. Considering the counting error of excess ²¹⁰Pb, a new method was proposed for the determination of meaningful thickness for sectioning. The authors applied this method to a core from Tokyo Bay. To increase the thickness with depth, the treatment is helpful in reducing the sample number for measurement and improving the dating accuracy. In addition, the averaging effect involved in sectioning was discussed, and it was confirmed that the averaging effect in the new method on ²¹⁰Pb geochronology may generally be neglected.  相似文献   

A Fluid Inclusion Study on Columnar Adularia from the Hishikari Low-sulfidation Epithermal Gold Deposit, Japan   总被引：2，自引：1，他引：2  

Jiro ETOH  Eiji IZAWA  Sachihiro TAGUCHI 《Resource Geology》2002,52(1):73-78

Abstract: In the Hishikari low-sulfidation epithermal gold deposit, Japan, columnar adularia crystals commonly precipitated directly on to the fracture surface of wall rock, and then electrum precipitated on the columnar adularia with fine-grained adularia and quartz. To reveal the characteristics of mineralizing fluids and the elevation of paleo-water tables at the earliest stage of mineralization in the Honko-Sanjin zone of the Hishikari deposit, the fluid inclusions in the columnar adularia in gold-bearing quartz–adularia veins were studied.
Coexistence of vapor-rich and liquid-rich two–phase primary fluid inclusions indicates the deposition of columnar adularia from boiling fluids. The precipitation temperatures range from 175 to 215C, and generally increase with depth. The temperatures of final melting point of ice range from –1.2 to –0.1C with an average of –0.5C, corresponding to salinity ranging from 0.2 to 2.1 wt% NaCl equivalent with an average of 0.9 wt% NaCl (eq.). Concentrations of non-condensable gases such as CO₂ were under the detection limit of a laser Raman microprobe spectrometer. From the precipitation temperature of columnar adularia in the Hosen–2 vein and the boiling point – depth curve for a 0.9 wt% NaCl (eq.) fluid, paleo-water table was estimated to be at an elevation of about +170 m. The elevation of the paleo-water tables for other veins was estimated to range from +140 to +215 m.  相似文献   

Gas Measurement of Fluid Inclusions from the Hishikari Epithermal Gold Deposit, Southern Kyushu, Japan, Using Laser Raman Microprobe     

Jiro Etoh    Sachihiro Taguchi  Eiji Izawa 《Resource Geology》2002,52(4):405-408

Abstract. Laser Raman microprobe analysis was performed on the fluid inclusions from the Honko-Sanjin zone in the Hishikari epithermal gold deposit, southern Kyushu, Japan. Gas concentrations of fluid inclusions through the zone were below detection limits (e.g., 5 mmole/kg H₂O for CO₂), with an exception at shallow portion in which the CO₂/N₂ mole ratio was determined to be 5.3. Boiling of hydrothermal solutions probably separated gases from ore fluids at the deep portion of the deposit, and migration of gases to shallow portion resulted in CO₂-rich steam-heated water and related acid alteration.  相似文献   

Gold-bearing Quartz Veins and Hydrothermal Alteration of the Paleozoic Epithermal System in the Francis Creek Area, North Queensland, Australia     

Agung Harijoko    Koichiro Watanabe    Yoshinobu Motomura  Eiji Izawa 《Resource Geology》2002,52(4):353-358

Abstract. The Francis Creek area located at the Sybil graben in North Queensland, Australia, has some features of epithermal gold mineralization such as gold-bearing quartz vein and silica body hosted in rhyodacitic rocks of the Late Carboniferous Hells Gate Formation. In order to understand the nature of the paleo-hydrothermal activity in this area and to aid exploration for an economic gold deposit in this area, we carried out hydrothermal alteration mapping surrounding the veins and silica body, over an area of about 7 times 5 km².
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area.  相似文献