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21.
Calcium and magnesium‐bearing sabugalite occurs as aggregations of yellowish platy crystals in veinlets or druses in conglomerate from the oxidized parts of the Tono uranium deposit, Central Japan. X‐ray powder diffractometry of this mineral has reflections consistent with previous powder diffraction data of sabugalite. It is included in the monoclinic system with space group C2/m and calculated cell parameters of a = 19.68Å, b = 9.89Å, c = 9.82Å α = γ = 90°, β‐96.93° and V = 1897.83Å3. Chemical analysis yields a formula of (Ca0.10 Mg0.09)Σ0.19Al0.53(UO2)2.04((PO4)1.99(AsO4)0.01)Σ2.00·11.22H2O. EMPA mapping shows that the mineral is compositionally uniform with no micron‐scale layering. Charge of cations including Ca and Mg in the cation‐H2O layer is 1.98 being identical to that of autunite group minerals. This suggests that the charge balance in the cation‐H2O layer of the mineral could be made by the alkaline earth or alkaline elements rather than by hydrogen ions. 相似文献
22.
We propose a new scenario of the lunar origin, which is a natural extension of planetary formation processes studied so far by us in Kyoto. According to these studies, the Earth grew up in a gaseous solar nebula and, consequently, the sphere of its gravitational influence (i.e., the Hill sphere of the Earth) was filled by a gas forming a dense primordial atmosphere of the Earth. In the later stages, this atmosphere as well as the solar nebula was dissipated gradually, owing to strong activities of the early-Sun in a T Tauri-stage.In the present and the subsequent papers, we study a series of dynamical processes where a lowenergy (i.e., slightly unbound) planetisimal is trapped within the terrestrial Hill sphere, under the above-mentioned circumstances that the gas density of the primordial atmosphere is gradually decreasing. It is clear that two conditions must be satisfied for the lunar origin: first, an unbound planetesimal entering the Hill sphere have to dissipate its kinetic energy and come into a bound orbit before it escapes from the Hill sphere and, second, the bound planetisimal never falls onto the surface of the Earth.In this paper we study the first condition by calculating the oribital motion of a planetesimal in the Hill sphere, which is affected both by solar gravity and by atmospheric gas drag. The results show that a low-energy planetisimal with the lunar mass or less can be trapped in the Hill sphere with a high probability, if it enters the Hill sphere at stages before the atmospheric density is decreased to about 1/50 of the initial value.In the subsequent paper, the second condition will be studied and it will be shown that a tidal force, among other forces, is very important for a trapped planetesimal to avoid collision with the Earth and stay eternally in the Hill sphere as a satellite. 相似文献
23.
Abstract. Sulfur isotope ratios are analyzed for a series of mudstones in a successive section in the Taiheizan area in the central Green Tuff region, northeast Japan. The δ34 S values for the Uyashinai Mudstone Member (Nishikurosawa stage), the Onnagawa Formation and the Funakawa Formation range from -45 to -14%, -20 to +4% and -30 to -10%, respectively. There is a marked positive shift in δ34 S values at the Nishikurosawa/Onnagawa boundary and an upward δ34 S-decreasing trend in the Onnagawa and Funakawa Formations. The present data provides evidence for environmental change in the form of stratification of the seawater, initiated at the Nishikurosawa/Onnagawa boundary and persisting during deposition of the Onnagawa Formation, followed by gradual oxygenation during deposition of the Funakawa Formation. 相似文献
24.
Intensive meteorological observations were carried out at three sites along the slope of Adélie Land, Antarctica, with the goal of documenting summertime meteorological features of the katabatic zone. Three observational sites were placed at 5 km (D10), 110 km (D47), and 210 km (D57) from the coast, and frequency distributions of meteorological parameters were obtained at each site. Some meteorological features at D47 and D57 (interior sites) were different than at D10 (the coastal site); namely, mean air temperatures averaged for the whole observational period showed more pronounced diurnal variations at the interior sites than at the coastal site. These variations could be represented by sinusoidal curves. Wind speeds also showed diurnal variations, whose extremes appeared several hours later than the temperature extremes. The prevailing wind direction for all sites was southerly, about 30° east of the fall line, with small variations in wind direction. The strength and the height of temperature inversions were examined in two different layers (0 to 50 m, 50 to 300 m) at D47. A strong, shallow inversion layer formed at night, however, completely vanished during the day. On the other hand, an upper level inversion whose strength was weak persisted. The katabatic characteristics of the surface wind found at D47 in summer could be due to this upper level temperature inversion.A contribution to I.A.G.O. (Interaction-Atmosphere-Glace-Ocean). 相似文献
25.
Collapse mechanism of the Paleogene Sakurae cauldron, SW Japan 总被引：1，自引：0，他引：1
The Paleogene Sakurae cauldron of SW Japan is characterized by a nested structure with a polygonal outline (21×13 km2) including a circular collapsed part (5 km in diameter). Total thickness of the caldera infill amounts to 2,000 m. The lower member of the infill consists mainly of felsic crystal tuff and lesser intercalated andesitic lava flows, whereas the upper member is composed of high-grade ignimbrite capped with a large rhyolitic lava dome. These members represent the first and second stage eruptions, respectively. Faults bounding the cauldron rim comprise intersecting radial and concentric faults, producing the polygonal outline of this cauldron. The primary collapse of this cauldron thus occurred as a polygonal caldera basin where products of the first stage eruption accumulated. In contrast, the inner collapse part is defined by a ring fracture system. This sector subsided concurrently with accumulation of the high-grade ignimbrite of the second stage eruption. This inner circular collapse thus represents syn-eruptional subsidence concurrent with the climactic eruption. Magma drainage during the first stage probably induced outward-dipping ring fractures in the chamber roof. Opening of the ring fractures following subsidence of the central bell-jar block caused rapid evacuation of magma as voluminous pumice flows, even though magma pressure may have decreased to some degree. 相似文献
26.
Joseph Onglo Espi Ken-Ichiro Hayashi Kosei Komuro Hiroyasu Murakami Yoshimichi Kajiwara 《Resource Geology》2007,57(3):249-268
The Bilimoia deposit (2.23 Mt, 24 g/t Au), located in the eastern Central Mobile Belt of mainland Papua New Guinea, is composed of fault‐hosted, NW–NNW‐trending Irumafimpa–Kora and Judd–Upper Kora Au‐quartz veins hosted by Middle–Late Triassic basement that was metamorphosed to medium‐grade greenschist facies between Middle–Late Triassic and Early–Middle Jurassic. Mineralizing fluids were introduced during crustal thickening, rapid uplift, change of plate motions from oblique to orthogonal compression, active faulting and S3 and S4 events in an S1–S4 deformation sequence. The Bilimoia deposit is spatially and temporally related to I‐type, early intermediate to felsic and late mafic intrusions emplaced in Late Miocene (9–7 Ma). Hydrothermal alteration and associated mineralization is divided into 10 main paragenetic stages: (1) chlorite–epidote‐selvaged quartz–calcite–specularite vein; (2) local quartz–illite–pyrite alteration; (3) quartz–sericite–mariposite–fuchsite–pyrite wall‐rock alteration that delimits the bounding shears; (4) finely banded, colloform‐, crustiform‐ and cockade‐textured and drusy quartz ± early wolframite ± late adularia; (5) hematite; (6) pyrite; (7) quartz ± amethyst‐base metal sulfides; (8) quartz–chalcopyrite–bornite–Sn and Cu sulfides–Au tellurides and Te ± Bi ± Ag ± Cu ± Pb phases; (9) Fe ± Mn carbonates; and (10) supergene overprint. Fluid inclusions in stage 4 are characterized by low salinity (0.9–5.4 wt% NaCl equivalent), aqueous–carbonic fluids with total homogenization temperatures ranging from 210 to 330°C. Some of the inclusions that homogenized between 285 and 330°C host coexisting liquid‐ and vapor‐rich (including carbonic) phases, suggesting phase separation. Fluid inclusions in quartz intergrown with wolframite have low salinity (0.9–1.2 wt% NaCl equivalent), aqueous–carbonic fluids at 240–260°C, defining the latter’s depositional conditions. The ore fluids were derived from oxidized magmatic source initially contaminated by reduced basement rocks. Wall‐rock alteration and involvement of circulating meteoric waters were dominant during the first three stages and early part of stage 4. Stage 5 hematite was deposited as a result of stage 4 phase separation or entrainment of oxygenated groundwater. Gold is associated with Te‐ and Bi‐bearing minerals and mostly precipitated as gold‐tellurides during stage 8. Gold deposition occurred below 350°C due to a change in the sulfidation and oxidation state of the fluids, depressurization and decreasing temperature and activities of sulfur and tellurium. Bisulfides are considered to be the main Au‐transporting complexes. The Bilimoia deposit has affinities that are similar to many gold systems termed epizonal orogenic and intrusion‐related. The current data allow us to classify the Bilimoia deposit as a fault‐controlled, metamorphic‐hosted, intrusion‐related mesothermal to low sulfidation epithermal quartz–Au–Te–Bi vein system. 相似文献
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28.
T. Okumura H. Nishido S. Toyoda T. Kaneko S. Kosugi Y. Sawada K. Komuro 《Quaternary Geochronology》2008,3(4):342-345
Detailed quantitative cathodoluminescence (CL) imaging analysis was carried out for radiation-damage halos observed by CL (CL halo) created in natural quartz by implantation of 4 MeV He+ ions. The band of CL halo was approximately 14 μm in width and was constant for any He+ ion dose. The width of the halo is consistent with the theoretical range of 4He ions in quartz. A quantitative response of CL intensity to He+ ion dose was obtained, leading to the application of CL halos to geodosimetrical use. The CL intensity increases exponentially in the luminescent band from the implantation surface to the inside, until it reaches a maximum at 14 μm depth, with a rapid decrease beyond this point. This result is as predicted by Bragg's law, although we find some differences between the CL intensity and the theoretical stopping power. 相似文献
29.
Masahiro Kayama Hirotsugu Nishido Shin Toyoda Kosei Komuro Adrian A. Finch Martin R. Lee Kiyotaka Ninagawa 《Physics and Chemistry of Minerals》2013,40(7):531-545
Cathodoluminescence (CL) spectra of unirradiated, He+ ion-implanted and electron-irradiated plagioclase minerals contain the following emission bands: (1) below 300 nm due to Pb2+, (2) at ~320 and ~350 nm to Ce3+, (3) at 380–420 nm to Eu2+, Ti4+ and/or Al–O?–Al/Ti defects, (4) at 560–580 nm to Mn2+ and (5) at 720–760 nm to Fe3+. During the implantation of He+ ion, much of their energy may be dissipated by partial destruction and strain of the feldspar framework, resulting in quenching of CL. Deconvolution of CL spectra acquired from albite and oligoclase reveals an emission component at 1.86 eV (666 nm) assigned to a radiation-induced defect center associated with Na+ atoms. As its intensity increases with radiation dose, this emission component has potential for geodosimetry and geochronometry. Electron irradiation causes Na+ migration in plagioclase, and then a considerable reduction in intensity of emissions assigned to impurity centers, which is responsible for an alteration in the energy state or a decrease in luminescence efficiency following the change of activation energy. Emission intensity at 1.86 eV positively correlates with electron irradiation time for unimplanted and He+ ion-implanted albite and oligoclase, but negatively for the implanted albite above 1.07 × 10?4 C/cm2. It implies that radiation halo produced by α-particles should not be measured using CL spectroscopy to estimate β radiation dose on albite in the high radiation level. 相似文献
30.
Chemical composition and mode of occurrences of (Au, Ag)Te2 minerals such as calaverite (AuTe2), sylvanite (AuAgTe4) and krennerite ((Au, Ag)Te2) in epithermal gold telluride ores from Suzaki, Kawazu and Teine are examined. In the ores from Suzaki, (Au, Ag)Te2 minerals occur in microbands of tellurides and fine quartz. The minerals in telluride bands change from krennerite, via calaverite‐native tellurium, to sylvanite, in the order of crystallization. A sample from Kawazu contains sylvanite and native tellurium with stutzite, hessite and tetradymite in the coarser gray quartz part. The Teine sample also contains sylvanite and native tellurium with barite and quartz. The peak patterns of XRD of calaverite, krennerite and sylvanite from Suzaki are almost identical to that of JCPDS 43–1472, JCPDS 8–20 and JCPDS 9–477, respectively. The Te, Au, Cu, and Ag contents of calaverite from Suzaki range from 56.4 to 57.9 wt.%, from 41.6 to 42.6 wt.%, from 0.28 to 0.45 wt.% and from 0.14 to 0.31 wt.%, respectively, corresponding to the formula Au0.97Ag0.01Cu0.02Te2. The Te, Au, Ag, and Cu contents of krennerite from Suzaki range from 59.6 to 61.4 wt.%, from 31.3 to 33.6 wt.%, from 4.91 to 6.13 wt.% and from 0.66 to 0.80 wt.%, respectively, corresponding to the formula Au0.71Ag0.22Cu0.05Te2 with Au and Ag ranging from 0.68 to 0.74 and from 0.20 to 0.25, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Suzaki range from 61.5 to 63.4 wt.%, from 24.1 to 27.4 wt.%, from 10.0 to 12.5 wt.% and from 0.00 to 0.12 wt.%, respectively. The Te, Au, Ag, and Cu contents of sylvanite from Kawazu range from 62.7 to 63.3 wt.%, from 23.5 to 24.1 wt.%, from 12.0 to 12.5 wt.% and from 0.09 to 0.16 wt.%, respectively. The Te, Au, Ag, Cu and Fe contents of sylvanite from Teine range from 61.8 to 63.5 wt.%, from 23.6 to 24.7 wt.%, from 11.9 to 13.3 wt.%, from 0.01 to 1.65 wt.% and from 0.00 to 0.02 wt.%, respectively. The average formulae of sylvanite from Suzaki, Kawazu, and Teine are expressed as Au1.06Ag0.94Cu0.02Te4, Au1.00Ag0.95Cu0.02Te4 and Au1.01Ag0.95Cu0.06Te4, respectively. Judging from the mineral assemblages of these ores and other localities, Au–Te mineralization in the Japanese Islands can be divided into four types: native gold–calaverite at Date and Agawa, krennerite(?native tellurium) at Osore‐zan and Mutsu, sylvanite–native tellurium–hessite at Teine, Kawazu, Kobetsuzawa, and Kato, and polyminerallic assemblages at Suzaki and Kushikino. The pH–Eh diagram of aqueous tellurium species and tellurium minerals at 250°C indicates that (Au, Ag)Te2 minerals in epithermal gold telluride mineralization would have been formed under middle to low Eh and acidic (to intermediate) pH conditions. It is possible that dilute tellurium‐containing fluid would scavenge dilute gold. 相似文献