Radioactive particles of around 50 µm size were collected from highly contaminated soil in the Fukushima Prefecture, Japan, and characterized using micro X–ray diffraction with synchrotron radiation (SR–µ–XRD). Two–dimensional diffraction patterns from individual particles rotated during X–ray irradiation were recorded on a flat imaging plate and a one–dimensional diffraction profile, as a function of 2θ, was derived from the pattern. Weathered biotite (WB) particles with plate–like morphology showed a broad peak corresponding to a basal reflection with d = 10–14 Å, indicating various degrees of vermiculitization. Another peak of ∼ 7 Å was also detected in these WB particles, suggesting the parallel growth of kaolinite in the biotite particles. These characteristics were also found in the WB collected from an Abukuma granitic body, which is widespread in the eastern part of Fukushima. SR–µ–XRD of radioactive soil particles consisting of fine minerals or of those rich in organic matter indicated that these particles contain very fine 2:1 type clay minerals alongside detrital rock–forming minerals such as quartz and feldspar.
Gem–quality Qinghai nephrites (QN) of NW China occur in a variety of distinctive colors (white, green–white, yellow, brown, blue–violet, viridis, green, and azure–green). This study investigates the mechanisms and chemical elements that lead to coloration of the QN. Mineralogy identification indicates that the main mineral component in QN samples of all eight colors is tremolite, which accounts for over 95 vol%. Chemical composition investigations reveal elevated concentrations of Fe2+, Fe3+, Mn, Cr, and Ti in all eight colors of QN. Electron paramagnetic resonance (EPR) spectra reveal three Mn2+ centers and a rhombic Fe3+ center at the octahedral sites [M1, M2, and M3]. However, the spectrum intensities of Mn2+ and Fe3+ are not directly correlated with the concentrations of these elements. The main reason being that Mn also occurs in higher valence states, leading to minor amounts of Fe3+ substituting for Si4+ at the tetrahedral sites (T1 and T2). Under conditions of oxidation, heating to 500 and 800 °C leads to fading of some QN colors, including the yellow, brown, and blue–violet, but darkening of the green–white, viridis, green, and azure–green colors. Ultraviolet–visible spectra (UV–vis spectra) of the faded samples show that the absorption bands near 550 or 560 nm gradually decrease with heating (and may disappear completely), and the absorption bands near 437 or 450 nm are enhanced in samples where the color darkens. In detail, the yellow colors of QN are caused primarily by O2− → Fe3+ ligand–to–metal charge transfer (LMCT) and Mn3+(5Eg) → 5T2g, the blue–violet colors by Fe2+ → Ti4+ inter–valence charge transfer (IVCT), and the brown color by the electron transitions 5Eg → 5T2g of Mn3+. Color fading in response to heating is due to oxidation of Fe2+ or Mn3+, which results in reducing concentrations of these ions. Meanwhile, the darkening of the QN colors in response to heating is due to the oxidation of Fe2+, leading to increasing Fe3+ concentration. In these cases, the viridis color is caused mainly by electron transitions: Cr3+(4A2) → 4T2, Cr3+(4A2) → 4T1 + 2E, and Fe3+(6A1) → 4E + 4A1(4G); the green–white color results from the electron transition Fe3+(6A1) → 4E + 4A1(4G); and the green and azure–green colors are caused mainly by IVCT of Fe2+ → Fe3+ and Fe2+(5T2) + Fe3+(6A1) → Fe2+(5E) + Fe3+(6A1).
The northern Kontum massif in central Vietnam, one of the most key tectonic and metallogenic terranes of the Indochina block, consists of numerous volcano–plutonic complexes including the Dai Loc granitic complex that formed an essential part of the early Paleozoic batholith of the massif. Rocks of the Dai Loc complex are granodiorite and granite in composition. Geochemically, the rocks are of sub–alkaline affinity and belong to high–potassium series. These rocks have moderate Aluminum Saturation Index (ASI) values of 0.76–1.19 and low Mg# values of 23–39. Zircon grains separated from the rocks have high εHf(t) values and old Hf model ages (TDM) which varying from −0.7 to +4.8 and 0.9 to 1.1 Ga, respectively. All these characteristics, in conjunction with trace element features, suggest generation by partial melting of crustal source rocks with additional input of mantle–derived material. Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA–ICP–MS) zircon U–Pb analytical results from two samples revealed emplacement ages of the granite at 423 ± 2.2 and 427 ± 9.9 Ma. Our geochronological data provide evidence for early Paleozoic crustal evolution in Central Vietnam.
In this study, some barometries and thermometries were used to calculate the crystallization temperature and pressure of amphiboles in intermediate to basic rocks from the Almogholagh pluton in western Iran. Intersection among geothermometers was introduced as a method to estimate crystallization temperature, and the results obtained were compared with those of other methods. Results showed that obtaining the average pressure from the intersections between geothermometers and geobarometers is a suitable approach to determine the crystallization pressure of the analyzed points of amphiboles, whereas the crystallization temperature can be appropriately determined from the intersection among geothermometers. In addition, the average temperature of the HB294 geothermometer is approximately equal to the average temperature in intersection among geothermometers. HB294 is apparently a suitable geothermometer to determine the crystallization temperature in intermediate to basic rocks. In this study, the average crystallization temperature and pressure using intersection methods were 714–719 °C and 6.5–7.5 kbar, respectively. Adopting these methods to the Almogholagh pluton, intermediate to basic rocks intruded at a depth of 24–28 km of the crust and at 674–759 °C.
The Chemical U–Th–total Pb isochron method (CHIME) dating was performed for internal domains and zones within monazites in garnet–biotite gneiss and garnet–biotite–cordierite gneiss from the Precambrian Southwestern Highland Complex (SWHC), Sri Lanka, to evaluate evolution of the metamorphic rocks which have been subjected to multiple thermal events during the Gondwana amalgamation. Monazites are abundant in garnet–biotite gneisses. The monazites have core–rim zoned, inherited core–bearing, complexly zoned, and oscillatory zoned type internal textures. The core domains of the core–rim zoned, inherited core–bearing, and complexly zoned type monazites show ages of 533–503, 1788–512, and 1686–678 Ma, respectively, and the rim domains show younger ages of 500–434 Ma. Even though its repeated zonings, oscillatory zoned type monazites show the only young age of 470 ± 45 Ma. The determined isochron ages are grouped into four clusters: group I of 1766 ± 140 and 1788 ± 30 Ma (at present 1686 ± 186 Ma age may be grouped into group I); group II of 679 ± 99 Ma; group III of ages in a range between 533 ± 22 and 481 ± 42 Ma; and group IV of ages in a range between 472 ± 17 and 433 ± 14 Ma. The ages of the group I may imply magma emplacement ages. The ages of the group II correspond to the stage of the most prominent thermal event recorded in the region. The groups III and IV can be identified as post–peak thermal events. The age data given for the monazites in the SWHC are consistent with the published data for the Central Highland Complex, and indicate that the SWHC has been subjected to the same thermal events as the Central Highland Complex.
Köttigite and parasymplesite form a solid solution of Zn3−x,Fex(AsO4)2•8H2O. The compositional variations in the köttigite–parasymplesite solid–solution system were determined by SEM/EDS with specimens from Mitate Mine, Miyazaki, Japan, and Ojuela Mine, Mapimi Durango, Mexico. Variations were observed in the direction perpendicular to the (010) plane in the continuous solid–solution system. A refinement of the crystal structure of Zn1.62Fe1.38(AsO4)2•8H2O [monoclinic, space group C2/m, a = 10.3417(13), b = 13.4837(16), c = 4.7756(5) Å, β =105. 306(4)°, V = 642.31(13) Å3, and Z = 4] converged into R = 0.0265 and S = 1.083 for 650 independent reflections in the single–crystal XRD data. The hydrogen bonds were described based on the hydrogen atom positions on the difference Fourier maps in reference to the bond valence calculations. The smaller Zn2+ ion prefers the larger M1 site and the larger Fe2+ ion prefers the smaller M2 site. This unique cation site preference reduces the structural distortions. The M2–O5 bond distance, where O5 is the oxygen of the H2O group, is shorter than that of M2–O2 and –O3, in which the oxygen atoms form edge–sharing M22O6(H2O)4 double octahedra. Only one hydrogen atom from the H2O group, H52, connects the respective complex sheets consisting of M22O6(H2O)4 double octahedra and AsO4 tetrahedra. The space between the respective complex sheets is filled with hydrogen. It is presumed that the movement of proton in this space is the fastest.
Vol.31 (1944) No. 5 and No.6 in the predecessor journal ″The Journal of the Japanese Association of
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