Norimasa Nishida

High temperature heating of the Allende meteorite

Abstract Allende bulk samples were heated up to 2000°C by DC arc and resistance heating. The chemical composition of evaporation residues was measured by instrumental neutron activation analysis (INAA) and electron probe microanalyser (EPMA). The evaporation sequence of elements observed was: (Na)-(Fe, Ni, Co, Au, Ir)—(Fe, Mn, Cr) (Mg, Si)-(Al, Ca, Ti, Sc, REE). Chemical compositions of 65% and 4% residual fractions were in agreement with those of a chondrule and a Ca, Al-rich inclusion of the Allende meteorite, respectively. Iridium was lost from residual solid in the early stage of heating. The early loss of the refractory siderophile elements may provide a clue to distinguish between two possibilities for the origin of Allende Ca, Al-rich inclusions: early condensates vs. evaporation residue. Ca, Al-rich inclusions (CAI) in the Allende meteorite may provide information on the physical and chemical conditions prevailing in the early solar system. So far we have two possibilities for the origin of CAI: 1. (1) High temperature condensates from a “hot” solar nebula (GROSSMAN, 1972, 1973; WANKE et al., 1974); 2. (2) Evaporation residues of the pre-existing primordial dust in the early solar system (KURAT, 1970; TANAKA and MASUDA, 1973; CHOU et al., 1976; CLAYTON, 1977). A condensation origin has been supported by theoretical considerations of equilibrium condensation from a cooling nebula, while an evaporation origin has received no endorsement from either theoretical or experimental approaches. We have heated bulk Allende samples to determine whether or not the chemical composition of CAI can be derived in the course of fractional vaporization of pre-solar matter which, in this experiment, is approximated by the bulk Allende composition.

Anorthite megacrysts from island arc basalts

Abstract Anorthite megacrysts are common in basalts from the Japanese Island Arc, and signally rare in other global fields. These anorthites are 1 to 3 cm in size and often contain several corroded Mg-olivine inclusions. The megacrysts generally range from An94Ab4Ot2 to An89Ab6Ot5 (Ot: other minor end-members, including CaFeSi3O8, CaMgSi3O8, AlAl3SiO8, □Si4O8) and show no chemical zoning. They often show parting. Redclouded megacrysts contain microcrystals of native copper with a distribution reminiscent of the shape of a planetary nebula. Hydrocarbons are also present, both in the anorthite megacrysts and in the olivines included within them. Implications of lateral variations in the Fe/Mg ratio of the included olivines, in Sr-content and in Sr-isotope ratio of the anorthite megacrysts with respect to the Japanese island arc, relate to mixing of crustal components and subducted slab-sediments into the basaltic magmas.

The chemistry of allanite from the Daibosatsu Pass, Yamanashi, Japan

Abstract The crystal structure of allanite from granitic pegmatite, the Daibosatsu Pass, Yamanashi, Japan, has been refined under the constraint of chemical composition determined by electron microprobe analysis of rare earth elements. Back-scattered-electron images and X-ray element maps of the allanites show that each of their crystal grains has chemically homogeneous distribution of major elements. A typical formula for the chemistry is: (Ca0.920 ⃞0.080)∑1.000(La0.238Ce0.443Pr0.048Nd0.100Sm0.019Th0.042Mn0.008 ⃞0.102)∑1.000(Al0.607Fe3+0.317Ti0.076)∑1.000(Al1.000)(Fe2+0.543Fe3+0.365Mn0.055Mg0.037)∑1.000(SiO4)(Si2O7)O(OH). The crystal structure of allanite, monoclinic, a 8.905 (1), b 5.7606 (5), c 10.123 (1) Å, β 114.78°(1), space group P21/m, Z = 2, has been refined to an unweighted R factor of 3.46% for 1459 observed reflections. Although the H atom position was not determined on the Difference-Fourier map, inspection of the bond valence sums demonstrates that the H atom is uniquely located at the O10 atom and involved in a hydrogen bond to O4. A systematic examination as to crystal chemistry of allanites suggests that the isolated SiO4 tetrahedron has the largest distortion of three kinds of the tetrahedron containing Si2O7 groups in the allanite structure. This observation is common to the epidote group minerals, while the larger distortion of A2 sites caused by occupancy by REE in allanites contrasts with the smaller one of A sites in other epidote group minerals. In the allanite groups the bond angles between the O10−H bond and hydrogen bond H…O4 are found to range from 170 to 180°. Compilation of the chemical compositions of the title allanite and the others from granitic rocks, Japan, which reveals Th-incorporation as the coupled substitution of 3Th4+ + ⃞ (vacancy) ⇌ 4REE3+, provides an explanation for the observation that higher Th concentrations characterize allanites from the island arcs. The ternary Al2O3-Fe2O3-∑REE diagram illustrates that allanites are grouped, according to their origins, into three classes suggestive of tectonic backgrounds for the crystallization localities; (1) intracontinental, (2) island arc and (3) continental margin.

Crystal chemistry of zircon from granitic rocks, Japan: genetic implications of HREE, U and Th enrichment

Zircon from granitic rocks, Japan is classified into two major types; based on the minor element content determined by electron microprobe, a heavy rare earth element (HREE)-U-Thpoor (Type I) and a HREE-U-Th-rich (Type 2). Zircons characteristically occurring in common granites of type-1 are relatively poor in HREE including Y and Sc, up to 2.72 wt% HREE2O3; up to 0.44 wt% ThO2; up to 2.10 wt% UO2, while zircons characteristically occurring in granitic pegmatites of type-2 are much richer in HREE including Y and Sc, up to 18.99 wt% HREE2O3; up to 11.09 wt% UO2; and up to 6.58 wt% ThO2 However, analyses showing a significantly high amount of REE+Y almost certainly represent altered zircon and/or accidental analysis of inclusions (Hoskin & Schaltegger 2003). Only crystal structure of zircon free of inclusions and zoning (type-2; Takenouchi granitic pegmatite) was refined to R = 4.3 % and for the first time has been confirmed that zircons of type-2 exist as a single-crystal phase in nature. .

Synthesis of thallium-leucite (TlAlSi 2 O 6 ) pseudomorph after analcime

Abstract Thallium leucite, TlAlSi2O6, has been synthesized at 450°C for 7 days, under ambient conditions, by the transformation of dehydrated analcime NaAlSi2O6 in the presence of excess TlCl. This substitution of Tl for Na leads to confirmation of a thallium-leucite pseudomorph after analcime. Their optical properties, X-ray powder diffraction patterns, electron microprobe analysis, infrared spectra, and X-ray photoelectron spectroscopy have characterized the synthetic Tl-leucites. The IR spectra show that the mid-IR modes T-O stretching and T-O-T bending vibrations for TlAlSi2O6 are more resemblant of those for analcime than for leucite, KAlSi2O6. This resemblance implies that Tl cation enters the W-site rather than the S-site in the analcime structure: Na (S) + H2O (W) ⇌ ⃞ + K (leucite) ⇌ ⃞+ Tl (Tl- leucite), where ⃞ represents an S-site vacancy. The mechanism of this substitution is supported by the crystal chemical constraints: inasmuch as the S-site is smaller than the W-site, Tl+ cations being larger than Na+ plainly prefer the latter site to the former. One inference from the binding energy for Tl+ by XPS is that Tl+ occupies the extra-framework site in synthetic leucite pseudomorph, rather than the smaller tetrahedral site. The difference in Al/Si disordering between analcime and leucite and the nonstoichiometry due to the solid solution of the ⃞Si3O6 component into the leucite structure may provide a fundamental insight into understanding why TlAlSi2O6 deviates from the trend defined by K-, Rb- and CsAlSi2O6 leucite series on the a-c parameter diagram, inasmuch as these three cations in the leucite structure occupy the W-sites. Finally, synthesis of TlAlSi2O6 leucite has an implication for the existence of other polymorphs due to different degrees of Al/Si disordering, except for high- and low-temperature leucites already known: natural leucites crystallized directly through igneous processes are different from those formed by substitution of K for Na in analcimes.

Rapid analytical method for trace Zn contents in some mafic minerals using the electron microprobe : potential utility as a metallogenetic and petrogenetic indicator

Abstract An analytical method using an electron probe microanalyser (EPMA) has been developed to enable rapid determination of trace Zn contents in mafic silicates. Total matrix correction factors of atomic number, absorption and fluorescence ( ZAF correction factors) for Zn are constant and virtually independent of solid-solution composition and mineralogy. Zn analysis confirmed by inductively coupled plasma-optical emission spectrometry (ICP-OES) reveals that this EPMA method is capable of analyzing Zn within only 30 s at a detection limit of 50 ppm. Preliminary studies of Zn abundance indicate that: (1) clinopyroxenes in skarn deposits tend to vary their Zn contents in accordance with the metal type, 500 ppm for the W type; (2) Zn contents of granitic biotites in the Ishikawa area, northeastern Japan, increase from 290 to 610 ppm with the advance of crystallization; and (3) Zn contents of chlorite in weathered granitic rocks are almost equivalent to those of its primary biotite. Therefore, this rapid EPMA method may have considerable potential for the use of trace Zn as a metallogenetic indicator and as a marker for crystallization or alteration processes.

Native Zinc, Copper, and Brass in the Red-Clouded Anorthite Megacryst as Probes of the Arc-Magmatic Process

This review of red-clouded feldspars [1] addresses the fundamental factors that underlie our understanding of a red schiller caused by reflection from submicroscopic inclusions of hematite, Fe203. Phenocrysts of aventurine labradorites [2, 3] contain microscopic metallic coppers causing a pink schiller. A recent finding from native coppers included by red-clouded anorthites [4] has stressed the importance of broadening this traditional interpretation. Furthermore, detection of hydrocarbons within the red-anorthite megacrysts provides mineralogists a clue as to their formation mechanism [5]. Microinclusions scattered throughout red-clouded anorthite megacrysts in the olivinebasaltic lava from the island of Hachijojima, Japan, were identified as native zinc, copper, and brass by comparison with the peak shift and band shape of Xray ZnLa and CuLc~ spectra of the standard samples measured by EPMA. This contribution reports the characterization of micron-sized native copper, zinc, and brass responsible for red aventurization within anorthite megacrysts, their petrogenetic and metallogenetic significance to the arc-magmatic process, and availability of chemical shift analyses of ZnLc~ and CuLa spectra by EPMA for micro-mineral identification.

The crystal structure, origin, and formation of idrialite (C22H14): Inferences from the microbeam and bulk analyses

Abstract Idrialite from Skaggs Springs, Sonoma County, California, was studied by microbeam and bulk analyses; the former include micro X-ray diffraction (μ-XRD), electron microprobe (EMP), and micro Fourier transform infrared (μ-FTIR) spectroscopic analyses, and the latter include powder XRD analysis, thermogravimetry-differential thermal analysis (TG-DTA), and carbon isotope analysis. Careful observation under a stereo-microscope clearly disclosed that the examined sample is composed of yellow and brown parts. The yellow parts were identified as idrialite with high crystallinity, whereas the brown ones were confirmed as amorphous matter by μ-XRD. Furthermore, the μ-FTIR spectra revealed that the yellow and brown parts contain hydrophobic and hydrophilic compounds, respectively. EMP analysis showed no chemical zoning and homogeneous distribution of S-bearing molecules in the yellow parts. TG-DTA disclosed that the present idrialite of the yellow part left no residue on heating up to 740 °C; this thermal behavior is similar to that of the other natural organic matter in liquid states such as petroleum and crude oil. The carbon isotopic composition was analyzed using an elemental-analyzer isotopic-ratio mass spectrometer (EA/IRMS). The δ13C value of the idrialite is -24.429 ± 0.090‰ (vs. V-PDB), which is akin to carbon isotopic compositions of the typical higher-plant triterpenoids contained in sedimentary organic matter. Both the yellow part (idrialite) and brown part (amorphous organic matter) occur on the coexisting minerals (opalline silica, metacinnabar, and siderite); the textural relationship indicates that the organic matter precipitated after crystallization of the associated minerals. Thus, it is suggested that the organic molecules were migrated by hydrothermal fluids and then separated into hydrophobic (idrialite) and hydrophilic (amorphous organic matter) molecules during the cooling process. Following the separation, idrialite was crystallized and then the amorphous organic matter was precipitated at the final stage of the hydrothermal activity.

Single crystal X-ray and electron microprobe study of Al/Si-disordered anorthite with low content of albite

Abstract The crystal chemistry of anorthite with low content of albite (An92.0 Ab3.4), part of a rapidly cooled anorthite megacryst occurring in 1940 ejecta from Miyake-jima volcano, Japan, has been investigated using a single-crystal X-ray diffractometer and an electron microprobe analyzer with wavelength dispersive X-ray spectroscopy (EMPA-WDS). The structure was refined in space group P1̅ and cell parameters, a=8.182(6) Å, b=12.883(4) Å, c=7.092(4) Å, α=93.19(4)°, β=115.91°(4), γ=91.18°(4). The final weighted R-factor is 3.77% for 1549 reflections. Averaged T-O distances are 1.681 Å for T1(0), 1.674 Å for T1(m), 1.677 Å for T2(0) and 1.680 Å for T2(m), indicating Al occupancies of 0.501, 0.453, 0.472, and 0.496, respectively. These results suggest that the Al/Si-distribution in the tetrahedral framework is highly disordered (QOD=0.06), which results in bisection of the c-period in Al/Si ordered anorthites (c∼14 Å). Chemical composition of the refined crystal obtained by EMPA-WDS is (Ca0.93 Na0.03 Fe0.02□0.01)(Mg0.01 Al1.94 Si2.05)O8. The extra-framework site-populations consist of the following two: (1) A(000) site occupied by Ca (86%), Na (8%), Fe2+ (4%) and □(2%), and (2) A(zi0) site by Ca (100%). The Al/Si tetrahedral framework is hence pseudo-face-centered in symmetry (C1ʩ so that both extra-framework cations and their defects appear to reduce the symmetry of the overall structure to P1ʮ Although the Al/Si disordered anorthite can be interpreted as a metastable phase, the observed chemical non-stoichiometry may stabilize such a metastable structure by introducing minor -Si4+-O-Si4+- bonds into the tetrahedral framework and anti-phase-boundary.

First report of natural oxyallanite: oxidation and dehydration during welding of volcanic tuff

The oxidation of Feto Fe, the release of H2, and the concomitant replacement of OH by O would produce an oxy-equivalent of allanite (CaREEAl2FeSi3O11O(OH)) (Dollase 1973). The reaction Fe + OH↔Fe+ O+ 1/2H2 is formally equivalent to the oxy-reaction observed in other hydrous Fe -bearing silicate minerals, such as mica and amphiboles (e.g., Hogg & Meads 1975; Ferrow 1987). However, occurrence of oxyallanite (CaREEAl2FeSi3O11O(O)) in natural environment has never been reported. The purpose of the preset study is to discuss occurrence of natural oxyallanite. Chemical compositions and crystal structures of the allanites from two rhyolitic rocks--(1) Youngest welded tuff from Toba (YTT), Sumatra, Indonesia and (2) volcanic ash from SK100 (SK100-VAB), Niigata, Japan--were determined by electron microprobe analysis and single crystal diffractometer, respectively. Despite the close similarity, in chemical composition, between YTT allalnites and SK100 ones, their unit-cell parameters are distinct from each other. The former have shorter b axis and longer c axis and larger β value in comparison with cell parameters of the latter. FT-IR analysis shows that YTT allanites have both the smaller OH-absorption band area and the shift of its bands to higher wavenumbers as compared to SK100 ones. Welding of the ash flow tuff including the allanites preformed in Youngest Toba welded tuff would cause them to undergo oxidations, dehydration and replacement. The sequential reaction would result in producing the present YTT allanite, namely oxyallanite. Although oxyallanite was only obtained by heating the natural allanite (e.g., Armbruster et al. 2006), this study first reports that oxyallanite may commonly occur in welded rocks at high temperatures.