著者

Yuta TSUCHIYA Masahiro KAYAMA Hirotsugu NISHIDO Yousuke NOUMI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.110, no.6, pp.283-292, 2015 (Released:2015-12-27)

参考文献数

34

被引用文献数

7 7

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Color cathodoluminescence (CL) images of zircon from southern Malawi (MZ) show mottled yellow CL emissions on a dull luminescent background by the annealing below 600 °C, and relatively homogeneous blue emissions above 800 °C. CL spectroscopy of the samples reveals a change of the luminescent features with an annealing temperature, and explains a variation of their colors and luminance observed by a CL microscope. Emission bands at 310 and 380 nm in an ultraviolet (UV) to blue CL are assigned to intrinsic centers in host lattice, narrow peaks at 475 and 580 nm to Dy3+ impurity centers, and broad bands at 500 to 650 nm to Frenkel–type defects and SiOmn− groups. The former two show increases in emission intensities against annealing temperature, but the latter exhibits an increase in intensity up to 300 °C and a decrease above 300 to 700 °C. An increase in an annealing temperature leads to a reproduction of the intrinsic centers, which is responsible for an increase in UV–blue emission, in host lattice accompanied with a recrystallization from metamict state. An increase in the intensities of narrow peaks activated by Dy3+ impurities may result possibly from a recovery of ionization due to the self–radiation and an energy transfer of other REEs to Dy3+ activator. A gradual increase in yellow emission bands up to 300 °C might be caused by a migration of the hole around a thermally–instable lattice defect and/or activated impurities into a more stable site related to Frenkel–type defects and SiOmn− groups, whereas the yellow should be subsequently reduced due to an elimination of these defects.

著者

Tatsuki TSUJIMORI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.112, no.5, pp.217-226, 2017 (Released:2017-11-15)

参考文献数

67

被引用文献数

13 14

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Paleozoic jadeitite–bearing serpentinite–matrix mélange represents the oldest mantle wedge record of a Pacific–type subduction zone of proto–Japan. Most jadeitites are fluid precipitates (P–type), but some jadeitites are metasomatic replacement (R–type) which preserve relict minerals and protolith textures. The beauty and preciousness of some gem–quality, semi–translucent varieties of jadeitites in the Itoigawa–Omi area led to the designation of jadeitite as the national stone of Japan by the Japan Association of Mineralogical Sciences. Zircon geochronology indicates jadeitite formed prior to Late Paleozoic Renge metamorphism that formed blueschist and rare eclogite. For example, in the Itoigawa–Omi and Osayama localities, older jadeitites and younger high–pressure/ low–temperature metamorphic rocks in a single mélange complex imply different histories for the subduction channel and jadeite–bearing serpentinite–matrix mélange. This suggests that the jadeitite–hosted mélange (or serpentinized peridotite) can stay within the mantle wedge for a considerable time; thus recrystallization, resorption, and re–precipitation of jadeitite can continue in the mantle wedge environment. Therefore, studies of Paleozoic jadeitites in Japan have great potential to elucidate the earliest stages of orogenic growth (oceanward–accretion and landward–erosion) associated with the subduction of the paleo–Pacific oceanic plates, and to test geophysical observations of modern analogues from a mixture of fossilized mantle wedges and subduction channels.

著者

Kazumasa SUGIYAMA Toru KAWAMATA Takahiro KURIBAYASHI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.210318, (Released:2021-11-09)

被引用文献数

1

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The crystal structure of prehnite Ca2(Al, Fe)(Si3AlO10)(OH)2 from Upper New Street Quarry, Paterson, Passaic County, New Jersey, USA was determined by single–crystal X–ray diffraction. The converged structural model in the space group P 2cm [a = 4.63309(9) Å, b = 5.4839(1) Å, c = 18.5100(3) Å, Z = 2] allowed for the investigation of an ordered Si/Al distribution together with the feasible hydrogen positions inferred from the difference Fourier maps.

著者

Masaki ENAMI Aya NISHII Takashi MOURI Motohiro TSUBOI Yui KOUKETSU

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.201204, (Released:2021-05-20)

被引用文献数

1

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Olivine is a major mineral in ultramafic and mafic rocks. Due to the higher Mg/Fe partition coefficient of olivine than the coexisting phases, the occurrences of Mg–poorer olivine grains, especially with Mg#[= Mg/(Mg + Fe2+)] = 0.2–0.6, are rarely reported, and thus, their spectroscopic data are limited. Fe–rich olivine phenocrysts showing compositional zoning with Mg# = ~ 0.5 (core) and ~ 0.3 (rim) and microphenocrysts with Mg# = ~ 0.4 (core) and ~ 0.2 (rim) occur in basaltic trachyandesite of Miocene Shitara volcanic rocks in central Japan. These olivine grains were investigated by Raman spectroscopy. Combining our data with the published values, we have revised the equation for Mg#–Raman spectrum relationship proposed by Mouri and Enami (2008) as follows: Mg# = 0.005446ω 2 − 0.20259ω + 1.8442 (correlation coefficient r 2 = 0.984), where ω is the difference between the doublet peak positions (κ2 − κ1).

著者

Sayantani CHATTERJEE Debaditya BANDYOPADHYAY Eiichi TAKAZAWA Katsuyoshi MICHIBAYASHI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.116, no.3, pp.170-175, 2021 (Released:2021-07-17)

参考文献数

27

被引用文献数

1

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Oxidation states within the planetary interior are intrinsically linked with the broad scale tectonism; however, it is difficult to estimate the actual oxidation conditions. Orthopyroxene–magnetite symplectite formed by olivine oxidation may provide a significant clue into such oxidation events. Here we report detailed mineralogical and petrological synthesis of such orthopyroxene–magnetite symplectites from olivine gabbros of Oman Ophiolite (Hole GT2A, ICDP Oman Drilling Project). In order to understand how oxidation affects different olivine compositions, we employed a phase equilibria approach and computed several temperature–composition diagrams at a fixed pressure (1 kbar). Our experiments predict the coexistence of olivine with Fo75–76 and Fo71 with the orthopyroxene (En79 and En76), respectively, which is remarkably similar to the mineral chemistry obtained from the Oman lower crustal gabbros. From the magnetite content, we also infer that the symplectite formation may have taken place over a range of temperatures (600–1000 °C) via subsolidus olivine oxidation and/or melt (oxidizing)–olivine interaction. The latter is more probable, considering the partial occurrence of orthopyroxene and clinopyroxene rim adjacent to the symplectites.

著者

Hiroaki OHFUJI Motosuke NAKAYA Alexander P. YELISSEYEV Valentin P. AFANASIEV Konstantin D. LITASOV

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.112, no.1, pp.46-51, 2017 (Released:2017-03-18)

参考文献数

19

被引用文献数

6

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This study revealed for the first time the microtexture and crystallographic features of natural polycrystalline diamond, yakutite found in placer deposits in the Siberian Platform, Russia. Yakutite consists of well–sintered nanocrystalline (5–50 nm) diamond and small amount of lonsdaleite showing distinct preferred orientations. Micro–focus X–ray and electron diffractions showed a coaxial relationship between lonsdaleite 100 and diamond 111, suggesting the martensitic formation of yakutite from crystalline graphite. These textural and crystallographic features are well comparable to those of the impact diamonds from the Popigai crater located in the central Siberia and strongly support the idea that yakutite is a product of long–distance outburst from the Popigai crater, which has been inferred merely from the geochemical signatures.

著者

Wataru YABUTA Takao HIRAJIMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.190831, (Released:2020-10-28)

被引用文献数

1

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We present the first report of okhotskite in a lawsonite–blueschist–subfacies metachert of the Hakoishi subunit, Kurosegawa Belt, Kyushu, Japan, which was metamorphosed at peak temperatures and pressures of 200–300 °C and 0.6–0.8 GPa. This okhotskite–bearing assemblage is particularly notable because it formed at higher pressures than that of previously documented okhotskite with available pressure estimations. Textural relationships indicate that okhotskite formed during peak metamorphism in equilibrium with piemontite, Na pyroxene, magnesioriebeckite, braunite, and hematite. Okhotskite shows a significant variation in Fe:Mn ratio (Fetot/Mntot = 0.13–0.56) and a following average empirical formula; (Ca7.62Mn2+0.16)Σ7.78(Mn2+2.71Mg1.29)Σ4.00(Mn3+4.13Fe3+2.26Al1.36V3+0.23Ti0.02)Σ8.00Si11.86O44.02(OH)16.98. Raman spectra of okhotskite are reported for the first time and show characteristic peaks at 362, 480, and 563 cm−1. The stability relationships between okhotskite and other Mn–bearing minerals, such as piemontite, sursassite, spessartine, braunite, and Mn–bearing lawsonite, are examined using a revised Schreinemakers’ analysis. The obtained petrogenetic grid provides tight constraints on the P–T relationship of natural mineral assemblages observed in Mn–bearing cherts within epidote–blueschist–grade and lawsonite–blueschist–grade. Furthermore, this petrogenetic grid predicts that the assemblage of okhotskite and Mn–bearing lawsonite should be stable at higher pressures. The higher–pressure stability suggests that highly oxidized Mn–bearing metacherts can transport water and buffer oxygen in the deeper parts of subduction zones, given that okhotskite and Mn–bearing lawsonite contain high water contents (6.9 and 11.3 wt% H2O, respectively) and trivalent manganese.

著者

Yuji ICHIYAMA Takahito KOSHIBA Hisatoshi ITO Akihiro TAMURA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.191205, (Released:2020-06-26)

被引用文献数

6

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Early Paleozoic serpentinite melanges in Japan preserve the oldest high–P metamorphic rocks in the circum–Pacific orogenic belt. To understand the tectonic regime at the subduction initiation of the proto–Japan convergent plate boundary, whole–rock geochemistry, and zircon U–Pb geochronology were investigated for amphibolite blocks in the Omi serpentinite mélange, central Japan. The studied amphibolites from two different localities have the mineral assemblage of albite + clinozoisite + amphibole ± rutile ± titanite, which characterize epidote–amphibolite facies metamorphism. Whole–rock trace element concentrations of the amphibolites suggest that gabbroic protoliths formed possibly in an oceanic setting. The zircon U–Pb weighted mean ages obtained from two amphibolite samples indicate that the protolith was formed in the Cambrian. The protolith ages of the studied amphibolites are comparable with those of reported Early Paleozoic ophiolite and high–pressure rocks in Paleozoic serpentinite mélanges in Japan. This fact implies that the young hot oceanic crust was subducting into the East Asian convergent plate margin during the Cambrian.

著者

Mayu KAKEFUDA Tatsuki TSUJIMORI Katsuyuki YAMASHITA Yoshiyuki IIZUKA Kennet E. FLORES

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.190731a, (Released:2020-03-04)

被引用文献数

1

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Awaruite (Ni2–3Fe) is a natural occurring Ni–Fe alloy in serpentinite, which represents a better candidate to assess Pb isotope signatures in the mantle wedge since the concentration of Pb in awaruite is almost ten times higher than that in serpentine minerals. Revisiting so–called josephinite from the Josephine Ophiolite confirmed that josephinite is characterized by aggregates of awaruite with minor Ni–arsenide. The Raman spectrum obtained from the josephinite–hosting serpentinite shows diagnostic peaks of antigorite, suggesting josephinite might have formed under stability field of antigorite. Using a stepwise leaching and partial dissolution method, we obtained Pb isotope ratios of josephinite by TIMS. Since all ratios converged to a homogeneous value towards the later steps of the partial dissolution, this allowed to calculate weighted mean values that give precise Pb isotope ratios: 206Pb/204Pb = 18.3283 ± 0.0020 (MSWD = 0.49), 207Pb/204Pb = 15.5645 ± 0.0020 (MSWD = 0.36), and 208Pb/204Pb = 38.0723 ± 0.0061 (MSWD = 0.50); these values can be evaluated as one of the reference Pb isotope ratios in serpentinites from supra–subduction zone ophiolite. The newly obtained Pb isotope ratios of josephinite are consistent with the previous reported isotope ratios, which are characterized by enriched 207Pb/204Pb ratio with MORB–source like 206Pb/204Pb and 208Pb/204Pb ratios. Although these Pb isotope features interpreted as a reflection of arc magmatism in the previous study, the presence of Ni–arsenide and enriched 207Pb/204Pb ratios may indicate an involvement of As–rich fluids derived from slab sediments.

著者

Daisuke NISHIO-HAMANE Masayuki OHNISHI Tetsuo MINAKAWA Jun-ichi YAMAURA Shohei SAITO Ryo KADOTA

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.1, pp.1-7, 2012 (Released:2012-02-29)

参考文献数

17

被引用文献数

3 7

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The first Cr-dominant amphibole, ehimeite, ideally NaCa2Mg4CrSi6Al2O22(OH)2, has been found in a chromitite deposit in the Akaishi Mine, Higashi-Akaishi Mountain, Ehime Prefecture, Japan. Ehimeite occurs as prismatic crystals of up to 1.5 cm in length and 0.5 cm in width and is found in association with chromite, kämmererite (Cr-rich clinochlore), Cr-poor clinochlore, phlogopite, and uvarovite. It is transparent, emerald green to pale green in color with pale green streaks, and has a vitreous luster. Optically, it is biaxial positive with α = 1.644(2), β = 1.647(2), γ = 1.659(2), and 2Vcalc. = 53°. It has a Mohs’ hardness of 6 and densities of 3.08(3) g/cm3 (measured using heavy liquids) and 3.121 g/cm3 (calculated from powder diffraction data and the empirical formula). The empirical formula is (Na0.88K0.07)Σ0.95(Ca1.89Na0.02Mg0.09)Σ2.00(Mg4.03Cr0.62Al0.19Fe3+0.07Fe2+0.07Ti0.03)Σ5.00(Si6.14Al1.86)Σ8.00O22(OH)2 on the basis of O = 22 and OH = 2, and ehimeite mainly forms a solid solution, NaCa2Mg4(Cr, Al)Si6Al2O22(OH)2, with pargasite. It has a monoclinic unit cell with a = 9.9176(14) Å, b = 18.0009(12) Å, c = 5.2850(7) Å, β = 105.400(7)°, V = 909.6 (17) Å3, and Z = 2, and it belongs to the space group C2/m, as refined from powder XRD data. The eight strongest lines in the powder XRD pattern [d (Å), I/I0, hkl] are (3.370, 58, 150), (2.932, 43, 221), (2.697, 81, 151), (2.585, 50, 061), (2.546, 100, 202), (2.346, 42, 351), (2.156, 35, 261), and (1.514, 55, 263). The crystal structure has been refined to R1 = 0.0488 using single-crystal XRD data. It has been concluded that ehimeite in the Akaishi Mine was formed by the reaction of chromitite and the metamorphic fluid in the retrograde stage of serpentinization during the Sanbagawa metamorphism.

著者

Takeshi SUGIMOTO Tomoyuki SHIBATA Masako YOSHIKAWA Keiji TAKEMURA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.101, no.5, pp.270-275, 2006 (Released:2006-10-14)

参考文献数

29

被引用文献数

16 20

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We have characterized the Sr-Nd-Pb isotopes and major and trace element compositions of 10 Quaternary volcanic rocks from the Yufu and Tsurumi volcanoes in northeast Kyushu, Japan. The enriched incompatible elements, negative Nb, and positive Pb and Sr anomalies are generally interpreted to be from island arc affinities of the lavas. However, the LREE/HREE ratio of the lavas (La/Yb = 8.5 ± 1.3) is greater than that from the island arc intermediate volcanics from northeast Japan (La/Yb = 3.8 ± 0.6), suggesting a different origin. One dacite sample had a Sr/Y ratio > 40, and the SiO2, Al2O3, MgO, Y, Yb, Sr, and 87Sr/86Sr compositions fell within the range of typical adakites. Other lavas were classified as normal island arc-type magmas. These results suggest that a partial melting of the subducting Philippine Sea Plate played a role in the genesis of the Yufu-Tsurumi volcanic rocks. The Sr, Nd, and Pb isotopic compositions show evidence of mixing between melts, derived from oceanic basaltic crust and subducted terrigenous sediments for the adakite magma, whereas another source is required to explain the enrichment in Sr-Nd isotopes and depletion in Pb isotopes of the island arc-type magma. Although the island arc-type magma appears to have a different source, a mixing of the adakite magma with this magma is apparent from our observations of the trace elements and isotopes.

著者

Daisuke NISHIO-HAMANE Yukikazu OGOSHI Tetsuo MINAKAWA

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.3, pp.121-126, 2012 (Released:2012-07-12)

参考文献数

12

被引用文献数

3 2

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Miyahisaite, (Sr,Ca)2Ba3(PO4)3F, a new mineral of the hedyphane group in the apatite supergroup, is found in the Shimoharai mine, Oita Prefecture, Japan. Miyahisaite is colorless and occurs as a pseudomorphic aggregate (up to about 100 μm in size) along with fluorapatite in the quartz matrix in a namansilite-rich layer of the chert. Its hardness is 5 on the Mohs scale, and its calculated density is 4.511 g/cm3. The empirical formula of miyahisaite is (Sr1.366Ca0.717)Σ2.083Ba2.911P3.002O12(F0.898OH0.088Cl0.014)Σ1.00, which is representatively shown as (Sr,Ca)2Ba3(PO4)3F. Its simplified ideal formula is written as Sr2Ba3(PO4)3F, which requires 23.25 wt% SrO, 51.62 wt% BaO, 23.89 wt% P2O5, 2.13 wt% F, and -0.90 wt% F = O, for a total of 100.00 wt%. The mineral is hexagonal with a space group P63/m, unit cell parameters a = 9.921 (2) Å, c = 7.469 (3) Å, and V = 636.7 (3) Å3, and Z = 2. The eight strongest lines in the powder XRD pattern [d (Å), (I/I0), hkl] are 3.427 (16) 102, 3.248 (22) 120, 2.981 (100) 121, 2.865 (21) 300, 1.976 (23) 123, 1.874 (16) 140, 1.870 (15) 004, and 1.864 (17) 402. The mineral was formed by the reaction between fluorapatite and the Ba-bearing fluid that produced the aegirine-rich layer with hydrous Ba-rich minerals during the late-stage activity.

著者

Satoko MOTAI Hiroki MUKAI Tetsu WATANUKI Kenji OHWADA Tatsuo FUKUDA Akihiko MACHIDA Chisaki KURAMATA Ryosuke KIKUCHI Tsuyoshi YAITA Toshihiro KOGURE

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.150722, (Released:2016-06-08)

被引用文献数

15

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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.

著者

Tomoki TAGUCHI Masaki ENAMI

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.109, no.4, pp.169-176, 2014 (Released:2014-08-25)

参考文献数

48

被引用文献数

4 20 2

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Coexistence of jadeite (Jd92) and quartz was newly found in an inner segment of a composite–zoned garnet from a metapelite in the southern albite–biotite zone of the Asemi–gawa region, Sanbagawa belt in central Shikoku, Japan. The assemblage of jadeite + quartz in garnet gives a minimum metamorphic pressure of 1.4–1.9 GPa at 500–700 °C, which was significantly higher than that previously proposed for epidote–amphibolite facies conditions in the albite–biotite zone. Garnet includes quartz retaining high residual pressure (Δω1 values up to 11.7 cm−1), which is comparable to the residual pressure reported in eclogite and metapelite within the eclogite unit in central Shikoku. These results imply that (1) the inner segment of the composite–zoned garnet records prograde recrystallization under high–pressure blueschist to eclogite facies conditions and (2) at least a part of the southern albite–biotite zone of the Asemi–gawa region recrystallized under higher pressure conditions prior to the regional metamorphism from the greenschist to epidote–amphibolite facies that formed the regional thermal structure of the Sanbagawa belt of central Shikoku.

著者

Kenta YOSHIDA Takao HIRAJIMA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.1, pp.50-55, 2012 (Released:2012-02-29)

参考文献数

21

被引用文献数

5 5

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Annular fluid inclusions were found in a foliation-parallel quartz vein intercalated with metapelites from the Besshi area of the Sanbagawa belt, SW Japan. The preserved “foam microstructure” of the quartz vein suggests low differential stress at high temperatures for its formation. Three types of fluid inclusions have been identified: the earliest one, FIA-I, is characterized by two phase inclusions arranged along intragranular planes and mainly composed of aqueous saline fluid and CH4 gas; FIA-II texturally comparable to FIA-I consists of CH4-N2-CO2-H2 gas phase inclusions with rare two-phase inclusions; the latest type, FIA-III, is characterized by arrangements along transgranular planes consisting of two-phase inclusions mainly composed of CH4-N2 vapor in aqueous saline fluid. Amongst them, FIA-I contains annular fluid inclusions, which are attributed to reequilibration due to a confining pressure increase, suggesting that the host rock underwent the compression after the entrapment of FIA-I. Textural observations and chemical characteristics show that FIA-I and -II were trapped during prograde or near the peak metamorphic stage, and that FIA-III was probably trapped at an early stage of the exhumation.

著者

Keiko MATSUMOTO Michihiko NAKAMURA

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.107, no.5, pp.206-211, 2012 (Released:2012-11-17)

参考文献数

23

被引用文献数

3

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Pyrrhotite (Po) occurs as inclusions and as isolated crystals in pumice from the 1914-15 eruption of the Sakurajima volcano, Kyushu, Japan. The Po crystals have partly reacted to form spongy Fe oxides. A similar texture has been reported in some previous studies (Hattori, 1993), but the mineral phases and formation processes of the spongy Fe oxides have not been clarified. Our quantitative and compositional map analyses with electron probe microanalysis (EPMA) reveal that the spongy Fe oxides are mostly magnetite (Mt), with a thin rim (<3 μm) of hematite on rare occasions. The spongy texture includes unreacted regions of Po, mesh-like pores, and S-rich spots, showing that it was formed by desulfidation of Po. No Ti was detected, even in the outermost rim; this indicates that the reaction occurred syn-eruptively. According to diffusion calculations, the spongy Mt was formed during the 4 h preceding quenching. Thermodynamic calculations showed that Po is stable at log fO2 < NNO + 2 at a pressure of 1 bar and magmatic temperature, which is 1-2 log units higher than the usual magmatic fO2. These constraints on the timing and oxidation condition of desulfidation lead to the conclusion that the reaction was caused by oxidation of the magma in a shallow volcanic conduit, not in magma chamber processes. The pumice groundmass consists mostly of glass, indicating that the rate of the desulfidation reaction is faster than the decompression-induced crystallization of microlites in the andesitic magma. Therefore, the desulfidation reaction of Po has the potential to be used as a geospeedometer for very fast magma ascent in vigorous explosive eruptions.

著者

Atsushi ISHIHARA Hiroaki OHFUJI

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.118, no.1, pp.230327, 2023 (Released:2023-11-21)

参考文献数

34

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In this study, we investigated the origin and formation process of zeolitized gastropod fossils in Neogene sediments (Shiote Formation) in Minamisoma, Fukushima, Japan using powder X-ray diffraction, SEM-EDS and micro-Raman spectroscopic analysis. The formation of zeolites was particularly pronounced in the upper chamber, which was not filled with detrital particles, of the gastropod fossils, where tabular crystals of heulandite were observed growing directly from the shell wall. The heulandite crystals are often covered by large euhedral crystals of calcite and occasionally by acicular crystals of mordenite. The formation of zeolite (heulandite) was also observed in the matrix of the host sandstone together with clay minerals (mostly montmorillonite), suggesting that the Shiote Formation experienced moderate metamorphism equivalent to zeolite facies during burial diagenesis. The Si/Al ratio of heulandite was found to decrease gradually from the bottom (∼ 4.5) to the top (∼ 3.1) within single crystals across the threshold (4.0) for clinoptilolite/heulandite classification boundary. This may reflect the increase in temperature of the surrounding environment with increase in the burial depth. The extensive growth of zeolites and calcite inside the gastropod fossils indicates that the shell provided semi-closed spaces in which pore fluid could be retained and condensed during diagenesis, thus promoting the crystal growth from the supersaturated solution.

著者

Yohey SUZUKI Takeshi SUKO

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.101, no.6, pp.299-307, 2006 (Released:2007-01-08)

参考文献数

79

被引用文献数

43 53

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Understanding the behavior of uranium (U) in the environment is essential not only for the protection of aquifers from U contamination but also for predicting the fate of U and other actinides disposed of in deep geological settings. It has long been believed that the redox chemistry of U can be simply predicted by thermodynamics and that the development of a low redox potential is a sufficient condition for U reduction. However, recent studies have demonstrated that redox transformations of U are controlled by kinetic factors that are strongly influenced by microbial activity. Although abiological U oxidation proceeds efficiently under oxygenic conditions, abiological reduction of U is inhibited by the formation of negatively charged U(VI)-CO3 complexes that prevail in nature. Phylogenetically diverse microorganisms are capable of enzymatically reducing U(VI)-CO3 complexes to form U(IV)-bearing minerals such as uraninite (UO2+x). The only abiological pathway currently known for the reduction of U(VI)-CO3 complexes involves the Fe(II) monohydroxo surface complex ≡FeIIIOFeIIOH0. This complex is mainly produced by the microbial reduction of Fe(III) in natural systems. Thus, U(VI) reduction is controlled both directly and indirectly, at least in part, by microbial activity. Several mechanisms of U oxidation under anoxic conditions have been revealed recently by laboratory and field studies. U(IV) is abiologically oxidized by Fe(III) and Mn(IV) oxides. Microbial reduction of nitrate to molecular nitrogen, which occurs following the depletion of O2, produces nitrogen intermediates including nitrite (NO2−), nitrous oxide (NO), and nitric oxide (N2O). Although the nitrogen intermediates oxidize U(IV), poorly crystalline Fe(III)-oxide minerals resulting from the oxidation of aqueous Fe(II) species by the nitrogen intermediates oxidize U(IV) more efficiently than the nitrogen intermediates alone. Remarkably, the formation of Ca-U(VI)-CO3 complexes resulting from increased levels of Ca2+ and/or HCO3− leads to the reoxidation of bioreduced U(IV) under reducing conditions. These geomicrobiological factors pose challenges in manipulating and/or predicting the mobility and fate of U in complex and heterogeneous environmental settings.

著者

Kenta YOSHIDA Takao HIRAJIMA

出版者

一般社団法人日本鉱物科学会

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.110, no.5, pp.197-213, 2015 (Released:2015-11-11)

参考文献数

49

被引用文献数

5

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Garnet with a complex compositional zoning was found from the northern edge of the Western Iratsu body in the Sanbagawa metamorphic belt of the Besshi district, southwest Japan. The studied garnet shows incipient Mn–reverse (increase) zoning from the center part and subsequent Mn–bell shape type (decrease) zoning towards the outer part, which is almost identical to the ‘Mn–caldera shaped zoning’ described by Xu et al. (1994) and Banno and Nakamura (2004). In order to display the chemical characteristics sterically, three–dimensional X–ray chemical mapping was performed for one very–coarse grain of garnet. The result clearly displays that there is a high–Mn layer with faceted euhedral shape of the garnet at the intermediate part, and that its composition continuously changes from the inside to the outside. Inclusion arrays in garnet getting across the high–Mn layer also suggest the continuous growth of the garnet. In the same sample, garnets without Mn–caldera shaped zoning are ubiquitously observed, which are relatively small in size up to 5 mm in diameter. Inclusion mineral assemblage in garnet and Raman barometry suggest the peak P–T conditions of the studied sample not having reached the eclogite facies, but being the epidote–amphibolite facies. The formation process of the ‘Mn–caldera shaped zoning’ can be best explained by the disequilibrium crystal growth under oversaturation of garnet in MnO–(MgO + FeO) binary system. Such oversaturation can be triggered by rapid heating. The finding of the remnant of rapid heating event would provide an important clue to discuss the exhumation history of the Sanbagawa metamorphic belt.

著者

Geoffrey H. GRANTHAM M. SATISH-KUMAR Kenji HORIE Henriette UECKERMANN H

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.230125, (Released:2023-05-16)

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The ~550 Ma Kuunga Orogeny extends from the Damara in Namibia, through the Zambesi and Lurio orogenic belts in Zambia and Mozambique, southern Africa, through Dronning Maud Land and Princess Elizabeth Land, Antarctica into western Australia. Sverdrupfjella is located at the western end of Dronning Maud Land where the Kuunga Orogeny is inferred to post-date and overprint the East African Orogeny.Three complexes are recognized in Sverdrupfjella western Dronning Maud Land , Antarctica. A western basal ~1140 Ma Jutulrora Complex, consisting mostly of arc-related tonalitic trondjhemitic orthogneiss with evolved Sr - Nd isotopic signatures with TDm ages >2 Ga. It is structurally overlain by the Fuglefjellet Complex, comprising supracrustal ~800 – 900 Ma carbonates intercalated with quartzo-feldspathic gneisses with detrital zircons of ~1000 - 1200 Ma age with ~500 Ma overgrowths. The Fuglefjellet Complex is overlain in the east by the Rootshorga Complex containing paragneisses with minor orthogneisses (~1100 – 1200 Ma), intruded by granitic orthogneiss of similar age. Strontium - Nd isotopic signatures from the Rootshorga Complex has TDm ages <1.8 Ga.D1 and D2 planar fabrics typically dip to SE with vergence top-to-NW in all complexes. D3 deformation verges top-to-the-SE. In the Jutulrora Complex, D3 comprises ~100m scale folds with NW dipping axial planes, cut by SE dipping dilational granite sheets. In the Rootshorga Complex D3 is characterised by syntectonic granite veins with extensional and compressional displacements with top-to-the SE shear. Discordancies are consistent with low angle thrust planes at Fuglefjellet and Kvikjolen with probable repetition of carbonate layers.Zircon ages of the granitic sheets are 490 - 500Ma. Strontium and Nd isotopic signatures of the granitic sheets intruded into all complexes are consistent with melting of Jutulrora Complex crust with Archaean and Mesoproterozoic xenocrysts in some samples. Top-to-SE shear zones displace pegmatites with an inferred age of 520 Ma and are syntectonic with layer parallel ~490 Ma granite sheets.P-T-t studies from the Rootshorga Complex yield isothermal decompression paths at ~ 800 – 900 oC with decompression from ~1.4 GPa at ~570Ma to ~700oC and ~0.7 GPa at ~500Ma whereas P-T-t estimates from the Jutulrora Complex are ~ 600 – 700 oC and <~0.8 GPa at ~500 Ma with a path consistent with crustal loading. The Rootshorga and Fuglefjellet Complex are inferred to comprise a mega-nappe, emplaced during the Kuunga Orogeny ~500 Ma ago, over the footwall Jutulrora Complex. Aerogravity, satellite gravity and seismic tomography data reflecting unusually thick crust are consistent with this interpretation.