著者

Keiko MORI Tatsuki TSUJIMORI Nelson BONIFACE

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.113, no.6, pp.316-321, 2018 (Released:2018-12-29)

参考文献数

43

被引用文献数

1 6

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We report a newly discovered assemblage of talc–kyanite in an amphibolite from the Isimani Suite of the Paleoproterozoic Usagaran Belt, central Tanzania. The amphibolite is characterized by the mineral assemblage of clinoamphibole, kyanite, talc with minor rutile, quartz, dolomite, and rare barite. The high Fe3+/(Fe3+ + Fe2+) ratio (0.48–0.80) of clinoamphibole and the presence of sulfate (barite) indicate a very–high oxidation state during metamorphism. P–T pseudosection modelling predicts that the studied talc– and kyanite–bearing amphibolites formed at high–pressure conditions (P > 1.0 GPa). Moreover, the modelling suggests formation of talc + kyanite + clinoamphibole at a highly oxidizing condition with CO2 fluid. This talc–kyanite association provides an index of high–pressure metamorphism of the Usagaran Belt and marks the oldest record of the talc–kyanite association in regional metamorphism in the Earth’s history.

著者

Tomomi HARA Tatsuki TSUJIMORI Kennet E. FLORES Jun–Ichi KIMURA

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.114, no.6, pp.296-301, 2019 (Released:2020-01-22)

参考文献数

38

被引用文献数

2

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Lawsonite, jadeite, and glaucophane are iconic minerals within a Pacheco Pass metagraywacke of the Franciscan Complex, California. Those minerals and the associated quartz form the distinctive very low–temperature and high–pressure metamorphic lawsonite–jadeite–glaucophane assemblage, which is diagnostic of ‘cold’ oceanic subduction zones. In this paper, we evaluate the ability of lawsonite geochemistry to trace protoliths with in–situ trace element and Sr–Pb isotope analyses in lawsonite from the Pacheco Pass blueschist–facies metagraywacke, a classical example of trench–fill sediments in subduction zones. Initial Sr isotope ratios are relatively high (87Sr/86Sr = 0.7071–0.7074), and initial Pb isotope ratios are 206Pb/204Pb = 18.74–19.66, 207Pb/204Pb = 15.58–15.70, and 208Pb/204Pb = 38.41–39.34, which range from a MORB trend to a cluster on the EMII component. These geochemical signatures suggest the protolith of the metagraywacke mainly contained material derived from continental volcaniclastic rocks and quartzofeldspathic sediments. There is also a possibility that the protolith contains plume–related oceanic island basalt that reached or intruded into the fore–arc sedimentary sequence of California. Considering the maximum depositional age of the metagraywacke at ~ 102 Ma, the subduction of the Farallon Plate beneath the continental crust of the North American Plate might have carried alkali basalt with OIB–like isotopic signatures to the Franciscan trench. Our study proves the advantage of in–situ lawsonite Sr–Pb isotope analyses to characterize protoliths of metamorphic rocks. The results would manifest that the Sr–Pb isotopic signature of Ca–Al silicate minerals, such as lawsonite, and possibly epidote and pumpellyite, in various types of metamorphic/metasomatic rocks, would be an effective tool for investigating convergent margins.

著者

Yuzuki SHINJI Tatsuki TSUJIMORI Tatsuhiko KAWAMOTO

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.114, no.6, pp.302-307, 2019 (Released:2020-01-22)

参考文献数

31

被引用文献数

2

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Late Paleozoic Yunotani eclogites in the Itoigawa–Omi area of the Hida–Gaien Belt were subjected to a blueschist–facies recrystallization and deformation after the peak eclogite–facies metamorphism. We studied fluid inclusions in quartz domains of different metamorphic stages in the retrograde eclogite. Coarse–grained quartz filling pressure shadow of porphyroblastic garnets contains transgranular fluid inclusions (Group–I) with high salinity [6.0–8.0 eq mass% NaCl, with a mean value 7.2 ± 0.6 eq mass% NaCl (n = 12)]. In contrast, transgranular fluid inclusions in later stage quartz–rich band (Group–II) in parallel to a penetrative foliation developed in matrix are characterized by lower salinity [1.1–5.8 eq mass% NaCl, with a mean value 3.4 ± 1.2 eq mass% NaCl (n = 12)]. The occurrences of fluid inclusion trails suggest that each group corresponds to the fluids entrapped prior to the blueschist–facies recrystallization and the fluids entrapped during the blueschist–facies stage, respectively. The Group–II fluid inclusions formed at blueschist–facies conditions support the idea that aqueous fluids in the subduction channel have a salinity similar to seawater (~ 3.5 eq mass% NaCl). Moreover, the Group–I fluid inclusions indicate a possibility that aqueous fluids at the eclogite–facies depth in subduction channels possess a salinity higher than seawater.

著者

Chinatsu YAMADA Tatsuki TSUJIMORI Qing CHANG Jun–Ichi KIMURA

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.114, no.6, pp.290-295, 2019 (Released:2020-01-22)

参考文献数

34

被引用文献数

6

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The antigorite–grade serpentinite and Late Paleozoic high–pressure schists are main components of a serpentinite–matrix mélange in the Itoigawa–Omi area, Hida–Gaien Belt, Japan. Based on the petrologic characteristics of the high–pressure schists, the mélange is divided into two units, namely an ‘eclogitic unit’ and a ‘non–eclogitic unit’. Our preliminary in–situ boron isotope analyses of five serpentinites using a laser–ablation multiple–collector inductively–coupled–plasma mass spectrometry (LA–MC–ICPMS) found a systematic difference of boron isotopic trends among the two units in the same mélange. The ‘eclogitic unit’ serpentinites from Yunotani and Kotagi–gawa are characterized by lower δ11B value (mostly lower than +10‰), whereas the non–eclogitic unit serpentinite from Omi–gawa is higher than +10‰. Although the δ11B value of <0‰ was not measured from the eclogitic unit serpentinites, the relatively low δ11B values of <+10‰ might have recorded the signature of fluids released from deep subducted dehydrating slab. In contrast, the non–eclogitic unit serpentinite might have been affected by fluids released from shallower portion. Our new data confirmed the potential sensitivity of the boron isotope signature of serpentinites reflecting variation of high–pressure metamorphism.

著者

Daisuke NISHIO–HAMANE Takahiro TANAKA Tadashi SHINMACHI

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.114, no.5, pp.252-262, 2019 (Released:2019-12-05)

参考文献数

30

被引用文献数

8

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Minakawaite, a new mineral with a RhSb composition, in association with a platinum–group mineral (PGM) placer is found from a small stream crossing the clinopyroxenite mass in serpentinite mélange of the Kurosegawa belt on the northeast side of Hikawa Dam, Haraigawa, Misato machi, Kumamoto Prefecture, Japan. Almost all PGM placer grains are based on isoferroplatinum, of which the rims are often covered by tulameenite and tetraferroplatinum. This isoferroplatinum–based grain contains small inclusions and accessories consisting mainly of osmium, erlichmanite, laurite, bowieite, cuprorhodsite, and ferhodsite–like mineral. Minakawaite occurs as the outmost surface layer with a rose gray metallic luster on the nub consisting of cuprorhodsite, ferhodsite–like mineral and/or Rh(Ge,Cu,Fe) mineral in association with an isoferroplatinum–based grain. The density of minakawaite is 10.04 g/cm3, calculated using the empirical formula and powder X–ray diffraction (XRD) data. Minakawaite has a pale gray color under the microscope in reflected light, and pleochroism is weak as a variation from pinkish pale gray to bluish pale gray. Anisotropy is moderate as reddish gray to bluish gray. Average results of ten energy dispersive X–ray spectroscopy (EDS) analyses give Rh 46.83, Sb 48.97, As 4.08 and total 99.88 wt%. The empirical formula is Rh0.998(Sb0.882As0.120)Σ1.002, based on 2 atoms per formula unit. Minakawaite is orthorhombic (Pnma) with a = 5.934(7) Å, b = 3.848(3) Å, c = 6.305(4) Å, and V = 144.0(2) Å3 (Z = 4). The seven strongest lines of minakawaite in the powder XRD pattern [d in Å(I /I0) (hkl )] are 2.860(63) (111), 2.774(35) (102), 2.250(47) (112), 2.199(100) (211), 2.162(38) (202), 1.923(49) (020), and 1.843(51) (013). Minakawaite is identical to the synthetic RhSb phase with MnP–type structure. PGM including minakawaite may occur with chromite in the magma chamber of the clinopyroxenite. Minakawaite was named in honor of Japanese mineralogist, Prof. Tetsuo Minakawa (b. 1950) of Ehime University for his outstanding contribution to descriptive mineralogy from Kyushu and Shikoku, Japan.

著者

Kenta YOSHIDA Tatsu KUWATANI Atsushi YASUMOTO Satoru HARAGUCHI Kenta UEKI Hikaru IWAMORI

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.171127, (Released:2018-06-07)

被引用文献数

3

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Conventional clustering algorithms such as k–means and fuzzy c–means (FCM) cluster analysis do not fully utilize the spatial distribution information of geologic samples. In this paper, we propose GEOFCM, a new clustering method for geochemical datasets with location coordinates. A spatial FCM algorithm originally constructed for image segmentation was modified for application to a sparse and unequally–spaced dataset. The proposed algorithm evaluates the membership function of each sample using neighboring samples as a weighting function. To test the proposed algorithm, a synthetic dataset was analyzed by several hyper–parameter settings. Applying this algorithm to a geochemical dataset of granitoids in the Ina–Mikawa district of the Ryoke belt shows that samples collected from the same geological unit are likely to be classified as the same cluster. Moreover, overlapping geochemical trends are classified consistently with spatial distribution, and the result is more robust against noise addition than standard FCM analysis. The proposed method is a powerful tool to use with geological datasets with location coordinates, which are becoming increasingly available, and can help find overviews of complicated multidimensional data structure.

著者

Daisuke NISHIO-HAMANE Takeshi YAJIMA Issei IKARI Yoshiya OHKI Hirofumi HORI Yoshihiro OHARA

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.230605, 2023 (Released:2023-10-12)

参考文献数

26

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Kiryuite and gunmaite were found as new minerals from Tsukubara, Kiryu City, Gunma Prefecture, Japan. Kiryuite is a Mn-rich analogue of viitaniemiite with an ideal formula of NaMnAl(PO4)F3 that mainly occurs as a white powder in cracks in triplite aggregate and occasionally forms porous plate-like aggregates up to 5 mm in size, while the grains are several micrometers in size. In most cases, the aggregates are also accompanied by small amounts of other minerals such as goyazite, gorceixite, and fluorite. Kiryuite shows white streaks with a vitreous luster, and its Mohs hardness is estimated to be 5 by analogy with viitaniemiite. The calculated density is 3.32 g·cm−3 based on the empirical formula and unit cell volume refined from powder X-ray diffraction (XRD) data. The empirical formula for kiryuite calculated on the basis of O = 4 and F + OH = 3 is Na0.97(Mn0.56Ca0.38Fe0.04Mg0.02)Σ1.00Al0.98P1.02O4(F2.29OH0.71)Σ3. Kiryuite is monoclinic (P21/m) with a = 5.425(4) Å, b = 7.128(4) Å, c = 6.817(6) Å, β = 109.41(7)°, and V = 248.7(3) Å3 (Z = 2). The parameters [d in Å (I/I0) hkl] for the six strongest lines associated with kiryuite in the powder XRD pattern are 3.123 (57) 002, 2.923 (53) 012 and 120, 2.877 (100) 121, 2.560 (27) 200, 2.263 (43) 103, and 2.155 (76) 221. Gunmaite is a new alunite-related mineral with a new structure type that has an ideal formula of (Na2Sr)Sr2Al10(PO4)4F14(OH)12. Gunmaite mainly occurs as a core in hexagonal tablet crystals that coexist with gorceixite and goyazite-like minerals. Gunmaite is colorless and transparent with a greasy to resinous luster and is non-fluorescent. As a bulk crystal including gunmaite, the Mohs hardness is 5, cleavage is perfect on {001} planes, and the tenacity is brittle. The calculated density based on the empirical formula is 3.38 g·cm−3 using the empirical formula and single-crystal XRD data. The empirical formula for gunmaite calculated on the basis of O = 16 and F + OH = 26 is (Na1.72Sr0.70Mg0.56Ca0.01)Σ2.99(Sr1.32Ba0.68)Σ2(Al9.82Mg0.18)Σ10P3.99O16F16.21(OH)9.79. Gunmaite is trigonal (R3m) with a = 6.9972(2) Å, c = 50.270(2) Å, and V = 2131.51(13) Å3 (Z = 3). The structure consists of two PO4, AlO2(OH)4, AlF6, AlOF3(OH)2, SrO6(OH)6, and NaF8 polyhedra. Kiryuite and gunmaite are products of the final stage of hydrothermal activity in association with greisenization.

著者

Daisuke NISHIO-HAMANE Takeshi YAJIMA Norimasa SHIMOBAYASHI Masayuki OHNISHI Takefumi NIWA

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.230711, (Released:2023-10-25)

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Asagiite, a newly-discovered mineral having the ideal formula NiCu4(SO4)2(OH)6·6H2O, is a member of the ktenasite group, representing a Ni analogue. It occurs as a secondary mineral on smithsonite aggregates that overlie fractures in a serpentinite found in the Nakauri mine within Aichi Prefecture, Japan. Asagiite exhibits a unique pale blue-green coloration and so is named after the traditional Japanese color “asagi-iro.” Asagiite occurs as thin plate-like crystals with perfect cleavage along {001} planes. The crystal size of this mineral is typically 0.1 to 0.2 mm, although in rare cases crystals may range up to 0.5 mm in length. These crystals are vitreous, transparent and non-fluorescent and have also been shown to be brittle with a Mohs hardness of 2½. The measured and calculated densities of asagiite are 2.90(3) and 2.92 g·cm-3, respectively. This mineral is optically biaxial (-) with α = 1.577(2), β = 1.620(2) and γ = 1.631(2) together with a 2Vcalc value of 52.4°. Electron microprobe analyses determined an empirical formula (based on 2S) of (Cu3.44Ni0.76Zn0.59Co0.18Fe0.01)Σ4.98S2O7.95(OH)6.05·6H2O. Based on single crystal X-ray diffraction data, the structure is monoclinic with space group P21/c and unit cell parameters a = 5.6095(8), b = 6.1259(7), c = 23.758(3) Å, β = 95.288(4)°, V = 812.92(17) Å3 and Z = 2. Single-crystal structural determination also gives an R1 value of 0.0303. The seven most intense peaks in the powder X-ray diffraction pattern [d in Å (I/I0) hkl] were found to be 11.830 (100) 002, 5.912 (64) 004, 4.845 (55) 013, 3.920 (45) 006, 2.953 (33) 008, 2.668 (57) 202 and 2.571 (36) 123, with unit cell parameters of a = 5.614(5), b = 6.108(8), c = 23.758(18) Å, β = 95.62(7)° and V = 810.8(14) Å3.

著者

Mutsuko INUI Shuto KOJIMA Yoshiya NAGATSUMA

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.221219c, (Released:2023-10-04)

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Albite porphyroblasts occur in schists in higher-grade zones of the Sanbagawa metamorphic belt, Japan. In this study of pelitic schists from the Nagatoro area of the belt, various microstructures in albite porphyroblasts were identified and indicate that grain size reduction of the albite porphyroblasts occurred after their formation. Schists with recognizable porphyroblasts contain fine grains of albite aligned in the matrix. In comparison, schists without recognizable albite porphyroblasts contain lenticular aggregations of albite grains in quartz-rich layers that suggest grain size reduction of the original porphyroblasts. These observations suggest that the absence of albite porphyroblasts does not necessarily indicate different pressure, temperature, or chemical conditions but can instead be explained by grain size reduction of albite porphyroblasts during deformation.

著者

MAMI TAKEHARA KENJI HORIE TOMOKAZU HOKADA SOTARO BABA ATSUSHI KAMEI IPPEI KITANO

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.230331, (Released:2023-09-07)

被引用文献数

2

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The Napier Complex in East Antarctica has a complex thermal history, including ultra-high-temperature (UHT) metamorphism. Geochronology, trace element, and isotope geochemistry of zircon, apatite, and monazite in three felsic gneisses collected from Harvey Nunatak were studied using a sensitive high-resolution ion microprobe (SHRIMP) for the first time. Most zircons showed nebulous to fir-tree zoning, which is a common feature of zircons in granulite facies rocks, regardless of the core or rim. The U-Pb dating and rare earth element abundance of zircon indicated that zircon crystallization by regional metamorphism continued from 2567–2460 Ma, consistent with the previously proposed timing of UHT metamorphism. The zircon grains contained a large amount of Li (59–668 ppm). Li was incorporated with Cl at the interstitial sites of the zircon structure, and the zircons crystallized in melts with an abundant supply of Li and Cl. Monazite crystallized from apatite after the UHT metamorphism events of 2071 Ma and 1799 Ma. The U-Pb system of apatite was completely disturbed by the crystallization of monazite at 1785 Ma. In addition, the U-Pb systems of apatite and monazite were disturbed at approximately 500 Ma.

著者

Naoki HIRAKAWA Yoko KEBUKAWA Takazo SHIBUYA Hisahiro UEDA Kensei KOBAYASHI

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.220913, 2023 (Released:2023-07-26)

参考文献数

53

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Several investigations have demonstrated that olivine may be used to simulate geochemical and cosmochemical reactions. Since olivine in extra-terrestrial samples has varying forsterite numbers and natural olivine contains inevitable impurities, synthetic olivine with the requisite forsterite number has been prepared for various experimental research. This study aimed to synthesize Fe-bearing olivine via synthetic experiments conducted at near-solidus temperatures and elucidate the formation and decomposition mechanisms of the obtained Fe-bearing olivine. Specifically, we attempted to synthesize Fo60 [Forsterite number = 100 × Mg/(Mg + Fe) = 60] olivine using a mixture of analytical-grade SiO2, MgO, and Fe2O3. To clarify the stability of the obtained olivine, the temperature range (1350-1500 °C) and heating durations (1.5 or 15 h) were controlled under a constant oxygen fugacity of QFM-1 log units.The target olivine (Fo60) was obtained via heating for 1.5 h at 1500 °C, corresponding to the solidus line temperature. However, maintaining the olivine obtained at this temperature for 15 h resulted in a much higher forsterite number owing to the formation of oxidized minerals of olivine (magnetite and pyroxene). Similar oxidation products were also obtained following heating at 1450 °C for 15 h. These results indicated the primary formation of Fe-bearing olivine during 1.5 h of heating and its subsequent decomposition to magnetite and pyroxene owing to the high-temperature oxidation at near-solidus temperatures during heating for 1.5-15 h. These findings highlight a strategy for synthesizing Fe-bearing olivine and the associated mechanism and provide experimental insights into the decomposition of olivine in natural igneous rocks.

著者

Kazumasa SUEYOSHI Manami KITAMURA Xinglin LEI Ikuo KATAYAMA

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.221014, 2023 (Released:2023-04-13)

参考文献数

32

被引用文献数

1

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The frequency characteristics of acoustic emission (AE) during triaxial compression of thermally cracked and unheated (‘fresh’) granite samples were investigated with the aim of understanding the influence of pre-existing cracks on precursor information regarding macroscopic failure. The peak frequency during the damage process was the same for thermally cracked and fresh granites. Analysis of AE signals showed that signals with low peak frequency appeared before failure of the sample, implying the initiation of macrocracks with progressive growth of cracks. The peak amplitude of the frequency spectrum recorded in the thermally cracked samples was much lower than that in the fresh samples. This result suggests two reasons for the difference in peak amplitude: reduction in shear modulus and the attenuation filtering phenomenon caused by thermal cracks (i.e., the differences in overall bulk properties). In particular, the maximum value of peak amplitude in the low-frequency band for the thermally cracked samples was smaller than that for fresh samples. This characteristic can be related to the properties of source of AE signals, such as the stress drop and crack size. Assuming that pre-existing thermal cracks grow during the pre-failure stage, the events with low peak frequency and low peak amplitude in the heat-treated samples are interpreted as exhibiting a low stress drop for individual events. Therefore, although AE signals with low frequency can be considered as precursors to rock failure, cracking behavior suggested by events with low frequency depends on the initial damage condition of the rock sample.

著者

Tetsuo KAWAKAMI Simon L. HARLEY

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.230131b, (Released:2023-04-25)

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Boron isotope compositions were measured in kornerupine and tourmaline from lenses consisting primarily of kornerupine, plagioclase and corundum. The lenses occur within hornblende-gneiss or along the boundary between this gneiss and an amphibolite lens at Akarui Point in the Lützow-Holm Complex, Prince Olav Coast, East Antarctica. The peak metamorphic conditions have been estimated to be ~ 800-900 oC and ~ 8-11 kbar. The δ11B compositions of kornerupine, which is interpreted to have been a stable phase at the metamorphic peak, are -11.6 ± 0.4 to -7.8 ± 0.5 ‰ and -9.8 ± 0.3 to -6.1 ± 0.2 ‰ in two different samples. Grains of prograde tourmaline included in kornerupine and corundum yielded δ11B = -2.1 ± 0.3 to +0.6 ± 0.3 ‰, and the secondary tourmaline replacing kornerupine yielded δ11B = -4.6 ± 0.2 to -3.7 ± 0.2 ‰. Therefore, the isotopic fractionation between kornerupine and tourmaline, △11BTur–Krn (= δ11BTur - δ11BKrn), of the average prograde tourmaline and average host kornerupine is +6.7 ± 1.5 ‰, which is interpreted to indicate isotopic equilibrium at the metamorphic peak on the basis of previous studies of isotope fractionation between tourmaline and minerals of the kornerupine-prismatine series. The δ11B values obtained on prograde tourmaline are between whole rock δ11B of MORB and mantle rocks and of some sedimentary rocks, and are similar to the δ11B of blackwall tourmalines that crystallized during the decompression stage following high-pressure metamorphism. We infer that the syn-metamorphic B-bearing fluid present in the kornerupine-plagioclase-corundum lens is likely sourced from a mixture of sedimentary, mafic and ultramafic lithologies in a subduction setting. The metabasic and meta-ultramafic lenses found in Akarui Point could be interpreted as the remnant of mixing zone of Ediacaran to Cambrian subduction channel.

著者

Fumiko Higashino Tetsuo Kawakami Tatsuro Adachi Masaoki Uno

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.230131a, (Released:2023-04-21)

被引用文献数

1

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This paper reports multiple fluid infiltration events during retrograde metamorphism in the Sør Rondane Mountains, East Antarctica. Pelitic gneisses from southern part of Perlebandet have cordierite-biotite intergrowth rimming garnet, implying that garnet breakdown occurred by fluid infiltration. Using the Raman peak of CO2 in cordierite and Cl-bearing composition in biotite, this study revealed that the cordierite-biotite intergrowth was formed in equilibrium with one-phase CO2-Cl-H2O fluid. The intergrowth texture is cut by thin selvages composed of Cl-bearing biotite, suggesting Cl-bearing fluid infiltration. Since andalusite is exclusively observed in the selvage, near isobaric cooling path is presumed for the pressure-temperature (P-T) path of these post-peak fluid-related reactions. The inconsistence with counter-clockwise P-T path reported from northern Perlebandet is probably due to the granodiorite/leucocratic granite bodies beneath the studied metamorphic rocks. In order to understand the tectonic evolution at the final stage of Gondwana amalgamation, therefore, effect of hidden igneous rocks needs to be taken into consideration.

著者

Kenta YOSHIDA Naoki AOYAGI Ryoji KATO 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.111, no.6, pp.398-404, 2016 (Released:2017-01-12)

参考文献数

35

被引用文献数

1 5

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Thermal structure of the Kebara Formation and its proximal areas in the western Kii Peninsula was examined by Raman spectra of carbonaceous material (RSCM) geothermometer for pelitic rocks. A mean temperature of 313 ± 5 °C is obtained for the Kebara Formation, which is comparable with that of the neighboring unit of the Mikabu belt (319 ± 5 °C). The Sanbagawa belt of the relevant area, within a few kilometers to the north of the Kebara Formation, shows a mean temperature of 285 ± 7 °C, which is slightly but evidently lower value than those of the above two units. Peak temperatures estimated from the Chichibu belt and Shimanto belt located to the south of the Kebara Formation are 289 ± 13 °C and 216 ± 24 °C, respectively. Published geochronological data of the Kebara Formation are slightly older than those of the Sanbagawa belt in the Kii Peninsula and are similar to those of the Mikabu belt in the relevant area. These two data sets (geothermometry and geochronology) suggest that the Kebara Formation is possibly correlated with the Mikabu belt, but is not coherent to the southern margin of the Sanbagawa belt in the western Kii Peninsula, in tectonic contact with each other.

著者

Hiroshi MORI Tetsuya TOKIWA Hiroki MIZUMURA Kohei YOSHIKAWA Yuki NOBE 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.221215, (Released:2023-04-14)

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We estimated the protolith age and peak metamorphic temperature of the Yokokawagawa metamorphic rocks (YMR) east of the Itoigawa–Shizuoka Tectonic Line using detrital zircon U–Pb dating and Raman carbonaceous material geothermometry, respectively. U–Pb dating of a psammitic rock yielded a youngest age of ∼100 Ma, which corresponds to the protolith age. Raman carbonaceous material geothermometry results for five pelitic rock samples give metamorphic temperatures of ∼350–380 °C. The protolith age is consistent with those of the Sanbagawa metamorphic rocks (SMR), strongly indicating that the YMR are an extension of the SMR. The increase in peak temperature toward intrusive rocks along the eastern margin of the YMR may indicate that the relatively young ages yielded by previous K–Ar dating of the YMR reflect thermal resetting due to contact metamorphism.

著者

Takashi HOSHIDE Masaaki OBATA Takashi AKATSUKA

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.223-239, 2006 (Released:2006-10-14)

参考文献数

43

被引用文献数

21 23

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The Murotomisaki Gabbroic Complex is a sill-like layered intrusion of up to 220 m in thickness and is located at Cape Muroto, Kochi Prefecture, Japan. There are several olivine-rich zones within the intrusion, which may have been formed through accumulation of olivine crystals. However, up to now it has not been clear as to whether all of the olivine-rich zones formed in this way. To clarify this, we reinvestigated the layered structure by collecting a consistent data set of modal composition, crystal size, and crystal number density of olivine from throughout the intrusion. It was found out that nearly all of the olivine crystals, in terms of crystal numbers, occur in the basal olivine-rich zone (within 40 m of the base of the intrusion), and the average value of the crystal number density of olivine throughout the entire intrusion coincides with the crystal number density of olivine in the outermost parts of the lower and upper chilled margins. Hence, we conclude that most primary olivine phenocrysts within the magma settled under the influence of gravity and accumulated to form the basal olivine-rich zone. The crystal number density of olivine within the mid-level zones (40-100 m from the base of the intrusion) is much less than the initial values, as indicated by values recorded in the chilled margins. It is proved that the increase of the olivine mode within this zone is attributed not to the crystal accumulation of olivine but to the increase of the crystal size of olivine, i.e., the crystal growth. In this way, considering the mode, crystal size, and crystal number density of olivine throughout the intrusion, the olivine-rich zones within the intrusion can be classified, in terms of their origin, as either crystal accumulation zone (AC zone) or crystal growth zone (GR zone). The growth of olivine crystals in the GR zone was apparently accompanied by an increase in MgO, FeO, and MnO concentrations to levels well above initial (i.e., the chilled marginal) values. This enrichment suggests that crystal growth occurred within a chemically open system in the sense that the increase in MgO content within the GR zone arose from material transfer between the boundary layer (the GR zone) and the overlying magma.

著者

Takehiro HIRAYAMA Tomoyuki SHIBATA Masako YOSHIKAWA Khadidja ABBOU–KÉBIR Kosuke KIMURA Yasuhito OSANAI Kaushik DAS Yasutaka HAYASAKA 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.117, no.1, pp.211217b, 2022 (Released:2022-11-30)

参考文献数

40

被引用文献数

1

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Granitic and gabbroic xenoliths have been found within dacitic lavas in the Hime–shima volcanic group (HVG) of northeastern Kyushu, Japan. The HVG is located near the boundary between the Ryoke and Sangun belts, suggesting that the HVG and associated crustal xenoliths may provide insights into the subsurface distribution of the Ryoke and Sangun belts in Kyushu. This study focuses on xenoliths obtained from the coastal boulders near the Kane Lava of the HVG. The HVG xenoliths consist of gabbro, gabbroic diorite, amphibolite, gneiss, basaltic andesite, and tuffaceous sandstone, with the latter two types resembling those found in the basement rocks of the HVG. The gabbroic xenoliths are geochemically similar to gabbros in the Ryoke belt. The U–Pb dating for zircon in the gneiss xenoliths yielded a metamorphic age of ~ 111 Ma with Th/U values <0.1, similar to the age obtained for metamorphic rocks in or of the Ryoke belt. The new data presented in this study indicate that the xenoliths in the HVG were derived from basement units associated with the Ryoke belt, which in turn, means that the HVG is tectonically underlain by the Ryoke belt. This also suggests that the Ryoke belt extends further north in Kyushu than was previously considered, as implied by the presence of this belt directly below the HVG.

著者

Daisuke NISHIO–HAMANE Koichi MOMMA Masayuki OHNISHI Sachio INABA

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.117, no.1, pp.220728, 2022 (Released:2022-11-29)

参考文献数

24

被引用文献数

1

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Oxyyttrobetafite–(Y) is the first member in the betafite group of the pyrochlore supergroup found in albite–rich pegmatite from Souri Valley, Komono, Mie Prefecture, Japan. This new mineral occurs as small anhedral grains with sizes of 20 to 200 µm in cylinder–shaped aggregates with a substrate of thalénite–(Y) and synchysite–(Y). Small amounts of aeschynite–(Y), thorianite, and thorite are also associated in the same occurrence with oxyyttrobetafite–(Y), and gadolinite–(Y) is also included at the boundary between the aggregate and albite. The physical properties are: brown in color, brittle, transparent, non–fluorescent, vitreous luster, white streak with a Mohs hardness of 5, and a calculated density of 5.54 g·cm−3. Oxyyttrobetafite–(Y) is an optically isometric material with brown color under the microscope with a refractive index of n = 2.3 calculated using the Gladstone–Dale relationship. The empirical formula of oxyyttrobetafite–(Y) calculated on the basis of B = 2 with A2B2X6Y composition is (Y1.58Dy0.13Yb0.07Er0.06Tm0.05Gd0.04Ho0.03Sm0.02Tb0.02Eu0.01Lu0.01)Σ2.02(Ti1.85Ta0.09Fe0.05Sn0.02Nb<0.01)Σ2O7.05 and leads to the ideal formula of Y2Ti2O6O, which requires TiO2 41.44 wt% and Y2O3 58.56 wt%, total 100 wt%. The structure is isometric cubic with the space group Fd3m and unit cell parameters of a = 10.11090(10) Å, V = 1033.64(3) Å3, and Z = 8 by single crystal X–ray diffraction measurements. The seven strongest peaks in the powder X–ray diffraction pattern [d in Å (I/I0) hkl ] were 2.918(100) 222, 2.527(18) 400, 2.321(13) 331, 1.788(53) 440, 1.525(46) 622, 1.162(13) 662, and 1.033(9) 844 with unit cell parameters of a = 10.121(3) Å, V = 1036.6(9) Å3, and Z = 8. The crystal structure was refined to R1 = 0.018 for 159 observed reflections with the criteria of I > 2σ (I ). Oxyyttrobetafite–(Y) is characterized by Y dominance at the A sites, Ti dominance at the B sites, and O dominance at the X and Y sites in the A2B2X6Y pyrochlore–type formula.

著者

Yu ITAMI Daisuke NAKAMURA Atsushi YASUMOTO Takao HIRAJIMA Martin SVOJTKA

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.117, no.1, pp.220221, 2022 (Released:2022-10-28)

参考文献数

52

被引用文献数

1

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The origins of eclogite associated with garnet peridotite in continent–continent collision belts are still debated. We performed petrological studies of eclogites collected from a garnet peridotite block from Nové Dvory in the Gföhl Unit of the Moldanubian Zone in the Variscan orogenic belt, Czech Republic. The eclogite was divided into three types: one kyanite (Ky)–bearing and two Ky–free types. Garnet and omphacite in the Ky–bearing eclogite have lower Fe contents than those in the Ky–free eclogite. Furthermore, the Ky–free eclogite was divided into two types on the basis of Ca content in garnet: Ca–rich (Xgrs > 0.32) and Ca–poor (Xgrs < 0.32) types, except for Ca–poor rim compositions. Application of conventional geothermobarometers to the Ky–bearing type and the Ky–free type with Ca–rich garnet yielded similar pressure–temperature (P–T) conditions (3.2–4.8 GPa and 920–1160 °C) to those of previous studies, whereas the Ky–free type with Ca–poor garnet yielded slightly lower P–T conditions (3.1–3.4 GPa and 950–990 °C) than the other two types. The observed chemical variation of garnet is probably due to the difference in origins, whereby, according to our new results and previous findings, the Ky–bearing eclogite was derived from plagioclase–bearing crustal gabbro, whereas the Ky–free eclogite with Ca–rich garnet was derived from a crystal cumulate possibly in the mantle wedge. In the Ky–free eclogite samples with Ca–poor garnet, chemical compositions of garnet and omphacite are different from those in the other Ky–free samples, and those samples with Ca–poor garnet would have a different origin from the others. One of the Ky–free type with Ca–poor garnet retains garnet grains with chemical zonings probably created during the prograde history, although the eclogite underwent the extremely high temperature (~ 1000 °C) metamorphism. Calculated diffusion distances in garnet reach 0.5 mm during 2 million years, even if we adopted a low value of diffusion coefficient data. Thus, the residence time of the eclogite at the peak meatamorphic conditions would have been shorter than at least 2 million years. The subsequent decompression and cooling after the peak metamorphism were also probably very fast to avoid the chemical homogenization of garnet.