Official journal of Japan Association of Mineralogical Sciences (JAMS), focusing on mineralogical and petrological sciences and their related fields. Journal of Mineralogical and Petrological Sciences (JMPS) is the successor journal to both “Journal of Mineralogy, Petrology and Economic Geology” and “Mineralogical Journal”. Journal of Mineralogical and Petrological Sciences (JMPS) is indexed in the ISI database (Thomson Reuters), the Science Citation Index-Expanded, Current Contents/Physical, Chemical & Earth Sciences, and ISI Alerting Services.
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.
It has been well established that the exchange partition coefficient for the exchange of Ca and Na between plagioclase and silicate melts [Kd = (Ca/Na)pl/(Ca/Na)melt] increases with increasing water content in the melt, but its atomistic interpretation is not well developed. This work presents new experimental data on the partition coefficient in an alkali basalt and a transitional tholeiite from the Oginosen volcano, southwest Japan and discusses the possible role of melt polymerization in the variations of the partition coefficient. The experiments were conducted at 0.1 MPa, and hydrous 100 MPa and 200 MPa conditions. The partition coefficient at 0.1 MPa increases from 0.8-1.4 to 1.5-1.8 over a temperature increase from 1090 °C to 1190 °C in the transitional tholeiite, and from 1.2 to 1.7 for 1090 °C to 1150 °C in the alkali basalt. The partition coefficient increases up to 4.1-4.2 in the presence of 3.4-3.5 wt% water in the melt in both basalts. The variations of the Ca-Na partition coefficient between the plagioclase and the melt is interpreted in terms of the degree of polymerization of the melt. The degree of polymerization of the melt decreases with the increase of temperature and water content, both of which increase the Ca-Na partition coefficient. The anorthite content of the core of natural plagioclase phenocrysts in the alkali basalt is 63-66 mol%, suggesting crystallization under water-undersaturated conditions. In the transitional tholeiite, some of the cores of the plagioclase phenocrysts have An81-85, which is formed in a water-supersaturated run at 100 MPa and 1085 °C; however, the significance of the presence of An81-85 is unknown and must be investigated further.
Secondary minerals of tungsten that are the products of alteration of scheelite present in quartz veins in the Ishidera area, Wazuka, Kyoto Prefecture, have been examined using XRD, SEM-EDS, EPMA, and XRF. From the results, three tungsten minerals were identified: anthoinite, mpororoite, and hydrokenoelsmoreite. The two former minerals have not been reported to be found in Japan. This is, therefore, the first discovery of anthoinite and mpororoite in Japan. The two minerals form a white powdery mixture with pseudomorphing scheelite. Chemical analysis of the mixture shows that the Al/W ratio is approximate to 1 and that the Fe2O3 content is very low, suggesting that the ideal formulae of anthoinite and mpororoite are WAlO3(OH)3 and WAlO3(OH)3·2H2O, respectively, even though the original mpororoite had a high content of Fe2O3 substituting for Al2O3. In addition to these two minerals, another tungsten mineral was also found within the scheelite-pseudomorphs. It occurs as aggregates of regular octahedral crystals up to 50 μm in length. The XRD data are in good agreement with those for hydrokenoelsmoreite, but chemical analysis shows that the major components are WO3, Al2O3, and H2O with no Fe2O3. Up to this time, only Fe-containing hydrokenoelsmoreite, once termed ferritungstite according to the old nomenclature, has been widely reported to be found in Japan. This paper is the first to report the occurrence of such an Fe-free hydrokenoelsmoreite in Japan. It is likely that these three secondary minerals of tungsten at Wazuka were formed in an environment where the supply of H2O and Al2O3 and the leaching of calcium ions from scheelite took place simultaneously. The source of Al is ascribed to the decomposition of muscovite in the quartz veins.
The eruptive history and magma systems of large-scale explosive eruptions (VEI >5) in eastern Hokkaido, Japan, are reviewed on the basis of recently reported high-resolution tephrostratigraphy. More than 70 large-scale explosive eruptions have been recorded from the Akan, Kutcharo, Atosanupuri, and Mashu caldera volcanoes in the past 1.7 Ma. The total tephra volume of these eruptions is estimated to be approximately 1000 km3. The discharge rate increases remarkably from 0.2 km3/kyr to 2.0 km3/kyr at approximately 0.2 Ma. The discharge rate is still high owing to the recent frequent activity of the Mashu caldera. The silicic magma systems of the Akan, Kutcharo, and Mashu calderas formed independently. On the other hand, the magma of Atosanupuri is associated with that of Kutcharo caldera.
We report first fluid inclusion data on amphibolite-facies pelitic schists from Bodonch area of western Mongolian Altai in the Central Asian Orogenic Belt. Three categories of fluid inclusions have been observed in quartz: dominant primary and secondary inclusions, and least dominant pseudosecondary inclusions. The melting temperatures of all the categories of inclusions lie in the narrow range of -57.5 °C to -56.6 °C, close to the triple point of pure CO2. Homogenization of fluids occurs into liquid phase at temperature between -33.3 °C to +19.4 °C, which convert into densities in the range of 0.78 g/cm3 to 1.09 g/cm3. The estimated CO2 isochores for primary and pseudosecondary high-density inclusions is broadly consistent with the peak metamorphic condition of the studied area (6.3-7.3 kbar at 655 °C). The results of this study, together with the primary and pseudosecondary nature of the inclusions, indicate CO2 was the dominant fluid component during the peak amphibolite-facies metamorphism of the study area. The examined quartz grains are texturally associated with biotite, kyanite and staurolite, which are regarded as high-grade minerals formed during prograde to peak metamorphism. Therefore quartz probably formed by high-grade metamorphism and the primary fluid inclusions trapped in the minerals probably preserve fluids at around peak metamorphism.
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.
The editorial office apologizes for the following misprints in the former issue (vol.106 no.6, December, 2011).
1. In the Editorial (page 275) The Editorial Board would like to thank Yuji ICHIYAMA.
2. In the first original Article entitled “Cooperation of upper and lower boundary-layer fractionations in a sheet-like intrusion: Composition and microstructure of the Aosawa dolerite sill in Yamagata Prefecture, northeastern Japan” by Yushi TAKADA and Kazuhito OZAWA (vol. 106, no. 6, 277-298, 2011). On page 298, the correct manuscript accepted date is “September 23, 2011”.
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