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 indexed in the ISI database (the Thomson Corporation), the Science Citation Index-Expanded, Current Contents/Physical, Chemical & Earth Sciences, and ISI Alerting Services.
The crystal structures of conichalcite [Ca(Cu,Mg)(AsO4)(OH)] samples obtained from Gozaisho mine, Fukushima, Japan, and Higgins mine, Arizona, USA, were refined by single-crystal X-ray diffraction (XRD) using an imaging plate detector. The results revealed that conichalcite is orthorhombic and belongs to the P212121space group. The positions of the hydrogen atom and the donor and accepter atoms in the structure were determined by difference Fourier and bond-valence sum methods. The crystal comprised three highly distorted coordination polyhedra: an AsO4 tetrahedron, a CuO4(OH)2 octahedron, and a CaO7(OH) square antiprism. The CuO4(OH)2 octahedron was distorted by the Jahn-Teller effect. The observed As-O distances were shorter than those predicted by ionic bonding. The electronic structure of the atoms affected the distortion of the polyhedra that did not have a symmetry center. The CuO4(OH)2 octahedron shared its edges to form linear chains, which were further linked by the vertices of the AsO4 tetrahedron and the CaO7(OH) square antiprism to form a three-dimensional network. The arrangement of these linear CuO4(OH)2 chains was very similar to that of CuO6 chains in CuGeO3, a spin-Peierls material. Comparisons with several isomorphous minerals revealed that the Jahn-Teller distortion effect caused by Cu atoms differed significantly between the minerals in the Ca series and those in the Pb series. Because of hydrogen bonding, the Cu-O(5) and Cu-O(5)* distances tended to become shorter than the other Cu-O distances in all isomorphous minerals.
We report the major and trace element chemistry and Sr and Nd isotopic composition of basaltic rocks from the Quaternary Tateshina volcano, central Japan, and model the composition of these rocks in terms of the partial melting and melt-solid reactions controlled by the addition of slab-derived fluid and silicate melt to the original wedge mantle beneath the Tateshina area. Tateshina basaltic rocks have a SiO2 content ranging from 50.06 to 53.28 wt% and a MgO content ranging from 5 to 7 wt%, indicating that these rocks are less fractionated. These rocks have a narrow range of Sr and Nd isotopic compositions (87Sr/86Sr = 0.703619-0.703807, 143Nd/144Nd = 0.512893-0.512945). There is no correlation between Tateshina basaltic rocks and crustal materials in terms of 143Nd/144Nd-Sm/Nd, indicating that Tateshina basaltic rocks have no crustal contamination. The wedge mantle peridotite would have experienced accumulated subduction events, including the addition of subduction components and the extraction of basalt magmas during the Tertiary period. In addition, we have accounted for the mantle motion accompanying slab subduction within the wedge mantle. Thus, we assumed that the mantle wedge before the effects of Quaternary subduction that produced the volcanic rocks of Tateshina volcano could have blended with residual mantle after the extraction of Tertiary basalt magmas with depleted MORB-source mantle (DMM). The model includes partial melting of the blended wedge mantle peridotite metasomatized by aqueous fluid and silicate melt derived from the dehydration of altered oceanic crust (AOC) and partial melting of oceanic sediments, respectively. The trace element and Sr isotope compositions of the basaltic rocks of Tateshina volcano can be reproduced by about 10% melting of the calculated wedge mantle peridotite modified by the addition of 0.8%-1.0% silicate melt from oceanic sediments and 0.2%-0.8% aqueous fluids from the AOC, respectively.
Mg-rich chloritoid with the ratio Mg/(Mg + Fe2+) = 0.37 to 0.49 was found in a corundum-bearing zoisite rock from the Besshi area in the Sanbagawa metamorphic belt, Japan. The zoisite rock consists mainly of zoisite, corundum, garnet, and amphibole. Corundum was retrogressively replaced by secondary chloritoid, zoisite, clinozoisite, chlorite, and paragonite. Staurolite rarely occurs in aggregates of the secondary phases (chloritoid, chlorite, and paragonite), which occur along the cracks in corundum, and is surrounded by chloritoid. This fact indicates that chloritoid was formed by the following retrogressive reaction: 7chlorite + 8corundum + 4staruolite + 15H2O →51chloritoid. The estimated temperature for the above univariant reaction in the MASH system is 637 ± 30 °C at 10 kbar and 744 ± 34 °C at 20 kbar. The textural evidence and the estimated temperature suggest that chloritoid formed during the exhumation stage from eclogite to epidote-amphibolite facies conditions.
We examined dike-like chlorite rocks that replaced isotropic gabbro and dolerite in northern Oman ophiolite in order to understand the chemical budget of hydrothermal alteration of the oceanic lithosphere. During chloritization, the concentrations of Si, Ca, Na, and K decreased, while those of Fe increased. REE (rare-earth elements), except Eu, which showed a strong depletion in the chlorite rocks, were immobile during chloritization, which was caused by the downward (recharge) flow of circulated seawater. A portion of Fe was supplied from the overlying mafic extrusives, possibly through the alteration of their plagioclases. We found Ti-rich minerals such as rutile and titanite to be the reservoirs of most REE in the chlorite rocks. If the residual fluid, after chloritization, moves upward, it can realize the positive Eu anomaly of the seafloor vent fluids. And, if the fluid is transported to deeper parts of the oceanic lithosphere, rodingites, serpentinites (antigorite rocks), and diposidites with a positive Eu anomaly are formed within gabbros and mantle peridotites.
Zálesíite is found to exist as hexagonal prismatic crystals (length: up to 1 mm; width: 10 μm) and fibrous aggregates in the alteration zone in crystalline limestone near gehlenite-spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. The mineral is pale green to emerald green in color with a silky to vitreous luster. Andradite, aragonite, bornite, cahnite, chalcocite, chalcopyrite, conichalcite, johnbaumite, and an unidentified Ca-Cu arsenate mineral coexist in the abovementioned limestone. From SEM-EDS analysis, the empirical formula of zálesíite is found to be (Ca0.74Bi0.26)Σ1.00(Cu5.80Ca0.18Ni0.01Zn0.01)Σ6.00[(As2.86Si0.12P0.02)Σ3.00(O11.14OH0.86)Σ12.00](OH)6·3H2O on the basis of the following calculation: 10 (M1 + M2 + X) + 6 (OH) + 3 (H2O). Zálesíite collected from the Fuka mine contains Bi and is free of REE. The unit cell parameters of the zálesíite crystals are a = 13.656(9), c = 5.850(4) Å, V = 945(1) Å3, and Z = 2. It is inferred that zálesíite is formed by the reaction between crystalline limestone, cahnite, johnbaumite, Cu sulfide, and a Bi-rich hydrothermal solution.
An ultra-high-pressure metamorphic condition (∼ 140 km) at ∼ 950 °C is identified from a garnet-pyroxenite, containing primary supersilicic clinopyroxene, as a part of the mafic-ultramafic lenses enclosed in the Gföhl granulite at the Horní Bory quarry of the Bohemian Massif, Czech Republic. Petrological data indicate that the garnet-pyroxenite was isothermally (∼ 900 °C) exhumed from the upper mantle (∼ 140 km) to the lower crust (∼ 50 km), and the supersilicic clinopyroxene was decomposed to sodic augite and quartz during the exhumation. This ultra-high-pressure metamorphic evidence is the first to be derived from the mafic rock directly enclosed within the Horní Bory granulite in the Moldanubian zone of the Bohemian Massif.
High temperature impedance spectra, up to 450 °C, were measured for a microcrystalline quartz aggregate (chalcedony), which initially contained 0.3 wt% of liquid-like water (H2O) dispersed in grain boundaries and fluid inclusions together with 0.3 wt% of hydroxyl (Si-OH) in the crystal structure. Infrared spectra obtained after heating, showed dominant dehydration of liquid-like water, while much hydroxyl remained stable. Electrical conductivities before (wet) and after heating to 450 °C (dry) gave linear Arrhenius relations with apparent activation energies of 11 ± 1 kJ/mol for initial heating of the wet sample versus 32 ± 3 kJ/mol for the subsequently dry sample. Compared with previously reported Arrhenius relations for α-quartz single crystals, our activation energies are much lower, and the absolute conductivities we obtained range from similar values to three orders of magnitude higher. We infer that the presence of grain boundaries and/or triple junctions containing liquid-like water greatly influences the electrical conductivity.
Mineral assemblages of sulfides in the mantle peridotite xenoliths embedded in the alkali basalts of the Kurose reef, northern Kyushu, Japan and the chemical compositions of the mineral assemblages are described. Sulfides occur as 1) inclusions and 2) interstitial sulfides in olivine or pyroxene. The mineral assemblages of sulfides that occur as inclusions are pentlandite, pentlandite + chalcopyrite, pentlandite + bornite, monosulfide solid solution (mss) + chalcopyrite ± pentlandite, pentlandite + pyrrhotite, and millerite; and the mineral assemblage of sulfides as interstitial sulfides is pyrrhotite + pentlandite + chalcopyrite. The contents of Ni, Fe, and S in pentlandite are 22.91-33.45, 18.77-28.82, and 46.57-48.31 at%, respectively. The chemical composition of mss is variable. On the basis of the crystallization temperature of olivine and/or pyroxene and the phase relationship between the Fe-Ni-S and the Fe-Cu-S systems, it can be inferred that the mineral assemblage of mss + chalcopyrite ± pentlandite found in olivine is considered to have been initially trapped as a solid-phase Cu-bearing mss and that the other mineral assemblages were trapped as a sulfide liquid. The diversity of mineral assemblages of sulfides in the mantle peridotite xenoliths and the various chemical compositions of the mineral assemblages are due to timing of differential crystallization of mss and its capture in silicate minerals. It can also be inferred that the chemical composition of the initial sulfide liquid in the Kurose lherzolite is the S-poor portion of the Cu-bearing mss. This suggests that initial sulfide liquids in the upper mantle might have similar compositions.
The garnet-kyanite-staurolite and garnet-biotite-staurolite gneisses were collected from a locality within Lukung area that belongs to the Pangong metamorphic complex in Shyok valley, Ladakh Himalaya. The kyanite-free samples have garnet and staurolite in equilibrium, where garnets show euhedral texture and have flat compositional profile. On the other hand, the kyanite-bearing sample shows equilibrium assemblage of garnet-kyanite-staurolite along with muscovite and biotite. In this case, garnet has an inclusion rich core with a distinct grain boundary, which was later overgrown by inclusion free euhedral garnet. Garnet cores are rich in Mn and Ca, while the rims are poor in Mn and rich in Fe and Mg, suggesting two distinct generations of growth. However, the compositional profiles and textural signature of garnets suggests the same stage of P -T evolution for the formation of the inclusion free euhedral garnets in the kyanite-free gneisses and the inclusion free euhedral garnet rims in the kyanite-bearing gneiss. Muscovites from the four samples have consistent K-Ar ages, suggesting the cooling age (∼ 10 Ma) of the gneisses. These ages make a constraint on the timing of the youngest post-collision metamorphic event that may be closely related to an activation of the Karakoram fault in Pangong metamorphic complex.
The eclogite-garnetite transformation experiments were conducted at 11 GPa and 1000-1550 °C using synthesized polycrystalline eclogite with MORB composition as a starting material. We found that the eclogite-garnetite transformation proceeds by two stages, (1) precipitation of majoritic garnet from clinopyroxene and (2) formation of majoritic garnet from original pyropic garnet by absorption of clinopyroxene. The 1st stage in the transformation proceeds at 1000 °C for 180 minutes, however the 2nd stage was not observed even at the high temperature of 1550 °C on the same time scale. The differences in kinetics are due to contrasting diffusivities between clinopyroxene and garnet. The kinetic effect would modify the mineralogy and rock microstructures in MORB, which provides important implications for dynamics of subducting oceanic crust by changing the density and viscosity relation.
Olivines with conspicuous iron-rich stripe patterns are found in serpentinized peridotites from Conical and South Chamorro Seamounts, Mariana forearc, western Pacific. The stable association of antigorite, diopside, and olivine in these peridotites indicates that antigorite, diopside, and olivine underwent serpentinization at approximately 450-550 °C. The iron-rich stripe patterns are formed in the olivine crystal (Fo90-92) as a parallel alignment of narrow straight parts of widths ranging from 0.5 to 2.0 μm. The iron-rich parts have compositions of Fo86-89. The iron-rich stripe patterns are well developed near the rim of the host olivine where fiber crystals of antigorite are pierced into olivine and these patterns are not found in the inside of olivine grain except in the periphery of cracks. Generally, olivine is highly deformed and has well-developed cleavages in (010), (100), and (001) directions. The stripe is commonly parallel to (100), but one olivine grain has two sets of stripes that are parallel to (100) and (001). Modes of formation of iron-rich stripe patterns in olivine suggest that the infiltration of iron-rich fluid along the cleavage trace or the subgrain boundary formed by dislocations is probably responsible for the formation of the iron-rich stripe patterns. The iron-poor parts intervened between the iron-rich parts are slightly lower in XMg[= Mg/(Mg + Fe2+)] than the inside of olivine grain that is homogeneous in composition and lacks iron-rich stripe patterns, suggesting that metasomatic alteration also occurred in iron-poor parts. Antigorite formation results in an extra iron component because XMg of antigorite (= 0.94-0.97) is significantly higher than that of host olivine. Therefore, the iron-rich fluid may have been produced by serpentinization and infiltrated through olivine crystal to form iron-rich stripe patterns.
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