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 local structures of tektites and natural glasses were studied by Zr K–edge X–ray absorption near edge structure (XANES) and extended X–ray absorption fine structure (EXAFS) measurements in order to obtain quantitative data on the Zr–O (bonding) distances and coordination numbers for the glasses. Zr4+ ions have different coordination environments. The structure of glass (tektite, impact–related glass, fulgurite, and volcanic glasses) is affected by the temperature during the glass–formation process. Differences in the formation processes for natural glasses result in different local structures for the zirconium ions. All tektites can be classified as being of the same type and as having 7–fold coordination Zr ions. The Zr–O distances in tektite glasses are 2.198–2.215 Å, and their XANES spectra are similar, too. Impact–related glasses can be classified into different types and are formed under different physical and geological processes at the impact event. Volcanic glasses, impact–related glasses, and fulgurite glasses have several local Zr structures with 6– and 7–fold coordinated Zr ions. It can thus be concluded that local structures of Zr in natural glasses are closely related to the formation temperature and quenching conditions of the glasses. The Zr XAFS spectra of natural glasses can be used to identify the naturalglasses.
Multiple generations of Na–Ca and Na pyroxenes (aegirine–augite, aegirine and jadeite) were found in a metamorphosed monzonitic dike from a coherent mafic layer of the Northern Chichibu belt in central Shikoku, Japan. The mafic layer was derived from alkaline basalt magma and its derivatives, and belongs to the Kamiyoshida unit (Middle Jurassic accretionary complex). The earliest–stage sodic pyroxene (jadeite–free Ti–rich aegirine–augite to aegirine) in the dike probably crystallized during a post–magmatic hydrothermal stage. Igneous Ti–rich augite phenocrysts were almost completely pseudomorphed by chlorite + phengite + Al–OH–rich titanite + sodic pyroxene (aegirine–augite with jadeite component) during early stages of subduction metamorphism. The earliest–stage sodic pyroxene and pseudomorphed Ti–rich augite were further overgrown by jadeite/aegirine fringes during high–P/T metamorphism. Jadeite/aegirine pyroxene also occurs as small (~ 50 µm long) neoblasts within pseudomorphs (albite + phengite + pumpellyite ± Ba–rich K–feldspar) after igneous plagioclase. Individual grains of the fringe/neoblastic pyroxene are zoned with a jadeite core (up to 98% jadeite content) and an aegirine rim (down to 25% jadeite content). Jadeite–rich pyroxene (up to 92% jadeite content) was also found in basaltic rock from the mafic layer. The absence of quartz and the alkaline affinity of the protoliths suggest that the jadeite formation can be explained by the reaction analcime = jadeite + H2O. If H2O fluid was present, the decrease in jadeite content in the fringe/neoblastic pyroxene implies decompression from ~ 0.6–0.7 GPa at 300 °C to ~ 0.4 GPa at 210–260 °C. The formation of the jadeite–to–aegirine pyroxene during exhumation probably resulted from the lowest–grade Sanbagawa metamorphism.
This paper reports on priderite (potassium titanate) and burbankite (alkali Sr–Ca–REE–Ba carbonate) from an orogenic garnet peridotite body enclosed in high–pressure garnet–kyanite–bearing quartzo–feldspathic Gföhl granulite in the Bohemian Massif of the Variscan belt. The garnet peridotite contains ubiquitous phlogopite and was interpreted to be derived from the mantle wedge formed at the convergent plate margin. The earliest generation of chromian spinel, surrounded by kelyphitized garnet, ubiquitously contains multiphase solid inclusions (MSIs), which are mainly composed of phlogopite, dolomite, calcite, apatite, graphite, monazite, thorianite, and sulfides, and priderite and burbankite are newly identified as rare accessory minerals in such MSIs. Most of these MSIs contained significant amounts of carbonates. The presence of peculiar accessory minerals in MSIs characterizes the nature of parental melts. The formation of priderite requires an ultrapotassic condition, which is usually defined by K2O >3 wt% and K2O/Na2O >2 in bulk composition, and high Cr2O3 content in priderite (15–18 wt%) suggests that it was formed as a reaction product between a melt inclusion and a host chromite. Burbankite contains significant amounts of Na2O and K2O (~ 3 wt%) and REE concentration (>31 wt%). The formation of burbankite requires a per–alkaline condition —K2O + Na2O > Al2O3 in mol— and requires more sodic composition. The presence of priderite and burbankite in MSIs suggests that some of them crystallized from ultrapotassic melts, whereas others crystallized from sodic peralkaline melts. Such alkali–carbonate melts could be present in the mantle wedge peridotite before its’ incorporation into the granulite.
Roweite occurs as reddish to dark brown granular crystals up to 0.8 mm across in crystalline limestone near gehlenite–spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. It is closely associated with uralborite. Associated minerals include shimazakiite, frolovite, bultfonteinite, fluorite and calcite. An electron microprobe analysis of roweite gave an empirical formula Ca2.006(Mn1.410Fe0.333Mg0.181Zn0.036Co0.004)Σ1.964B4.017O6.989(OH)6.011 based on O = 13. The unit cell parameters are a = 9.057(2), b = 13.335(3), c = 8.284(3) Å. The calculated density is 2.92 g cm−3. The roweite from the Fuka mine was probably formed as a secondary mineral from calcium borates such as uralborite in a reaction with manganese–bearing late hydrothermal solution.
The Mikame ultramafic body, located in westernmost central Shikoku, Japan, forms a nappe accompanied by the Maana Formation and low– to medium–pressure Oshima metamorphic rocks. This body is divided into the Shigiyama and Korotokibana masses. The Shigiyama mass is composed of very fresh dunite, wehrlite and pyroxenite; whereas the Korotokibana mass is composed of antigorite–bearing meta–serpentinite derived from dunite and wehrlite. Estimated equilibrium temperatures are 600–700 °C for the Shigiyama mass and 400–500 °C for the Kototokibana mass, respectively. The geological and petrological characteristics of the Mikame ultramafic rocks are similar to those of the Higo belt in central Kyushu, rather than those of the Mikabu and Kurosegawa belts, and the Mikame body is possibly equivalent to the Higo belt. The Shigiyama ultramafic rocks are subdivided into Mg– and Fe–rich suites based on their olivine and chromian spinel compositions. The Mg–rich suite is characterized by magnesian olivines (Fo84–92) and high–Cr# [= Cr/(Cr + Al) = 0.5–0.8] spinels. On the other hand, the Fe–rich suite contains less magnesian olivines (Fo74–88) and low–Cr# (= 0.3–0.4) spinels. The Mg– and Fe–rich suites of the Shigiyama ultramafic rocks are cumulates formed from depleted and less depleted magmas, respectively. The chemistry of the chromian spinels in the Mikame ultramafic rocks indicates that they formed by crystal accumulation from magmas generated in an arc setting. The Korotokibana meta–serpentinites resemble those from the Mariana forearc regarding their mineral assemblage, and olivine and chromian spinel compositions. The Korotokibana meta–serpentinites experienced dehydration at 400–500 °C, after serpentinization caused by addition of H2O released from a subducting slab, whereas the Shigiyama ultramafic rocks contain no evidence for dehydration. The Mikame ultramafic body may have been the lower forearc crust produced by magmas with various degrees of depletion, later subjected to diverse hydration and dehydration processes.
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