Recent progress in the study of kelyphites is reviewed. Petrographic characters of two major types of kelyphites are summarized and the reaction mechanism and material transfer associated with Type 1 kelyphite formation (a metamorphic reaction between garnet and olivine) is dealt with in detail. The significance of the shell form of kelyphite is emphasized and it is suggested that the occurrence of internal stress, which is theoretically believed to be generated by the reaction occurring within the kelyphite shell, plays a key role in determining the mode and the flux of material transfer across the kelyphite shell. It is shown that bulk composition of the kelyphite and the occurrence of nodular spinels at the peripheries of the kelyphite shell are best explained in terms of a model assuming a constant volume for the kelyphite shell, which is considered to be the most rigid and competent material among the constituent units of the kelyphite complex. It is emphasized that the process is essentially a mechanochemical one and a better understanding of such processes requires a theoretical development for thermodynamics for open system incorporating the stress as an intensive variable in a stress-gradient field.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 16
The style and explosivity of volcanic eruption are thought to be controlled by outgassing during magma ascent in a volcanic conduit. We have investigated the mechanism and rate of outgassing, which is based on laboratory experiments that simulate the magma ascent, coupled with microstructural observation of pyroclasts and lavas. The microstructure of bubbles in pyroclasts and fault texture in lavas indicate that shear deformation in flowing magma enhances outgassing. To quantify the rate of outgassing of the sheared magma, we performed torsional deformation experiments and measured the gas permeability of the sheared magma. This experiment demonstrated that shear deformation strongly increases the gas permeability. Moreover, we observed that magma ascending in the conduit can always obtain a gas permeability that is high enough to cause efficient outgassing if magma behaves as a Newtonian fluid. This efficient outgassing reduces the magma explosivity, which may make it difficult to induce explosive volcanism. Further, in situ X-ray radiographic and computed tomographic observations of magma deformation at high temperature show that shear localization in magma inhibited deformation and outgassing elsewhere. Thus, once shear localization starts during magma ascent, magma maintains its explosivity and causes explosive volcanism. On the other hand, non-explosive lava effusion occurs when magma is sheared well and efficient outgassing is experienced. To explore the cause of the variation in eruption style and explosivity, we need to understand elementary processes of the magma ascent such as magma rheology, vesiculation, outgassing, and fragmentation. In addition, it is important to understand how these processes affect one another, as indicated in the coupled effect of magma outgassing and rheology in this paper.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 17
Considerable amounts of carbonates are introduced deep into the Earth's interior by the subduction of oceanic plates. Here I report on high-pressure and high-temperature experiments involving carbonates and silicates up to 100 GPa and 3200 K, corresponding to depths within the Earth of approximately up to 2200 km. The experiments are intended to represent the decomposition process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO3 (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO3 (magnesite) via reactions with Mg-bearing silicates under conditions that are 200-300 K colder than the mantle geotherm. With increasing temperature, the magnesite is decomposed into an assemblage of CO2-V + perovskite via reactions with SiO2. Diffraction experiments for CO2-V show that the phase is consistently interpreted in terms of a β-cristobalite structure, which has been indicated by theoretical studies. Furthermore, CO2-V itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for diamond formation in the lower mantle.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 18
Trans Vietnam Orogenic Belt distributed in north to central Vietnam includes various types of metamorphic rocks. Most metamorphic rocks show the Permian-Triassic ages and are characterized by decompressional evolution with various metamorphic thermal gradients (8-25 ℃/km). In contrast, some metamorphic rocks having the Ordovician-Silurian age show isobaric heating prograde stage at low-pressure condition (25-30 ℃/km). Granitic rocks also show the Permian-Triassic or Ordovician-Silurian ages. The older granitoids have volcanic arc chemical signature, some of which were metamorphosed at the Permian-Triassic. These results suggest that island arc tectonic setting at the Ordovician-Silurian, where arc magmatism heated the arc crust and caused the low-pressure (with isobaric heating) metamorphism at this period. The Permian-Triassic metamorphic rocks and granitoids were formed by subsequent continental collision and subduction of the Indochina craton together with the past Ordovician-Silurian island arc beneath the South China craton.
Japan Association of Mineralogical Sciences Award for Applied Mineralogy, No. 8
Thermoelectric materials, which have the ability to convert heat into electricity, potentially could be used to capture much of the low-grade waste heat now being lost. Oxide based thermoelectric materials are many advantages for environment such as nontoxicity, thermal stability, and high oxidation resistance. Resonant X-ray scattering technique was applied for determine the charge transfer correlation in thermoelectric properties in the mixed valence oxide. The Ruddlesden-Popper structure with formula of La2−2xCa1+2xMn2O7 exhibits low thermal conductivity awing to the enhancement of phonon scattering at the interface of layer. The imprint thermoelectric modules made of oxide materials and thermoelectric power generator have been development and available for energy recovery from the waste water vapor that is discharged from the industrial waste incinerator.
The new allanite-group minerals vanadoallanite-(La) CaLaV3+AlFe2+Si3O12(OH), ferriakasakaite-(La) CaLaFe3+AlMn2+Si3O12(OH), and ferriandrosite-(La) MnLaFe3+AlMn2+Si3O12(OH) were found in the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan. Allanite-group is a member of rare-earth element (REE)-rich monoclinic epidote-supergroup minerals, with space group P21/m and the general formula A1A2M1M2M3(Si2O7)(SiO4)(O,F)(OH,O)(Z = 2). The relation between epidote- and allanite-groups was characterized by the coupled substitution: A2Ca2+ + M3Me3+ ↔ A2REE3+ + M3Me2+. The root name is defined by the dominant cations at the M3 and A1 sites. However, determination of the site occupancy at each site is not straightforward because of the complicated chemical compositions due to homovalent and coupled ionic substitutions and variable oxidation states of transition elements. This paper introduces the procedure for the determination of cation distributions among the cation sites in the allanite-group minerals, which led the finding of three new allanite-group minerals.
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