Minerals in meteorites give constraints on the formation history of not only meteorites, but the solar system. Here I introduce some characteristic minerals in meteorites. Enstatite chondrites contain abundant unusual sulfide and metallic minerals that were formed under highly reducing conditions. Refractory inclusions were formed in the earliest stage of the solar system. They typically contain Ca-Al-rich minerals. A new mineral, kushiroite, is one of such minerals, and formed under rapid crystallization conditions. Ultrahigh-pressure minerals are commonly encountered both in chondrites and differentiated meteorites, indicative of pervasive impact processes in the early solar system. An eclogitic mineral assemblage encountered in a CR chondrite suggests the possibility that asteroids were primarily larger than previously estimated.
Japan Association of Mineralogical Sciences Award, No. 12
Recent progress in theoretical mineral physics based on the ab initio quantum mechanical computation method has been dramatic in conjunction with the advancement of computer technologies. It is now possible to predict stability and several physical properties of complex minerals quantitatively not only at high pressures but also at high temperatures with uncertainties that are comparable to or even smaller than those attached in experimental data. Our present challenges include calculations of high-P,T elasticity to constrain the lower mantle mineralogy, transport properties such as lattice thermal conductivity, and further extensions to terapascal phase equilibria of Earth materials for studying planetary interiors.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 13
Maximum friction coefficients of common minerals can be characterized by empirical Byerlee's rule, however, some important fault-forming minerals such as mica and clay minerals have ultimately low friction coefficient. The layered structure and high affinity to water should be related to the low friction coefficient. We have investigated the interlayer bonding energy, adsorption energy of water molecules, and physical properties of adsorbed water by using molecular simulations, surface x-ray scattering, and surface forces measurements. These results were used for interpreting the weak friction coefficients of layered minerals.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 14
Granitic rocks (sensu lato) are major constituents of the upper continental crust. Recent reviews that provide estimates of the composition of continental crust have established that the average composition of the upper continental crust is granodioritic. Although the oceanic arcs are regarded as a site producing continental crust material in an oceanic setting, intermediate to felsic igneous rocks occurring in the modern oceanic arcs are dominantly tonalitic to trondhjemitic in composition and have lower incompatible element contents than the average upper continental crust. Therefore, the juvenile oceanic arcs require additional processes to transform into the mature continental crust enriched in incompatible elements. Neogene granitoid plutons are widely exposed in the Izu Collision Zone in central Japan, where the northern tip of the Izu-Bonin arc (juvenile oceanic arc) has been colliding with the Honshu arc (mature island arc) since middle Miocene. The plutons in this area are composed of various types of granitoid ranging from tonalite to trondhjemite, granodiorite, monzogranite and granite (sensu stricto). Three main granitoid plutons are distributed in this area: Tanzawa plutonic complex, Kofu granitic complex, and Kaikomagatake pluton. Tanzawa plutonic complex is characterized by low concentration of incompatible elements and has chemical characteristics of juvenile oceanic arcs. In contrast, Kaikomagatake pluton and Kofu granitic complex have chemical compositions comparable to the average upper continental crust. The petrogenetic models of the Izu Collision Zone granitoid plutons collectively suggest that collision with another mature arc/continent, hybrid lower crust formation and subsequent hybrid source anatexis are required for juvenile oceanic arcs to produce granitoid magmas with compositions comparable to the average upper continental crust. The Izu Collision Zone granitoid plutons provide an exceptional example of the collision-induced transformation of a juvenile oceanic arc into the mature continental crust.
Japan Association of Mineralogical Sciences Award for Young Scientists, No. 15
Chemical weathering (dissolution) rate of rhyolites from Kozushima over 52000 years of weathering determined by a field-based study was lower than those obtained by a laboratory dissolution experiment by a factor of 12-1000. In order to perform a reactive transport modeling to bridge the field and laboratory rates, detailed characterizations of the reaction and transport properties of the rhyolite were conducted. Hydraulic conductivity and diffusion coefficient were significantly affected by the degree at which pores were saturated with water, whereas reactive surface area was relatively unaffected. The modeling revealed the followings: (1) Owing to temporal decrease of dissolution rate associated with a change of solid surface reactivity, whole rock dissolution rate decreased with time and approached to the ‘field rate’ in relatively early stage of weathering; (2) Saturation index (proximity to chemical equilibrium) was large at the initial stage of weathering but became smaller as weathering proceeded.
Japan Association of Mineralogical Sciences Award for Applied Mineralogy, No. 7
Three-dimensional visualization system VESTA and maximum-entropy method (MEM) analyses program Dysnomia have been developed for mineralogical and crystallographic studies. VESTA seamlessly visualizes multiple numbers of crystal, volumetric and morphology data in a same graphic window. It can calculate and output a variety of crystallographic information. Dysnomia is much faster than its predecessor PRIMA, and has several new features including a brand-new L-BFGS algorithm and a new type of constraints. Dysnomia is virtually integrated with a pattern fitting system RIETAN-FP for the MEM-based pattern fitting. These programs have been widely used in thousands of researches not limited to mineralogy but also in a variety of areas including chemistry, materials science, bioscience, electronic state calculations and so on.
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April 11, 2015
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