Corundum and zincian spinel were found in a drill core of thermally metamorphosed rock at 2843 m in depth of the deep research well, WD-1, in the Kakkonda geothermal area, northeastern Japan. Corundum is surrounded by K-feldspar, and the occurrence suggests that corundum was formed by the decomposition of muscovite. Andalusite occurs in the same sample, without sillimanite. The petrography and previous works on phase relations between aluminous minerals suggest that corundum was formed at 600-700°C and 100 MPa at the peak of contact metamorphism. The ZnO content of spinel exceed 20 wt.%, and has a gahnitic composition. Zincian spinel is surrounded by K-feldspar as well as corundum, and it is assumed that spinel was formed by a similar reaction to the case of corundum. Two-phase vapor-rich and liquid-rich fluid inclusions occur in corundum, and they probably represent fluids formed at the metamorphic stage. A laser Raman microprobe analysis detected the presence of CO2, H2S and N2 in the fluid inclusions. The occurrence and analyses of the fluid inclusions indicate that the fluid produced during the thermal metamorphism at Kakkonda was low-salinity with gases and water.
Considering textures, chemical analyses and mineral assemblages of the Sambagawa metamorphic rocks, some insight to the growth stage of albite-porphyroblasts was obtained. There are two types of titanite in the pelitic schists studied: 1) minute grains (up to 0.35 mm in length) in the matrix and 2) euhedral coarse grains (up to 0.6 mm in long axis) included in albite porphyroblasts. The minute titanite formed during the prograde stage, because it is a member of the main foliation-forming minerals. It suggests that albite-porphyroblasts crystallized after the titanite had formed. The textures and chemical compositions of garnet suggest that its growth finished near the thermal climax of metamorphism. The euhedral titanites with inclusions of euhedral garnet formed at the culminating stage of metamorphic temperature, therfore the albite porphyroblasts including the euhedral titanites formed during a retrograde stage.
Crystallization experiments were carried out on powdered glasses having the composition Di23Es53An24 at temperatures of 1250, 1275, 1300, 1325 and 1350°C. The resulting crystalline phases are clinopyroxenes and a trace of unknown oxide crystals. The pyroxenes grown at 1325 and 1350°C are stoichiometric clinopyroxenes rich in Al and Fe. Those grown at the lower three temperatures are non-stoichiometric clinopyroxenes which are extremely rich in Al and contain only negligibly small amounts of Mg. Non-stoichiometric clinopyroxenes are shown not to be characteristic products of high pressure conditions.
Thermal expansion behaviors in a- and c-axes in quartz are formulated in terms of the rotational motions of the corner-linked rigid SiO4 units around the <100>hex and the expansion of the tetrahedral units. Collective transfer motions of atoms between the double-wells of potential energies, observed in a previous molecular dynamics study, are the major component of the rotational motions in the β-phase and at higher temperatures in the α-phase. The thermal expansions in the α-phase arise mainly from the decrease of effective deviations from the β-orientation during the collective transfer motions. It is greater than the bond-length change which contribute to the total expansion. In the β-phase, the increase of the amplitudes of the transfer motions works to cancel or overwhelms the positive effects due to the expansions of the constituting units and the increase of the transfer frequency. For this reason, the temperature variation of cell dimensions of β-phase is very small or even negative. The slight thermal expansions, experimentally observed in the range 20 to 100 K above the transition temperature, are related to the appearance of transitional states.