A metapelite preserving prograde and retrograde zoning in garnet from Mefjell, southern Sør Rondane Mountains (SRM), East Antarctica is described in detail and U-Th-Pb geochronological data are presented. Garnet, sillimanite, staurolite and biotite are in textural equilibrium in the matrix. The garnet shows three distinct compositional zones comprising core, mantle and rim. From core to the mantle, the spessartine content represents a bell-shaped profile. From mantle to the rim, spessartine content increases and pyrope decreases. Kyanite is present as tiny inclusions in the garnet core. The core also contains aggregates of sillimanite with radial cracks around them, interpreted to have resulted from the inversion of kyanite. The prograde P-T path recorded in the garnet is heating to approximately 700°C at 5.6 kbar with a slight increase in pressure. U-Th-Pb dating of monazite grains yields a large range of age distribution between 700 and 540 Ma. The inferred prograde metamorphism of the metapelite sample in this study might be related to subduction and/or tectonic loading explained by a collision tectonic model of the SRM .
Graphite-bearing polycrystalline olivine and polycrystalline clinopyroxene with submicron to micron grain size were successfully sintered from a single crystal of naturally occurring olivine ). The milled powders of both these crystals were sintered under argon gas flow at temperatures ranging from 1130 to 1350 °C for 2 h. As the sintering temperature increased, the average grain size of olivine increased from 0.2 to 1.4 µm and that of clinopyroxene increased from 0.1 to 2.4 µm. The porosity of sintered samples remained at an almost-constant volume of 2-5% for olivine and 3-4% for clinopyroxene. The samples sintered from powders milled with ethanol exhibited trace amount of graphite, identified via Raman spectroscopy analysis. As the sintering temperature increased, the intensity of the graphite Raman peak decreased, compared with both olivine and clinopyroxene peaks. The carbon content of the sintered samples was estimated to be a few hundred ppm. The in-plane size (L a ) of graphite in the sintered olivine was estimated to be <15 nm. Our experiments demonstrate new possibilities for preparing graphite-bearing silicatemantle mineral rocks, and this method might be useful in understanding the influence of the physical properties of graphite on grain-size-sensitive rheology or the seismic velocity of the Earth's mantle.
The sintering behavior of diopside nano-sized powder was studied. We successfully fabricated diopside nanosized powders from naturally occurring diopside single crystal (Ca 0.92 Na 0.07 Mn 0.01 Mg 0.93 Fe 0.01 Al 0.06 Si 2 O 6 ). Diopside polycrystalline is sintered from powders with an average particle size of <100 nm under argon flow at temperatures ranging from 1130-1280°C for 0.5-20 h. The average grain size increased with increasing sintering time and sintering temperature while porosity remained nearly constant value of 3-4 vol%. The experimental data of grain growth at 1180°C can be fit for the following equation G 3 − G 0 3 = kt, where G is the grain size after time t, G 0 is the grain size at t = 0, and k is a rate constant.
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