Subhajit Ghosh (Université d'Orléans, ISTO) donnera, dans l'amphitéâtre de l'OSUC (E018), un séminaire intitulé : Synthesis and diffusion creep of dry fine-grained diopside.
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Résumé :
Diopside is one of the major rock-forming minerals in the lower crust and upper mantle. In comparison to other dominant mineral phases like olivine, plagioclase, or enstatite (orthopyroxene), much less attention has been given to explore the grain-size-sensitive rheology of the diopside. To meet this gap in knowledge, we have carried out a high-temperature creep test of synthetic, highly dense (99.9%), fine-grained (≤1μm) pure (96 vol %) diopside (CaMgSi2O4) aggregates with either 4 or 10 vol% of forsterite and 10 vol% of anorthite. We are able to synthesize such high-quality aggregates by using the spark plasma sintering (SPS) technique for the first time. We changed the average grain size in the diopside aggregate from 0.43 to 4.07 μm by changing the proportion of forsterite to reveal the grain size sensitivity of the creep rate. Mechanical data are obtained at a stepped load (i.e., applying multiple loads) for a temperature range of 1100° to 1250°C. Creep results indicate that the aggregate deforms by diffusion creep mechanism at stress below 100 MPa. The observed strain rates are best explained by stress and grain size exponent values of 1 and 2, respectively, and activation energy of ~720 kJ/mol, all of which indicate lattice diffusion creep.