High-temperature deformation of clinopyroxene and clinopyroxene-plagioclase aggregates

I have performed an experimental study to determine the high temperature creep behavior of clinopyroxene and clinopyroxene-plagioclase aggregates under dry deformation conditions. Sleaford Bay diopsidite and Adirondack anorthosite powders with homogeneous grain size distributions were mixed at various volume fractions and hot-pressed at 300 MPa and ;The natural clinopyroxenes deformed by dislocation creep while a transition from diffusional to dislocation creep accommodated by grain boundary sliding was observed in the hot-pressed samples. No clear dependence of creep behavior on oxygen fugacity was discerned. However, samples that were not dried prior to deformation were weaker by about an order of magnitude. The determination of a dislocation creep flow law for dry clinopyroxene yielded a stress exponent of ;Existing theoretical models that provide constraints on the strength of a mixed-phase aggregate from the end-member flow laws were tested using experimental creep data. Strength envelopes plots of differential stress versus depth for crustal settings on Earth and on Venus were extrapolated from the experimentally determined rheologies. The results suggest that in a continental crust setting, deformation in a dry lower crust will occur only through episodic hydration or strain localization in ductile shear zones.