High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

:, ~ varied most significantly with temperature, ranging from limited slip and twinning at 400°C, limited recrystalliza,t ,tion at 500°C, widespread recrystallization at 600 and 7QOoC, to grain growth at 800-900°C. Variations in ! confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. : Aragonite grew in 10-6-10-7 S-l strain rate tests conducted for 18-524 h at confining pressures of 1.7-2.0 GPa and temperatures of 5QO-{jQOoC. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on calcite grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 4QO°C, 2.0 GPa and 10-4 S-l strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10-7 S-l, a temperature of~C and a pressure of2.0 GPa. At 500°C, porphyroblastic l00-200.um aragonite crystals grew at a rate faster than 8 x 10-10 m S-l. At ~C, the growth of aragonite neoblasts was slower, -6 x 10-11 m S-l, and formed 'glove-and-finger' cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features.