Experimental Recrystallization of Dolomite and Comparison of Preferred Orientations of Calcite and Dolomite in Deformed Rocks

Specimens of Dover Plains dolomite, Knox dolomite, and Solenhofen limestone were recrystallized under stress and by annealing (after previous cold working) to find the preferred orientations of c-axes in recrystallized grains. The experiments were performed in a constant strain-rate apparatus. The recrystallization took place at a temperature of 1,000° C and a confining pressure of 15 kbar. The preferred orientations of c-axes in a marble and a dolomite naturally deformed under similar conditions were also measured and compared. In dolomite specimens recrystallized under stress, the new grains have their c-axes at small angles to the maximum principal compressive stress axis, the same as that previously found in calcite. The information about preferred orientation of c-axes in specimens recrystallized by annealing is inconclusive. In specimens of Dover Plains dolomite recrystallized under stress, a weak tendency was also observed for the c-axes of new grains to be inclined at angles of 30°-60° to the c-axes of the grains in which they grow. The textures of the deformed specimens show that the mechanism of recrystallization involves nucleation of new grains and their growth at the expense of old grains. The similarity between the preferred orientations of c-axes in experimentally and naturally recrystallized calcite and dolomite suggests that slip and twinning mechanisms do not contribute to the development of the preferred orientations and that the mechanism of development of preferred orientatation in nature is similar to that operative in the experiments.