DYNAMIC RECRYSTALLIZATION DURING CREEP OF SINGLE-CRYSTALLINE HALITE - EXPERIMENTAL-STUDY

Single crystals of pure and impure halite have been dynamically recrystallized during compression creep at temperatures between 250o and 790oC and stresses between 1.5 and 120 bars. Recrystallization was found to occur by two different mechanisms at lower temperatures and stresses the new grains result from the rotation of subgrains without grain boundary migration (rotation recrystallization), and at higher temperatures and stresses the final texture results from the migration of the high-angle grain boundaries of the rotated subgrains. Migration recrystallization was shown to occur for critical stress and temperature conditions, allowing rapid grain boundary migration. A curve separates the two domains in the sigma, T plane and moves to higher temperatures and stresses for crystals of higher impurity content; for natural crystals, only rotation recrystallization can occur. In each recrystallization regime the recrystallized grain size is uniquely related to the applied stress, thus yielding two different geopiezometers, which should not be applied indiscriminantly to natural tectonites to determine lithospheric or mantle deviatoric stresses. The experimental results are interpreted by the Lucke et Stuwe theory for impurity-controlled grain boundary migration.-Authors