Mechanisms of dynamic recrystallization in naturally deformed dolomite inferred from EBSP analyses

In order to investigate the mechanisms of dynamic recrystallization in dolomite, single grain orientation measurements on a mantled porphyroclast have been carried out by means of electron back-scattered patterns (EBSPs). The local orientations in the grain fabric were analysed to establish meaningful orientation families. In addition to a twinned grain, the porphyroclast consists of two domains, each with a specific orientation pattern. Both domains are polygonized by subgrain rotation, which gives great- and small-circle dispersion patterns of the crystal orientation data in the pole figures. However, even the simple and well-defined dispersion patterns for which one can assume a single slip system are not consistent with any of the theoretical dispersion patterns of the known slip systems. Additional mechanisms like rigid body rotation, nucleation and/or combinations of different slip systems are the likely explanation. No definitive orientation relationship has been found between the porphyroclast and the mantle. The lack of such a relationship, together with the shape of the grain boundary, point to grain boundary migration. The texture of the mantle agrees with the global texture of the sample, indicating that mechanisms of crystal plasticity were active during flow around the clast. The results demonstrate the potential of EBSP data for the deduction of active mechanisms, but a proper interpretation requires a better theoretical foundation. This could be achieved by modelling dispersion patterns for different mechanisms and different combinations, and by including orientation correlations. (C) 1999 Elsevier Science B.V. All rights reserved.