Rheology of dolomite : Large strain torsion experiments and natural examples

A set of large strain deformation experiments is presented to better constrain the conditions in which grain size sensitive mechanisms are dominant during deformation of dolomite. Experiments were made on an internally heated gas apparatus equipped with torsion facilities. The rheological data set was fitted to an empirical flow law that allows extrapolation to natural conditions. Fabric evolution with increasing strain was investigated by means of optical and electron microscopy (electron backscattered diffraction). Extrapolation of the laboratory data to geologically relevant conditions of temperature and strain rate was tested on a natural case of a deformed dolomite–calcite sequence across the contact aureole of the Adamello pluton (southern Alps, Italy). Both the geological data and the laboratory measurements indicate that at high temperature an inversion of the relative strength occurs between the two carbonates, with calcite being the weak phase at low temperature and dolomite being the weak phase at high temperature.