Pianea, Claudio Delle Burlini, Luigi Grobéty, Bernard 2007-01-13 We investigated the mechanical behaviour and microstructural evolution of a dolomite marble from Mt. Frerone (Adamello, N-Italy) during decarbonation to calcite and periclase in torsion experiments. Tests were performed in a Paterson gas-medium apparatus on cylindrical samples of 10 mm diameter and 10 mm length. Experiments were conducted at 800 °C, 300 MPa confining pressure under both vented and non-vented conditions, up to a maximum bulk shear strain of about <i>γ</i> = 1.8, at different strain rates (3 × 10^{− 5} s^{− 1} up to 3 × 10^{− 4} s^{− 1}). Under hydrostatic conditions the nominal equilibrium P(CO₂) should be around 100 MPa, but in the vented experiments the CO₂ was free to escape, causing the breakdown of dolomite.During the decomposition, deformation was systematically localized at the ends of the specimens, near the porous spacers into a fine-grained mixture of calcite and periclase.Due to the low permeability of the marble, pore fluid could not escape from the central part of the sample building up CO₂ pressure which suppressed the decarbonation reaction. The fluid pressure embrittled the material and caused the development of en-echelon tension fractures, inclined opposite to the sense of shear.We conclude that decarbonation produced a weak polyphase matrix composed of submicron sized reaction products. Such a small grain size induced strain localization which was probably promoted by a switch from grain-size insensitive to grain-size sensitive deformation mechanism. application/pdf https://folia.unifr.ch/global/documents/300682 https://folia.unifr.ch/documents/300682/files/grobety_ris.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1016/j.epsl.2007.01.012 info:eu-repo/semantics/openAccess License undefined Earth and Planetary Science Letters. - 2007, vol. 256, no. 1-2, p. 36-46 shear zone reaction softening strain localization deformation mechanism dolomite decarbonation info:eu-repo/classification/udc/55/56 Reaction-induced strain localization: torsion experiments on dolomite http://purl.org/coar/resource_type/c_6501