Faculté des sciences

Reaction-induced strain localization: torsion experiments on dolomite

Pianea, Claudio Delle ; Burlini, Luigi ; Grobéty, Bernard

In: Earth and Planetary Science Letters, 2007, vol. 256, no. 1-2, p. 36-46

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... Plus

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    Summary
    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 γ = 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.