MIT, USA

Natural hazards events such as Earthquakes or volcanic eruptions involve activation of coupled thermo-hydro-chemo-mechanical processes in rocks. A workshop sponsored by the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV), the French Centre National de Recherche Scientifique (CNRS) and Exon-Mobil, was held in Erice, Italy, to explore how rock physics experiments and models can help understand natural hazards mechanisms, and, to foster cross-disciplinary collaborations.

We performed experiments to determine melt concentration and strain distributions around basalt dykes in a San Carlos olivine matrix containing 10 wt% MORB. Undrained triaxial compression tests were conducted at 1473 K and confining pressure of 300MPa, at constant stresses (80-160 MPa) and constant strain rates ranging from 5x10-5s-1 to 3x10-4s-1, respectively. Melt distribution in the dyke/matrix interface was determined by image analysis and chemical profiles. Melt migration appears to be enhanced by porosity of the microstructure and by the loading conditions. The presence of the dyke does not influence the bulk strength of the sample. Highest melt concentrations, and presumably, the highest stress concentrations, are found at the tip of the dyke. The matrix deformation appears to be controlled by granular flow, but dilatancy occurs near the tip of the dyke, indicating coupled MORB transport and granular flow.

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We investigated the mechanics of basalt dyke emplacement during laboratory deformation experiments at up to 300 MPa confining pressure and temperatures up to 1200 °C. Experiments have been conducted on two-phase samples of a basalt (MORB) dyke and a matrix of 90% San Carlos Olivine plus 10% MORB. No migration of MORB is observed when samples have been hot isostatically pressed. Conversely, significant diffusion of basalt into the matrix is found when a deviatoric stress is applied. Creep (80-160 MPa) and strain-rate experiments (from 3 x 10 -4 to 5 × 10 -5 s -1) induced melt propagation up to 50% of the initial dyke length/width ratio. The kinematics of deformation are essentially plastic and show a strong dependence on the load applied and the dyke geometry. Local pressure drops, due to dilatancy, are suspected to have enhanced melt migration.