Program > Browse abstracts by speaker > Pongrac Petar

Deformation experiments under controlled conditions have become an essential method for studying the rheology of rocks. The data obtained by deformation experiments are crucial for developing deformation maps and mechanical stability models for rocks and minerals that control the ultimate crustal strength. While selecting appropriate experimental conditions allows for extrapolation to natural settings, the geometry of the experimental setup directly influences the mode of deformation. In coaxial geometrical setups, mechanical data closely correlate with pure shear in most of the deformation apparatuses. However, coupling mechanical data with simple shear deformation using classic 45°-sample-slices geometries often yields considerably lower success for some materials. This limitation stems partly from insufficient friction between the forcing blocks and the sample, often resulting in slipping of the forcing block across the sample at stresses lower than necessary flow stresses. Other technical challenges include the increased risk of forcing blocks fracturing at thinner corners or enhanced formation of Mode-I cracks in initially incoherent (powdered) samples, when the tensile forces exceed friction. In this study, we performed deformation tests in the Griggs-type solid-medium apparatus, using an innovative sample-to-forcing-block geometry. The aim of the tests was to produce larger shear zones that could provide better microstructural overviews and more effective coupling of mechanical data with shear microstructures. First experimental data on natural quartzite samples highlighted the importance of the strain rate, where higher strain rates promote mylonitization over formation of a shear zone. This finding may allowed for identification of a transitional strain rate between the mylonitization and viscous/ductile shearing, offering additional rheological insights into the tested material.