Program > Browse abstracts by speaker > Précigout Jacques

Quantifying rock rheology is fundamental to understanding and modelling the lithosphere's dynamics. However, although most rocks of the lithosphere deform at high (> 0.5 GPa) – to very high (> 3 GPa) – pressure over geodynamic events, available mechanical laws have been produced at low pressure (0.3 GPa) using gas-medium deformation apparatuses. To explore rock rheology at higher pressure – typically above 1 GPa – a solid-medium apparatus is required, which involves substantial friction-related stress overestimations while the sample is deforming within the confining medium. Here we provide a series of deformation experiments that aim to quantify such a stress overestimation in the new generation Griggs-type apparatus. The main goal is to better estimate how the friction “baseline” evolves with pressure, alongside defining the starting point of the strain-stress curve more accurately. To do so, we performed general shear experiments of Carrara marble at a confining pressure ranging from 0.3 to 1.8 GPa, while systematically applying a temperature of 650 °C and a displacement rate of 10-4 mm.s-1. Using relaxation steps to highlight the friction baseline in a ‘force-displacement' plot, we document a slope that increases exponentially with pressure, from 0.2° to 2.7°. Moreover, none of the highlighted baselines crosses the conventional hit-point, which is the commonly used reference to define the “zero” point of strain-stress curves in the Griggs-type apparatus. Such a mismatch involves additional stress over- (or under-) estimations that we propose to correct by using a new “hit-point” at the intersection between the baseline and mechanical curve. Thanks to the latter and applying a “baseline” correction, we document stress measurements equivalent to the ones documented for Carrara marble using the gas-medium Paterson press.