Brittle failure at high-pressure conditions: the key role of reactioninducedvolume changes

Abstract

International audienceMetamorphic reactions can lead to drastic changes in rocks mechanical properties. Indeed, duringsuch transformations, the nucleation of new phases with different strength, grain size and/ordensity compared to the primary phases is enhanced, and transient processes due to the ongoingreaction are then activated.Eclogitization of lower crustal rocks during continental subduction constitutes an emblematictransformation illustrating these processes. In such tectonic context, it has been shown thateclogitization seems to be closely associated with the occurrence of seismogenic events. However,the mechanisms that trigger brittle failure in such high pressure environments remain highlydebated. Indeed, whether the change in density or the change in rheology can lead toembrittlement is still enigmatic.By using 2D compressible mechanical numerical models we studied the impact of the strongnegative volume change of the eclogitization reaction on the rocks rheological behaviour. We showthat eclogitization-induced density change occurring out of equilibrium can, by itself, generatessufficient shear stress to fail the rocks at high-pressure conditions.Rupture initiation at depth in continental subduction zones could therefore be explained byvolume changes, even without considering the modifications of the rheological properties inducedby the transformation. Our results also indicate that the negative volume change associated withbrittle failure can enhance the propagation of the eclogitization process by a runaway mechanismas long as the reaction is not limited by the lack of reactants.Powered b