Reaction-induced volume change triggers brittle failure at eclogite facies conditions

Abstract

Metamorphic reactions can lead to important changes in rock strength and density. Eclogitization constitutes one of the most emblematic transformations in continental subduction zones, where conversion of lower crustal rocks into eclogite facies rocks correlates with the occurrence of seismogenic events. The relationship between eclogitization and seismicity has been highlighted in several studies, but the processes that trigger brittle failure remain highly debated. Indeed, whether the change in density (from ∼2850 kg.m−3 to ∼3300 kg.m−3) or the change in rheology can lead to embrittlement is still enigmatic. Here we show that eclogitization-induced volume change occurring out of equilibrium can, by itself, generate sufficient shear stress to fail the rocks at high-pressure conditions. Intermediate-depth earthquakes in continental subduction zones could therefore be explained by volume changes, even without considering rheological modifications induced by mineral reactions. Our results also indicate that interplay between negative volume change and frictional plastic yielding can enhance the propagation of the eclogitization process by a runaway mechanism as long as the reaction is not limited by the lack of reactants.