Abstract Coseismic fracturing in the strong, dry, and metastable plagioclase‐rich lower‐crust is an effective mechanism for creating pathways for fluids to infiltrate the host rock, kick‐start metamorphism, and potentially lead to rheological weakening. In this study, we have characterized the damage zone flanking a lower‐crustal pseudotachylyte (solidified frictional melt produced during seismic slip) within an anorthosite to determine the mechanisms of incipient aqueous fluid infiltration and redistribution in a…

Abstract. The transition from strong to weak mechanical behaviour in the Earth's continental middle crust is always caused by an initiation of viscous deformation. Microstructural evidence from field examples indicates that viscously deforming polymineralic shear zones represent the weakest zones in the crust and may dominate mid-crustal rheology. The results of recent experiments (as in companion paper 1) demonstrate that the observed weak behaviour is due to the activation of dissolution-precipitation creep (DPC…

Abstract. Dissolution-precipitation creep (DPC) is considered as one of the main processes accommodating localized strain in polymineralic shear zones of the Earth’s crust. Extensive field evidence for DPC in natural shear zones supports the importance of this process. The spatio-temporal evolution and the level of compositional heterogeneity that facilitate the nucleation of such polymineralic shear zones remain poorly understood. A series of new experiments was conducted on a granitoid fine-grained ultramylonite…

Abstract Understanding the interplay of various energy sinks during seismic fault slip is essential for advancing earthquake physics and improving hazard assessment. However, quantifying the energy consumed by major dissipative processes remains a challenge. In this study, we investigate energy partitioning during laboratory earthquakes (“lab‐quakes”) by performing general shear stick‐slip experiments on synthetic granitic cataclasites at elevated confining pressure. Using ultrasound, microstructural, and novel ma…

The strength and deformation behaviour of the Earth are necessary parameters to model and fundamentally understand crustal scale deformation. In the case of the Earth’s continental middle crust, so far, most models use extrapolated physical parameters from monomineralic deformation experiments, assuming pure quartz to represent the weakest rheological phase at mid-crustal conditions. This is an oversimplification as the Earth’s continental middle crust mostly consists of polymineralic granitoid…