New paper on the causes of brittle-to-viscous transition in crustal rocks

Our new paper on “Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐viscous Flow of Crustal Rocks:Experiments on Quartz – Feldspar Aggregatesbased on experiments from Saleh al Nasser’s second generals project is just published in Journal of Geophysical Research: Solid Earth. Congrats to Saleh!

Fault slip occurs over a vast range of rates and depths in nature. Earthquakes are generated by this fault motion and therefore we need to understand the mechanical properties of fault rocks. To study the mechanism or rock failure at pressures and temperatures corresponding to about 30 km depth, we deformed rocks in the laboratory and analyzed their mechanical behavior. We further studied the samples after deformation using electron microscopy to identify features that are responsible for the measured mechanical behavior. We find that failure occurs due the development of nano‐crystalline to amorphous zones that interconnect upon highest stress and cause sample weakening. Such zones represent a failure mechanism in its own right, distinct from brittle cracks developing at lower pressures and temperatures or crystal‐plastic flow at higher pressures and temperatures. The development of these zones introduces a fluid‐like behavior in small parts of the sample which results in a mixed mechanical behavior: parts of the sample are solid and break and parts of the sample are fluid and flow. This mechanical behavior and its connection to the earthquake cycle is currently only poorly understood and hence is generally not incorporated in models of fault slip