Program > Browse abstracts by speaker > Silva Souza Danielle

Deep-focus earthquakes offer insights into Earth's mantle and support plate tectonics. Since high pressures and temperatures hinder brittle failure, their mechanisms differ from shallow quakes. Dehydration embrittlement, dominant at 100–350 km depth, involves fluid release from minerals like serpentine, increasing pore pressure and triggering failure. However, serpentine dehydration decreases pressure, requiring low-permeability layers to trap fluids for seismic failure. Experiments also show that serpentine dehydration often leads to ductile weakening without acoustic emissions.

To better understand the micro-mechanisms of serpentinite dehydration, particularly at its incipient stage, we conducted high-pressure, high-temperature experiments under isostatic and non-isostatic conditions. Serpentinite cores (2 mm diameter) were mounted in cubic assemblies (12 mm edge) and deformed in a 6-Ram multi-anvil press at the Bayerisches Geoinstitute. Experiments at 5 GPa reached 15% strain at strain rates of 1.67×10⁻⁴ s⁻¹ to 2.91×10⁻⁶ s⁻¹. Temperature was constant: isostatic experiments at 550 °C and 784 °C, non-isostatic at ~650 °C.

Results show that isostatic dehydration of antigorite at 5 GPa starts at ~550 °C and completes at ~800 °C. Between 550–650 °C, incipient dehydration is marked by olivine and phyllosilicate growth at antigorite grain boundaries, without failure microstructures. Pores appear between olivine and enstatite in fully dehydrated serpentine. Under deformation, olivine and phyllosilicate cluster into microscopic shear bands oblique to stress. These results indicate that serpentinite dehydration and failure are complex. Pre-existing microstructural heterogeneities may influence nucleation of olivine and phyllosilicates. Pore overpressure may not be the sole failure mechanism. Further work is needed to assess the role of dehydration product strength in localized failure.