P. Goncalves associate professor at the Chrono-Environnement Lab of the University of Bourgogne Franche-Comté will give a talk titled 'Rock record of deep Slow Earthquakes in continental collision settings: The Suretta nappe and Tauern Window examples (Alps)'
Since the discovery of Non-Volcanic Tremors (NVT) and Low Frequency Earthquakes (LFE) coupled with slow slip events (SSE) at the beginning of the 21st century, the question of the source mechanism of this seismicity in the ductile realm has arisen. The approach followed to understand the processes responsible for deep slow EQ includes rock physics experiments, numerical modeling and finally the quest of geological records. In all cases, they assume that slow EQ are mostly subduction related. Therefore experiments, models and field analog studies were designed to match this unique geodynamic setting. Here, we explore the possibility that slow EQs may also be produced in continental collision settings by studying exhumed deformed crustal nappes from the Alps (Tauern windown and Suretta nappe).
Field observations, petrological and microtextural analysis and modeling performed on exhumed shear zones developed in undeformed late variscan magmatic rocks suggest that burial of continental units is characterized by concomitant frictional and viscous deformation in the ductile realm at temperature above 450° for a depth range between 18 and 25 km of depth. Strain is partitioned, at all scales, between a network of anastomosed weak and high strain ductile shear zones bounding high strength and low strain domains. This mixed rheology characterized by strong viscosity and strain rate contrasts is strongly enhanced by syn-kinematic metasomatic reactions localized in fractures and shear zones. Although the kinetic of these mineral transformations is difficult to quantify, we speculate that this is a short-lived and transient process with a duration in the same order of magnitude as slow earthquakes.
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