Abstract
Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is thus crucial to understanding how water impacts Earth’s geodynamics. Here we demonstrate that ductile flow exerts a dynamic control on water-rich fluid circulation in mantle shear zones. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. We also give evidence of cracking induced by fluid pressure where the highest amount of water is expected. These results emphasize long-term fluid pumping attributed to creep cavitation and associated phase nucleation during grain size reduction. Considering the ubiquitous process of grain size reduction during strain localization, our findings shed light on multiple fluid reservoirs in the crust and mantle.
Highlights
Water plays an important role in geological processes
Fluid migration is observed where mineral aggregates dominantly deform by grain-size-sensitive (GSS) creep, commonly including a component of grain boundary sliding (GBS)[13,14,15]
Providing evidence of long-term water pumping during shear strain localization in upper mantle peridotites, our findings strongly suggest that water converges through the opening of micro-cavities coupled with phase nucleation processes
Summary
Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is crucial to understanding how water impacts Earth’s geodynamics. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. When GBS cannot be fully compensated by diffusive or plastic processes, some micro-cavities open and close in a continuous process because of local dilatancies, giving rise to creep cavitation[16,17,18] This might result in fluid pumping— including water—towards the shear zone centre. Providing evidence of long-term water pumping during shear strain localization in upper mantle peridotites, our findings strongly suggest that water converges through the opening of micro-cavities coupled with phase nucleation processes
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