Abstract
Fluid migration may be associated to several processes involved in ore deposit or the formation of forarc volcanoes that have explosive eruption. Fluid migration may also be also associated to change of rheological behavior of dehydrating serpentinite responsible of earthquakes triggering in subduction zones. However, the coupling between mechanical properties of dehydrating serpentinites, fluid migration and kinetics of dehydration reactions remains poorly constrained. This thesis provides new constraints on the link between these properties by combining a study on natural dehydrated serpentinites and experimentally dehydrated serpentinite and by evaluating the impact of metamorphic compaction, which drives fluids motion, on dehydrated serpentinites.Both natural and experimental dehydration of serpentinites produce metaperidotites that shows granular olivines or olivines elongated in the foliation plane. Both types of olivine have strong crystal preferred orientation and are correlated to antigorite as it is visible with [100] axes of granular olivines and [010] axes of elongated olivines parallel to [001] axes of antigorite. Markers of deformation were observed in foliated metaperidotites.Both naturally and experimentally dehydrated serpentinites shows fractures in which olivines have texture of rapid growth. Olivines from fractures in naturally dehydrated samples have strong crystal preferred orientation correlated to the plane of the fracturesPartially dehydrated serpentinite from Cerro del Almirez massif shows minor amount of clinoenstatite lamellae in orthoenstatite grains randomly oriented that may have been formed by martensitic transformation (mechanical twinning) of orthoenstatite. Completely dehydrated serpentinites at two meters of distance have higher amount of clinoenstatite that have two different orientations. Stress direction calculated is randomly oriented in partially dehydrated serpentinite and strongly oriented in completely dehydrated serpentinite.Results are consistent and the interpretation proposed in this thesis is that fluid migration is recorded by textures of products of dehydration reactions. Slow and pervasive fluid migration produces granular olivines with crystal preferred orientation correlated to crystal preferred orientation of antigorite by topotaxial relationships, which are fixed arrangements of crystallographic axes between two minerals due to oriented growth. Focused fluid migration change mechanisms of grain growth resulting in oriented growth of olivines in foliation plane or in plane of veins because of fluid pressure gradient. Fluid extraction lead to metamorphic compaction, which expulse residual fluids from the pores and triggered non-hydrostatic stress field. This non-hydrostatic stress field is responsible of deformation and the martensitic transformation of orthoenstatite to clinoenstatite.