Serpentinites in subduction zones – fluids transport

Subduction zones are the setting of intense fluids/rock interactions due to seawater percolation at the initiation of the subduction and continuous fluid trap and release during the multiple hydration/dehydration reactions occurring during slab burial. We focus on the behavior of serpentines (hydrous phyllosilicates) as their presence affects the rheology at the interface of the slab, the path of the percolating fluids and geochemical cycles of elements such as halogens. Within this scope, we investigate experimentally the rheological behavior of serpentinites under subduction conditions (P,T, water saturation) to better constrain deformation mechanisms of these phases within their stability fields or during dehydration and how they affect the decoupling between the downgoing slab and the mantle wedge. We also provide insights on the paths that can be taken by the fluids expelled from the dehydrating slab. During hydration/dehydration reactions, chemical elements can be mobilized in the fluids and constraining the solubility and partitioning of elements such as halogens during these episodes can provide informations on the contribution of serpentinite dehydration to mantle metasomatism, arc magmatism, and deep geochemical cycles. The transfer of redox during serpentinite dehydration is another key issue to understand chemical transfers towards overlying lithologies and eventually towards the mantle wedge. Strong redox gradients are expected in the heterogeneously hydrated lithospheric mantle within the subducting slab, which may level out with increasing metamorphic grade. Speciation of redox-sensitive elements such as Fe, S, C under subduction zone conditions is of primary importance to model the potential of serpentinites to transfer their RedOx.

Contacts:
– A-L. Auzende
– S. Schwartz
– S. Guillot
– B. Malvoisin
– F. Brunet