Program > Browse abstracts by speaker > Sanchez-Valle Carmen

High pressure slab-derived aqueous fluids (aqueous fluid, hydrous melt or supercritical fluid?) are major vectors for mass transfer and element recycling in subduction zones. However, the poor understanding of the atomic-scale mechanims that controls the mobilization and transport of elements by aqueous fluids limits the quantitative modelling of fluid-rock interactions at depths and the estimates of mass recycling. Experimental studies involving fluids remain a real experimental challenge due to their unquenchable nature and chemical reactivity, which requires in situ analytical probes.

In the last decade, new experimental designs combining high pressure vessels and advanced micro-analytical and spectroscopic techniques have opened the possibility for monitoring in situ the chemical composition, the molecular structure and thermodynamic quantities of high-pressure fluids. Here, emerging views on the mobility and transport of elements by subduction zone fluids will be discussed in the light of spectroscopic studies and fluids sampled as synthetic fluid inclusions. Specifically, I will review the results of experimental studies that constrain: 1) the properties of the solvent (H2O and NaCl-H2O) in response to increasing pressure and temperature, 2) the role of coordination chemistry involving halogen ligands (e.g., Cl and F) and polymerized silicate species (Si-Al-Na) in the mobility and transport of key trace (REE, HFSE) and redox sensitive (Fe, C) elements by slab fluids. The picture that is emerging from these studies is that ligand-bearing aqueous phases may have comparable efficiency to hydrous silicate melts in the mobilization and fractionation of trace elements, and that their role as mass transfer agents in subduction-related processes may have been underestimated until now. The implications of these results for the nature of the slab flux and for the geochemical signature of arc magmas, including their oxidation state, will be discussed.