Ferric Iron in serpentinites as proxy for abiotic H2 production

Serpentinization is considered as among the most important processes sustaining redox conditions suitable for the synthesis of natural H2 and abiotic CH4. This process is documented at mid ocean ridges but also occur in subduction zones. In the latter context the potential for serpentinization to generate natural H2 and abiotic CH4 is not well understood. Since the release of reduced fluids is guided by the oxidation of ferrous iron into ferric iron hosted in secondary minerals (mainly serpentine and magnetite), the definition of the Fe3+/FeTot ratio in high-pressure serpentinites is fundamental to provide new insights on the magnitude of redox transformation and the related deep H2-CH4 formation in subduction zones. Here, we aim to determine the Fe3+/FeTot concentration by looking at the Fe K-edge pre-edge feature in different arrays of minerals formed in ancient subduction zones, now exhumed to the surface.