Using potential field data to investigate high-pressure sources of energy in deeply serpentinized mantle rocks

Serpentinization of ultramafic rocks is a key process in forming natural hydrogen. In deep settings, such as subduction zones, this process can be kinetically favored by high P-T conditions making the study of mantle rocks from these settings a compelling target for high-pressure sources of energy. Serpentinization of peridotites can lead to the formation of magnetite and it is commonly associated with a decrease in density and an increase in magnetization of the protolith rock. Gravity and magnetic methods can therefore be used to map and quantify the extent and degree of serpentinization. Here, we used a comprehensive dataset consisting of ground and Unmanned Aerial Vehicle (UAV) magnetic data, gravity data, and an extensive petrophysical data collection to explore the natural hydrogen potential in exhumed mantle rocks from the Monte Maggiore (MM) massif, in Corsica. The MM massif consists of a 4 km2 peridotite body, intruded by mafic pods and gabbroic dykes and surrounded by blueschist-facies continental units. It represents sub-continental mantle that underwent tectonic and magmatic evolution during the rifting stage of the Jurassic Ligurian Tethys oceanic basin and successive Alpine subduction to blueschist-facies conditions. On-going geochronological and geochemical investigations suggest that serpentinization occurred primarily in subduction making this area a suitable case study to investigate the formation of high-pressure sources of energy in such settings. We analyzed densities and magnetic properties of rocks from more than 100 sites across the massif and we used these data to identify domains exhibiting different degree of serpentinization and to model the current 3D structure of the massif using both forward and inverse modeling approaches. We estimated a minimum volume of the MM massif of 1.2 km3 and a vertical extent to a depth of 428 m below sea level. We used the modeled volumes and the amount of magnetite within each domain as a proxy for a conservative estimation of natural H2 production.