Understanding Tectonic and Sedimentary Controls for the Reconstruction of the Hydrothermal History in Magma-poor Rifted Margins

The spatio-temporal reconstruction of the sedimentary and thermal state in magma-poor rifted margins, along with fluid-rock interactions driven by hydrothermal activity is key to support the understanding of processes leading to the accumulation of resources as, for example, base metals and Rare Earth elements, in these settings. One specific example is natural hydrogen, which is becoming a key player in the energy mix. Beyond the various sources of currently produced synthetic hydrogen, a recent focus is being given to natural (white) and stimulated (orange) geological hydrogen. A key production mechanism for the abiotic generation of natural hydrogen is the geochemical process known as serpentinization, which results from the reaction of water with low-silica, ferrous minerals at the adequate pressure and temperature conditions. For serpentinization to occur, the ultramafic rocks in the lithospheric mantle need to fracture to allow for water to infiltrate. This chiefly happens when rocks are mechanically stressed by tectonics, and can be further supported by local stresses generated by the same metamorphic reactions associated to serpentinization. More generally, further understanding of the effects of geological controls and structural plate tectonic positions on thermal and hydrogeologic regimes, as well as their coupling with fluid dynamics, fluid chemistry, fractures and faults, and lithological sequences is needed for the historic analysis of hydrothermal systems. Numerical simulations are suitable for investigating these multicomponent systems, as they allow for sensitivity analyses of individual processes and interactions, including appropriate time and length scales. Here we focus on the continent-ocean transition (COT) of magma-poor rifted margins. By means of basin-scale numerical simulations we analyze the interactions between tectonics, sedimentary and hydrothermal processes. While it has long been acknowledged that the patterns of impermeable sediment blankets are a strong control on hydrothermal activity, here we first show how tectonics and these sedimentary structures relate to patterns of fluid circulation and temperature at the basin scale and at geological scales. We further relate them with historic reconstructions of advective and conductive heat flow in rifted margins, and finally give consideration to the serpentinization and generation of potential natural hydrogen reservoirs.