Alain Prinzhofer, Joao Françolin, Christophe Rigollet, Nicolas Lefeuvre and Paulo Emilio Valadão de Miranda
Hydrogen exploration in the municipality of Maricá (Rio de Janeiro State, Brazil) indicates that large hydrogen and helium gas fluxes are emitted through reactivated Neoproterozoic thrust faults. The gas concentrations in the soils, and the modelled gas fluxes, are the most intense measured so far in the world. This exploration has shown new surface expression of hydrogen micro-seeps observed along reactivated large tectonic accidents, instead of “fairy circles”, most common proxy for hydrogen systems at the surface of the Earth. Also, association of hydrogen and helium measurements during surface geochemistry reduces the risk of misinterpretation of surface hydrogen measurement, since the risk of drill bit metamorphism or superficial biological activity inducing hydrogen artefacts is always a possibility. In this area, it is possible to assess a quantification of hydrogen flux of 0.8 m3.m-2.day-1and a flux of helium of 0.03 m3.m-2.day-1.