Petrological and geophysical characterization of a paleo natural hydrogen kitchen – serpentinites of the Münchberg Massif, Germany

One of the main challenges in studying a natural hydrogen system is that ultramafic rocks - potential source rock for hydrogen generation by serpentinization - are often buried deep within the subsurface. The serpentinites of the metamorphic Münchberg Massif, obducted during the Variscian orogeny in Devonian times, offer a unique window into deep crustal and upper mantle processes. As part of an integrated study, we have acquired airborne magnetic and strapdown gravity data, seismic reflection profiles, as well as detailed petrological and geochemical analysis. This approach enables a multi-scale interpretation of the tectonic evolution, serpentinization processes, and associated fluid-rock interactions, mineralogical transformations, and implications for paleo-natural hydrogen generation in the Münchberg Massif. 

Serpentinite rock bodies are exposed at multiple outcrops across the Münchberg Massif. Geochemical analyses of major and rare earth elements indicate that serpentinites from both the Peterleinstein (west) and the Zell region (south) share a similar protolith of harzburgitic composition. However, different serpentine minerals dominate at the different locations. The Zell serpentinites, predominantly antigorite, appear to have undergone serpentinization at greater depths and higher temperatures than the Peterleinstein serpentinites, which are dominated by lizardite. Conversely, Peterleinstein demonstrates a higher degree of serpentinization, likely indicating increased fluid availability during the process. The sequence of events during serpentinization is evident in spatially resolved analyses of different generations of serpentine minerals in thin sections using microscopic and Raman micro-spectroscopic analyses.

Initial interpretation of the airborne magnetic data reveals a series of positive high-frequency anomalies with amplitudes of up to ~160 nT, associated with magnetite enrichment, a by-product of serpentinization and hydrogen generation across the Münchberg Massif. Petrological analyses confirm the presence of magnetite-bearing serpentinites. However, preliminary on-site magnetic susceptibility measurements do not resolve differences in the degree of serpentinization. Combined petrophysical, seismic, gravity and magnetic interpretation and modeling will constrain the extent of serpentinization in the subsurface and evaluate the role of major faults as fluid conduits during serpentinization.