Imaging of Serpentinites beneath the Münchberg Massif (Germany) using Joint Gravity and Magnetic Inversion

Serpentinisation is a water–rock reaction in ultramafic lithologies that can generate natural hydrogen and strongly modifies rock density and magnetic susceptibility. Quantifying the spatial distribution of serpentinized bodies is therefore essential for assessing the subsurface potential of natural hydrogen systems.

The Münchberg Massif (northern Bavaria, Germany) is an exhumed stack of tectonic nappes of different metamorphic grades that hosts several outcropping serpentinite bodies. This provides a rare opportunity to study serpentinisation in a setting that is typically buried at considerable crustal depths. The serpentinites are mainly exposed in the southern and southeastern part of the massif and coincide with pronounced, high-amplitude magnetic anomalies attributed to elevated magnetite contents. Despite detailed petrological and geochemical studies, the structural continuation of these bodies toward the north and northwest beneath overlying nappes remains poorly constrained.

We address this problem through joint inversion of gravity and magnetic data, exploiting the characteristic properties of reduced bulk density and elevated magnetic susceptibility in serpentinized ultramafic rocks relative to the surrounding crystalline basement. We integrate newly acquired high-resolution airborne gravity and magnetic observations with vintage seismic reflection constraints and site-specific petrophysical measurements (density and magnetic susceptibility) conducted on samples collected from surface outcrops. We used topography-aware forward modelling and wavelet compression to efficiently handle dense airborne datasets. Geological and petrophysical information is incorporated through bound/interval constraints, while seismic reflectors provide structural guidance to steer the inversion toward geologically plausible geometries and reduce non-uniqueness.

Preliminary joint inversion results of serpentinites reproduce the observed magnetic anomaly patterns consistent with outcrop-based measurements. First joint gravity–magnetic models indicate that combining density and susceptibility constraints with structural guidance from vintage seismic reflection data improves the robustness of inferred serpentinite geometries compared to magnetic-only inversions, particularly with respect to thickness distribution and subsurface continuity beneath the massif.

The Münchberg Massif thus serves as a natural test site for developing and validating geophysical workflows to characterize potential natural hydrogen systems in settings where serpentinites are concealed beneath crystalline or sedimentary cover.