Serpentinization in the Münchberg Massif: New petrological and geochemical data

During the serpentinization process of ultramafic rocks, hydrogen is generated. Since ultramafic rocks are often buried deep within the subsurface, it is difficult to study the genesis of hydrogen by serpentinization. The Münchberg Massif in northern Bavaria is a stack of nappes, one of which contains numerous serpentinite bodies. The exposure of these serpentinite bodies at the surface at several locations offers an excellent opportunity to study the serpentinization process of ultramafic rocks.

We present new petrological and chemical data of serpentinites from two locations in the Münchberg Massif: Peterleinstein in the west and Zell in the southeast. The petrological, mineralogical and geochemical composition of the serpentinites at both locations are slightly different. Thin section analyses show different degrees of serpentinization at Peterleinstein and Zell. While rocks at Peterleinstein are almost completely serpentinized, those at Zell still show a certain amount of relic minerals. X-ray diffraction analyses reveal several serpentine minerals in both locations but in different amounts with the dominant serpentine mineral antigorite in Zell and lizardite in Peterleinstein. Major and rare earth elements indicate that the serpentinites at Peterleinstein have a protolith of depleted harzburgitic composition, whereas the serpentinites at Zell have a harzburgitic to dunitic composition. Furthermore, major and trace elements indicate that the protoliths for Peterleinstein come from an abyssal setting and the protoliths for Zell are from a subduction zone setting. Therefore, we suppose that the protoliths for both locations may have been situated at distinct locations within or close to a subduction zone.