Operando 4D synchrotron tomography resolves multiphase hydrothermal dolomitization in a natural carbonate rock

Hydrothermal dolomitization is a critical process in carbonate diagenesis, capable of nonlinearly and heterogeneously restructuring pore networks, thereby fundamentally affecting permeability and fluid pathways in carbonate-hosted geothermal systems. Reaction rates and mechanisms in natural rocks remain poorly constrained, as few experimental setups permit direct observation of the process. Here, we present early analyses of operando (4D) µCT data acquired at the PSICHÉ beamline of Synchrotron SOLEIL (France) that document hydrothermal dolomitization in a fractured limestone from the Terwagne Formation of the Lower Carboniferous Kohlenkalk sequence (North Rhine-Westphalia, Germany). Our data provide mechanistic insights that cannot be obtained from conventional experimental approaches.The fine-grained oosparitic limestone contains microstylolites, which are likely to be diagenetic. A cylindrical core (20.08 × 9.76 mm) was drilled sub-parallel to bedding and axially fractured ex situ (UCS = 98.1 MPa) to promote fluid flow in an otherwise low-porosity (