Microstructure and fluid flow in rift border fault-bounded basins – insights from the Dombjerg Fault, NE Greenland

In this contribution, we elucidate the interaction of structural deformation, fluid flow, and diagenesis in hanging wall siliciclastic deposits along rift basin-bounding faults, exemplified at the Dombjerg Fault in NE Greenland. Due to fault-controlled fluid circulation, fault-proximal syn-rift clastic deposits experienced pronounced calcite cementation and became lithified, whereas uncemented clastic deposits remained porous and friable. Correspondingly, two separate deformation regimes developed to accommodate continuous tectonic activity: discrete fractures formed in cemented deposits, and cataclastic deformation bands formed in uncemented deposits. We show that deformation bands act as partial baffles to fluid flow. This led to localized host rock alteration, which caused a chemical reduction of pore space along the bands. Where cemented, porosity was reduced towards zero and fracture formation created new pathways for fluid migration, which were subsequently filled with calcite. Occasionally, veins comprise multiple generations of microcrystalline calcite, which likely precipitated from an abruptly super-saturated fluid that was injected into the fracture. This suggests that cemented deposits sealed uncemented deposit bodies in which fluid overpressure was able to build up. We conclude that compartmentalized fluid flow regimes may form in rift fault-bounded basins, which has wide implications for assessments of potential carbon storage, hydrocarbon, groundwater, and geothermal sites.