Continuous versus punctuated vein widening in the Marcellus Formation, USA: the fine line between pressure fringes and hydraulic fractures

Abstract Calcite veins are common in organic-rich mudrocks, but their genesis and ability to transmit fluids debated. A combined microstructural isotopic investigation of an array calcite recovered core from the Marcellus Formation reveals that grew via a combination continuous fibrous growth punctuated fracture-opening increments. Continuous opening is result pressure-solution creep involves no mechanical fracturing, rather pressure fringe around pre-existing, sealed fracture. In contrast, incremental accomplished by overpressured, mineral-saturated fluid, which repeatedly ruptures rock at cement / host-rock interface. Punctuated increments occurred throughout otherwise protracted, history, indicating present structures preserve hybrid deformation conditions between brittle, fluid-assisted cracking plastic strain. Stable signatures match those regional opening-mode fracture set formed response catagenetic fluid overpressures amid tectonically imposed (Alleghanian) stress field. It concluded form as hydraulic fractures susceptible brittle reactivation, even while inelastic processes widen fill with cement.