Regional scale, fault-related fluid circulation in the Ionian Zone of the Hellenides Fold-And-Thrust Belt: clues for fracture sealing in carbonates?

Assessment of the fault-related fluid flow properties in carbonates pertaining to fold-and-thrust belts is challenging task. In fact, fold-and-thrust belts are characterized by a prolonged deformation history including pre-orogenic burial diagenesis and foreland flexure, syn-orogenic accretion, and post-orogenic extensional collapse. In this context, the Ionian zone of the Hellenides fold-and-thrust belt offers a natural laboratory for fault-related fluid flow assessment in a tectonically complex carbonate-hosted fold-and-thrust. In this work, we combine mesoscale structural and microstructural analyses with carbon and oxygen stable isotope analyses performed on syntectonic calcite veins and fault slickenfibers sampled in the Araxos promontory area, eastern Greece. The goal is to propose a conceptual model of regional scale fault-related fluid flow. The pre-orogenic structural assemblage consists of bed perpendicular, NNE and ESE trending calcite veins, the syn-orogenic assemblage of N-S trending strike-slip faults, E-SE-dipping thrusts, and bed parallel calcite veins; whereas the late- to post-orogenic assemblage of NE and SE strike-slip faults, and E-W normal faults. The pre-orogenic assemblage shows ?18O values comprised between +24 ? and +26 ?, and ?18C values between +2 ? and -9 ?. This is consistent with calcite precipitation from fluids buffered by the carbonate host rock (i.e. formation water), and from meteoric-derived fluids. The synorogenic assemblage shows ?18O values ranging from +22 ? and +29 ? and ?18C values from +2 ? and -4 ?, which suggests calcite precipitation from fluids also buffered, at various extents, by the carbonate host rock. The post-orogenic assemblage shows ?18O values comprised between +24 ? and +27 ?, and ?18C values between -2 ? and -12 ?, which indicates calcite precipitation from meteoric fluids enriched in light organic carbon due to interactions with organic-rich soils. The proposed conceptual model of fault-related fluid circulation hence implies a transition from a closed fluid system during pre- and syn-orogenic deformation, characterized by fluids buffered by the host rock, to a late- to post-orogenic infiltration of meteoric-derived fluids. We note that data obtained for pre-orogenic veins are also consistent with early barren fractures sealed by meteoric-derived water during late- to post-orogenic times.