CLUMPED ISOTOPES REVEAL TEMPORAL VARIABILITY IN THE DISTRIBUTION OF PERMEABILITY AT THE FAULT-SEGMENT SCALE ON THE MOAB FAULT, UTAH

Carbonate cements associated with fault-hosted fluid flow provide an important window into the relationships among faulting, fluid flow and diagenesis. Using clumped isotope paleothermometry and carbon and oxygen stable isotopes, we investigate carbonate cementation associated with fluid migration along the Moab Fault, southeast Utah. The deformation history of the Moab Fault comprises multiple structural styles, including early-forming deformation bands and later jointing. Both of these structures are associated with carbonate cementation. Outcrop observations suggest that deformation bands occur fairly consistently along the fault zone, while jointing is focused around fault segment intersections and zones of structural complexity. Because fault systems are thought to develop by growth and linkage of individual fault segments, the observed variability may not have always been during fault zone evolution. Our stable isotopic data and outcrop to thin section scale observations of carbonate cements span the length of the Moab Fault, sampling multiple fault segments and intersection zones. Clumped isotope values reveal precipitation temperatures from ~20°C to over 120°C, reflecting both shallow and deep cementation. Cements precipitated from warm fluids tend to be spatially associated with intersections or zones of structural complexity, while cements precipitated from cooler fluids are more widely distributed. Widespread cool-fluid cements associated with deformation bands suggest these structures developed early and controlled fluid distribution even during the first stages of burial. In contrast, focused jointing around segment intersections appears to have localized warm-fluid flow later in the deformation history, after deeper burial. We suggest that grain-scale processes within deformation bands control early fault permeability, while segment-scale processes dominate at later stages of fault zone development.