Concurrent Evolution of Structural Deformation and Carbonate Diagenesis within the Moab Fault, UT

Abstract:

Fluid-driven diagenetic processes within the fault damage zone drive direct feedbacks to mechanical and fluid-permeability properties of the host rock. Because these factors can be of great importance to fault seismicity and reservoir integrity, it is important to constrain their evolution over the lifespan of a fault zone. The Moab Fault, SE Utah, is a prime location to address these questions, representing an exhumed fault system offsetting a package of paleo-reservoir rocks. We return to a well-studied segment linkage zone, Courthouse Junction, building upon detailed earlier work. Here, the fault zone contains multiple phases of structural deformation, expressed as distinct structural elements. Associated carbonate mineralization provides a record of past fluid flow through the fault zone. Earlier bulk and clumped isotope measurements of the carbonate have demonstrated a range of isotopic compositions and precipitation temperatures. In this work, we apply new carbonate isotope and trace element geochemistry, cathodoluminescence microscopy, and fluid inclusion analysis to synthesize the structural and diagenetic histories of the Moab Fault. Carbonate trace element signatures and clumped isotope-based precipitation temperatures allow us to identify variability in parent fluid composition and characterize fluid sources, constraining migration pathways through the fault zone. Distinct phases of carbonate deposition display different cathodoluminescence, allowing us to observe their textural relationships to the host rock and each other, as well as constrain the relative timing of episodes of carbonate deposition and structural deformation. Taken together, these data provide new perspective into the co-evolution of permeability and structural deformation in the Moab Fault by connecting variability in fluid transmission and source to changes in the style of structural deformation.