IDENTIFYING STRUCTURAL CONTROLS ON DIAGENETIC FLUID MIGRATION USING CARBONATE CLUMPED ISOTOPE GEOCHEMISTRY: APPLICATION TO THE MOAB FAULT, UTAH

Detailed characterization of structures and diagenetic carbonate cements along the Moab Fault at the Courthouse Junction fault intersection, southeast Utah, has provided valuable insight into structural controls on fluid migration, carbonate deposition, and diagenesis. We build upon the careful mapping and interpretations of earlier workers to constrain the spatial distribution of chemically distinct carbonate cements and vein fills. Earlier work has used carbonate clumped isotope thermometry to identify two groups of diagenetic calcite cements along a single transect line across Courthouse Junction. Each group has distinct precipitation temperatures: a “warm” group with precipitation temperatures of ~40 to 90 °C and a “cool” group with precipitation temperatures between ~10 and 35 °C. The distributions of these two groups along the transect are distinct, with the “cool” carbonates contained behind an E-W trending deformation band fault. “Warm” carbonates are not limited by this E-W trending structure, and are distributed across the entire transect. While this observation is intriguing, the linear nature of the transect hinders a robust description of the spatial distribution of carbonate cements and their relationship to the variety of observed structures at Courthouse Junction. We approach this problem with the analysis of two new sampling transects to produce a map of paleo-fluid temperature in the fault intersection zone Using a combination of clumped isotope thermometry, cathodoluminescence, and micro- and meso-scale observations, we describe the interplay between fault-hosted fluid migration, carbonate precipitation, and structural deformation across the sandstone pavement exposed around this fault intersection zone. Fault architecture has clearly had a prominent role in controlling fluid migration, where fluids of different composition are associated with different sets of structures, suggestive of heterogeneity in the permeability of the Moab Fault system. This heterogeneity may reflect differences in the permeability associated with separate fluid sources, or temporal variability in migration pathways due to the sequence of formation, cementation, and reactivation of structures at Courthouse Junction.