TRACING PALEOFLUID SOURCES USING CLUMPED ISOTOPE THERMOMETRY OF DIAGENETIC CEMENTS ALONG THE MOAB FAULT, UTAH

Interactions among fluids, deformation structures, and chemical changes in sediments impact deformation of the shallow crust, influencing the preservation and extraction of the economic resources it contains. These interactions have been studied along the Moab Fault, in the Paradox Basin, Utah, where diagenetic cements, joints, cataclastic deformation bands and slip surfaces developed during faulting are thought to control fault permeability. Previous fluid inclusion micro-thermometry and stable isotopic data from calcite cements collected along segments of the Moab Fault suggest cements precipitated from hot basin fluids that migrated up the fault and interacted with a shallower meteoric groundwater source. In this study, we investigate the interactions of these fluids with deformation structures using clumped isotope thermometry of calcite cements along the Moab Fault. Guided by prior high-resolution mapping of deformation structures and calcite cements, we measured the growth temperature of calcite cements collected at varying distance from fault segments and fault intersections. Cement temperatures from individual segments vary greatly; cements along a relatively simple fault segment indicate temperatures ranging from 67 to 128 degrees C, similar to previously published fluid inclusion homogenization temperatures from a cement sample collected in the same locality, while a nearby fault intersection hosts cements with temperatures of 13 to 88 degrees C. The spatial pattern of cement temperatures revealed by clumped isotope thermometry suggests that intensely jointed zones associated with fault intersections enable rapid down-fault migration of cool surface waters and that deformation-band faults with their associated slip surfaces may further compartmentalize fluid flow, restricting fluid sources to warm waters thermally equilibrated with the country rock outside the jointed zone. Our data confirm that the relationship between faults and fluid flow can vary greatly over short length scales, and suggest that some fracture zones can be highly conductive to depths as great as 2 km.