DEFORMATION CONTEXTUALIZED CARBONATE CEMENTS REVEAL 100-MILLION-YEAR HISTORY OF FLUIDS IN THE MOAB FAULT ZONE, COLORADO PLATEAU (SE UTAH) (Invited Presentation)

Faults exert strong controls on energy and mass transfer through the lithosphere by serving as both conduits and barriers to fluid migration and related advective heat transfer. The permeability of a fault zone evolves with structural evolution and diagenesis of the fault rocks. Quartzose sandstones of the Colorado Plateau record intertwined structural and diagenetic histories of faulting because of their relatively simple physical characteristics and mineralogy: deformation bands (unique to porous granular materials) capture the earliest history of faulting, and variably alter fault zone permeability and rock strength; carbonate cements are constructed with elements sourced outside the clean eolian sands, and thus record fluid migration into the fault zone.

We examined carbonate cements from deformation structures in the Moab Fault north of Arches National Park, where it cuts the porous Moab Tongue sandstone. Building on abundant prior work characterizing the fault’s structural and diagenetic history, we use thin sections, stable isotopes and clumped isotope paleothermometry to show that the Moab Fault conducted and trapped fluids from its inception through burial and exhumation. The earliest phase of carbonate cement is contained within deformation bands and formed from marine fluids at cool (average 16°C) temperatures. These likely reflect cementation associated with incipient faulting in the early Cretaceous prior to significant burial. Later deformation, around the time of peak burial (~2 km), was characterized by fracturing within the fault damage zone, especially at fault segment boundaries. These fractures accommodated the circulation of warm (average 54°C) fluids and the formation of crystalline calcite veins with an isotopic composition distinct from the early cements. The vein-filling cements show evidence of subsequent alteration and a range of precipitation temperatures (as low as 19°C) and isotopic compositions that we interpret to suggest intermittent interaction with rock-buffered fluids during exhumation to Earth’s surface. Active springs confirm that the Moab Fault remains an important fluid conduit today. Careful observation of the deformation context of carbonate cements enabled tracking of fluid composition and temperature through the full evolution of the fault zone.