GSA 2020 Connects Online

Paper No. 83-5
Presentation Time: 2:50 PM

GEOCHRONOLOGY REVEALS EOCENE FLUID-ROCK INTERACTION AND FAULT-CONTROLLED FLUID FLOW IN THE PARADOX BASIN


BAILEY, Lydia R.1, KIRK, Jason1, HEMMING, Sidney R.2, KRANTZ, Robert W.1 and REINERS, Peter W.1, (1)Department of Geosciences, University of Arizona, Tucson, AZ 85721, (2)Columbia University, Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY 10964

Understanding how the sources and migratory pathways of fluids in sedimentary basins evolve through time requires geochronologic constraints on fluid-rock reaction products. The Paradox Basin of the Colorado Plateau has a long history of subsurface fluid flow and hosts a wide variety of fluid types and fluid flow manifestations such as bleached sandstones, carbonate and silica metasomatism, Cu, U-V, Fe-Mn mineral deposits, and oil and gas fields. Here we show a widespread 40-50 Ma phase of fault activity contemporaneous with fluid flow and mineralization in the Paradox Basin, suggesting a close relationship between fluid movement and deformation in an enigmatic time interval. To date fault activity, we applied K-Ar and Rb-Sr geochronology to multiple size fractions of XRD-characterized clay-rich fault gouge from six faults. To date mineralization and fluid-rock reaction we also applied K-Ar geochronology to separated size fractions of clay from bleached sandstones, and Re-Os isochrons on bornite and chalcocite.

We quantified 2M1 (detrital) and 1Md (authigenic) illite polytypes for each clay fraction then applied illite-age-analysis to determine authigenic endmember ages. We measured an age of 62.9 ± 9.4 Ma (±1σ) for fault gouge on the Moab Fault, and an age of 42.9 ± 1.1 Ma for the Moab Fault Splay to the north. The nearby Lisbon Valley and GTO Faults yielded ages of 45.6 ± 0.72 and 44.2 ± 1.2 Ma; the latter also yielded an illite Rb-Sr age of 50.9 ± 3.5 Ma. Authigenic clay from a paleo-oil reservoir near the Moab Fault Splay gave an age indistinguishable from the fault, at 41.1 ± 2.6 Ma. This clay formed from the interaction of reduced fluids and oxidized red beds, suggesting the fault acted as a conduit for hydrocarbons. We also found a Re-Os age of 47.5 ± 1.5 Ma on Lisbon Valley bornite, reinforcing contemporaneous fault activity, fluid flow, and mineralization. However, an older Re-Os age of 112 ± 3.8 Ma for chalcocite and high initial 187Os/188Os from the younger bornite suggests multiple phases of fluid flow and mineralization at Lisbon Valley. Our results fall in a time where little is known about the exhumation history of the Paradox Basin, raising questions about fluid flow driving forces. Extension and/or local removal of Mancos Shale following the Laramide Orogeny may have influenced hydrogeologic flow patterns.