2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 46-44
Presentation Time: 9:00 AM-5:30 PM


BRINK-ROBY, David, Earth and Environmental Studies, University of Rochester, 227 Hutchison Hall, Rochester, NY 14627, MITRA, Gautam, Department of Earth & Environmental Sciences, University of Rochester, 208A Hutchison Hall, Rochester, NY 14627, YONKEE, Adolph, Department of Geosciences, Weber State University, 2507 University Circle, Ogden, UT 84408 and EVANS, Mark A., Department of Geological Sciences, Central Connecticut State University, 1615 Stanley Street, New Britain, CT 06050, david.brink.roby@gmail.com

During mountain-belt formation, fluid migration plays an integral role in heat transport, mass transport, hydrocarbon accumulation, and rheology. To better understand the spatial and temporal patterns of regional fluid-flow systems, we integrate structural, petrologic, SEM/EDS, fluid inclusion, and stable-isotope (C and O) geochemical data for the well characterized Wyoming salient of the Sevier fold-thrust belt. We seek to characterize fluid sources (e.g. meteoric waters, connate waters, and metamorphic fluids), driving forces (e.g. topographic relief between the high hinterland and lower foreland, thermally and/or chemically generated gradients, and tectonic loading by thrust sheets and sediment burial), and fluid pathways (e.g. primary and secondary porosity, both within hydrostratigraphic units and along faults).

Focusing on limestone units in the Jurassic Twin Creek Formation, Triassic Thaynes Formation, and Missisippian Lodgepole Formation and correlatives, we identified systematic suites of mesoscopic structures, including veins and multiple minor fault sets. Surveys of cross-cutting relationships establish relative timing of these structures. SEM backscatter and X-ray analysis reveal minor variation in vein geochemistry and reactivation of previous structures. Image analysis of sample-area scans shows that cross-strike veins are most prevalent and have the largest apertures. Analysis of two-phase, aqueous fluid inclusions within veins reveals a decrease in Th from more interior to exterior thrust sheets, suggesting a combination of migrational cooling, shallower structural depths, and meteoric fluid influence. C-O isotopes analysis of paired vein (cross-strike set) and host rock carbonate samples reveal equal δ13C values for vein-host rock pairs; δ18O values decrease for both veins and host rock from west to east, showing that host composition altered during regional flow. Along regional faults, analysis reveals low levels of δ18O within veins relative to host rock, a distinct fluid signature that implies channelized flow and meteoric influence. This data supports the hypothesis that fluid migration ahead of the wedge weakens rock, which undergoes distributed layer parallel shortening, and this deformation and fluid flow are then concentrated along major faults.