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Abstract

Cathodoluminescent microstratigraphy in epigenetic dolomite cements correlates over a north-south distance of >275 km across the Ozark Mountains. Trace elements in dolomite show coherent regional variations. Ubiquitous coeval Pb- Zn mineralization contains fluid inclusions with homogenization temperatures >100°C. All suggest the flow of brines (mainly) north from the Arkoma Basin through Cambrian sandstone and carbonate aquifers. The observation that brines still fill Ordovician and Cambrian strata ringing the Ozark Plateau constrains the cumulative flow that has occurred. If the Mid-Continent sediment cover was thick and insulating, brine flow driven by topographic differences in hydrologic head could have been slow enough to avoid salt flushing and still accommodate the fluid inclusion homogenization data. If the cover was thermally conductive and thin, as seems most geologically reasonable, flow at the rates required to explain the homogenization temperatures would have quickly flushed salt from the aquifers in contradiction to present observations. Topographically driven hydrologic flow across the Arkoma basin could not have continued uninterrupted for protracted periods. Given the present high permeability of the Pb-Zn deposits, there is no obvious way to limit or pulse cross-basin hydrologic flow. The simplest explanation is that brines were expelled by compaction or gas displacement. High temperature, low salinity fluid inclusions in the Ozark Cambrian aquifers probably represent the incursion of meteoric water into outcrop areas warmed by pulses of brine outflow. Channeling of fluid flow and the relation of alteration and fluid inclusions to flow channels need to be further investigated theoretically and in the field.

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