NOBLE-GAS COMPOSITION OF DEEP BRINES FROM THE PALO DURO BASIN, TEXAS

Deep groundwaters in sedimentary basins can be sufficiently old (> 10 m.y.) to have accumulated both radiogenic 4He and 40Ar*. Differences in the ratio of (U + Th)/K for aquifer lithologies lead to variations for 4He/40Ar* in the groundwater. These variations can be used to resolve chronologically significant noble gas components. Application of a binary model to brine samples from the Palo Duro Basin, Texas yields (U, Th)-4He residence times of 100 to 300 m.y. Concentrations of two non-radiogenic noble gases (20Ne and 36Ar) provide information on the salinities of the water that recharged these aquifers.