87Sr/86Sr Ratios in Thermal Water from the Southern Upper Rhine Graben, Germany ☆

The present study of thermal water from Bad Bellingen, Steinenstadt, Bad Krozingen, Mooswald, and Weinheim located in the southern part of the Upper Rhine Graben was undertaken in the framework of a multidisciplinary hydrogeochemical research project and concerns 87Sr/86Sr isotope investigation. The aquifer lithologies of thermal waters are Triassic Upper Muschelkalk, Jurassic Hauptrogenstein and Tertiary Miocene sediments. The 87Sr/86Sr ratios (N=9) range from 0.70912 to 0.71096. The Sr isotopic composition of thermal water is controlled by the fault system of the Rhine Graben rift. Fluids from Upper Muschelkalk aquifers ascent along the Eastern Boundary fault zone. The deep-water ascent most likely reaches into the crystalline basement.