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Open Access Publications from the University of California

Isotopic Geochemistry and Hydrology of Geothermal Waters in the Ethiopian Rift Valley


The primary aim of the project was the characterization of the isotopic variations of hydrogen and oxygen (D/H and O18/O16 ratios) in surface and ground waters and geothermal water and steam in the Lakes District of the Ethiopian Rift Valley. Additional studies carried out in the course of this study included the following: (1) Field measurements of temperature, conductivity, and pH, and measurements of approximate chloride concentration; (2). Measurement of carbon isotope variations (C13/C12 ratios) in dissolved carbon in waters and CO2 in the gas phase in geothermal discharges; (3) Chemical analysis of water samples; (4) A survey of helium concentrations in ground water and in geothermal waters and gases, made in the field with a portable mass spectrometer; (5) Laboratory measurements of helium and neon concentrations

and of the isotopic composition of helium (He3/He4 ratios) in water and gas samples; (6) Measurements of the oxygen isotope ratio (O18/O16) in dissolved sulphate in geothermal waters, for use as a possible subsurface geothermometer. Additional gas samples were collected for chemical analysis and measurement of D/H, C13/C12, and N15/N14 ratios in methane, hydrogen, and nitrogen. The tritium content of some water samples is being measured by allowing He3 , the daughter product of tritium decay, to grow in. These studies are not yet completed, and the results will be submitted in a later, supplementary, report.

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