Boron isotope geochemistry of thermal springs from the northern Rift Valley, Israel
A boron isotope study was carried out on groundwaters from the northern Rift Valley, Israel. The relatively high salinity (18 000 mgCl l-1), boron content (3.9 mg l-1), and δ11 B value (44‰) and the low B/Cl ratios of the saline Tiberias Hot Spring suggest dilution of deepseated trapped CaCl2 brines with a δ11B ≈ 44‰, which is consistent with previous interpretations based on Na/Cl (0.58) and δ18O (-3‰) values. The δ11B values of the springs in Hammat Gader decrease gradually from δ11B of 41.9‰ to 20.9‰ with increasing salinity (70 to 497 mgCl l-1), temperature (25° - 50°C), and boron content (0.1-0.3 mg l-1). The δ11B values suggest that boron is derived from leaching of calcium carbonate or desorption of clay minerals of a δ11B = 14‰ and mixing with meteoric water of a high δ11B value. The relatively low δ11B values of two low salinity springs (1240 and 2700 mgCl l-1) along the Sea of Galilee (δ11B = 31.6‰ and 31.8‰) and the lake itself (24‰) suggest that a significant fraction of boron in these waters is also derived from rock leaching. The influence of boron that is leached from the rocks is limited and can be recognized mainly in boron-depleted groundwater. The variations of δ11B, Na/Cl, and δ18O parameters in the Hammat Gader springs demonstrate the sensitivity of each element to different sources. Whereas oxygen-isotope compositions reflect the meteoric source, the major ions (e.g. Na/Cl and Br/Cl ratios) record the influence of the deep-seated brines, and boron isotopes in diluted groundwater are sensitive to water-rock interaction. © 1994.
Vengosh, A; Starinsky, A; Kolodny, Y; Chivas, AR
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