• journal_title：Geology
• Contributor：Avner Vengosh ; Abraham Starinsky ; Yehoshua Kolodny ; Allan R. Chivas ; Menahem Raab
• Publisher：Geological Society of America
• Date：1992-
• Format：text/html
• Language：en
• Identifier：10.1130/0091-7613(1992)020<0799:BIVDFE>2.3.CO;2
• journal_abbrev：Geology
• issn：0091-7613
• volume：20
• issue：9
• firstpage：799

Examination of boron isotopes, elemental B, Br, and Li in brines, and coprecipitated salts during fractional evaporation of sea water shows that Br, Li, and B in the evaporated sea water have lower concentrations than expected, as determined from mass-balance calculations. The deficiency is found beyond a degree of evaporation of ∼30 and is associated with a gradual increase in the δ¹¹B values of the evaporated sea water, from 39‰ to 54.7‰ (relative to standard NBS 951). The high δ¹¹B values of the brines and the relatively lower δ¹¹B values of the coexisting precipitates (MgSO₄ and K-MgSO₄ salts; δ11B = 11.4‰ to 36.0‰) suggest selective uptake of ¹⁰B by the salts. Applying Rayleigh distillation equations, the empirical fractionation factors for the depletion of the salts in ¹¹B are estimated as 30‰ (α = 0.969) for the early stages of precipitation (gypsum and halite range) and 20‰ (α = 0.981) for the late stages (K-MgSO₄ minerals). Coprecipitation of B(OH)₄^- species with the salts, and/or precipitation of Mg-borate minerals with a coordination number of 4 are the proposed mechanisms for boron isotope fractionation during fractional evaporation of sea water. The boron isotope composition of sea water (δ¹¹B = 39‰) is significantly higher than that of continental water (δ¹¹B = -3‰ ±5‰). Our study shows that salt deposits may be depleted in ¹¹B by 20‰ to 30‰ relative to their parent brines. These variations suggest that boron isotopes can be used to determine the origin (marine vs. nonmarine) of brines and ancient evaporitic environments.