The boron isotope systematics of Icelandic geothermal waters: 1. Meteoric water charged systems

We have measured the boron isotope composition and boron and chloride concentrations of 27 Icelandic geothermal fluids from both high- and low-temperature systems. The δ¹¹B values range from −6.7‰ in the Krafla system, to +25.0‰ in a warm spring from the Southern Lowlands. In addition, we have also determined the δ¹¹B values of basaltic glass from Nesjavellir (−5.3 ± 1.4‰) and travertine from Snaefellsnes (−22 ± 0.5‰). The B isotope and Cl/B systematics of the high-temperature systems are dominated by the composition of the local basalts. The lower temperature systems show evidence for mixing with B and Cl of a marine origin, together with some uptake of B into secondary mineral phases. The data from the Snaefellsnes geothermal system indicate that the fluids have undergone interaction with basalts that have undergone significant low-temperature alteration by seawater.