A geochemical investigation of trace elements in well RN-17 at Reykjanes geothermal system, SW-Iceland

摘要

Here we present the results of an investigation of well RN-17 at Reykjanes geothermal system (Reykjanes Peninsula, SW-Iceland). We show that the adoption of micro-spot secondary ion mass spectrometry (SIMS) together with bulk-rock techniques, such as X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and thermal ionisation mass spectrometry (TIMS) carried out on 10 basaltic drill-cuttings over a depth of 3000 m gives us insights into the geochemical characteristics of the well. Whole rock and mineral phases, i.e., plagioclase, clinopyroxene, epidote and amphibole, indicate that the rocks pertaining to the cuttings were affected by hydrothermal alteration that has been able to modify significantly the Sr isotope ratios and the concentration of K, Rb, Cs, Ba and B. Seawater/rock ratio, evaluated for ~(87)Sr/~(86)Sr, achieved its maximum for the shallow cutting RN-17-650, decreasing although not systematically with depth, with the minimum value for the deep cutting RN-17-2800. Moreover, the occurrence of Na-rich plagioclase, epidote and amphibole down to the well bottom are evidence of the persistence of fluid/rock interaction at depth.