Fluid Inclusions in the Deepest Part of the IDDP-2 Drill Core, Reykjanes Peninsula, Iceland

Abstract

We studied geothermal fluid, trapped as fluid inclusions in felsic minerals, from the bottom ( more than 4500 m) of the IDDP-2 borehole, Iceland. Petrographic observations suggest that the fluid at this depth is separated to a vapor phase and a solute-rich brine. Based on fluid inclusion homogenization experiments, the temperature of the geothermal fluid is estimated to be 60020 °C and the pressure corresponds to near hydrostatic conditions (~50 MPa) at the bottom of the borehole. The vapor phase is dominated by H2O, containing minor CO2, H2S and H2, whereas the solute-rich brine is dominated by Fe-K-chloride-hydroxides at room temperature and can contain up to 1.2 wt% Cu in the form of Cu-Fe-sulfide. Potassic silicate melt inclusions associated with the geothermal fluid are also present and they are the witnesses of melt-fluid interactions. Furthermore, they indicate that there is a danger of drilling into magma in similar depth at the Reykjanes peninsula.