Hydrogen isotope exchange and REE redistribution through a rock surface in the Bohus granite, southwest Sweden

Abstract

Hydrogen and oxygen isotopes have been analysed from biotite separates from the Bohus granite, southern Sweden. The separates were extracted from slices of drill cores and represent different depths. The cores were drilled vertically, perpendicular to a rock surface, striated by Weichaselian ice. Analyses of trace elements (including REE) in whole-rock samples were also carried out. The δD-values of biotite reveal that the surface corresponds to an old fissure which has been open for circulation of hydrothermal fluids. These fluids also leached the granite for light REE as well as other trace elements. A gain of heavy REE and Ta is also observed. The imprint from the deuterium-rich hydrothermal fluids was overprinted by a later circulation of cold meteoric water. Maximum penetration for the fluid responsible for this low-temperature δD exchange has been 7 cm over a period of 10,000 yr.