Oxygen and hydrogen isotope studies on the basal complexes of the Canary Islands: implications on the conditions of their genesis

Abstract

18O/16O and D/H ratios have been measured in rocks and mineral separates from the basal complexes of Fuerteventura, Gomera and La Palma. These complexes comprise alkali plutonic rocks ranging from olivine gabbros to syenites and dikes of various mineralogy cutting them, all metamorphosed under greenschist conditions. K-Ar determinations gave ages from 48 to 17 My. The δ18O's and δD's of these rocks range from −1,4 to +11 and −113 to −45 respectively, with a majority of rocks depleted in heavy isotopes relative to normal, deep seated values. These values do not correspond to those found in ophiolitic sequences, which, for a comparable temperature range, give minimum δ18O's>3. These values are explained in terms of water-rock interactions involving limited amounts of meteoric waters from high elevations. This implies the existence of a very important volcanic edifice over Fuerteventura in the Miocene Oligocene period with elevations between 2,500 and a maximum of more than 4,000 m.