The plutonic rocks of the Basal Complex of La Gomera, Canary Islands,
Spain, were studied by means of major and trace element contents and by
H-O-Sr-Nd isotope compositions in order to distinguish primary magmatic
characteristics and late-stage alteration products. Deciphering the
effects of alteration allowed us to determine primary, plume-related
compositions that indicated D- and (18)O-depletion relative to normal
upper mantle, supporting the conclusions of earlier studies on the
plutonic rocks of Fuerteventura and La Palma. Late-stage alteration took
place during the formation of the intrusive series induced by
interaction with meteoric water. Inferred isotopic compositions of the
meteoric water indicate that the water infiltrated into the rock edifice
at a height of about 1500 m above sea level, suggesting the existence of
a subaerial volcano which was active during the intrusive activity and
that it has been either distroyed or remain buried by later volcanic and
landslide events.