Crustal contamination of carbonatites indicated by δ34S-δ13C correlations (Fuerteventura, Canary Islands)

Abstract

The magmatic activity of Fuerteventura (Canary Islands) has had an extended history. Initial submarine alkaline basaltic series and simultaneous pyroxenite, gabbro and syenite intrusions were followed by later syenite-carbonatites complexes. Based on a δ13C-δ18O-δD study, Demény et al. (1998) have proposed a model in which the carbonatite-bearing syenite magma suffered sediment contamination during storage in shallow magma chambers. The degree of contamination shows areal variation. The syenite-carbonatite complexes contains Fe-sulfides and Ba- and Sr-sulfates as disseminated grains. A δ34S study of these sulfur minerals has been undertaken to provide information on the mantle fluids on one hand, and to serve as a test of the contamination model on the other. For the least-contaminated complex (Ajui-Solapa), igneous sulphide has a δ34S value of -2.5‰, whereas the sulfate δ34 value is +4.5‰. The presumed most contaminated carbonatite (Esquinzo) contains only sulfate with δ34 values from +10.1 to +12.4‰. This positive shift cannot be related to differences in T and fO2, but it correlates well with the δ13C data of the carbonatites. The observed δ13C-δ34S correlation fits well with possible carbonatite-sediment mixing model curves.