Crustal contamination and fluid/rock interaction in the carbonatites of Fuerteventura (Canary Islands, Spain): a C, O, H isotope study

Fuerteventura-the second largest of the Canary Islands consists of Mesozoic sediments, submarine volcanic rocks, dike swarms and plutons of the Basal Complex, and younger subaerial basaltic and trachytic series. Carbonatites are found in two Basal Complex exposures: the Betancuria Massif in the cent ral part of the island and the Esquinzo area in the north. delta(13)C value s of the carbonatites increase progressively from south to north of the isl and. This phenomenon is attributed to different degrees of assimilation of sedimentary carbonate. Homogeneous, typically magmatic delta(18)O values fo r carbonatites which have preserved primary igneous textures and minerals s uggest a well-mixed reservoir where changes in delta(13)C values result fro m the storage of carbonate magmas at different structural levels. The magma storage allowed assimilation of sediment to varying degrees before final e mplacement of carbonatites. Shifts in delta(18)O towards more positive and negative values from presumed primary compositions are observed in the carb onatites. On the basis of the oxygen isotope compositions of calcite, mica and K-feldspar, and the hydrogen isotope compositions of micas, the changes in the delta(18)O values of the carbonatites can be related to fluid/rock interactions. (C) 1998 Elsevier Science B.V. All rights reserved.