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 central part of the island and the Esquinzo area in the
north. delta(13)C values of the carbonatites increase progressively from
south to north of the island. This phenomenon is attributed to different
degrees of assimilation of sedimentary carbonate. Homogeneous, typically
magmatic delta(18)O values for carbonatites which have preserved primary
igneous textures and minerals suggest a well-mixed reservoir where
changes in delta(13)C values result from the storage of carbonate magmas
at different structural levels. The magma storage allowed assimilation
of sediment to varying degrees before final emplacement of carbonatites.
Shifts in delta(18)O towards more positive and negative values from
presumed primary compositions are observed in the carbonatites. 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.