Evidence for fractional crystallization of periodically refilled magma chambers in Tenerife, Canary Islands

Major and trace element data on basanitic to phonolitic lavas of different ages and from different parts of Tenerife (Canary Islands), and their mafic silicates have been used to obtain more detailed information about process es taking place in crustal magma chambers associated with ocean island magm atism in Tenerife. Clinopyroxene phenocrysts in basanitic to phonolitic lav as consist of diopside-salite (referred to as Al-salite) with alternating n ormal and reverse zoning, and commonly contain a rounded or corroded core o f homogeneous Na-rich diopside salite (referred to as Na-salite). In genera l Al-salite contains lower amounts of rare earth elements (REE) and Y, and more Mg, Al, Ti, Cr, Sc and Ni than Na-salite. Variations in trace element concentrations and ratios are only weakly related to variations in mg-numbe r. Petrographic and compositional relations among the lavas and mafic silic ates are interpreted as the results of fractional crystallization in period ically refilled magma chambers (FCM processes). The FCM processes took plac e at temperatures of 1040-1260 degrees C and pressures of about 0.2-0.5 GPa ; that is, partly within the old oceanic crust and partly within the overly ing sequence of Canary Islands lavas. FCM processes may lead to significant fractionation between incompatible trace elements whose ratios in mafic ma gmas are used to characterize their mantle source(s). Melts subjected to FC M processes will, furthermore, produce significantly larger masses of cumul ates than melts of similar mg-number that have only been subjected to simpl e fractional crystallization.