Détermination de 87Sr86Sr dans les andésites cénozoïques et les laves associées de Sardaigne Nord occidentale (Italie)

Initial isotopic ratios of strontium have been determined in some calc-alkali rocks of Sardinia. The values of these ratios are from 0.7044 and 0.7047 in two basalts, and from 0.7063 to 0.7081 in five andesites. A dacite and a rhyolite have intermediate values of 0.7056 and 0.7058.It is suggested that increase of radiogenic strontium in andesite is most likely related to a contamination process involving water expelled from an underthrusting plate. This water also contributes to the increase in the potassium and related trace element contents in andesites.In spite of the87Sr86Sr difference between basalt and andesite, a cogenetic relationship between these two kinds of rocks cannot be precluded