THE ORIGIN OF ALPINE PLUTONS ALONG THE PERIADRIATIC LINEAMENT

Numerous geological, geochemical, and geochronological studies of Olig ocene Alpine plutonism have been published over the last similar to 15 years. In this paper we review the major results of these works, and provide hitherto unpublished Nd-Sr isotope data from mafic dykes and a cidic intrusions. Geochemical data require that the source materials o f these plutons be mixtures between partial melts from the lithospheri c mantle and melted continental crust. Comparisons with simple thermal melting models furthermore indicate that the large amounts of tonalit e present in the intrusions resulted from widespread melting of a mafi c lower crust induced by a major thermal perturbation. Physical consid erations suggest that neither subduction zone melting nor extensional decompression melting were the cause of melt generation. Models based on the loss of the lithospheric mantle root during lithospheric thicke ning, such as breakoff of subducted oceanic lithosphere, bear the clos est similarity to the observations in the Alps. As a result lithospher ic weakening by rising melts might have focused deformation into the P eriadriatic Lineament, along which the intrusions were emplaced.