The magmatic evolution of the late Miocene laccolith-pluton-dyke granitic complex of Elba Island, Italy

Since late Miocene time, post-collisional extension of the internal parts of the Apennine orogenic belt has led to the opening of the Tyrrhenian basin. Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Italian mainland during this time, building up the Tuscan Magmatic Province as the fold belt was progressively thinned, heated and intruded by mafic magmas. An intrusive complex was progressively built on western Elba Island by emplacement, within a stack of nappes, of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dyke swarm, all within the span from about 8 to 6.8 Ma. New geochemical and Sr-Nd isotopic investi- gations constrain the compositions of materials involved in the genesis of the magmas of Elba Island compared to the whole Tuscan Magmatic Province. Several distinct magma sources, in both the crust and mantle, have been identified as contributing to the Elba magmatism as it evolved from crust-, to hybrid-, to mantle-dominated. However, a restricted number of components, geochemically similar to mafic K-andesites of the Island of Capraia and crustal melts like the Cotoncello dyke at Elba, are sufficient to account for the generation by melt hybridization of the most voluminous magmas (c. ? (t) -8.5, 87Sr/86Sr 0.715). Unusual magmas were emplaced at the beginning and end of the Nd igneous activity, without contributing to the generation of these hybrid magmas. These are repre- sented by early peraluminous melts of a different crustal origin (?Nd(t) between -9.5 and -10.0, 87Sr/86Sr variable between 0.7115 and 0.7146), and late mantle-derived magma strongly enriched in incompatible elements (? (t) = -7.0, 87Sr/86Sr = 0.7114) with geochemical-isotopic characteristics Nd intermediate between contemporaneous Capraia K-andesites and later lamproites from the Tuscan Magmatic Province. Magmas not involved in the generation of the main hybrid products are not volu- metrically significant, but their occurrence emphasizes the highly variable nature of crust and mantle sources that can be activated in a short time span during post-collisional magmatism.