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 investigations 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. ε_Nd(t) −8.5, ⁸⁷Sr/⁸⁶Sr 0.715). Unusual magmas were emplaced at the beginning and end of the igneous activity, without contributing to the generation of these hybrid magmas. These are represented by early peraluminous melts of a different crustal origin (ε_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 (ε_Nd(t) = −7.0, ⁸⁷Sr/⁸⁶Sr = 0.7114) with geochemical–isotopic characteristics 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 volumetrically 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.

Provenance studies most commonly apply the classical approach based on petrographic modal analysis of arenites. In this paper, a modal analysis of arenites is combined with both a petrographic study on conglomerate clasts and a geochemical investigation of major and trace elements of pelites. The Ligure-Piemontese oceanic basin, a branch of Western Tethys, and its continental margins were consumed during the Eocene collisional events that led to the formation of the Alpine-Apennine belt. Remnants of Cretaceous sedimentary successions supplied by the continental margins are today preserved as tectonic units in the Alpine-Apennine belt: Balagne Nappe in Alpine Corsica and Internal and External Ligurian units in the Northern Apennines. The petrography of pebbles from rudites and lithic fragments from are-nites shows that Corsica and Internal Ligurian units contain debris from granitoids, low-grade metamorphic rocks, and carbonate platform rocks, while the External Ligurian units contain debris from low- to high-grade metamorphic rocks, a mantle-rock source, carbonate platform, and pelagic siliceous and carbonate rock sources. Geochemical data on pelites indicate a more mafic-ultramafic character for External Ligurian units (enrichment in Cr, Co, Ni, and Th/Sc/Cr/V/Ni relationships that show a systematic shift toward an ultramafic contribution). Petrographic and chemical data indicate that the source for sediments of Corsica and Internal Ligurian units was made up of the upper part of a continental basement and its carbonate sedimentary cover (the Corsica-Europe continental margin). On the other hand, the External Ligurian units were supplied by a source area where a complete lithospheric section was exposed, from the upper mantle up to the deep-sea sedimentary cover (the Adria continental margin). These findings are useful in order to unravel the processes related to the opening mechanisms of the Ligure-Piemontese oceanic basin: among the different rifting models in existence, our data support an asymmetric mechanism dominated by a west-dipping detachment fault, with the Adria margin acting as the lower plate.

At Elba Island, Italy, nine shallow-level late Miocene granite porphyry layers connected by feeder dikes built up three nested Christmas-tree laccoliths. Detailed mapping and reconstruction of tectonic history led to restoration of the original 5-km-thick sequence and determination of the dimensional parameters of each intrusive layer. The laccolith layers were emplaced at depths between 1.9 and 3.7 km, exploiting physical discontinuities that served as crustal magma traps inside a stack of nappes. The intrusive layers are 50–700 m thick, with diameters between 1.6 and 10 km. Length to thickness relationships for individual laccolith layers show a power-law correlation that does not fit the known dimensional distribution for laccoliths, but instead fits a line with a slope typical of the theoretical vertical-inflation stage of laccolith development. This is interpreted as the first reported natural example of the occurrence of a vertical-inflation stage during laccolith growth. The dimensional data for Elba intrusive layers also suggest that laccoliths and plutons commonly form by amalgamation of smaller sheet-like bodies, while multilayer laccoliths form when coalescence fails, possibly owing to the large availability of crustal magma traps.