THE MAGMATIC EVOLUTION OF THE WESTERN AND CENTRAL ELBA INTRUSIVE COMPLEX, ITALY

Post-collisional extension of the internal parts of the Apennine orogenic belt led to the late Miocene opening of the Tyrrhenian basin. Extensive 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. Between 8 to 6.8 Ma, an intrusive complex was progressively built on western Elba Island by emplacement of multiple, shallow-level porphyritic laccoliths, a major pluton, and a final dike swarm, all within a stack of nappes. Compositions of materials involved in the genesis of the magmas of Elba Island, as compared to the whole Tuscan Magmatic Province, are constrained by new geochemical and Sr-Nd isotopic data. 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 dike at Elba, are sufficient to account for the generation by melt hybridization of the most voluminous magmas (ca. e _Nd (t) –8.5, ⁸⁷Sr/ ⁸⁶Sr 0.715). Peculiar 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 (e _Nd (t) between –9.5 and –10.0, ⁸⁷Sr/ ⁸⁶Sr Sr variable between 0.7115 and 0.7146), and late mantle-derived magma strongly enriched in incompatible elements (e _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.