Journal of the Virtual Explorer

The Italian territory occupies a central position in the Mediterranean area, one of the most complex geodynamic regions on Earth.

The present-day geological configuration of the central-western Mediterranean area and, in particular, of the Italian territory is the expression of two main orogenic phases, namely the Alpine and Apennine orogenesis. Both took place within the geodynamic framework of continuous convergence between Africa and Europe plates, a process which started in Cretaceous times and is still going on at present (e.g., Doglioni et al., 1998).

The Alpine chain is the result of a first stage of Africa vs. Europe continental collision which followed the south-eastward immersion of the Alpine Tethys oceanic branches (i.e., Piemonte-Liguria and Valais) beneath the Adriatic continental plate, a promontory of the African plate (Handy et al., 2010 for a review).

Starting from Eocene, the Apenninic subduction developed to the east of the former Alpine collision zone, in particular along its conjugated back-thrust belt, which should likely have been the southward prolongation of the Southern Alps. The former Alpine nappe stack was progressively buodinated and deformed by the back-arc extension behind the Apennine compression zone (e.g., Doglioni et al., 1998). The compressional front and the associated backarc extension progressively migrated eastward and southward in response to slab-rollback-driven Apennine trench retreat. This determined diachronous rifting and opening of the Liguro-Provençal (~34-15 Ma) and Tyrrhenian (~15–0 Ma) sea basins and the counter-clockwise rotation and eastward drifting of continental blocks rifted off the southern European margin (e.g., Corsica-Sardinia and Calabro-Peloritano blocks).

Such a complex succession of geodynamic events was accompanied by widespread magmatism. Compositions of magmas are variable and cover almost entirely the whole range of magmatic rocks occurring worldwide. Most of these magmas are of ultimate mantle origin, although they suffered important evolutionary processes during ascent to the surface, sometimes changing significantly their pristine petrological and geochemical features. A few magmas with a crustal anatectic origin are present in some places along the Alps and in Tuscany, central Italy.

According to many authors, the magmatism in Italy can be divided into two large groups, exhibiting distinct petrological, geochemical and isotopic signatures (e.g., Peccerillo, 2002; Lustrino & Wilson, 2007). One group ranges from arc tholeiitic (TH), calcalkaline (CA), high-K calcalkaline (HKCA) to shoshonitic (SHO) and potassic alkaline, is enriched in Large Ion Lithophile Elements (LILE: Rb, Cs, Th, U, Pb, LREE) relative to High Field Strength Elements (HFSE: Ta, Nb, Hf, Zr, Ti), and is believed to reflect a generation within mantle sources that were modified by addition of fluids or melts from the subducting oceanic or continental lithosphere (Peccerillo, 2005a and references therein). These rocks are generally referred to as “orogenic”, or also as “subduction-related”. They crop out over a wide area that includes the Alps, Sardinia, the Tyrrhenian Sea floor, the Aeolian Archipelago, and the Tyrrhenian border of the Italian peninsula, from the Naples area until Tuscany. Among orogenic rocks we also include the few crustal anatectic intrusive and extrusive bodies that are found along the Alps and in Tuscany.

Another group of rocks ranges from tholeiitic (TH) to Na-alkaline, is depleted in LILE relative to HFSE, and is believed to reveal a generation within mantle sources that did not suffer compositional modification by young subduction processes (Peccerillo, 2005a and references therein). These rocks are generally referred to as “anorogenic” and occur over a wide area, either related to backarc extension or to melting of mantle sources of the foreland (see Bianchini & Beccaluva, this issue).

Such a twofold division of magmatism is overly simplistic, since there are several rocks which possess both “orogenic” and “anorogenic” compositional features (e.g., Plio-Pleistocene magmatism of Sardinia, Mount Vulture; Lustrino et al., 2004; De Astis et al., 2006). These were likely derived from mantle sources that had been affected by subduction-induced compositional modification, but preserved some signatures typical of intraplate magmas either for the scarce effect of subduction processes or/and for the involvement of other enriched sources, such as those that give OIB-type magmas.

In this paper, we review the main petrological, geochemical and isotopic characteristics of the Tertiary to present orogenic magmatism in Italy. A summary of occurrences, ages and compositions are reported in Table 1 (below) and Table 2 (available as a separate download - see note). We will briefly report on the most important data for various occurrences, discuss evolutionary processes occurred during magma emplacement, and explore implications for mantle source processes and the geodynamic setting in which they took place. This is a companion paper to those of Bianchini & Beccaluva and Conticelli et al., which are respectively focused on anorogenic magmatism and on ultrapotassic volcanism of central Italy, one of the most intriguing issues of Italian geology. The ultrapotassic magmatism will be only briefly addressed in this paper.