5.1. Spatiotemporal Distribution
 An important outcome of the kinematic reconstruction is the apparent link between the propagating tear faults and the spatial and temporal distribution of magmatism (Figure 6 and Table 1). Magmatism in Italy is manifested by a large spectrum of magmas ranging from subduction-related calc-alkaline and ultra-potassic magmas to intraplate oceanic island basalts (OIB), and Mid Oceanic Ridge Basalts (MORB) (Figure 7) [Peccerillo, 2005]. Here we show that the geochemical affinities of these magmas are generally consistent with our geodynamic model, thus further supporting the suggestion that the Apennine subduction zone was subjected to segmentation through slab tear faulting. Our model, however, does not attempt to explain all the complex features of the petrology of the volcanic edifices [e.g., Peccerillo, 2001, 2005; Gasperini et al., 2002; Panza et al., 2007].
Figure 7. Spatial distribution and petrochemical affinity of young (< 10 Ma) magmatic centers in the Italian peninsula, Sicily and the Tyrrhenian Sea [after Peccerillo, 2005]. OIB-type magmatic centers in the African foreland (e.g., Hyblean Mountains, Pantelerria, Linosa) and in Sardinia are not included. Numbers correspond to the list in Table 1.
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Table 1. Magmatic Centers in the Italian Region and Corresponding Geochronological Agesa
|1||Montecatini Val di Cecina and Orciatico||4.1|
|3||Capraia||7.5–7.1 & 4.8|
|8||Castel di Pietra and Gavorrano||4.4–4.3|
|12||Mt. Capanne, Elba||8.5–6.2|
|13||Porto Azzurro, Elba||5.8–5.1|
|22||Vico and Sabatini||0.8–0.1|
|27||Ponza||4.2–3.0 & 1.0|
|44||Enarete and Eolo seamounts||0.8–0.6|
|46||Filicudi||1.02 & 0.4–0.04|
 The early stage of magmatic activity in the Tyrrhenian Sea, which followed abundant calc-alkaline magmatism in Sardinia, was associated with 9–6 Ma intrusive and extrusive magmatism in Capraia, Elba, Montecristo and Vercelli seamount (Figures 6a and 6b). Magmatism appears immediately above the Miocene subducting slab and is attributed to the subduction-related magmatic arc. By ∼5 Ma, this magmatic arc has migrated eastward [Civetta et al., 1978] from Capraia, Vercelli Seamount, Montecristo, and western Elba to eastern Elba and Giglio islands (Figure 6c). In the southern Tyrrhenian, direct evidence for subduction-related magmas is less clear, but there have been suggestions for the existence of a submerged Pliocene subduction-related volcanic arc [Sartori, 1986, 2005]. The location of this arc [see Sartori, 1986, Figure 3] exactly corresponds to the geometry of the subduction zone at 6–4 Ma, as shown in Figure 6c.
 Simultaneously with the production of Pliocene subduction-related magmas, further magmatism was generated by decompressional melting of asthenospheric mantle in extensional regions and gaps in the slab corresponding to tear faults. One of these tear faults propagated from the northern tip of Corsica to southern Tuscany, producing, at ∼4.8 Ma, mantle-derived shoshonites in Capraia that are characterized by lower ratios of Large Ion Lithophile Elements versus High Field Strength Elements (LILE/HFSE) compared with the older activity (see section 5.2). Further east, the crustal uplift in southern Tuscany and the production of anatectic felsic magmas (San Vincenzo, Castel di Pietra and Gavorrano) along the same fault (Figure 6c) are also interpreted to result from the combination of slab tearing and arc magmatism. Contemporaneous volcanism located along tear faults also occurred further south in Anchise Seamount and Ponza Island. The latter was subjected to magmatism from 4.2 to 1 Ma [Cadoux et al., 2005], and is considered as the northern end of the southern Tyrrhenian Pliocene arc [Sartori, 1986], which was transected by the tear fault of the 41°N parallel line.
 The distribution of some of the younger (4–2 Ma) magmatic activity was also focused along the deeper tear faults (Figure 6d). This includes a cluster of subduction/tear-related magmatic centers (Tolfa, Manziana and Cerite) in the area where the deep tear fault parallel to latitude 42°N intersected with the Italian peninsula. In the south, the occurrence of magmatism in Volturno (>2 Ma) and Ponza (4.2 to 1 Ma) also coincide with slab tearing. Subsequently, during the last 2 Ma (Figure 6e), the central Apennines were subjected to widespread tear-related magmatic activity and magmatism induced by breakoff of the lithospheric slab [De Astis et al., 2006; Panza et al., 2007]. We interpret this magmatic phase as the geodynamic expression for the formation of the central Apennine asthenospheric window following slab segmentation, and the local destruction of the subduction system. Further south, arc magmatism in the Aeolian Islands has been generated by subduction of the narrow Ionian slab, whereas the combination of rapid slab rollback and slab tearing resulted in asthenospheric upwelling at Mt Etna [Gvirtzman and Nur, 1999; Doglioni et al., 2001; Schiano et al., 2001].
5.2. Geochemical Evidence
 The link between the regional geodynamics and geochemical evidence on the depth of melting and extent of mantle metasomatism is not straightforward. Compositional variations and mantle heterogeneity can be modified by rollback-related horizontal mantle flow [Funiciello et al., 2003; Kincaid and Griffiths, 2003; Schellart, 2004] and are affected by variable types and intensities of metasomatism [Panza et al., 2007]. However, whereas some element abundances and ratios (e.g., LILE/HFSE) and isotopic signatures depend on nature and intensity of metasomatism, other compositional features, such as HFSE ratios do not depend so much on metasomatism but reflect premetasomatic mantle sources. Some major element ratios (e.g., Ca/Al of primary melts, which have not suffered clinopyroxene and/or plagioclase fractionation) depend on source mineralogy. The combination of all these features provides a further support for the geodynamic reconstruction (Figure 6).
 Most significant geochemical evidence includes elemental LILE/HFSE ratios, such as La/Nb and radiogenic isotopes (e.g., 87Sr/86Sr). In Figure 8 we use La/Nb and 87Sr/86Sr values to identify different degrees of mantle metasomatism. Low La/Nb and 87Sr/86Sr values in mafic magmas indicate mantle source, probably asthenosphere, which suffered lesser degree of subduction-related mantle metasomatism. OIB-type magmas typically have low La/Nb. Strongly fractionated and anatectic melts have relatively low (but highly variable) La/Nb and high 87Sr/86Sr values, while magmas derived from a subduction-metasomatized mantle are characterized by high La/Nb and variable 87Sr/86Sr values.
Figure 8. La/Nb versus 87Sr/86Sr values for the young (< 10 Ma) Italian magmatic rocks listed in auxiliary material Table S1 and Figure 7. Data are classified on the basis of the geodynamic context as shown in Figure 6, and are presented in two diagrams to enhance readability. Numbers refer to localities in Figure 7. (a) Data from the Tuscan magmatic province and rift-related magmatism. (b) Data from the southern Tyrrhenian and central-southern Italy. The Roman magmatic province is shown in both figures for reference. All data are taken from the compilation of Peccerillo .
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 Continental arc-related magmatism in central Italy is characterized by moderately elevated 87Sr/86Sr values (around 0.708–0.709), LREE/HREE values (La/Yb ∼ 20–30) and LILE/HFSE values (La/Nb > 2 in mafic-intermediate rocks; Figure 8a). In contrast, 143Nd/144Nd values are relatively low. We find these ratios in 7.5 Ma old intermediate calc-alkaline volcanic rocks at Capraia, mafic inclusions in granites (Elba), and predominantly granitic-anatectic rocks (Elba, Montecristo, Giglio, Vercelli Seamount) derived from the mixing of calc-alkaline melts with crustal anatectic magmas. Some of these geochemical affinities coincide with the characteristics of the younger (supposedly slab breakoff-related) magmas of the Roman Magmatic Province (see below).
 The majority of the Tuscan magmas are strongly evolved, and are largely derived from melting of the Tuscan basement [Poli, 2004]. Mantle-derived mafic magmas contain subduction components but there are rocks with higher La/Nb and Ca/Al (e.g., shoshonites versus older calc-alkaline rocks at Capraia). Higher Ca/Al and lower Sr isotope ratios mean higher proportions of asthenospheric component than metasomatized lithospheric mantle, which agrees with the presence of deep faults allowing deep mantle to contribute to magmatism. We therefore interpret such magmatism as slab tear-related magmatism (Figure 9) involving deeper asthenospheric mantle-derived melts, which either rose to the surface and produced relatively primitive magmas (shoshonites of Capraia and Campiglia dyke) or provided additional heat for the melting of the lithospheric mantle and continental crust (Tolfa-Manziana-Cerite, Roccastrada, San Vincenzo, and southern Tuscany granitoids). We emphasize, however, that the more evolved felsic magmas do not enable us to constrain the geochemical characteristics of the mantle. Their association with possible tear faulting is therefore predominantly based on their temporal and spatial distribution.
Figure 9. Simplified 3-D sketch of the subducting lithosphere beneath Italy showing the approximate spatial distribution of tear faults and the geometry of the central Apennine slab window. Selected tear-related and slab breakoff-related magmatic centers are also shown.
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 In the central Apennines, slab breakoff following tearing coincided with the generation of magmas in the Roman Magmatic Province (Vulsini, Vico-Sabatini and Alban Hills, Figure 9). These relatively late (<1 Ma) volcanic complexes are characterized by potassic and high-potassic magmas, developed in a zone of NW-SE trending normal faults [Peccerillo, 1990, 2005]. These magmatic centers are situated northwest of the central Apennine asthenospheric window (Figure 6e), and could have possibly been triggered by the final breakoff of the lithospheric slab. Activity at Mt Ernici and Roccamonfina marks the transition between the slab breakoff magmatism and the tear-related activity of the Pontine Islands (Ponza, Ventotene, and Palmarola) and Campania province (Ischia, Procida, Phlegrean Fields, and Vesuvius).
 The two most striking examples of asthenospheric upwelling along slab tear faults are Mt Etna [Gvirtzman and Nur, 1999; Doglioni et al., 2001; Trua et al., 2003] and Mt Vulture [De Astis et al., 2006] (Figure 9). These volcanoes are situated on the margin of the foreland and are therefore much less affected by subduction processes. Mt Etna is characterized by a typical Ocean Island Basalt (OIB) composition with some arc signatures in the younger products [Schiano et al., 2001] (Figure 8b). The source of magmatism in Vulture is similar to the Campanian-Pontine volcanoes (Vesuvius, Phlegraean Fields), but its position over the edge of the Adriatic continental lithosphere resulted in a higher level of intraplate (OIB type) mantle influence [De Astis et al., 2006].
 The Aeolian Islands and associated seamounts are typical subduction-related volcanoes, with the oceanic or thinned continental Ionian slab actively subducting beneath their eastern sector. They are characterized by relatively low 87Sr/86Sr values (Figure 8b) in the western sector, and represent oceanic arc volcanism. We recognize, however, an enhanced magmatic activity (Vulcano, Lipari and Salina) and an apparent offset along the tear fault that connects the arc with Mt Etna to the southeast (Figure 5). The westernmost island of Alicudi is characterized by rather low La/Nb and 87Sr/86Sr values, similar to those of Etna and Ustica, suggesting a stronger asthenospheric influence. Also the Island of Stromboli has relatively low LILE/HFSE, resembling Campanian volcanoes for several incompatible element ratios and radiogenic isotope signatures [Peccerillo, 2001]. Its position at the margin of the arc and similar geochemical signatures as the Campanian rocks also support input of OIB-type components for Stromboli. The south Tyrrhenian seamounts and ocean floor with MORB, back-arc, and OIB affinity are also related to the asthenospheric upwelling that accompanied the opening of the Tyrrhenian Sea.
 The role of slab tearing seems to be somewhat less significant in controlling the distribution of kamafugitic-melilititic and lamproites magmas in the northern Apennines. Figure 8a shows the geochemical similarity between the kamafugitic-melilititic magmas and the slab breakoff magmas of the Roman Magmatic Province. This suggests a common metasomatized lithospheric mantle origin [Peccerillo, 2005]. However, their spatial distribution was predominantly controlled by crustal structures associated with a rift-related postcollisional environment [Peccerillo, 2005; Peccerillo and Martinotti, 2006]. Similarly, the ascent of lamproitic magmas, originated from a metasomatized lithospheric mantle [Peccerillo and Martinotti, 2006] with a strong crustal signature (Figure 8a), was controlled by extensional crustal structures.