ETH

N/A

We report results from mineralogical, geochemical and isotopic analyses of the three youngest pyroclastic products (ca. 86 ky) belonging to the Sabatini Volcanic District (Roman Province, central Italy). By means of thermometers, hygrometers and oxygen barometers, we have estimated that the crystallization temperature of magma progressively decreases over time (910–740 °C),whereas the amount ofwater dissolved in the melt and fO2 progressively increases as compositions of magmas become more differentiated (4.5–6.4 wt.% H2O and 0.4–2.6 ΔQFM buffer, respectively). Thermodynamic simulations of phase equilibria indicate that geochemical trends in mafic magmas (MgO N 4 wt.%) can be reproduced by abundant fractionation of olivine and clinopyroxene (~50 wt.% crystallization), while the trends of more evolved magmas (MgO ≤ 4 wt.%) originated by fractional crystallization of plagioclase and sanidine (~45 wt.% crystallization). The behavior of trace elements highlights that magmatic differentiation is controlled by polybaric differentiation that includes: (1) prolonged fractionation of mafic, anhydrous minerals from a primitive, H2O-poor magma at depth and (2) extraction of a more evolved, H2O-rich magma that crystallizes abundant felsic and subordinated hydrous minerals at shallow crustal levels. Assimilation and fractional crystallization modeling also reveal that magmas interacted with the carbonate rocks of the subvolcanic basement. The effect of carbonate assimilation accounts for both trace element and Sr–Nd isotopic variations inmagmas, suggesting amaximumdegree of carbonate assimilation of less than 5 wt.%.

This paper presents a velocity model of the Italian (central Mediterranean) lithosphere in unprecedented detail. The model is derived by inverting a set of 166,000 Pg and Pn seismic wave arrival times, restricted to the highest-quality data available. The tomographic images reveal the geometry of the subduction-collision system between the European, Adriatic, and Tyrrhenian plates, over a larger volume and with finer resolution than previous studies. We find two arcs of low-Vp anomalies running along the Alps and the Apennines, describing the collision zones of underthrusting continental lithospheres. Our results suggest that in the Apennines, a significant portion of the crust has been subducted below the mountain belt. From the velocity model we can also infer thermal softening of the crustal wedge above the subducting Adriatic plate. In the Tyrrhenian back-arc region, strong and extensive low-Vp anomalies depict upwelling asthenospheric material. The tomographic images also allow us to trace the boundary between the Adriatic and the Tyrrhenian plates at Moho depth, revealing some tears in the Adriatic-Ionian subducting lithosphere. The complex lithospheric structure described by this study is the result of a long evolution; the heterogeneities of continental margins, lithospheric underthrusting, and plate indentation have led to subduction variations, slab tears, and asthenospheric upwelling at the present day. The high-resolution model provided here greatly improves our understanding of the central Mediterranean’s structural puzzle. The results of this study can also shed light on the evolution of other regions experiencing both oceanic and continental subduction.