Upwelling of deep mantle material through a plate window: Evidence from the geochemistry of Italian basaltic volcanics

Abstract

À12, e Hf = À11) accounts for the enrichment of K and other large-ion-lithophile elements in the Italian volcanics. As shown by the relationship in e Hf -e Nd space and the lower-thanchondritic Hf/Sm ratio, this crustal component is dominated by pelagic sediments rather than terrigenous material. The overall scarcity of calc-alkaline compositions in the Italian volcanics and the presence of a HIMU component, which is the hallmark of hot spot basalts, raise the question of how plume mantle source contributes to volcanism in a subduction environment. At about 13 Ma, the Apennine collision terminated the westward subduction of the Adria plate under the European margin and rotated the direction of convergence to the northwest. The cumulative differential of subduction between the fossil plate under Tuscany and the active plate under Sicily since the opening of the Tyrrhenian Sea amounts to at least 300 km and is large enough to rift the dipping plate and open a plate window beneath the southern part of the peninsula. This model is consistent with recent high-resolution seismic tomography. We propose that the counterflow of mixed upper and lower mantle passing the trailing edge of the rifted plate is the source of Italian mafic volcanism. Alternatively, material from a so-far unidentified plume may be channeled through the plate window. The crustal signature is probably acquired by interaction of the mantle advected through the window with the upper part of the subducted plate.

Cenozoic Mg-rich potassic rocks in the Tibetan Plateau: Geochemical variations, heterogeneity of subcontinental lithospheric mantle and tectonic implications

“…In terms of geochemistry, Hf is very similar to Zr and is present in significant amounts, up to several wt.%, in refractory zircons (Gasperini et al, 2002). In addition, dense detrital zircons are concentrated on continental margins in terrigenous material (e.g., detrital sediments and turbidites) rather than in pelagic material (e.g., argillaceous sediments) (Gasperini et al, 2002).…”

Origin and evolution of Cenozoic magmatism of Sardinia (Italy). A combined isotopic (Sr–Nd–Pb–O–Hf–Os) and petrological view

“…Arculus (2003). The red dashed line separates the tholeiitic from the calcalkaline fields (Miyashiro, 1974 Blusztajn and Hegner, 2002;Jung et al, 2005;Pfander et al, 2012) and Italy (Roman and Tuscan Provinces; Gasperini et al, 2002;Conticelli et al, 2007) are reported for comparison. The Italian subduction-related rocks plot towards very radiogenic Sr and unradiogenic Nd isotopic compositions, indicated by the arrow in Fig.…”

Constraints on mantle circulation around the deforming Calabrian slab

“…Quaternary sodic alkaline basalts crop out at Pantelleria, Linosa and Ustica island, Etna, Iblei, Prometeo and Vulture (Figure 1). These volcanic suites are geochemically and isotopically akin to OIB [e.g., Cinque et al, 1988;Civetta et al, 1998;Beccaluva et al, 1998Beccaluva et al, , 2002Gasperini et al, 2002;Trua et al, 2003]. Calc-alkaline volcanic activity is represented by the Aeolian arc and other Tyrrhenian seamounts [e.g., Francalanci et al, 1993;Savelli, 2002].…”