CARATTERI GEOCHIMICI DEL MANTELLO SORGENTE DEL MAGMATISMO NAPOLETANO: NUOVE CONOSCENZE DALLO STUDIO DELLE OFIOLITI DEL SETTORE LUCANO DELL’APPENNINO MERIDIONALE

Introduction The Mediterranean area is one of the most complex geodynamic settings of the world (e.g., Carminati et al., 2012, and references therein) as clearly illustrated by the huge variety of igneous lithologies. On the basis of trace element concentrations, and isotopic compositions, the latter being extremely variable from typical mantle to typical crustal values, sectors characterized by either anorogenic (Lustrino and Wilson, 2007) or orogenic magmatism (Harangi et al., 2006; Lustrino et al., 2011) are usually distinguished in the Central-Western Mediterranean area, including Italy. Since the Cenozoic to the Present, the Central-Western Mediterranean area has been the site of intense but discrete magmatic activity. The products show a wide compositional range, from sub-alkaline (tholeiitic and calc-alkaline) to alkaline (sodic, potassic, and ultrapotassic) and from mafic/ultramafic to felsic (Peccerillo, 2005, and references therein). Many are the hypotheses about magmagenesis and geodynamic significance of these rocks (e.g., Peccerillo and Lustrino, 2005), but most of the Mediterranean orogenic magmatism might reasonably be the result of partial melting of mantle sources modified by slab materials during and/or after subduction event(s). For the Italian magmatism in particular, this hypothesis is supported by a considerable amount of studies that highlight its post-collisional character (e.g., Peccerillo, 1999; Beccaluva et al., 1991; Conticelli et al., 2002, 2004, 2007, 2009; D’Antonio et al., 1996, 1999a, 2007, 2013; Francalanci et al., 2004, 2007; Tonarini et al., 2004; Duggen et al., 2005; Harangi et al., 2006; Avanzinelli et al., 2008, 2009; Bianchini et al., 2008; Prélevic et al., 2008; Nikogosian and van Bergen, 2010; Lustrino et al., 2011). Furthermore, the Italian magmatism has been related to the subduction of the Ionian oceanic lithosphere, being part of the wider Tethys Ocean (Gvirtzman and Nur, 1999; Faccenna et al., 2007). The genesis of magmas in the “subduction factory” is very complex because of the large number of variable factors involved, such as the original chemical and mineralogical composition of mantle, presence of fluids and their nature, depth of the source, degree of partial melting, temperature and confining pressure (e.g., Class et al., 2000; Hanyu et al., 2006; Handley et al., 2007; Leslie et al., 2009; Vigoroux et al., 2012). Nevertheless, worldwide subduction-related mafic volcanic rocks have distinctive incompatible elements patterns, characterized by strong enrichment in LILE and Pb with respect to HFSE (noticeable is the Nb-Ta-Ti depletion), and REE. This depends on the interaction between pre-enrichment mantle wedge and enriching agents coming from the slab. The mantle wedge before the enrichment is generally considered either MORB-like (e.g., Münker, 2000) or OIB-like (e.g., Peate et al., 1997). The exact nature can be inferred by investigating elements, such as some HFSE, not mobilized by any fluid phase during the subduction process. Concerning the nature of the enriching agents there are several hypotheses. Some authors consider the main role of hydrous fluids released during the dehydration of basaltic crust and pelagic sediments (e.g., Ryan et al., 1995; Bizimis et al., 2000; Dorendorf et al., 2000; Handley et al., 2007; Vigoroux et al., 2012); others invoke also the involvement of partial melting of sediments (e.g., Elliott et al., 1997; Turner et al., 1997; Elburg and Foden, 1998; Johnson and Plank, 1999; Class et al., 2000; Hanyu et al., 2006; Leslie et al., 2009). The isotopic and trace element characteristics of the basaltic and sedimentary cover in a subducting slab are generally different, though hardly quantifiable. The different mobility of some incompatible trace elements in slab-derived hydrous fluids and melts is typically used in geochemical modeling to distinguish between these two extreme cases (Brenan et al., 1995; Ayers, 1998; Johnson and Plank, 1999; Pearce et al., 1999; Becker et al., 2000; Walker et al., 2001; Hanyu et al., 2006; Handley et al., 2007; Leslie et al., 2009; Vigoroux et al., 2012). LILE are more easily mobilized from slab and transferred to the mantle if the metasomatizing agents are hydrous fluids. On the other hand, HFSE have a little mobility because of their low compatibility in hydrous fluids (Plank and Langmuir, 1998). Conversely, if the main enriching agents are melts, HFSE can be partly mobilized together with LILE. However, it is not always easy to determine which elements, and in which amounts are retained in the slab, and which transferred to the fluid phase (hydrous and/or melts) because this depends on the presence of residual mineral phases in the slab and the geothermal gradient. Anyway, if the behavior of trace elements is taken into account, it is possible to discriminate the different contributions provided by hydrous fluids and/or melts to the mantle enrichment. Current views of the enrichment of mantle beneath the Central-Western Mediterranean area involve either subduction-derived material (e.g., Peccerillo, 1999; Beccaluva et al., 1991; Conticelli et al., 2002, 2004, 2007, 2009; Francalanci et al., 2004, 2007; Tonarini et al., 2004; Duggen et al., 2005; Harangi et al., 2006; Avanzinelli et al., 2008, 2009; Bianchini et al., 2008; Prélevic et al., 2008; Nikogosian and van Bergen, 2010; Lustrino et al., 2011) or fluids metasomatizing a plume-type mantle source, calling for a within-plate geodynamic setting (Bell et al., 2013, and references therein). The latter hypothesis is simply ruled out on the basis of the major oxides content of the mafic volcanic rocks, that are typical of melts coming from restitic mantle sources, at variance with the typical fertile sources of plumes (as discussed, for instance, by Conticelli et al., 2004). In the framework of the complex magmatism of Western Mediterranean, the volcanic area of Campania (Southern Italy) is one of the most interesting. This area has been the site of intense volcanism during Plio-Quaternary times. Over the past ~40 ka, volcanism has been localized mainly at the Mt. Somma-Vesuvius complex (SV) and the Phlegrean Volcanic District (PVD), that includes the Campi Flegrei caldera as well as the Ischia and Procida islands in the Gulf of Napoli (Orsi et al., 1996). The products of all these volcanoes show geochemical and isotopic features typical of subduction-related volcanic rocks. The aim of this study is twofold. The first aim is to better identify the composition of the pre-enrichment mantle sector underlying the Neapolitan volcanic area, still poorly known due to the scarcity of suitable primitive mafic rocks; the second aim is to characterize the nature of the subduction-related components (fluids and/or melts from sediments and/or altered oceanic crust) that modified the pre-enriched mantle sector. In previous attempts to model the mantle enrichment for the PVD, average subducted slab material compositions from literature have been utilized (D’Antonio et al., 1999a, 2007, 2013; Tonarini et al., 2004; Piochi et al., 2004). For the purposes of the present work, the igneous rocks and associated sedimentary cover of the Mt. Pollino ophiolitic sequences, have been studied as possible contaminants that more realistically enriched the mantle source region of Campania during subduction. They represent ocean-derived terrains obducted on the western margin of the Adria continental micro-plate during the Apennine orogenesis (Vitale and Ciarcia, 2013, and references therein), and should be the best representative of the material that was subducted into the Western Mediterranean mantle during the closure of the Ligurian branch of Tethys (Bortolotti and Principi, 2005 and references therein). Abyssal peridotites and Alpine-type peridotite ophiolite massifs, together with mantle xenoliths associated with alkaline rocks, provide a good opportunity to investigate the physical state, chemical composition and mineralogy of the upper mantle. As a result of both alteration and metamorphism, ophiolite rocks commonly occur on Earth surface with chemical and mineralogical modifications. However, they have a wider distribution with respect to mantle xenoliths. Also, knowledge of ophiolites and modern oceanic lithosphere were fundamental for the development of a conceptual model of the oceanic crust. According to this model, the oceanic crust consists of a 4 to 6 km thick igneous crust (pillow basalts, sheeted dykes and gabbroic layer, from top downward) produced by melts formed by decompression melting of ascending asthenospheric mantle, overlying a peridotite basement. Moreover, the igneous pile may be overlaid by a few hundred meters of pelagic/terrigenous sediments. During the last thirty years, the study of peridotites from the Mediterranean Area has provided a wealth of information, constraining the composition and, partially, the evolution of the Mediterranean Lithospheric Mantle. In Italy, ophiolites occur in scattered outcrops located mainly in the Alps and Northern Apennine (Piccardo et al., 2009 and references therein). In Southern Apennine, ophiolite outcrops are very rare, occurring only in southern Basilicata and northern Calabria (Beccaluva et al., 1983; Spadea, 1994) and like as olistoliths in Miocene turbidites of Cilento Group at Monte Centauino (Di Girolamo et al., 1992) in Southern Campania. Ophiolites from the Alpine and Apennine orogenic terranes are believed to represent fragments of oceanic lithosphere of the Ligurian-Piedmontese (Ligurian Tethys) basin that formed during Late Jurassic between the Europe and Adria continental blocks, following extension driven by far field tectonic forces and that were obducted on continental crust during the closure of this ocean (Bortolotti and Principi, 2005). More information on the mineralogy and geochemistry of the Mediterranean upper mantle has been derived especially from the largely studied Northern Apennine ophiolite sequences. In the past decades, the Southern Apennine ophiolites have been largely studied (Lanzafame et al., 1978, 1979a, 1979b; Beccaluva et al., 1983; Di Girolamo et al., 1992; Spadea, 1994; Piluso et al., 2000; Liberi et al., 2006; Cristi Sansone et al., 2011) but no significant petrographic, geochemical and isotopic inferences on the upper mantle they represent have been reported. The use of Tethyan sediments as a contaminant for the mantle could better constrain the enrichment event(s) of the mantle sector underlying the PVD, allowing a more complete understanding of the complex geochemical and isotopic features of erupted magmas. To achieve this goal, new geochemical and Sr-Nd-isotopic data are presented on representative samples of the pillow-lavas and meta-sedimentary cover of the Timpa delle Murge Formation ophiolites, and of the Crete Nere Formation, in order to fully characterize the material subducted during the orogenesis. Using the acquired data a geochemical and isotopic model is proposed to highlight a possible link between the oceanic crust subducted during the Tethys closure and the geochemical features of the Plio-Quaternary subduction-related Neapolitan Volcanic Area, as these sedimentary and igneous rocks, or other similar, may have changed the composition of the upper mantle underlying a large region of the Mediterranean Area. PART 1: Petrological characterization of Mt. Pollino ophiolites Geological setting In Italy, ophiolites occur in scattered outcrops located mainly in the Alps and Northern Apennine (Robertson, 2002; Bortolotti and Principi, 2005). In Southern Apennine, ophiolite outcrops are very rare, occurring only in Southern Campania, Basilicata and Northern Calabria (Beccaluva et al., 1983; Di Girolamo et al., 1992; Spadea, 1994; Tortorici et al., 2009; Vignaroli et al., 2009). Southern Apennine ophiolites are in many ways different from tipical ophiolite sequences. In fact, the Alpine-Apennine ophiolites consist of a serpentinized peridotite basement (direct exposure of mantle peridotites on the sea-floor) and a reduced crustal sequence characterized by lack of sheeted-dyke complexes, relatively small volumes of gabbros intruded in the peridotite basement, and a discontinuous basaltic and oceanic sediments cover. They are believed to represent fragments of Tethys oceanic crust that were obducted on continental crust during the closure of the Ligurian branch of Tethys ocean prior to 35 Ma ocean (Bortolotti and Principi, 2005; Liberi et al., 2006). Bonardi et al. (1988) ascribed these fragments to the Liguride Complex, a Cretaceous-Oligocene accretionary complex representing the highest structural element of the Apennine Chain, thrust over the Mesozoic carbonate units. In the Mt. Pollino area, the Liguride Complex covers the carbonate terrains of the Alburno-Cervati Unit, and includes three distinct tectonic units named Frido Unit, Episcopia-San Severino Mélange, and North Calabrian Unit. The Episcopia-San Severino Mélange includes dark green cataclastic serpentinite exposed in scattered outcrops, likely representing fragments of an upper mantle portion, associated with garnet gneisses and amphibolites (Spadea, 1982), recently attributed to old crust, both oceanic and continental (Frido Unit; Vitale et al., 2013). The North Calabrian Unit, divided into Timpa delle Murge Formation, Crete Nere Formation, and Saraceno Formation from base upwards, crops out widely on Timpa delle Murge Hill, along the boundary between Basilicata and Calabria, close to Mt. Pollino. In particular, the Timpa delle Murge formation is an ophiolite sequence including small gabbroid bodies, abundant and well-preserved pillow lavas, and a pelagic sedimentary cover. The latter is made up of silicified red-green shales affected by a pencil cleavage, containing several layers of quartz-arenites, followed by green-red radiolarites with nodular structures, with thin intercalations of calpionella marly limestones. Upwards, the succession continues with intercalated quartz-arenites and black shales that mark the transition to the Crete Nere Formation. The latter covers a large time span, from Late Cretaceous to Late Eocene, although most deposition occurred in Middle Eocene (Bonardi et al., 1988b). The radiolarian cherts of the Timpa delle Murge Formation were paleontologically dated at ~160 Ma (Marcucci et al., 1987). In our opinion, this age can be confidentially considered to define the end of oceanic crust generation in that area. Given the marked temporal hiatus between the two formations, it is clear that the Timpa delle Murge ophiolites were tectonically embedded in the much younger Crete Nere Formation terranes, that crop out both below and over them. The ophiolite sequences of Basilicata and Calabria were affected by subduction-related HP/LT metamorphism, marking a burying episode followed by exhumation occurred during the Late Oligocene-Early Miocene Apennine orogenesis (Piluso et al., 2000; Liberi et al., 2006; Cristi Sansone et al., 2011). However, the Timpa delle Murge ophiolites suffered such metamorphism to a much lesser extent than all other ophiolite sequences in Southern Italy, attaining the green schist facies only, due to either ocean-floor metamorphism or accretionary wedge tectonic evolution (Cristi Sansone et al., 2011). Thus, the original geochemical and isotopic features of these rocks should be quite well preserved. However, despite the large wealth of studies, no petrographic, geochemical and isotopic data are available for the sedimentary terrains associated with these ophiolites. Field and Laboratory activities Ninety samples of either mafic or ultramafic igneous rocks, and some sedimentary rocks of the ophiolitic sequence that crop out in a few Southern Lucanian localities (Episcopia, San Severino Lucano, Timpa Pietrasasso and Timpa delle Murge) have been collected. At the University of Napoli Federico II, the most representative samples were cut with a saw and crushed in a jaw crusher, and powders were produced in a low-blank agate mortar from clean chips first washed in distilled water. Major oxides and some trace elements (Sc, V, Cr, Ni, Rb, Sr, Ba, Y, Zr and Nb) were analyzed by X-ray fluorescence using a sequential X-ray spectrometer Philips PW2400 at the Centres Cientìfics i Tecnològics de la Universitat de Barcelona (CCiTUB), Spain. The volatile content (LOI) was measured using standard thermogravimetric methods at the CCiTUB. Other trace elements including the Rare Earth Elements (REE) were analyzed by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) using a Perkin Elmer Elan 6000 at the CCiTUB. Whole rock powders were dissolved with high-purity HF + HNO3 + HClO4 mixtures. Relative precision was generally better than 1–2% for major oxides and better than 5–10% for trace elements. Sr- and Nd-isotopic compositions of Mt. Pollino volcanic and sedimentary rocks were determined on whole rocks (~0.1 g). Whole rock powders were leached with warm HCl for 10 minutes and dissolved with high-purity HF + HNO3 + HCl mixtures. Sr and Nd were separated using standard column chromatographic methods, using Dowex AG50W X-8 (200-400 mesh) and Ln Spec cation exchange resins for Sr and Nd, respectively. Sr- and Nd-isotopic ratios were measured by thermal ionization mass-spectrometry (TIMS) using a ThermoFinnigan Triton TI at the Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli, Osservatorio Vesuviano. The internal precision of each measurement is expressed as ± 2 times the standard error (2se), where se = /√n. In the period of sample measurements, the NIST-SRM 987 standard gave a mean value of 87Sr/86Sr = 0.710249 (2 = 1.47 x 10-5; N = 67), and the La Jolla standard gave a mean value of 143Nd/144Nd = 0.511833 (2 = 7.65 x 10-6; N = 21). The Nd-isotopic ratios measured on the samples were normalized to the accepted values of the La Jolla standard (143Nd/144Nd = 0.51185). The mineral compositions were obtained with a SEM-WDS Cameca SX100 microprobe at CCiTUB, equipped with four INCA X-act detectors, operating at a 15kV beam voltage, with a 50–100mA filament current, variable spot size and 50s net acquisition time. Precision and accuracy were controlled using an internal standard. Trace element contents in clinopyroxene and host glassy matrix were determined by laser ablation-inductively coupled plasma-sector field mass spectrometry (LA-ICPSFMS) at CNR–Istituto di Geoscienze e Georisorse (IGG, Pavia, Italy). The microprobe has a double-focusing sector field analyzer (Finnigan Mat, Element I) coupled with a Q-switched Nd:YAG laser source (Quantel Brilliant). The fundamental emission of the laser source (1,064 nm, in the near-IR region) was converted to 213 nm by three harmonic generators. Spot diameter varied in the range of 40–60 m. Precision and accuracy (both better than 10% for concentrations at ppm level) were assessed by means of repeated analyses of NIST SRM 612 and BCR-2g standards. The modal composition of gabbros was determined with an optical microscope, coupled with a Leica DFC-280 camera and software Leica QWin at University of Naples Federico II. Results Ultramafic Rocks All peridotite samples contain large amount of serpentine and other phyllosilicates such as chlorite and pumpellyte. The mineralogical composition of residual primary paragenesis is very homogeneous, so that the original composition must have been peridotite for all samples. Three samples are characterized by millimeter-sized porphyroclasts of olivine and orthopyroxene, varying from anhedral to subhedral. Both olivine and orthopyroxene show internal deformation (deformation lamellae along the slip planes, kink banding and wavy extinction). Clinopyroxene is present as small crystals or as exsolution lamellae in orthopyroxene. Spinels are typically anhedral. Rare is the presence of anhedral crystals of amphibole. The remaining samples show porphyroblastic textures with millimeter-sized porphyroclasts of brecciated olivine, and kink-banded and plastically deformed orthopyroxene. Olivine and orthopyroxene grains are commonly elongated. The elongated coarse grains (up to a few centimeters) give a well-developed foliation to the rock. Spinels occur as disseminated, completely anhedral or amoeboid interstitial grains and sometimes as inclusions in olivine. Clinopyroxene occur as intercumulus small crystals or as exsolution lamellae in orthopyroxene. Olivine is generally uniform in composition and its forsterite (Fo) content is variable in the ranges 90.1–90.6 in peridotites with amphibole, and 91.2–91.9 in peridotites without amphibole (Fig. 7.1). NiO wt% of olivine composition ranges between 0.22 and 0.42 in peridotites with amphibole, and between 0.42 and 0.69 in peridotites without amphibole, so there is a decrease in Fo and NiO values of the olivines from peridotites without amphibole to peridotites with amphibole (Fig. 7.2). The concentrations of Mn, Al, Ca and Ti are negligible. Orthopyroxene (Fig. 7.6) is generally enstatite in composition (En = 88-92 mol%), with Cr2O3 contents up to 1.2 wt% and Al2O3 variable in the range 1.5-2.8 wt.%. Clinopyroxenes are diopside in composition (Fig. 7.6) and show Mg# in the range 88-93, high Cr2O3 content (1-3 wt.%), very high CaO contents (20-24 wt.%) and low TiO2 (< 0.5 wt.%). REE contents of clinopyroxene (Fig 7.36) are about 10xChondrite in MREE and HREE region where the patterns are almost flat, while the LREE contents are considerably depleted, with a significant difference between peridotites with amphibole (LaN = 1-4xChondrite) and peridotites without amphibole (LaN = 0.05-0.5xChondrite). Spinel of peridotites (Fig. 7.9) is chromiferous (Cr# = 19-26 in peridotites with amphibole, and 42-59 in peridotites without amphibole) and aluminiferous (3

Open-system magma evolution and fluid transfer at Campi Flegrei caldera (Southern Italy) during the past 5 ka as revealed by geochemical and isotopic data: The example of the Nisida eruption

We have carried out a detailed petrological investigation on products of the poorly understood Nisida eruption, one of the most recent volcanic events (~4 ka BP) at Campi Flegrei caldera. We present major oxide contents and Sr–Nd isotopic data determined on bulk rock, groundmass and separated phenocrysts, along with major and volatile elements (H2O, Cl, S and CO2) content of clinopyroxene-hosted melt inclusions from pumice fragments representative of the eruption. We use these to elaborate the role of magmatic evolution processes and fluid transfer prior to, and during, the Nisida eruption. The results indicate that the eruption was triggered by the arrival of a volatile-rich, shoshonite–latite magma. This magma was similar in terms of Sr and Nd isotopes (87Sr/86Sr ~0.70730; 143Nd/144Nd ~0.51250) to the Astroni 6 magmatic component. We infer that emplacement of this magma triggered resurgence of the caldera floor, and fed a large part of the volcanic activity at Campi Flegrei caldera during the past 5 ka. The new data on the Nisida eruption and other recent eruptions at Campi Flegrei, together with published data, suggest that fractional crystallization, and potentially fluid transfer from deep to shallow depths may account for most of the chemical variability of the erupted melt. Additional processes, such as magma mingling/mixing, and/or entrapment of antecrysts into the magma prior to the Nisida eruption are required to explain the large isotopic variation displayed by the analyzed products. The Nisida eruption occurred in the eastern sector of the resurgent Campi Flegrei caldera. In this sector, presently affected by an extensional stress regime, previous studies suggest that a Nisida-like eruption would be likely if the level of activity in the caldera were to intensify. In an area with such structural conditions, the ascent of a volatile rich magma such as that which erupted at Nisida should generate geophysical and geochemical signals detectable by an efficient monitoring network. The results of this investigation should inform the study of other active calderas worldwide that are experiencing persistent unrest, such as Rabaul, Aira, Iwo-Jima, Santorini, Long Valley and Yellowstone

A high resolution tephrochronological record of MIS 14-12 in the Southern Apennines (Acerno basin, Italy).

Lithological, mineralogical, and glass chemical analyses on juvenile fragments extracted from 20 tephra layers embedded within the lacustrine sediments of the Acerno basin (Southern Apennines, Italy) were carried out together with four sanidine 40Ar/39Ar age determinations. The measured ages span the interval between 561 and 493 ka. Middle Pleistocene eruptive activity at Roman Province volcanoes was identified as the main possible source of the investigated tephra layers. Some of them were correlated with precise terrestrial counterparts corresponding to large explosive events of the Sabatini (e.g. Tufo Giallo della Via Tiberina) and Alban Hills volcanic districts (e.g. Tufo Pisolitico di Trigoria). The integration of tephrochronology and pollen analyses allowed the Acerno lacustrine sedimentation to be constrained between MIS 14 and 12, which overlaps with several well-studied, lacustrine successions of the Southern Apennines. The correlation with other tephrostratigraphic records from intramontane basins in central-southern Apennines testifies to the wide dispersal of at least three tephra layers that serve as marker layers, thus improving the resolution of the Middle Pleistocene Italian tephrostratotype

Subduction-related enrichment of the Phlegrean Volcanic District (Southern Italy) mantle source: new constraints on the characteristics of the sedimentary components

The Neapolitan volcanic area (Southern Italy), which includes the Phlegrean Volcanic District and the Somma– Vesuvius complex, has been the site of intense Plio-Quaternary magmatic activity and has produced volcanic rocks with a subduction-related geochemical and isotopic signature. High-Mg, K-basaltic lithic lava fragments dispersed within hydromagmatic tuff of the Solchiaro eruption (Procida Island) provide constraints on the nature and role of both the mantle source prior to enrichment and the subduction-related components. The geochemical data (Nb/Yb, Nb/Y, Zr/Hf) indicate a pre-enrichment source similar to that of enriched MORB mantle. In order to constrain the characteristics of subducted slab-derived components added to this mantle sector, new geochemical and Sr–Nd-isotopic data have been acquired on meta-sediments and pillow lavas from Timpa delle Murge ophiolites. These represent fragments of Tethyan oceanic crust (basalts and sediments) obducted during the Apennine orogeny, and may be similar to sediments subducted during the closure of the Tethys Ocean. Based on trace element compositions (e.g., Th/Nd, Nb/Th, Yb/Th and Ba/Th) and Nd-isotopic ratio, we hypothesize the addition of several distinct subducted slab-derived components to the mantle wedge: partial melts from shales and limestones, and aqueous fluids from shales, but the most important contribution is provided by melts from pelitic sediments. Also, trace elements and Sr–Nd-isotopic ratios seem to rule out a significant role for altered oceanic crust. Modeling based on variations of trace elements and isotopic ratios indicates that the pre-subduction mantle source of the Phlegrean Volcanic District and Somma–Vesuvius was enriched by 2–4% of subducted slab-derived components. This enrichment event might have stabilized amphibole and/or phlogopite in the mantle source. 6% degree of partial melting of a phlogopite-bearing enriched source, occurring initially in the garnet stability field and then in the spinel stability field can generate a melt with trace elements and Sr– Nd-isotopic features matching those of high-Mg, K-basalts of Procida Island. Furthermore, 2% partial melting of the same enriched source can reproduce the trace elements and isotopic features of the most primitive magmas of Somma–Vesuvius, subsequently modified by assimilation of continental crust during fractional crystallization processes at mid-lower depth. Combined trace element and Sr–Nd isotope modeling constrains the age of the enrichment event to 45 Ma ago, suggesting that the Plio-Quaternary magmatism of the Neapolitan area is postorogenic, and related to the subduction of oceanic crust belonging to the Tethys Ocean