Evolution and Genesis of Calc-Alkaline Magmas at Filicudi Volcano, Aeolian Arc (Southern Tyrrhenian Sea, Italy)

Lithos 72 (2004) 73–96 www.elsevier.com/locate/lithos Evolution and genesis of calc-alkaline magmas at Filicudi Volcano, Aeolian Arc (Southern Tyrrhenian Sea, Italy) A.P. Santoa,*, S.B. Jacobsenb, J. Bakerc a Dipartimento di Scienze della Terra, Universita` di Firenze, Via Giogio La Pira 4, Florence I-50121, Italy b Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA c Royal Holloway University of London, Egham, Surrey TW20 OEX, UK Received 9 July 2002; accepted 29 August 2003 Abstract Petrological, trace element and Sr, Nd, Pb isotopic data are reported for volcanic rocks from the island of Filicudi, Aeolian Arc, Southern Tyrrhenian Sea. The volcano consists of several monogenic and polygenic centres built up through four major phases of explosive and effusive activity started before 1 Ma. Rock composition ranges from calc-alkaline basalts to high-K andesites. There is a negative correlation between silica and MgO, CaO, TiO2, FeOtotal, and a positive trend for K2O, Na2O and P2O5. LILE and HFSE increase with silica, whereas ferromagnesian trace elements have an opposite tendency. Incompatible elements, such as Zr, Ba, Rb, La, display well-defined positive correlations on elemental variation diagrams; weak correlations are shown by the other incompatible elements; Sr and compatible elements define negative, roughly curvilinear trends with incompatible elements. 87Sr/86Sr is poorly but significantly variable (0.704016–0.704740) and shows overall higher values in the mafic than in the sialic rocks. Nd isotope ratios range from 0.512670 to 0.512760 and are negatively correlated with 87Sr/86Sr. Pb isotope ratios cluster around 206Pb/204Pb = 19.31–19.67, 207Pb/204Pb = 15.64–15.69, 208Pb/204Pb = 39.11–39.47. Major, trace element and isotopic variations reveal complex, multistage polybaric evolutionary processes for the Filicudi magmas. It is clear that crystal-liquid fractionation processes determined many of the petrologic and geochemical characteristics of these magmas. However, elemental variations when coupled with isotopic variations (in particular Sr isotopes) demonstrate that mixing processes and interaction of the magmas with older crustal material also played an important role. When compared with other Aeolian arc volcanoes, Filicudi shows petrological and geochemical characteristics similar to those of the nearby islands of Salina and Alicudi. The three islands consist of calc-alkaline rocks, but the degree of magma evolution increases going from the Alicudi to Salina. These variations are likely related to the plumbing system of the three volcanoes. However, trace element and isotopic evidence also suggests significant variations of primary magmas, which reveal a zoned source which suffered different types of metasomatism. D 2003 Elsevier B.V. All rights reserved. Keywords: Aeolian arc; Calc-alkaline magma; Evolutionary processes; Mafic magmas; Mantle metasomatism 1. Introduction * Corresponding author. Tel.: +39-55-2757503; fax: +39-55- Several petrological and geochemical studies on 290312. calc-alkaline volcanic centres provide evidence for E-mail address: [email protected] (A.P. Santo). the important role played by fractional crystallization, 0024-4937/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2003.08.005 74 A.P. Santo et al. / Lithos 72 (2004) 73–96 magma mixing and crustal contamination in the wide compositional variability, from calc-alkaline to evolution of calc-alkaline suites (e.g. Grove et al., shoshonitic up to potassic alkaline. It, thus, represents 1982; Brophy, 1987, 1990; Kerr et al., 1995). Vari- a key locality for studying the relative role of low- able combinations of these low-pressure magmatic pressure evolutionary processes and that of source processes have been documented in many igneous heterogeneity in determining the geochemical charac- provinces (e.g. Medicine Lake volcano; central Aleu- teristics of magmas (e.g. Crisci et al., 1991; Peccerillo tian arc; N–W Scotland). However, in most cases it and Wu, 1992; Francalanci et al., 1993; De Astis et al., is not clear which compositional characteristics de- 1997, 2000). pend on the source anomalies and heterogeneities, In this paper, we report results of a detailed and which ones result from evolution processes. Such petrological and geochemical investigation undertak- a problem is critical for volcanic arcs standing on en on the Filicudi volcano, in the western Aeolian continental margins. Archipelago (Fig. 1). The island consists almost The Aeolian archipelago is a recent to active entirely of typical calc-alkaline volcanic rocks of volcanic arc rising on a continental margin in the mafic to intermediate composition. Previous studies southern Tyrrhenian sea (Fig. 1). It consists of seven (Santo, 1990, 1998, 2000; Francalanci and Santo, main islands and several seamounts, which display 1993; Manetti et al., 1995) brought to the recon- Fig. 1. Schematic bathymetric and geological map of the island showing the main outcropping formations: a = Zucco Grande formation; b, c = Filo del Banco formation and Bue Marino formation; d, e, f = Sciara, Timponazzo and Mt. Montagnola formations; g, h, i = Monte Palmieri formation, Canale and Monte Terrione lavas; j, k = Monte Guardia and Capo Graziano formations; l = Valle la Fossa formation (Benefizio synthem); m = La Canna formation. Cycle I: >1 Ma; cycle II: 0.39 Ma; cycle III: 0.25–0.19 Ma; cycle IV: 0.04 Ma (Santo et al., 1995). 1 = Bathimetry; 2 = Lava dome; 3 = Land slide scar; 4 = Crater. Modified after Santo (2000). A.P. Santo et al. / Lithos 72 (2004) 73–96 75 struction of the geological history of the island and (Calanchi et al., 1995). It developed over a 18-km provided preliminary data on age and compositions of thick continental crust (Morelli et al., 1975), largely rocks. These revealed scattered distribution of many consisting of Palaeozoic rocks, Jurassic ophiolites, major and trace elements, which made it difficult to Mesozoic and recent rocks (e.g. Barker, 1987; Rottura constrain petrogenetic processes and called for further et al., 1989; Caggianelli et al., 1991). Several, partially investigation. overlapping, eruptive centres constitute the volcanoes New major element, trace element and isotopic of Filicudi. Two centres (La Canna and Banco di data on Filicudi volcanic rocks are reported in order Filicudi) are now partially or completely submerged. to shed light on the role played by the source and by Rocks range in composition from basalts to basaltic the different evolutionary processes in determining andesites up to high-K andesites and often contain a geochemical characteristics of calc-alkaline magmas. variety of xenoliths of magmatic and metamorphic On this basis, the paper also deals with the magmatic origin. setting of Filicudi in the framework of the Aeolian arc The eruptive history of the island has been de- magmatism. scribed in detail by Santo (2000), and it will be briefly summarised here. Fig. 1 is a schematic map of the island showing the main units. These were 2. Geology, petrology, geochemistry formed during four main distinct cycles of activity. The first cycle emplaced the Zucco Grande formation 2.1. Volcanological setting and eruptive history (1.02 Ma), in the present northeastern sector of the island. This formation is made up of pyroclastics, The Filicudi island (Fig. 1) represents the emergent whose juvenile component is of andesitic composi- part of a complex 20 km long structure, elongated tion, and of basaltic and basaltic andesitic lava flow. NW–SE, parallel to the main regional lineaments The age of 1.02 Ma (Santo et al., 1995) has been Fig. 2. Classification potassium-silica diagram (Peccerillo and Taylor, 1976). Data are plotted on water-free basis. 1 = high-K basalt; 2 = basalt; 3 = high-K basaltic andesite; 4 = basaltic andesite; 5 = high-K andesite; 6 = andesite; 7 = high-K dacite; 8 = dacite; 9 = rhyolite. For comparison are reported fields for other Aeolian Islands: Alicudi (Peccerillo and Wu, 1992), Salina (Gertisser and Keller, 2000), Lipari (Crisci et al., 1991). 76 A.P. Santo et al. / Lithos 72 (2004) 73–96 measured in a rock sample of this lava flow which, 1: Monte Palmieri, Canale and Monte Terrione for- thus, could represent the oldest rock dated on the mations; Unit 2: Sciara and Monte Montagnola for- island and in the entire Aeolian arc. However, very mations; Unit 3: Monte Guardia and Capo Graziano recently, a younger K–Ar age (211 F 5 ka) has been formations). Basaltic and basaltic andesitic lava flows reported for the Zucco Grande lava flow (De Rosa et characterize the initial stage of this cycle with the al., 2003). Subsequently, after a long period of emplacement almost simultaneously of Sciara, Monte quiescence, the activity shifted to the north–west Palmieri and Monte Guardia formations; the third with the emission of the basaltic lava flows of Filo cycle is closed, after an interruption, by the emission del Banco (0.39 Ma) and Bue Marino formations. In of the high-K andesites of Sciara formation, of the following eruptive activity (third cycle; 0.25– Timponazzo and Canale lavas and of the domes of 0.19 Ma) three different units are distinguished (Unit Monte Montagnola, Monte Terrione, and Capo Gra- Table 1 Major (%) and trace (ppm) element composition of selected Filicudi volcanics Cycle I Cycle II Cycle III M. Palmieri M. Terrione Fil 66 Fil 65 Fil 113 Fil 64 Fil 17 Fil 86 Fil 76 Fil 78 Fil 87 Fil 93 Fil 36* Fil 63* Fil 53 Fil 39* Fil 33 Fil 22 Fil 23 Fil

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