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 5 Fil 6

SiO2 50.94 51.08 52.98 53.00 60.09 49.07 50.03 51.07 51.15 50.49 50.76 51.96 52.41 52.5 53.25 53.66 61.21 57.74 58.59 TiO2 0.73 0.73 0.85 0.62 0.55 0.70 0.72 0.71 0.73 0.69 0.78 0.76 0.73 0.77 0.70 0.68 0.62 0.62 0.59 Al2O3 19.21 18.51 18.45 19.25 16.05 18.53 18.95 19.77 18.46 19.44 19.21 21.04 18.97 18.93 18.42 16.80 15.78 17.84 17.79 Fe2O3 3.86 3.68 3.19 2.67 4.24 8.55 3.68 3.60 4.45 3.63 3.62 2.67 2.73 4.69 4.07 4.38 2.58 2.38 2.10 FeO 5.56 5.60 4.60 5.45 2.28 0.80 5.12 4.68 4.88 5.00 5.36 5.08 5.64 4.12 4.48 3.72 3.72 4.20 3.80 MnO 0.18 0.17 0.15 0.16 0.14 0.17 0.17 0.16 0.17 0.17 0.16 0.15 0.16 0.16 0.18 0.16 0.16 0.14 0.14 MgO 4.98 5.20 4.46 5.18 2.35 5.73 5.80 3.52 5.23 5.51 4.76 3.25 4.71 4.32 4.05 3.55 2.18 3.15 3.03 CaO 10.77 10.78 10.19 9.48 6.73 11.85 11.39 11.11 10.59 10.96 10.81 10.3 9.97 10 9.40 10.21 6.13 7.62 7.33

Na2O 2.39 2.34 2.72 2.40 3.09 2.12 2.31 2.69 2.42 2.32 2.46 2.78 2.50 2.46 3.03 2.82 3.72 3.01 3.10 K2O 1.12 1.31 1.50 1.44 2.42 0.98 1.10 1.26 1.35 1.22 1.33 1.57 1.53 1.46 1.74 1.92 2.43 2.31 2.48 P2O5 0.12 0.12 0.31 0.15 0.14 0.14 0.16 0.14 0.12 0.15 0.13 0.17 0.15 0.13 0.18 0.22 0.21 0.17 0.18 L.O.I. 0.13 0.48 0.60 0.20 1.92 1.37 0.59 1.29 0.44 0.43 0.62 0.28 0.51 0.46 0.50 1.88 1.25 0.82 0.88 Mg# 52.73 54.14 54.71 57.15 43.83 57.73 58.19 47.35 54.36 57.42 52.76 46.78 54.07 51.16 50.16 48.39 42.20 50.13 51.87 Rb 31 30 52 35 82 20 23 33 31 34 30 47 31 40 56 64 78 73 76 Sr 710 731 803 700 640 703 687 741 733 708 717 802 724 725 693 718 734 686 672 Y 18171919131617181819201818212019182120 Zr 77 76 97 85 113 73 75 92 79 81 60 96 81 55 101 105 122 112 115 Nb 77111097786 7 6 86 69911109 Ba 360 415 503 390 628 326 352 415 387 404 364 468 437 491 514 494 530 574 589 Ni 14 16 18 18 3 26 23 11 18 12 15 8 14 11 9 12 3 7 6 ** * * ** * * ** ** * * ** * Cs 0.70 1.10 1.30 0.70 0.26 1.30 1.30 0.85 1.30 1.5 La 21.0 18.1 30.0 18.0 28.2 15.2 16.5 21.0 19.4 24.2 23.0 27.9 28.2 Ce 36.0 36.0 57.0 33.0 51.0 31.0 34.0 52.0 38.0 45.0 43.0 51.0 53 Nd 17.0 16.0 25.0 17.0 20.0 15.0 17.0 24.0 17.0 20.0 21.0 22.0 22 Sm 4.20 3.50 4.62 4.90 3.34 3.27 3.60 3.90 3.75 3.93 4.10 4.29 4.13 Eu 1.10 1.19 1.41 1.10 0.86 1.09 1.00 1.10 1.48 1.48 1.20 1.69 1.24 Tb 0.42 0.40 0.50 0.54 0.40 0.40 0.48 0.56 0.50 0.50 0.52 0.60 0.5 Yb 2.30 1.53 1.78 1.70 1.61 1.55 2.00 2.00 1.74 1.86 2.10 1.91 1.84 Lu 0.22 0.26 0.30 0.24 0.23 0.27 0.25 0.27 0.34 0.27 Hf 1.50 1.60 1.70 1.50 2.30 1.50 2.00 2.30 1.40 2.00 2.20 2.30 2.5 Ta 0.18 < 0.5 0.50 0.25 0.90 0.50 0.44 < 0.5 0.70 < 0.5 < 0.5 Th 4.1 3.7 6.3 3.8 7.4 2.8 3.0 2.8 4.3 4.8 4.5 6.0 6.9 U 1.60 2.10 2.80 0.80 1.02 1.50 2.10 1.30 2.50 2.7 Sc 30 33 29 32 17 32 30 22 31 19 32 23 20.6 Cr 41 23 69 28 15 42 68 20 21 10 15 11 11 Co 30 30 23 30 14 33 30 17 30 21 32 27 20

(La/Sm)N 3.23 3.34 1.59 0.90 2.07 3.00 2.96 3.48 3.34 3.98 1.37 1.59 1.67 (Sm/Eu)N 1.45 1.11 11.61 15.78 13.76 1.14 1.36 1.34 0.96 1.01 12.11 8.99 11.80 (La/Yb)N 6.55 8.49 12.09 7.59 12.56 7.03 5.92 7.53 8.00 9.33 7.86 10.48 10.99 Data are from Santo (2000); * this work; ** from Francalanci and Santo (1993). Chondrite-normalising values are from Sun and McDonough (1989). Blank values indicate not determined values. A.P. Santo et al. / Lithos 72 (2004) 73–96 77 ziano. The final activity (fourth cycle) emplaced the is holocrystalline or hypocrystalline seriate. Pheno- basalts and basaltic andesites of La Canna neck (0.04 cryst mineralogy of basaltic rocks consists of plagio- Ma) and nearby islets and the andesitic pyroclastic clase (plg), clinopyroxene (cpx) and olivine (ol). materials (Valle la Fossa formation in Benefizio Small amounts of microphenocrystic orthopyroxene synthem; Manetti et al., 1995) which unconformably (opx) are also present in a few samples. Fe–Ti oxides, overlie most of the older units. occurring as microphenocrysts, are rare. Basaltic andesites closely resemble basalts in their mineralogy 2.2. Mineralogy and petrography but with a lower content of olivine. In some samples accessory amounts of orthopyroxene occur instead of The Filicudi volcanics are porphyritic with a phe- olivine; in a few cases, opx and ol coexist in the same nocryst content ranging from 30 to 50 vol.%. Texture rock. High-K andesites show plagioclase, as the

Canale Cycle III Sciara Montagnola Fil 13* Fil 46 Fil 47 Str 169* Fil 120 Fil 74 Fil 91 Fil 68* Fil 89* Fil 72* Fil 85 Fil 79 Fil 82 Fil 83 Fil 110 Fil 116 Fil 27 Fil 30 56.52 58.28 58.41 60.64 50.22 51.61 54.26 54.32 54.52 54.63 55.39 56.44 57.03 59.29 60.78 60.78 62.17 62.36 0.65 0.60 0.61 0.54 0.68 0.78 0.68 0.71 0.72 0.66 0.69 0.62 0.60 0.62 0.50 0.63 0.55 0.51 17.96 17.65 17.93 16.85 19.29 18.60 18.81 17.68 18.50 18.42 17.73 17.52 17.68 17.79 17.22 15.91 17.02 16.96 2.62 2.41 1.97 2.36 4.07 3.80 2.50 3.06 4.72 2.95 3.07 3.47 2.00 2.16 3.77 2.36 2.01 2.74 4.44 3.75 4.28 3.00 4.36 5.20 5.06 4.92 3.72 5.00 4.92 3.92 4.60 3.88 2.16 3.80 3.44 2.56 0.15 0.14 0.14 0.12 0.16 0.16 0.15 0.18 0.18 0.17 0.17 0.14 0.14 0.14 0.12 0.15 0.15 0.14 3.46 3.01 3.03 2.81 5.04 5.15 3.87 3.56 3.72 3.82 3.84 3.51 4.35 3.28 2.87 2.16 2.13 1.99 8.23 7.53 7.31 6.57 11.09 10.49 8.85 10.36 8.84 8.62 8.51 8.22 8.06 7.19 6.01 6.24 5.72 5.22 2.96 2.98 2.79 3.52 2.40 2.41 2.71 2.72 2.81 2.98 2.76 2.96 2.80 3.07 3.25 3.57 3.50 3.44 2.07 2.51 2.38 2.77 1.21 1.38 1.86 1.60 1.67 1.98 1.96 1.99 1.93 2.06 2.73 2.38 2.49 2.59 0.17 0.18 0.18 0.18 0.15 0.13 0.16 0.17 0.15 0.17 0.19 0.14 0.17 0.18 0.15 0.21 0.22 0.21 0.78 0.97 0.97 0.63 1.33 0.29 1.09 0.71 0.44 0.59 0.77 1.06 0.63 0.35 0.44 1.81 0.61 1.27 50.72 50.72 50.32 52.58 55.97 54.73 51.72 48.40 48.56 50.23 50.28 50.21 57.90 53.26 51.13 42.46 45.09 44.49 69 75 76 80 27 29 36 55 62 68 60 69 60 64 83 80 87 88 652 676 664 620 707 748 691 678 713 634 727 665 651 645 571 737 695 631 21 20 20 17 18 18 19 14 22 22 19 19 18 19 19 19 18 17 95 115 116 95 82 77 88 68 68 89 91 112 101 107 124 123 132 138 810910777 9 9109991010111213 495 588 586 594 398 402 467 433 448 525 485 564 557 595 685 543 610 641 1077 3 1916141210799164 7 122 * * ** * ** * ** ** * ** * ** * * ** * 2 1.60 2.10 1.10 1.30 1.20 1.20 0.80 1.10 2.20 26.9 28.1 29.6 32.0 29.6 23.0 22.7 25.0 31.0 22.6 30.0 26.2 30.0 31.0 33.9 39.0 38.0 51 52.0 56.0 46.0 56.0 47.0 43.0 40.0 52.0 45.0 52.0 48.0 47.0 55.0 63.0 64.0 69.0 21 21.0 23.0 18.0 23.0 21.0 19.0 15.0 24.0 20.0 18.2 20.0 21.0 21.0 26.0 23.0 26.0 3.91 4.03 4.07 4.90 4.07 4.10 3.60 4.70 4.80 4.29 4.60 3.88 4.60 3.90 4.69 5.20 4.46 1.14 1.10 1.10 1.10 1.10 1.20 0.99 1.30 1.20 1.00 1.10 0.98 1.10 0.99 1.59 1.30 1.28 0.5 0.50 0.40 0.41 0.40 0.54 0.40 0.56 0.53 0.50 0.53 0.40 0.48 0.50 0.60 0.58 0.50 1.82 1.76 1.76 1.60 1.88 2.10 1.66 2.10 2.30 1.78 2.00 1.79 2.10 1.69 2.34 2.40 2.29 0.27 0.27 0.27 0.25 0.28 0.26 0.27 0.45 0.27 0.27 0.38 0.26 0.34 0.32 0.36 2.9 2.20 2.90 2.00 1.70 2.50 1.80 1.80 2.20 2.10 2.40 2.00 1.70 2.70 2.50 2.70 2.60 < 0.5 < 0.5 < 0.5 0.49 < 0.5 < 0.5 0.39 0.50 0.80 0.50 < 0.5 0.28 0.60 < 0.5 0.66 < 0.5 6.5 6.9 7.8 6.5 3.5 5.9 5.2 5.3 7.1 5.1 8.5 6.2 7.0 9.3 7.7 9.0 10.0 3 2.80 3.40 1.70 1.80 2.70 2.20 2.20 0.38 3.80 3.00 0.32 3.90 22.8 20 20 16 32 28 26 24 21 24 22 25 28 18 15 14 13 16 10 12 14 18 16 28 16 15 19 24 63 100 9 1 18 2 22 19 19 15 30 27 25 25 24 24 21 21 27 19 15 14 15 1.68 1.71 1.80 1.60 3.27 1.37 1.54 1.30 1.58 1.29 1.60 1.65 1.60 1.95 1.77 1.84 2.09 12.15 12.98 13.11 15.78 1.08 12.11 12.88 12.81 14.17 15.20 14.82 14.03 14.82 13.96 10.45 14.17 12.35 10.60 11.45 12.06 14.35 6.87 7.86 9.81 8.54 9.67 9.11 10.76 10.50 10.25 13.16 10.39 11.66 11.90 (continued on next page) 78 A.P. Santo et al. / Lithos 72 (2004) 73–96 dominant mineral phase, and smaller amounts of cpx consists of complexly zoned, variously twinned phe- and opx; biotite and brown hornblende occur in the nocrysts and microphenocrysts, often displaying sieve most evolved rocks. Biotite is often partially or texture or patchy zoning. Cores of plagioclase phe- completely transformed into opaque minerals. Ti- nocrysts from single rocks exhibit a wide range of magnetite, ilmenite and apatite are found in accessory compositions (An% = 50–95) with a bimodal distri- amounts. Generally, the groundmass is microcrystal- bution well developed in the andesites. An content of line and consists of the same mineral phases as the groundmass plg is in the range 53–88%. phenocrysts. A complete data set of mineral phase Clinopyroxene phenocrysts are ubiquitous and composition is included in Santo (1990, 2000). variable in amounts (20–2 vol.%). Phenocrysts are Plagioclase represents by far the most abundant colourless, euhedral to rounded, dusty and frittered. mineral (20–39 vol.%) in all rock types. It generally Phenocrysts and microphenocrysts have augitic or

Table 1 (continued) Cycle III M. Guardia Capo Graziano Cycle IV La Canna Fil 12 Fil 11 Fil 10 Str 199 Fil 7 Fil 14 Fil 48 Fil 8* Str 200 Fil 1 Str 171 Fil 124 Str 197 Str 196 Fil 122

SiO2 48.17 48.23 49.15 49.28 50.86 51.64 52.10 54.27 55.69 61.7 63.20 50.26 50.81 51.15 52.47 TiO2 0.64 0.75 0.78 0.74 0.70 0.75 0.70 0.64 0.66 0.52 0.52 0.83 0.83 0.79 0.73 Al2O3 13.11 16.69 19.31 18.73 18.04 20.07 18.70 17.61 17.46 17.25 16.23 17.14 16.88 17.23 16.19 Fe2O3 4.56 3.83 4.13 3.78 4.37 4.17 4.88 3.44 2.04 2.56 2.67 3.91 4.49 2.70 5.13 FeO 5.88 6.40 5.84 5.72 4.92 4.76 4.48 4.28 5.92 2.86 2.24 5.36 4.31 5.76 3.24 MnO 0.21 0.19 0.19 0.20 0.17 0.16 0.16 0.15 0.17 0.11 0.11 0.15 0.15 0.16 0.14 MgO 10.34 6.99 5.04 3.47 5.12 4.02 3.40 4.22 3.64 2.62 2.31 6.65 6.47 6.63 6.51 CaO 14.51 12.91 11.43 11.46 11.58 9.55 9.59 9.82 8.36 5.89 5.86 10.94 11.00 10.81 10.14

Na2O 1.23 1.97 2.29 2.43 2.15 2.75 3.26 2.69 3.02 3.29 3.43 2.22 2.38 2.19 2.42 K2O 0.62 0.93 1.19 1.20 1.28 1.38 1.42 1.79 1.81 2.62 2.89 1.66 1.82 1.82 1.85 P2O5 0.09 0.15 0.18 0.22 0.13 0.18 0.25 0.15 0.19 0.24 0.18 0.28 0.30 0.31 0.28 L.O.I. 0.65 0.96 0.45 2.75 0.68 0.56 1.06 0.93 1.03 0.35 0.36 0.60 0.56 0.47 0.90 Mg# 67.70 58.96 51.63 43.50 53.93 48.87 43.68 53.64 48.69 50.64 50.17 60.25 61.06 62.09 62.65 Rb 16 26 30 33 36 28 29 46 66 70 85 54 57 61 58 Sr 461 661 795 814 750 772 719 616 626 601 608 626 630 628 591 Y 171920201820202023181519201919 Zr 55 72 79 82 82 80 70 81 82 110 123 87 86 88 86 Nb 6 7 8 8777610121015151713 Ba 175 256 321 315 336 379 378 402 415 613 646 398 399 431 374 Ni 50 34 18 14 25 10 12 16 11 6 2 42 40 43 40 * ** ** ** * ** ** * ** ** ** ** ** Cs 0.80 0.59 0.64 1.10 1.00 1.30 La 12.7 16.0 22.0 25.0 19.3 23.0 22.0 24.1 31.0 33.0 25.0 26.0 23.0 Ce 26.0 36.0 46.0 57.0 39.0 39.0 33.0 47.0 52.0 54.0 44.0 44.0 41.0 Nd 14.0 19.0 20.0 25.0 18.0 20.0 21.0 20.0 19.0 25.0 20.0 17.0 20.0 Sm 3.17 3.90 4.10 4.80 3.73 4.50 4.50 4.09 4.90 5.40 4.40 5.80 4.50 Eu 0.95 1.10 1.10 1.30 1.03 1.30 1.30 1.20 1.20 1.10 1.20 1.30 1.10 Tb 0.20 0.58 0.56 0.64 0.50 0.62 0.53 0.50 0.63 0.49 0.59 0.48 0.46 Yb 1.36 1.70 1.90 2.00 1.69 1.90 2.10 1.79 1.90 1.80 1.90 1.60 2.10 Lu 0.23 0.25 0.30 0.34 0.26 0.30 0.30 0.40 0.30 0.30 Hf 1.20 1.80 1.70 2.00 1.60 1.80 2.00 2.50 1.90 2.60 2.00 1.60 2.30 Ta < 0.5 0.44 < 0.5 0.33 0.22 < 0.5 0.50 0.49 0.53 0.85 0.68 Th 1.6 3.0 3.5 4.1 4.1 3.9 3.7 5.6 5.9 8.7 4.5 3.9 3.9 U 0.40 0.74 0.90 0.95 1.80 2.30 Sc 70 46 33 27 32 25 26 26 21 17 37 37 35 Cr 150 99 18 21 32 7 15 26 46 12 184 175 194 Co 47 43 39 32 33 28 28 25 25 13 32 31 32

(La/Sm)N 2.59 2.65 3.46 3.36 3.34 3.30 1.96 1.44 1.55 1.50 3.67 2.89 1.25 (Sm/Eu)N 1.26 1.34 1.41 1.40 1.37 1.31 12.26 12.08 14.47 17.39 1.39 1.69 14.49 (La/Yb)N 6.70 6.75 8.31 8.97 8.19 8.68 7.51 9.66 11.70 13.15 9.44 11.66 7.86 A.P. Santo et al. / Lithos 72 (2004) 73–96 79

Fig. 3. Variation diagrams of major elements (wt.%) against silica (wt.%). Data are plotted on water-free basis. 80 A.P. Santo et al. / Lithos 72 (2004) 73–96 diopsidic compositions (Wo 38–40%, En 38–50%, elements than the corresponding rocks (see Santo, Fs 5–20%) often occurring together within a single 1998). Mg–number (Mg#) also shows complex sample or a single complexly zoned crystal. Trace variations (Santo, 1998). All these features reveal element abundances are also variable; in particular, strong chemical disequilibrium in the analysed they display a wider variability of incompatible trace rocks.

Fig. 4. Variation diagrams of trace elements (ppm) against silica (wt.%). Symbols as in Fig. 3. A.P. Santo et al. / Lithos 72 (2004) 73–96 81

Olivine is generally subhedral and occurs as colour- from La Canna neck, generally consist of quartz, K- less euhedral crystals in the basaltic rocks and as feldspar and plagioclase. They commonly display corroded crystals in basaltic andesites. It exhibits equigranular granoblastic textures and numerous triple sometimes an iddingsitic rim or is mantled by cpx in points. In most cases, a thin film of glass or micro- basalts and by opx in basaltic andesites. Its composition crystalline material separates the mineral grains. lies in the range Fo 60–86%. Crystals displaying different core composition sometimes occur together 2.3. Geochemistry within a single sample clearly indicating disequilibrium with the host magma. Zoning is slight, both normal 2.3.1. Major and trace elements and reverse. The Filicudi rocks lie in a relatively restricted Orthopyroxene is compositionally uniform and range of composition, from basalts to basaltic ande- unzoned; it sometimes shows a reaction rim to cpx. sites, up to high-K andesites (Fig. 2). Basalts display The overall composition is in the range En 64–72%. the high Al2O3 content (>16.5%) typical of high- The Filicudi rocks contain xenoliths of both mag- alumina basalts (e.g. Kuno, 1960; Crawford et al., matic and metamorphic origin. Igneous lithologies are 1987). Major and trace element abundances for rep- represented by gabbros, granodiorites, and lava sam- resentative samples are reported in Table 1 (the ples of basaltic to andesitic composition. Xenoliths of complete data set of geochemical data can be obtained volcanic rocks display porphyritic textures and miner- from the corresponding author on request); variation alogical composition similar to that of the outcropping diagrams of major and trace elements vs. SiO2 are lavas. A few xenoliths, predominantly made up of shown in Figs. 3 and 4. plagioclase and hornblende, display cumulate texture. The analysed rocks display negative correlation Intrusive xenoliths are medium to coarse grained and between silica and MgO, CaO, TiO2 and FeOtotal, consist of plagioclase, K-feldspar, quartz, biotite, and and positive trends for K2O and Na2O. P2O5 shows hornblende. Rare muscovite is sometimes present. strong scattering. LILE and HFSE increase with silica, Metamorphic xenoliths, particularly abundant in rocks whereas ferromagnesian trace elements have an oppo-

Fig. 5. Mantle-normalised trace element patterns for Filicudi basalts. Normalisation values from Sun and McDonough (1989). 82 A.P. Santo et al. / Lithos 72 (2004) 73–96 site tendency. Scattering of data, particularly evident in the basaltic and basaltic andesitic rocks, is observed for some elements (e.g. Al2O3,P2O5, Sr, Rb, La). Incompatible elements, such as Zr, Ba, Rb, and La display well-defined positive correlations on inter- elemental variation diagrams; Sr defines scattered a negative correlation; Ni and Cr (not shown) describe

negative, roughly curvilinear trends with incompatible 0.704368 0.704434 0.704415 0.704740 a elements. a REE patterns are fractionated with flat HREE, as

observed in many arc volcanics (Gill, 1981). La/Sm 0.704440

(chondrite-normalised; Sun and McDonough, 1989) a progressively increases from basalts to basaltic- 0.512724 andesites and to high-K andesites whereas La/Yb 0.704360 C. Graziano Cycle IV La Canna ratios vary from 5.9 to 14.3 (Table 1);LREE 19.464 15.661 39.263 a enrichment ranges from 37 to 80 times chondritic in the basalts. A few samples display a slight positive Eu anomaly. 0.704270 Mantle-normalised (Sun and McDonough, 1989) a incompatible trace element patterns of basaltic rocks are generally characterised by moderate fractionation, 19.34915.670 19.31339.207 15.677 39.214 19.674 15.686 39.472 19.531 15.671 39.320 with small negative anomalies of HFSE and positive spike of Sr (Fig. 5). 0.704421 0.704570

Xenoliths of magmatic origin have variable com- a position and define continuous trends on the Harker diagrams (Santo, 1990). Cumulitic xenoliths are sim- 0.704340 ilar or more mafic than the outcropping lavas; volca- a nic inclusions exhibit major and trace element

abundances in the range of the exposed lavas. 0.704643 0.704370 0.704294 0.704016 0.704288 0.704330 0.704380 0.704600 a

Metamorphic xenoliths are characterised by high to a extreme enrichment in silica and variable content of a a a major and trace elements. These xenoliths show 19.540 15.650 39.260 0.704380 geochemical characteristics similar to acidic crustal a a a rocks, e.g. low Sr, Ti and HFSE. a 0.704580 0.704330 0.704650

2.4. Sr, Nd, Pb isotopes a a a a a . Isotopic compositions of representative Filicudi 0.704290

volcanics are reported in Table 2. Sr isotopic ratios a show relatively small variations (0.704016– 0.704740). Analysed rock samples define two different groups (Fig. 6): (1) a small group of samples (H–Srisotope) of basaltic and basaltic andesitic com- 87 86 position displaying relatively high values of Sr/ Sr Francalanci and Santo (1993) Cycle IFil 65 Fil 17 Cycle Fil II 76 Cycle III Fil 74 Sciara Fil 91 Fil 89 Fil 72 Fil 83 Fil 116 Fil 30 Fil 36 Montagnola Cycle Fil III 39 M. Palmieri Fil 33 Fil 47 Canale Str 169 ratios (0.704460–0.704740) and (2) a rock group Cycle III M.Fil Guardia 12 Fil 11 Fil 10 Str 199 Fil 15 Fil 7 Fil 14 Fil 48 Fil 8 Str 200 Str 171 Str 197 Fil 122 Nd 0.512750 0.512744 0.512733 0.512684Nd 0.512719 0.512666 0.512757 0.512722 0.512739 0.512700 0.512756 0.512726 (L–Srisotope) consisting of basalts, basaltic andesitic Pb 19.672Pb 15.673Pb 19.464 39.447 15.671 39.313 19.500 15.650 39.230 Pb 19.404Pb 15.653Pb 19.412 39.205 15.667 39.247 19.460 15.673 39.294 19.340 15.640 39.110 Sr 0.704344 0.704358 0.704450 Sr 0.704362 0.704730 144 144 204 204 204 204 204 204 Data from 86 86 and high-K andesitic magmas which display lower a Nd/ Pb/ Pb/ Pb/ Nd/ Pb/ Pb/ Pb/ Sr/ Sr/ 143 Table 2 Isotopic composition of selected Filicudi volcanics 87 143 206 207 208 87 206 207 208 Sr isotopic ratios (0.704270–0.704450). In addition, Blank values indicate not determined values. A.P. Santo et al. / Lithos 72 (2004) 73–96 83

87 86 Fig. 6. Variation diagram of Sr/ Sr isotope ratios against SiO2 (wt.%). Symbols as in Fig. 3. Fil 116 = rock sample from the Mt. Montagnola dome (see text for details).

Fig. 7. Variation diagram of 87Sr/86Sr isotope ratios against 143Nd/144Nd. Symbols as in Fig. 3. Inset: data fields for Salina, Alicudi, Vulcano and Stromboli from Peccerillo et al. (1993). 84 A.P. Santo et al. / Lithos 72 (2004) 73–96 the lowest 87Sr/86Sr value (0.704016) has been found 3. Discussion in a lithic fragment (Fil 116), collected in the pyroclastic unit at the base of Monte Montagnola dome. 3.1. Magma evolution Interestingly, the highest abundances of radiogenic Sr have been found in some of the less evolved rocks Major, trace element and isotopic variations sug- whereas high-K andesites display overall lower Sr gest complex evolutionary processes for the Filicudi isotopic ratios. Nd isotopic ratios range from magmas. A crystal-liquid fractionation process, as 0.512666 to 0.512757 and show well-defined nega- indicated by the general trends observed in the tive correlation (Fig. 7) with 87Sr/86Sr, though sam- variation diagrams against silica and the presence ples from Monte Montagnola formation fall outside of cognate cumulitic xenoliths, has determined many the main trend. of the petrologic and geochemical characteristics of The Pb isotope ratios (Fig. 8) exhibit a relatively these magmas. Nevertheless, other evidence (Santo, small range of variation: 206Pb/204Pb (19.313–19.672), 2000), such as: (i) textural and compositional char- 208Pb/204Pb (39.110–39.472) and, 207Pb/204Pb acteristics of mineral phases, (ii) the recurrent rever- (15.640–15.686). The variability of Pb isotope ratios sals of magmas to more basic compositions over is, however, higher in basalts than in basaltic andesites time, (iii) the scattered abundances of some trace and high-K andesites. elements, (iv) the small but significant variations of Sr and Nd isotope ratios, (v) the relationships between incompatible element abundances and ratios and radiogenic isotope ratios clearly indicates that other processes also occurred during the evolution of the Filicudi magmas. Small but significant geochemical differences ex- ist among the products from the different volcanic eruptive centres at Filicudi. This fact, together with the field evidence, indicates that the evolution of each volcano took place separately in time and/or space. Therefore, the evolutionary processes of the main eruptive cycles will be discussed in the next sections.

3.1.1. First cycle The volcanic products of the oldest Filicudi activity (Zucco Grande formation) are exposed over a small area. The scarcity of data, therefore, makes it difficult to model magma evolution. The data obtained indicate variable major and trace element compositions. 87Sr/86Sr isotopic ratios of two samples (Fil 65 basalt; Fil 17 high-K andesite) show similar values, fallinginthefieldoftheL–Srisotope group. This suggests an evolution from basaltic to andesitic magmas through a fractional crystallisation (FC) process. However, the Zucco Grande data do not fit FC models. Furthermore, mafic rocks from this cycle display wide variability of abundance and ratios of Fig. 8. Plot of 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb. Symbols as in Fig. 3. Cross represents the composition of a schist incompatible trace elements (e.g. Rb, Yb, La—not collected as a xenolith in the Filicudi volcanics (Francalanci et al., shown, Ba/Rb—Fig. 13), which calls for different 1993). types of mafic magmas refilling the volcanic system. A.P. Santo et al. / Lithos 72 (2004) 73–96 85

3.1.2. Second cycle and (3) a paragneiss from the Calabro-Peloritano Volcanic products of the second cycle of activity basement (Rottura et al., 1989). These rocks are (Filo del Banco and Bue Marino formations) were considered to broadly represent the basement compo- extensively eroded and successively covered by the sition beneath the Aeolian Arc. In the AFC models the Sciara formation rocks. At present time they are rate of assimilation vs. crystallisation (r) has been exposed only in a restricted area and, thus, our study chosen at 0.1, 0.2 and 0.5. is again limited to a few outcrops. AFC models (Fig. 10) show that the Monte The analysed rocks have basaltic composition with Palmieri, Canale and Monte Terrione rocks fit rather variable abundances and ratios of some elements (e.g. well an AFC trend in which the contaminant rock has Mg#—not shown, Ba/Rb, La/Nb—Fig. 13), suggest- the composition of the schist xenolith from Filicudi ing the existence of a number of compositionally volcanics; the rate of assimilation is low (0.1–0.2). distinct mafic magmas. They exhibit smooth negative Table 3. trends of incompatible trace elements and positive correlations of compatible trace elements against 3.1.3.2. Unit 2: Sciara and Monte Montagnola MgO (not shown). Such trends seem indicate a role formations. The Sciara formation consists of basalts, of fractional crystallisation processes. 87Sr/86Sr ratio basaltic andesites and high-K andesites. The Monte has been measured only on one rock sample from Filo Montagnola formation is represented exclusively by del Banco formation. The obtained value (0.704450) high-K andesites. 87Sr/86Sr ratios are variable and fall belongs to the L–Srisotope group. The lack of other Sr in both L–Srisotope and H–Srisotope groups (Fig. 6). isotopic data does not allow us to test possible Therefore, the samples coming from this cycle of contamination processes for these magmas. activity show large Sr isotope variation, a feature which will be observed in all the younger activity. 3.1.3. Third cycle Note that a lithic fragment of andesitic composition Rocks erupted during the third cycle of activity are from this formation has the lowest 87Sr/86Sr value the most extensively exposed; this allowed detailed found at Filicudi. investigation on a large number of samples and L–Srisotope samples display variable silica contents. discussing evolutionary processes for different erup- However, only a fractional crystallisation (FC) process tive units. cannot be invoked to explain the characteristics of this suite of magmas as the Sr isotopic ratios display weak 3.1.3.1. Unit 1: Monte Palmieri, Canale and Monte but significative variations, with high-K andesitic Terrione formations. The Monte Palmieri formation rocks showing lower 87Sr/86Sr value in respect to less consists of mafic lavas (SiO2 = 51.0–53.5%) with evolved magmas. The high-K andesitic magmas of variable content of some elements such as Fe, Mg, Sciara formation could derive from a different basic P, Ni, Rb, and Sr. The Monte Terrione-Canale rocks magma which is not represented by the analysed have higher silica, but plot on variation diagrams (Fig. samples. The Monte Montagnola high-K andesites 3) on the same trend as Monte Palmieri rocks. Sr exhibit higher TiO2, FeO, MnO and Sr and lower Ba isotopic ratios are low (0.704330–0.704434) and and Th content in respect to the high-K andesites from 87 86 display positive correlation with SiO2 and incompat- Sciara formation but similar Sr/ Sr ratio. Overall, ible elements (Fig. 9), and a negative correlation with the data of the L–Srisotope group suggest an evolution Sr (Fig. 9) and compatible elements (not shown). This dominated by fractional crystallisation, starting from is clearly consistent with an assimilation-fractional slightly different parental magmas. Mixing processes, crystallization (AFC) process (De Paolo, 1981).Such however, also had a role in the evolution, as suggested a process has been quantitatively tested. Because of also by petrographic evidence described earlier. the heterogeneity of the Aeolian basement rocks, three The H–Srisotope group could derive from L– different compositions of the assimilated material Srisotope by AFC processes. AFC modelling shows have been used in the models and precisely: (1) a that the geochemical and isotopic variations observed schist collected as a xenolith in the Filicudi volcanics in the Sciara samples fit for some element abundan- (Francalanci and Santo, 1993), (2) a felsic granulite, ces and ratios an AFC process in which the contam- 86 A.P. Santo et al. / Lithos 72 (2004) 73–96

87 86 Fig. 9. Plot of Sr/ Sr vs. SiO2 (wt.%) and incompatible elements (ppm) for Cycle III, Unit 1 (Monte Palmieri, Canale and Monte Terrione) rock samples. inant material is a felsic granulite from the Calabro- ces. The lavas of Capo Graziano formation, emplaced Peloritano basement (Fig. 11; r = 0.1, 0.2, 0.4, 0.5). during the final activity of this volcanic centre and Thus, in this case, in respect to Unit 1 magmas, the separated by a compositional gap from the previous AFC model requires a different contaminant compo- products, are high-K andesitic in composition. sition, possibly due to a variation in depth occurred 87Sr/86Sr isotopic ratios measured on these rocks in the system for a migration of the magma chamber. again fall in two fields. The L–Srisotope group consists The amount of material assimilated is variable from of basalts, basaltic andesites and high-K andesites, 30% to 10% depending on the trace element consid- whereas the H–Srisotope group consists exclusively of ered (Fig. 11). In conclusion, it is necessary to take basalts and basaltic andesites. into consideration that the AFC process is not able to 87Sr/86Sr vs. Mg# (not shown) displays complex completely describe the trace element abundances variations, which may suggest several evolution and ratios of H–Srisotope samples. trends. FC process could be responsible of evolution of magmas with similar 87Sr/86Sr, whereas AFC could 3.1.3.3. Unit 3: Monte Guardia and Capo Graziano be responsible for evolution from L–Srisotope and H– formations. The products of Monte Guardia forma- Srisotope magmas (Fig. 12). tion are basalts and basaltic andesites displaying a In spite of the similar Sr isotopic ratios, a FC large variability of major and trace element abundan- process is not able to reproduce the trace element A.P. Santo et al. / Lithos 72 (2004) 73–96 87

Fig. 10. AFC models for Monte Palmieri, Canale and Monte Terrione samples (Cycle III, Unit 1). Lines are trends of bulk assimilation of a schist Filicudi xenolith (Francalanci et al., 1993), a felsic granulite and a paragneiss (Rottura et al., 1989). Symbols along the lines indicate increasing amount of assimilated crustal material. Data used in the models are reported in Table 3 and references therein. abundances of Capo Graziano high-K andesites, start- as Na, Ca and Sr. A different basic magma probably ing from a basaltic composition such as that of Fil 12. originated Capo Graziano volcanics or, as in the other In fact, rock samples from Capo Graziano do not plot volcanic centres, additional mechanisms, like mixing on continuous trend with the volcanics of Monte among cogenetic magmas, could have been active Guardia: this is particularly evident for elements such during magma evolution.

Table 3 Trace element abundances (ppm) and 87Sr/86Sr isotopic composition of contaminants and bulk coefficients (D) used in the AFC models Rb Sr Y Zr Nb Ba La Yb Th Ni Sc Cr 87Sr/86Sr Schist 132 73 29 46 3 419 19 1.7 2.9 5 n.a. n.a. 0.714530 Paragneiss 141 216 36 225 18 676 40 3.1 15.5 60 24 131 0.726310 Granulite 67 236 47 238 17 716 40 5.2 11.9 56 46 75 0.719130 D 0.01 0.6 0.15 0.1 0.1 0.2 0.1 0.4 0.1 2.5 1.8 6 Compositional data on the schist from Francalanci and Santo (1993); on the paragneiss and granulite from Rottura et al. (1989) and Caggianelli et al. (1991). Partition coefficients from Francalanci and Santo (1993) and references therein. For further details see text. 88 A.P. Santo et al. / Lithos 72 (2004) 73–96

Fig. 11. AFC models for H–Srisotope group (Sciara and Monte Montagnola formations—Cycle III, Unit 2). Lines are trends of bulk assimilation of a felsic granulite (Rottura et al., 1989). Symbols along the lines indicate increasing amount of assimilated crustal material. Data used in the models are reported in Table 3 and references therein.

Significant 87Sr/86Sr variations observed in the L– composition is difficult; indeed, magmas showing the 87 86 Srisotope and H–Srisotope group call for interaction of lowest Sr/ Sr ratios display low Mg#, low Ni and magma with wall rocks. However, results of assimi- Cr abundances and rather high abundances of incom- lation and fractional crystallization modelling conflict patible trace elements. Regardless of the choice of with this hypothesis. The choice of starting magma assimilated material and of rate of assimilation, the A.P. Santo et al. / Lithos 72 (2004) 73–96 89

Fig. 12. Plot of 87Sr/86Sr versus Mg# for Monte Guardia and Capo Graziano rocks (Cycle III, Unit 3).

AFC process is not capable to generate the geochem- In conclusion, the Filicudi rocks show complex ical characteristics of magmas in question and gives petrological and geochemical variations. These are contradictory results; thus, as for the described previ- difficult to model by any simple evolution process ous units, the geochemical variability observed in and suggest complex evolution of various batches of basic and evolved magmas does not fit simple evolu- magmas in different magma reservoirs. This conclu- tion processes. sion is strongly supported by volcanological evidence. Indeed, the Filicudi magmas have erupted over a wide 3.1.4. Fourth cycle time span from various eruptive centres. This fits the The pyroclastic formation of Valle la Fossa (Bene- idea that several batches of magmas were emplaced in fizio synthem—Manetti et al., 1995) consists of an magma reservoirs where they underwent various types andesitic ash-flow, rich in pumices, lithics and clino- of evolutionary processes before being erupted at the pyroxene whereas the lavas forming La Canna neck surface to give several partially superimposed but and the nearby islets are basaltic and basaltic andes- distinct volcanic centres. itic. Some geochemical characteristics (high K/Na, Mg/Al, Rb/Sr (not shown) and low Ba/Nb, Ba/Rb, 3.2. Genesis of mafic magmas La/Nb (Fig. 13) ratios) displayed by these magmas, in respect to the other basic Filicudi magmas, are con- Previous discussion highlighted the role of low sidered to reflect a derivation from a different mantle pressure processes in the evolution of Filicudi rocks. source (Santo, 2000). Based on Sr isotope ratios, two groups of rocks, 87 86 The Sr/ Sr ratios of two rock samples from La indicated as L–Srisotope and H–Srisotope, have been Canna centre (87Sr/86Sr = 0.70444, 0.70474) suggest recognized. The occurrence of a third more primitive crustal assimilation. In this case, quantitative model- group of rocks is suggested by the occurrence of a ling, by using only two available values are unable to single lava xenolith displaying Sr isotope ratio as low explain variations of some incompatible element as 0.704016. Overall, there is a very rough decrease of abundances and ratios. Anyway, the abundance of Sr isotope ratios with increasing magma evolution, crustal xenoliths in the La Canna rocks represents with an overall positive trend between 87Sr/86Sr and an important evidence of this process. MgO. The oldest exposed rocks all belong to the L– 90 A.P. Santo et al. / Lithos 72 (2004) 73–96

Fig. 13. Variation diagrams of incompatible trace element ratios against SiO2 (wt.%) in basaltic Filicudi rocks.

Srisotope group, whereas the H–Srisotope group appears, homogeneous melts and the wall rocks. Positive in addition to L–Srisotope rocks during the third and correlations between MgO and Sr isotopic ratios at fourth cycles of activity. Therefore, stratigraphic evi- Alicudi (Peccerillo and Wu, 1992) were interpreted to dence suggests that increasingly radiogenic magmas reflect a higher degree of crustal assimilation by more where emplaced into the shallow reservoir, where mafic and hotter magmas. However, mixing processes these underwent complex evolution by fractional with newly injected primary melts were hypothesised, crystallization, mixing and moderate interaction with in order to prevent magmas to evolve toward sialic wall rocks. Most of the magmas display scattered compositions. Since continuous mixing with primary incompatible trace element ratios, which, however, melts occurs more easily in deep seated magma fall in the same overall field (Fig. 13) despite the chambers, it was suggested that at Alicudi assimila- provenience from different eruptive vents and cycles. tion and mixing occurred at high pressure. An exception is given by the latest erupted products of In principle, Filicudi mafic magmas may be gen- La Canna neck, which have distinct potassium, in- erated in an isotopically heterogeneous source. This compatible element abundance and ratios. may result from addition of various amounts of slab A main problem of the Filicudi magma is to material to the mantle wedge. However, there is no understand whether magmas with variable isotopic relation between isotope ratios and incompatible ele- signatures were generated in a zoned source or they ment ratios such as Ba/La, Th/Ta which are believed are the product of interaction between isotopically to reflect slab contribution. On the other hand, evi- A.P. Santo et al. / Lithos 72 (2004) 73–96 91 dence for high-pressure evolution of Filicudi magmas Consequently, a different mantle source region should is numerous. These include high Al2O3 content of be assumed. Some geochemical characteristics, like Filicudi basalts and clinopyroxene crystal chemistry for instance the higher MgO and lower Al2O3, could (Malgarotto et al., 1993; Santo, 1998; Nazzareni et al., result from the melting of a residual and modified 2001). A prevailing fractionation of femic phases at peridotitic mantle from which basaltic magmas have high pressure and a delayed plagioclase crystallisation been already extracted. The derivation from a different (e.g. Yoder and Tilley, 1962; Nicholls and Ringwood, magma source could be connected with the hypothesis 1973), are able to drive residual liquids to high Al2O3 that isotherms under the Aeolian islands have under- content (Gust and Perfit, 1986). The limited role of gone an uplift since 6 Ma (Wang et al., 1989; Della plagioclase crystallisation in the Filicudi basalts and Vedova and Pellis, 1992) and display now a progres- the high Al2O3 content measured in their ground- sively upward shift proceeding from west to east masses (Santo et al., 1991), and the small volumes of (Ventura, 1995). Geochemical characteristics similar clinopyroxene cells found by Malgarotto et al. (1993) to those of La Canna magmas have been also ob- and Nazzareni et al. (2001) are, thus, in agreement served in magmas erupted during the recent activity of with the existence of a rather deep magma chamber. Vulcano island. Geochemical differences between old Geochemical models reported previously have and young Vulcano magmas have been imputed to shown that a transition from L–Srisotope group to different litospheric mantle sources modified by var- H–Srisotope group is, in some cases, possible by iable degrees of metasomatism (De Astis et al., 1997, AFC processes, by assuming a mafic granulite of 2000). the Calabro-Peloritano basement as contaminant. These rocks are typically deep seated and reinforce 3.3. Comparison with other Aeolian arc volcanoes the hypothesis of a high-pressure evolution of Filicudi magmas. On a regional scale, the metasomatism of the In conclusion, we suggest that the Filicudi magmas mantle source beneath the Aeolian Arc has been underwent a polybaric evolution. The high pressure recognised by previous studies and has been related stage of AFC and mixing generated a range of to subduction (e.g. Ellam et al., 1988; Peccerillo and isotopically different mafic magmas, which ascended Wu, 1992; Francalanci et al., 1993; De Astis et al., at the surface undergoing additional complex evolu- 1997, Peccerillo, 2001a,b). tion in several shallow level reservoirs. H–Srisotope When compared with other Aeolian arc volcanoes, magmas appear later and simultaneously to the L– Filicudi shows petrological and geochemical charac- Srisotope, in agreement with a continuing evolution in teristics similar to those of the nearby islands of Salina the deep reservoir, which generated increase in Sr and Alicudi. The three islands, in the western sector of isotope ratios with time and a general complexity of the arc, consist of calc-alkaline rocks, but the degree the system. However, eruption of H–Srisotope magmas of magma evolution increases going from Alicudi to may be related to modification in the plumbing system Salina (Fig. 2); rocks from the central islands of of Filicudi volcano. We hypothesize that at a certain Vulcano and Lipari, including also abundant shosh- stage of activity, before and/or during the third erup- onites and some KS, display isotopic signature similar tive cycle, a modification of the volcanic system in part to those of the western sector; in the eastern occurred, which allowed H–Srisotope magma group Aeolian arc, rocks from Stromboli volcano are calc- to rise to the surface. This period represents the most alkaline, shoshonitic and potassic and display geo- active of Filicudi volcano when three different vents chemical and isotopic characteristics different from were simultaneously erupting and some crater collap- those of western and central islands. Indeed, the ses occurred. Therefore, the arrival of isotopically western and central Aeolian arc show typical arc distinct types of magmas is coeval with important signature; on the contrary, Stromboli rocks display volcano-tectonic events that affected Filicudi about lower LILE/HFSE ratios and higher Sr isotopic ratios. 200–150 ka (Ventura, 1995). In terms of Sr isotope ratios, Alicudi, Filicudi and The geochemical characteristics of La Canna mag- Salina calc-alkaline rocks represent the least radio- mas are difficult to explain by any evolution process. genic of the entire archipelago. In particular, Filicudi 92 A.P. Santo et al. / Lithos 72 (2004) 73–96 magmas are more radiogenic than Alicudi products, the primary magmas, revealing a zoned source which which represent the most primitive magmas of the suffered different types of metasomatism. However, Aeolian arc (Peccerillo and Wu, 1992); instead, the some of these variations may also be related to the range of 87Sr/86Sr Salina values encompasses that of plumbing system of the volcanoes, as previously Filicudi magmas (Gertisser and Keller, 2000; Pecce- shown for Filicudi mafic magmas. rillo, unpublished data); thus, Sr isotopic composi- In terms of Pb isotope ratios, the western islands tions define a continuous increasing trend going from display overall similar values (Del Moro et al., 1998; the less radiogenic Alicudi to the intermediate Filicudi De Astis et al., 2000; Gertisser and Keller, 2000; to Salina magmas. Trace element and isotopic evi- Peccerillo, unpublished data; Fig. 14); the Pb isotope dence indicates that there are significant variations of ratios of the Filicudi rocks are very similar to those of

Fig. 14. Plot of 207Pb/204Pb (a) and 208Pb/204Pb (b) versus 206Pb/204Pb for Filicudi rocks (open circles). Fields for other Aeolian Islands: Stromboli (McDermott and Hawkesworth, 1991; Francalanci et al., 1993); Salina (Gertisser and Keller, 2000); Alicudi (Peccerillo, unpublished data). Fields for: Calabro-Peloritano basement (Rottura et al., 1989; Caggianelli et al., 1991), Atlantic sediments (Hoernle et al., 1991), Pacific sediments (McDermott and Hawkesworth, 1991), MORB (Saunders et al., 1988). A.P. Santo et al. / Lithos 72 (2004) 73–96 93

Salina, Alicudi and Vulcano; in comparison with evolution processes. Several, partially overlapping, Stromboli volcano, they exhibit higher 206Pb/204Pb eruptive centres, whose geometrical relationships are and 208Pb/204Pb ratios whereas 207Pb/204Pb ratios fall very complex, constitute the volcano Filicudi. Geo- in the larger Stromboli range (McDermott and Haw- chemical and field evidence indicates that the evolu- kesworth, 1991; Francalanci et al., 1993). tion of each eruptive centre took place separately in The variability of Pb isotope signature of the time and/or space. Consequently, the magma evolu- Aeolian magmas has been attributed to a large-scale tion processes have been considered for each eruptive heterogeneity in the mantle source (e.g. Ellam and centre. However, in spite of the observed geochemical Harmon, 1990). A MORB-like source, metasomatised differences, all magmas display parallel trends on by variable proportions of aqueous fluid and melts variation diagrams. This feature suggests that basical- released from the slab has been suggested by Franca- ly similar evolutionary processes affected all the lanci et al. (1993) to explain the geochemical variation Filicudi mafic magmas. Geochemical and isotopic of the CA suites along the arc. In the Fig. 14, the Pb characteristics exhibited by the Filicudi magmas sug- isotopic data from Filicudi are reported together with gest a complex petrogenetic history, during which a Pb radiogenic ratios from different areas. In terms of complex interplay of fractional crystallization, crustal 206Pb/204Pb and 208Pb/204Pb ratios the Filicudi rocks assimilation and magma mixing processes originated fall in the MORB field toward the radiogenic end of the products of this volcano. the MORB array; 207Pb/204Pb ratios lie between The scattered distribution of the different eruptive MORB and pelagic Pacific sediments fields. Howev- centres suggests also the occurrence of several small er, such a sediment involvement in the source of magma bodies and conduits. The plumbing system Filicudi magmas is not supported by the low Sr could have consisted in a deep mafic magma chamber isotopic ratios of Filicudi magmas. An alternative that fed several small-sized scattered reservoirs situ- source metasomatizing agent is an aqueous fluid ated at shallower depths. released from the oceanic slab. Low Th/Yb and high The mafic magmas erupted during the first three Sr/Nd ratios are generally regarded to reflect the cycles of activity display a common geochemical addition of fluids from the subducting slab (e.g. signature. During the last activity cycle of Filicudi Turner et al., 1997; Elliot et al., 1997); indeed, Th were emplaced the lavas forming La Canna neck and Nd behave as immobile elements in aqueous displaying some different geochemical characteristics fluids whereas Sr and Yb have the opposite behaviour. (higher K/Na, Mg/Al, Rb/Sr and lower Ba/Nb, Ba/Rb Filicudi mafic magmas show low Th/Yb and high Sr/ ratios). These differences are considered to reflect a Nd values thus suggesting an important role of an derivation from a different mantle source. aqueous fluid contaminant in the source. This result is All Filicudi mafic magmas do not exhibit charac- in agreement with the hypothesis reported by De Astis teristics of primary mantle-derived melts since they et al. (2000) for Alicudi and older Vulcano mafic have high phenocryst content, low Mg#, low Ni and rocks. The similarity of the western and, in part, Cr abundances (Francalanci and Santo, 1993). Con- central side of the source of Aeolian arc magmas is sequently, the most primitive rocks of Filicudi are supported also by the similar Ba/La, Rb/Nb, La/Ta already more or less differentiated; thus, they may ratios (Gertisser and Keller, 2000; De Astis et al., have assimilated lower continental crust during ascent 2000) observed in Alicudi, Filicudi, Salina and old to shallow crustal levels. In addition, ratios of incom- Vulcano mafic rocks. patible trace elements, such as Ba/Rb, Ba/Nb and La/ Nb display a certain variability that testify that some geochemical characteristics have been inherited from 4. Concluding remarks the source. The data discussed in this paper suggest for Fili- New petrological, trace element and isotopic (Sr, cudi primitive magmas a derivation from a mantle Nd, Pb) data reported for volcanic rocks from the MORB-like source which underwent contamination island of Filicudi helped to put constraints on the trough slab derived fluids. We conclude that the petrogenesis of Filicudi mafic magmas and on their variability observed among Filicudi magmas is caused 94 A.P. Santo et al. / Lithos 72 (2004) 73–96 by the combined effect of both a heterogeneous and This program corrects for interelement interferences, metasomatised source and different interplaying evo- U fission production and typically measures two or lutionary processes. more spectra per element. A weighted average of accumulated counts for the various spectra, based on counting statistics, is used to compute element con- Acknowledgements centrations. Precision is better than 10%. The 87Sr/86Sr and 143Nd/144Nd isotopic ratios were Financial support was provided by Italian C.N.R. measured using a Finnigan MAT262 9-collector ther- (Italian Council of Research) NATO fellowship to mal ionization mass spectrometer at the Department of A.P.S. Tsegaye Abebe is thanked for his kind help. Earth and Planetary Science, Harvard University, Cambridge, Massachussets (USA). The ratios were corrected for mass spectrometric fractionation using Appendix A exponential law and normalized to 86Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219. Precision (2r is F 0.00002. A.1. Sampling and analytical techniques Additional details about chemical and mass spectrometric laboratory procedures are reported by Jacobsen A large number of lavas, dikes, scoriae, pumices and Dymek (1988). and xenoliths were collected during the field work. Pb was separated from rock powders that were Samples selected for the present study were chosen leached in 6 M HCl for 1 h at 180 jC prior to as representative of the different formations outcrop- digestion in concentrated HF and HNO3 acid. Pb ping on the island and belonging to the four main separation followed a modified method of Manhes eruptive cycles. Trace elements, REE and isotopic (1978) using standard anion exchange resin techni- determinations were carried out on a restricted num- ques. Sample matrix was eluted in 1 M HBr, fol- ber of samples. A more extensive whole-rock and lowed by collection of Pb in 6 M HCl. Total Pb xenolith compositional database can be found in procedural blanks were between 200 and 500 pg and Francalanci and Santo (1993). Description of sample insignificant. Pb isotope ratios were determined in locations and the complete data set of geochemical static mode using the VG354 5-collector mass spec- data are available from the corresponding author trometer of the London University radiogenic isotope upon request. facility at Royal Holloway. All Pb data were normal- Major element compositions were obtained by ised to SRM981, using the Catanzaro values. Within- 206 204 combined wet chemical techniques [Na2O, MgO, run error was less than F 0.004 on Pb/ Pb. SRM FeO and loss on ignition (LOI)] and X-ray fluores- 981 was reproducibile to F 0.011 (2sd) for 206Pb/ cence. Rb, Sr, Y, Zr, Nb, Ba, and Ni concentrations 204Pb. Pb isotopic data were normalized for mass were measured by X-ray fluorescence using several fractionation (ca. 0.13%/amu) to SRM 981 values of international rock standards for curve calibration. 16.937, 15.491 and 36.72 for 206Pb/204Pb, Precision is better than 5% for Ni, Rb and Sr and 207Pb/204Pb and 208Pb/204Pb, respectively. better than 10% for Y, Zr and Nb. Analyses were carried out at the University of Firenze, Dipartimento References di Scienze della Terra. The rare earth elements (REE), Cr, Sc, Co, Cs, Th, Barker, D.S., 1987. Rhyolites contaminated with metapelite and U, Ta, Hf have been determined at the X-ray Assay gabbro, Lipari, Aeolian Islands, Italy: products of lower crustal Laboratories, Don Mills, Ontario, Canada, by Instru- fusion or of assimilation plus fractional crystallization? 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