Campania volcanoes

5 Campania volcanoes: petrology, geochemistry, and geodynamic significance Angelo Peccerillo Retired from Department of Earth Sciences, University of Perugia, Perugia, Italy

Introduction The Campania Volcanic Province (Fig. 5.1) consists of the active centers of SommaeVesuvio, Campi Flegrei (Phlegraean Fields) and Ischia, in addition to the islands of Procida and Vivara. The volcanoes are sited between the Southern Apennines and the Tyrrhenian Sea basin, in a tectonically subsided area cut by NW-SE and E-W trending faults and filled with thick piles of sediments (e.g., Milia and Torrente, 2003, 2015; Fowler, 2019, this book and references therein). Measured ages of volcanism range from about 0.2 Ma to 1944 AD, when the last eruption of Vesuvio took place. Older PlioPleistocene volcanism is buried beneath the Campanian Plain, covered by the thick successions of the Campi Flegrei volcano. Because of their location in an intensely populated area and the violently explosive nature of eruptions, the Campania volcanoes have attracted the attention of scholars since ancient times. An enormous amount of data has been collected in the last decades. Yet, several volcanological, petrological, and geodynamic aspects of the volcanism remain controversial. In this chapter, the main petrological and geochemical characteristics of the Campania volcanic centers are summarized, and the hypotheses on magma genesis and evolution are discussed. The geodynamic significance, in the ambit of the Italian Quaternary volcanism, will be finally addressed.

Vesuvius, Campi Flegrei, and Campanian Volcanism. https://doi.org/10.1016/B978-0-12-816454-9.00005-5 Copyright © 2020 Elsevier Inc. All rights reserved.

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Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.1 Location of the Campania volcanic centers with simplified distribution of volcanic products. Relief shaded map is from Tarquini et al. (2012).

Structural setting of volcanism in the Italian peninsula The Campania magmatism is a part of a long Plio-Quaternary volcanic belt running from Southern Tuscany to the Aeolian Islands. Rock compositions show all orogenic-type trace element signatures such as high ratios of large-ion lithophile elements (LILE) versus high field strength elements (HFSE) (i.e., La/Ta, Th/Ta, Rb/Nb, etc.) and moderately to strongly radiogenic Sr isotope ratios. However, there are many along-belt compositional variations that allow distinguishing several distinct magmatic provinces (e.g., Peccerillo, 2002, 2017). Such a subdivision is not a merely speculative petrological exercise but reveals distinct petrogenetic processes for magmatism along the Italian peninsula, with profound implications for geophysics and geodynamics (Peccerillo, 2017 and references therein). The distribution of magmatic provinces is reported on a structural model of the Apennines and back-arc regions (Fig. 5.2), simplified after Pierantoni et al. (2019, this book). It is obvious that each magmatic province, as defined by magmatological characteristics, occupies a distinct structural segment behind the Apennine chain. This is a clear evidence for the close relationships between magmatism and geodynamics along the Italian peninsula. The main orogenic volcanic provinces include 1. Tuscany Province, consisting of a Miocene to Pleistocene association of a very wide variety of rock types, including

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.2 Structural framework of the Italian peninsula and position of magmatic provinces. Simplified after Pierantoni et al. (2019, this book).

2.

3.

4.

5.

6.

peraluminous crustal anatectic granites and rhyolites, calcalkaline and shoshonitic suites, and lamproites. Intra-Apennine Province, containing a few 0.8e0.4 Ma old lava and pyroclastic deposits showing ultrapotassic kamafugitic compositions. Some carbonate-rich pyroclastics have been interpreted as carbonatites. Roman Province, made up of huge amounts of potassic and ultrapotassic rocks erupted in the last 0.8 Ma by large stratovolcanoes and volcanic complexes with polygenetic calderas (Vulsini, Vico, Sabatini, Colli Albani). The Roman Province defined here is much more restricted than the original one recognized by Washington (1906), which also included Ernici, Roccamonfina, and Campania volcanoes. Ernici-Roccamonfina Province, made up by comparatively low volumes of about 0.6e0.1 Ma-old products that show a very wide range of compositions, from calcalkaline and shoshonitic to ultrapotassic. The calcalkaline to potassic volcanics show geochemical affinities with the Campania Province. Pontine Islands Province, consisting of several centers with trachybasaltic to rhyolitic compositions and ages ranging from 4.2e0.13 Ma. Campania Province, formed by the dormant volcanoes of SommaeVesuvio, Campi Flegrei, and Ischia and by the island of Procida and the nearby islet of Vivara. Rock compositions

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range from trachybasalt to trachyte and phonolite. Leucite tephrite to leucite phonolite are restricted to SommaeVesuvio. 7. Apulian or Lucanian Province, formed by the isolated volcano of Monte Vulture (w0.8e0.1 Ma) that erupted various types of undersaturated rocks (melilitites, tephrites, foidites, etc.) rich in both Na2O and K2O, in addition to late carbonatite lavas and pyroclastics. Vulture magmas are petrologically distinct from Campania volcanics, although there is an overlap of radiogenic isotope compositions. 8. Aeolian arc Province, consisting of seven major islands, some islets, and a number of seamounts. Volcanological, geochemical, and petrological evidence highlights the occurrence of three distinct sectors: western, central, and eastern. Surprisingly, the easternmost island of Stromboli shows closer geochemical affinities with the Campania volcanoes than with other nearby Aeolian centers. There are other Quaternary volcanic provinces in Sicily, Sardinia, and in the Tyrrhenian Sea. These mostly have Ocean Island Basalts (OIB)e to Mid-Ocean Ridge Basalts (MORB)etype anorogenic geochemical characteristics whose role in the origin of Campania magmatism will be recalled during the following sections.

A volcanological overview of the Campania Province The Campanian volcanoes show variable volcanological characteristics. Activity has been prevailingly explosive, but lavas are abundant at SommaeVesuvio (e.g., Santacroce, 1987). The erupted mafic products show moderately potassic alkaline affinity and degree of silica undersaturation. However, strongly undersaturated ultrapotassic- and leucite-bearing rocks are abundant at SommaeVesuvio (Fig. 5.3). SommaeVesuvio is a stratovolcano consisting of an older cone (Somma) with a polygenetic caldera where the Vesuvio cone has been built up during the last 2000 years. Volcanic sequences overlay a suite of about 2 km thick sedimentary and volcanoclastic material, sitting over 6e8 km thick Mesozoic carbonates that are commonly found as lithic ejecta, often intensively affected by metamorphism and metasomatism (e.g., Fulignati et al., 2000 and references therein). Hercynian crystalline basement occurs at depth, over a Moho at about 30 km (e.g., Berrino et al., 1998; Tondi and De Franco, 2003; De Natale et al., 2006).

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

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Figure 5.3 (A) Total alkali versus silica (TAS; Le Maitre, 2002) classification diagram of SommaeVesuvio rocks; the dashed line is the boundary between the alkaline and subalkaline fields of Irvine and Baragar (1971). Data normalized to 100% on an LOI-free basis; (B) DQ versus K2O/Na2O diagram. DQ is the algebraic sum of normative quartz minus undersaturated minerals leucite, nepheline, kalsilite, and olivine; rocks with DQ < 0 and DQ > 0 are undersaturated and oversaturated in silica, respectively (Peccerillo, 2017). The shaded area is the field of mafic rocks (MgO > 4.0 wt%). Samples with LOI higher than 4% have been excluded because of possible secondary modifications. Data from Joron et al. (1987), Ayuso et al. (1998), Rolandi et al. (1998), Somma et al. (2001), Paone (2006, 2008), Piochi et al. (2006), Di Renzo et al. (2007), Aulinas et al. (2008), Sulpizio et al. (2010).

The Somma activity started about 33 ka BP. with prevailing emission of lava flows and scoriae, presently cropping out along the caldera walls and at a few parasitic centers (Santacroce, 1987; Macdonald et al., 2015). Starting from around 18.3 ka (Pomici di Base eruption), volcanism become more explosive, with Plinian eruptions and several phases of caldera collapses separated by mildly explosive interplinian stages (e.g., Rolandi et al., 1998; Somma et al., 2001). Vesuvio started to grow after the 79 AD eruption and has been active until 1944, giving several explosive and lava eruptions interrupted by periods of dormancy. Borehole drilling on the southern flank of Vesuvio found lavas and pyroclastic that yielded 40Ar/39Ar ages of about 0.4 Ma, the oldest products in the Campania Province (Brocchini et al., 2001). Campi Flegrei is a large volcanic complex with two calderas and several intracaldera centers. Volcanism has been mostly explosive, from phreatomagmatic to Plinian. Oldest ages (40Ar/39Ar) of 205 and 157 ka have been measured at Taurano, east of Naples, in an area outside the calderas (De Vivo et al., 2001). Younger activity includes the Campanian Ignimbrite (w39e40 ka; e.g., Gebauer et al., 2014; Rolandi et al., 2019, this book and references therein) and the so-called Neapolitan Yellow Tuff (w15 ka; e.g., Deino et al., 2004). The following volcanism gave a number of hydrovolcanic explosions with formation of tuff rings, tuff cones, and a

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few maar volcanoes. The last eruption in 1538 AD built up Monte Nuovo, a pyroclastic cone near the town of Pozzuoli (Piochi et al., 2005). Campi Flegrei is well known for its slow vertical ground movements (bradeysism) continuing from at least Roman times to present day (Cannatelli et al., 2019, this book). The volcano feeding system consists of a 3e4 km deep trachytic reservoir, periodically refilled by about 8 km deep mafic magma chamber (e.g., Zollo et al., 2008; De Siena et al., 2010; D’Antonio, 2011). The shallow reservoir is probably hosted in siltite, sandstone, and shale sediments; the deeper chamber is within the Hercynian crystalline basement (e.g., Pappalardo et al., 2002; Piochi et al., 2014). Carbonate series such as those of the SommaeVesuvio area seem to be absent beneath Campi Flegrei (D’Antonio, 2011). The exposed Phlegraean volcanism was preceded by about 2 Ma-old volcanism found by borehole drilling in the Campanian Plain. Rocks are typically mafic-intermediate calcalkaline in composition, indicating that subalkaline magmatism preceded alkaline activity in the Campanian Plain (Barbieri et al., 1979). Ischia is the remnant of a large volcano shaped by a prevailingly explosive activity, volcanotectonic collapses, gravitational sliding, and erosion. Its volcanic history and the stratigraphic succession are complex. The lowest exposed rocks are older than 150 ka; a main phase of activity occurred at about 55 ka with the emplacement of the Monte Epomeo Green Tuff ignimbrite and the formation of a caldera; younger activity took place between 16 ka to Middle Ages. The latest eruption emplaced maficintermediate lavas and scoriae in the Arso area, eastern Ischia, in 1302 AD (Gillot et al., 1982). The Islands of Procida and the nearby islet of Vivara are sited between Campi Flegrei and Ischia. They have been constructed by both phreatomagmatic and magmatic explosive activity, from about 70 to 15 ka (e.g., D’Antonio and Di Girolamo, 1994; De Astis et al., 2004; Fedele et al., 2006). The two islands are made of trachybasalt to trachyte pyroclastic rocks. However, calcalkaline basalts are found among lithic clasts, suggesting that subalkaline magmatism preceded the potassic alkaline activity that built up the two islands.

Petrology and geochemistry of the Campania volcanoes Petrological and geochemical characteristics of Campania volcanics show strong differences among the various volcanoes and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

within single centers. A summary of compositions is reported in Table 5.1. Most of the variability is an effect of shallow level evolutionary processes, but it also records heterogeneities of the mantle sources. Discriminating between the two factors is difficult, but it is crucial for placing constraints on the compositions of parental melts and upper mantle, and for understanding geodynamic setting.

SommaeVesuvio The SommaeVesuvio rocks range from trachybasalt to phonotephrite, tephriphonolites, trachyte, and phonolite (Fig. 5.3A). Mafic rocks (here defined as those with MgO >4.0 wt%) range from slightly to strongly undersaturated in silica (Fig. 5.3B), the latter containing leucite as a main phenocryst and groundmass phase. Based on major and trace element variations, three main suites of rocks have been recognized at SommaeVesuvio by Joron et al. (1987). Such a partition is followed in this chapter, with a few modifications of time limits between the series, which have no effects on petrological discussion. One rock series consists of moderately silica-undersaturated trachybasalts, shoshonites, latites, trachytes, and trachyphonolites. These were prevailingly erupted before about 9 ka (Fig. 5.3) and will be here referred to as the Older Series. A second series consists of prevailing undersaturated tephriphonolites and phonolites, which were mainly emplaced between the Older Series and the early historical times; this will be referred to as Prehistorical Series. Finally, a third suite of rocks consists of strongly undersaturated phonotephrite to phonolite, erupted from 79 AD to the present (Younger Series). All the rocks have variably porphyritic textures; olivine phenocrysts occur in the mafic rocks of the Older and Younger Series. Clinopyroxene is ubiquitous; plagioclase is particularly abundant in the Older Series. Leucite is a common phase of the Younger Series, whereas it is present in the trachybasalts of the Older Series and the intermediate rocks of the Prehistorical Series. K-feldspar is restricted to evolved rocks; FeeTi oxides, apatite, garnet, and amphibole are common accessories in the felsic rocks. Nepheline appears in the most evolved rocks of the Prehistorical and Younger Series (Joron et al., 1987). Evolution processes of SommaeVesuvio and other Campania magmas are complex, as discussed by Fowler (2019, this book). However, first-order information can be provided by some key interelement variation diagrams (e.g., Ayuso et al., 1998;

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Table 5.1 Major trace element and radiogenic isotope compositions of selected Campania volcanics. Sample

1

2

3

Volcano

Sommae Vesuvio Older series

Sommae Vesuvio Older series

Sommae Vesuvio Older series

Locality/ eruption SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Sc V Cr Co Ni Rb Sr Y Zr Nb Cs

K-trachybasalt scoria 48.10 1.08 16.10 8.10 0.12 4.20 9.18 3.96 2.34 0.74 2.82 18 55 26 34 390 750 40 265 43 14.2

4

Sommae Vesuvio Prehistorical series Phonotephrite Trachyphonolite Phonotephrite lava pumice pumice 49.50 57.70 50.90 1.01 0.39 0.70 18.09 17.80 18.40 8.20 3.77 6.42 0.14 0.15 0.14 3.95 0.55 2.79 7.67 3.30 7.66 2.48 3.46 3.39 6.61 7.78 6.57 0.79 0.13 0.39 0.32 3.97 1.49 3 11 231 47 51 28 3 17 34 3 11 247 315 350 1322 715 890 32 40 33 319 355 270 52 46 36 14.0 18.9 21.7

5

6

7

9

10

11

12

13

Sommae Vesuvio Younger series Phonotephrite scoria 47.50 0.96 16.10 8.17 0.15 5.16 9.88 2.37 6.90 0.83 0.35

Sommae Vesuvio Younger series Foidite pumice 49.10 0.50 20.80 4.59 0.14 1.10 5.90 5.28 9.05 0.21 1.74 3

Campi Campi Flegrei Flegrei

8

Ischia

Ischia

10

10

14

Trachybasalt scoria 48.25 1.27 16.20 8.55 0.14 8.58 12.04 2.84 1.78 0.34 0.10

Trachyte pumice 59.56 0.45 19.20 3.86 0.17 0.62 2.61 4.62 8.78 0.12 2.00

20 9 <10 285 >1500 25 290 92 15.2

Latute scoria 53.98 1.13 18.13 6.95 0.14 3.76 7.28 4.67 3.47 0.49 0.71 17 163 46 22 32 183 638 30 183 28 8.3

Trachyte lava 62.21 0.57 18.46 3.41 0.31 0.45 1.10 7.27 6.18 0.04 1.94 3 32

107 29 17 268 1050 28 233 32 14.0

Latite lava 53.35 0.84 17.87 1.90 0.13 2.56 6.18 5.22 3.34 0.58 1.53 11 206 8 15 5 315 919 31 240 30 12.7

202 338 40 125 57 532 22 114 13 2.2

34 e 1 292 341 35 371 61 18.2

Basaltic lithic 48.35 1.24 15.48 7.88 0.14 9.54 12.01 2.85 1.47 0.28 0.77 37 207 421 42 150 46 492 21 102 12

Trachyte pumice 59.88 0.45 18.21 4.38 0.12 0.62 2.73 4.13 9.27 0.21 3.96 3 65

361 409 38 318 38

2 542 20 68 1041 147 27.2

Ba La Ce Nd Sm Eu Gd Tb Yb Lu Hf Ta Pb Th U 87 Sr/86Sr 143 Nd/144Nd 206 Pb/204Pb 207 Pb/204Pb 208 Pb/204Pb Source of data

1220 52 90 45.7 10.8 2.20 1.10 2.20 0.30 5.90 2.80 22 20.9 4.7 0.70711 0.51250 19.049 15.652 39.149 Ayuso et al. (1998)

2522 84 167 71.9 13.3 3.30 9.70 1.34 2.50 0.36 6.90 3.30 38 25.2 6.8 0.70687 0.51255 19.095 15.741 39.356 Di Renzo et al. (2007)

1050 68 124 45.8 9.6 1.97

1450 68 119 44.9 9.1 2.01

2360 51 99 47.9 9.7 2.50 7.52 1.08 1.96 0.26

1950 101 162 48.7 7.6 1.70

1651 58 114 51.3 10.1 2.60 8.00 1.03 0.87 0.70 1.10 3.02 2.18 1.80 2.40 0.42 0.30 0.20 0.40 7.23 5.40 5.00 2.89 2.07 1.50 4.00 1.90 44 53 30 84 29.6 28.5 27.4 19.9 42.2 20.5 8.1 8.3 6.8 14.7 6.0 0.70765 0.70752 0.70685 0.70700 0.70772 0.51243 0.51247 0.51245 0.51249 0.51257 18.956 18.955 18.977 19.024 19.016 15.636 15.639 15.647 15.646 15.68 38.981 38.98 39.005 39.22 39.126 Piochi et al. Somma et al. Somma et al. Paone DAntonio (2006), (2001) (2001) (2006) et al. Paone (2006) (1999)

345 81 153 54.5 10.2 2.20 8.20

1135 53 95 48.4 9.1 2.20 7.90 1.02 2.80 2.56 0.40 0.38 4.31 1.50 60 12 30.0 14.7 3.9 0.70751 0.70636 0.51255 0.51254 18.926 18.993 15.682 15.69 38.953 39.134 Orsi et al. Casalini (1995), et al. DAntonio (2017, et al. 2018) (2007)

10 161 295 119.2 18.5 1.04 16.92 2.33 10.54 1.66 25.99 9.16 60 93.3 10.4 0.70775 0.51255 19.222 15.708 39.355

561 18 38 22.0 5.1 1.64 0.75 1.86 0.30 2.75 0.89 7.9 3.4 0.9 0.70524 0.51269 19.088 15.678 39.153 De Astis et al. (2004)

78 86 165 63.0 10.9 2.33

521 14 32 18.3 4.4 1.47 4.58 1.21 0.72 3.38 1.83 0.51 0.27 8.12 2.70 3.90 0.86 47.9 13.45 32.2 2.9 10.7 1.0 0.70678 0.70514 0.51254 0.51272 19.24 18.675 15.699 15.637 39.342 38.682 De Astis Mazzeo et al. et al. (2004) (2014)

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Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Mastrolorenzo et al., 2006; Paone, 2006; Piochi et al., 2006; Santacroce et al., 2008; Sulpizio et al., 2010). Na2O shows a moderate increase with decreasing MgO (Fig. 5.4A) in the mafic-intermediate composition to rise sharply in the trachytephonolite rocks; several samples, mostly from the Prehistorical Avellino eruption, plot along linear (mixing) trends, mostly extending form intermediate to felsic compositions (dashed lines). TiO2 (and FeOtotal, not shown) remains rather constant at high-intermediate values of MgO but decreases sharply in the evolved samples. Again linear trends between intermediate and felsic compositions are defined by the Avellino eruption and a few other samples (Fig. 5.4B). Al2O3 shows somewhat scattered negative trend with MgO for most samples, except for the intermediate-felsic rocks of the Older Series that plot along a flat trend (Fig. 5.4C).

Figure 5.4 Variation diagrams of selected major and trace elements for SommaeVesuvio rocks. Dashed lines indicate possible mixing trends. Solid lines with arrows are fractionation crystallization trends. Source of data as for Fig. 5.3.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

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Trace elements furnish additional details. Sr increases with decreasing MgO for the Younger Series and for some samples of the Older Series, whereas it remains constant in the mafic range to decrease in the felsic compositions for the other rocks (Fig. 5.4D). The samples of the Prehistorical Series again plot along two distinct trends, both connecting intermediate and felsic composition, one being linear (mixing) and the other curvilinear (fractional crystallisation). Similar, through more scattered, distribution is shown by Ba (not shown). Sr versus Th diagram shows an overall positive trend for the Younger Series and for the mafic rocks of the Older Series (Fig. 5.5A). Negative trends with different slopes are observed in the Prehistorical Series and in the intermediate-felsic samples of the Older Series. Ba has a similar behavior, though with more scattering for the Younger Series (Fig. 5.5B). Distinct curvilinear and liner trends are particularly well observed on some compatible

Figure 5.5 Interelement variations diagrams for SommaeVesuvio. Dashed lines are mixing trends. Solid lines with arrows are fractionation crystallization trends of different mineral assemblages. Source of data as for Fig. 5.3.

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Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

versus compatible element diagrams, such as V versus Ni (Fig. 5.5C). Compatible versus incompatible element plots (e.g., Ni vs. Zr) show negative trends for all the three series with sharp increase in the incompatible elements for the most evolved samples of the Prehistorical Series (Fig. 5.5D). SreNd isotopic ratios are rather variable 143 (87Sr/86Sr ¼ 0.7062e0.7078; Nd/144Nd ¼ 0.51225e0.51257). There is no clear correlation with MgO, CaO, or SiO2, except for a very weak positive correlation between Nd isotope ratios and MgO in the Older Series (not shown). Pb isotope ratios are poorly 206 207 variable with Pb/204Pb w18.90e19.10, Pb/204Pb 208 207 w15.55e15.75, and Pb/ Pb w38.80e39.40. There are no systematic differences of radiogenic isotope compositions from one series to the other (Fig. 5.6). Overall, SreNdePb isotope ratios of SommaeVesuvio partially overlap the compositional field of Stromboli volcano (eastern Aeolian arc). Relationships with other magmatic provinces in Italy will be further addressed in the discussion section. Oxygen isotope ratios are rather high both in the whole rocks and separated phases. Ayuso et al. (1998) found whole rock d18O& ¼ 7.3e10.2 relative to SMOW, with a positive trend with CaO wt%. Dallai et al. (2011) find d18OSMOW ¼ 5.5e7.1& in olivine and 6.0e7.5& in clinopyroxenes. Distribution of major and trace elements suggests complex evolution processes for SommaeVesuvio with an interplay of fractional crystallization, wall rock assimilation, and mixing. However, the fractionating mineral assemblages changed from

Figure 5.6 SreNdePb isotope variations in the Campania Province. Fields of other volcanic provinces are from Peccerillo (2017) and references therein. Source of data as for Figs. 5.3, 5.8, 5.10.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

one series to the other and with the degree of evolution of single series (e.g., Joron et al., 1987; Ayuso et al., 1998; Piochi et al., 2006; Santacroce et al., 2008; Pappalardo and Mastrolorenzo, 2010; Fowler, 2019, this book; Stabile and Carroll, 2019, this book). Fractional crystallization of mafic phases, especially clinopyroxene, dominated magma evolution for all the series, joined by feldspars and accessory phases (Ti-magnetite, apatite, garnet) especially in the intermediate-felsic compositions (see solid lines in Figs. 5.4 and 5.5). Clinopyroxene-dominated fractionation generated positive trends of SreBa versus Th and other incompatible elements in the Younger Series and some samples of the Older Series; in contrast, heavy alkali feldspar and plagioclase fractionation are responsible for decrease in SreBa with evolution (increasing Th and decreasing MgO) in the other rocks. Some leucite could have fractionated in the magmas of the Prehistorical and Younger Series. However, this mineral has partition coefficients higher than one only for Rb and Cs (Francalanci et al., 1987) and cannot be responsible for BaeSr decrease in the felsic rocks. Assimilation involved different types of magmas and wall rocks. Assimilation of carbonate rocks in the Younger Series has been demonstrated by oxygen isotope variation in the phenocrysts from Vesuvio (Dallai et al., 2011). Note that carbonate assimilation favors clinopyroxene crystallization (e.g., Iacono Marziano et al., 2008), which favored the continuous increase in Sr and Ba through the Younger Series. Assimilation of silicic rocks may be responsible for SreNd isotope variation in the Older Series (e.g., Pappalardo et al., 2002). Finally, some linear trends observed in the interelement variation diagrams clearly point to magma mixing. Such a process operated in all the magma series, but it is particularly evident for the Prehistorical Avellino rocks (Ayuso et al., 1998; Paone, 2006; Sulpizio et al., 2010). Complexities of magma evolution reveal modification of the magma plumbing system through time. The feeding system of SommaeVesuvio volcano is believed to consist of several magma chambers sited at different depths beneath the surface (De Vivo et al., 2010; Pappalardo and Mastrolorenzo, 2010; Nunziata et al., 2019, this book). It is likely, therefore, that various reservoirs were active at different stages of volcano evolution, giving distinct suites of magmas. Limestones and dolostones host one of the shallow reservoirs, as demonstrated by the large amounts of skarn xenoliths found in the SommaeVesuvio products (e.g., Fulignati et al., 2000 and references therein). Evolution within such a reservoir

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had paramount petrological consequences, in particular for the degrees of silica undersaturation, which are unique in the Campania Province. Pichavant et al. (2014) provided experimental evidence supporting an origin of all the SommaeVesuvio magmas from a single type of parent magma (see Stabile and Carroll, 2019, this book). Accordingly, the various suites would be related to different amounts and types of wall rock assimilation, in addition to separation of distinct mineral assemblages. In particular, heavy carbonate assimilation by the Younger Series along with heavy clinopyroxene fractionation generated strong silica undersaturated compositions. In contrast, the other magmas, especially those of the Older Series, evolved by fractional crystallization of clinopyroxene and feldspars and assimilation of wall rocks with siliceous compositions. As a consequence, they did not attain strongly undersaturated compositions, though starting from the same parental magma as the Younger Series. The hypothesis of a single parental magma and variable fractionation paths is strongly supported by geochemical data that basically overlap in the mafic range and define different trends only in the evolved compositions. The complex evolution history of SommaeVesuvio makes it difficult recognizing primary mantle equilibrated composition, which is crucial for understanding the nature of the sources. Incompatible element patterns normalized to primordial mantle (Sun and McDonough, 1989) for mafic rocks (MgO > 3.5 wt%) are very similar to each other, except for modest differences of absolute element abundances (Fig. 5.7A). Moreover, radiogenic isotope signatures do not change strongly with evolution. These data seem to suggest that incompatible element ratios and radiogenic isotope signatures of mafic rocks were not heavily affected by fractional crystallization and assimilation and might be considered as representative of their sources.

Campi Flegrei (Phlegraean Fields) The Campi Flegrei rocks range in composition from shoshonite and latite to dominant trachytes and phonolites, sometimes peralkaline (Fig. 5.8A). Latites and shoshonites are restricted to the younger activity, after the eruption of the Neapolitan Yellow Tuff at 15 ka (e.g., Armienti et al., 1983; Rosi and Sbrana, 1987; Melluso et al., 2012). Most rocks are slightly undersaturated in silica and have moderate potassic alkaline affinity (Fig. 5.8B). Shoshonites and latites contain clinopyroxene, plagioclase, rare olivine, and biotite phenocrysts, set in a groundmass made of abundant sanidine, FeeTi oxides, and glass. Trachytes and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Figure 5.7 Mantle normalized incompatible element patterns for mafic rocks from the Campania Province. Symbols of SommaeVesuvio as in Figs. 5.3e5.6. Juvenile (asterisks) and lithic lasts (crosses) are distinguished for Procida volcano. Normalizing values and Ocean Island Basalt (OIB, stars) are from Sun and McDonough (1989). Depleted and Enriched Mid-Ocean Ridge Basalts (D-MORB and E-MORB, crosses in panel A and C) are from Gale et al. (2013). Source of data as in Figs. 5.3, 5.8, 5.10.

phonolites have phenocrysts of alkali feldspar, minor clinopyroxene, biotite, plagioclase, and rare amphibole, nepheline, and sodalite-group minerals. Accessory phases include FeeTi oxides, apatite, britholite, zircon, spinel, and titanite (Armienti et al., 1983; Rosi and Sbrana, 1987; Pappalardo et al., 2002; Melluso et al., 2012). Leucite has been rarely observed (Astroni products, Tonarini et al., 2009). Variations of major and trace elements show a decrease in CaO with decreasing MgO, whereas FeOtotal, TiO2, P2O5 V, Sr, and Ba remain constant in the shoshonite-latite field to decrease sharply in the most evolved rocks (Fig. 5.9). Alkalies, Rb, Th, Zr, Y, and rare-earth elements (REE) increase sharply from mafic to evolved

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Figure 5.8 (A) Total alkali versus silica (TAS) classification diagram of Campi Flegrei rocks; (B) DQ versus K2O/Na2O diagram. For explanation of the diagrams, see caption of Fig. 5.3. The shaded area is the field of mafic rocks (MgO > 3.5 wt%). CI, Campanian Ignimbrite; NYT, Neapolitan Yellow Tuff. Data from Orsi et al. (1995), Civetta et al. (1997), DAntonio et al. (1999), Pappalardo et al. (1999, 2002), Fedele et al. (2008); Pabst et al. (2008), Tonarini et al. (2009), Di Renzo et al. (2011), Piochi et al. (2014), and references therein.

rocks, reaching very high enrichments in the trachyte-phonolite field. The highest concentrations of incompatible element have been found in the Averno 2 and the Monte Nuovo phonolites (Pappalardo et al., 2002). Some samples of the younger activity plot along linear trends between mafic and felsic compositions. Incompatible element patterns normalized to mantle compositions (Sun and McDonough, 1989) of the most mafic samples (MgO > 3.5 wt%) have a shape and degree of element enrichment that resemble closely to SommaeVesuvio (Fig. 5.7B). Abundances of several elements overlap average OIB or E-MORB, but LILE, light rare-earth element (LREE), and Pb are enriched relative to these compositions, as typically observed in subduction-related magmas. SreNd isotope ratios (Fig. 5.6) range from 87Sr/86Sr ¼ 0.7067e0.7086 and 143Nd/144Nd ¼ 0.51239e0.51260 (Orsi et al.,1995; D’Antonio et al., 1999; Pappalardo et al., 1999; Pabst et al., 2008; Di Renzo et al., 2011 and references therein). There is a clear trend of 87Sr/86Sr ratios to increase with MgO, mirrored by an opposite tendency for NdePb isotope ratios (Fig. 5.9E and F). Such a trend is particularly evident if samples younger than 15 ka are considered separately. However, younger activity does not show significant time-related variations of isotopic signatures. Yet, Pappalardo et al. (2002) demonstrate that there is an overall increase of Sr isotope ratios from older to younger activity at Campi Flegrei. Such a time-related isotopic trend is better

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Figure 5.9 Variation diagrams of selected major and trace elements and of SrePb isotope ratios against MgO for the Campi Flegrei rocks. Dashed lines indicate possible mixing trends. Source of data as in Fig. 5.8.

highlighted by the few available uranogenic Pb isotope ratios, which decrease significantly from rocks older than 35 ka and the Campanian Ignimbrite (39 ka) to the Neapolitan Yellow Tuff (15 ka) and the younger activity (Fig. 5.9F). Major and trace element variation diagrams suggest that fractional crystallization of clinopyroxene and feldspars was a

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leading process during magma evolution at Campi Flegrei (e.g., Pappalardo et al., 1999, 2002; Fowler, 2019, this book and references therein). Study of melt inclusions indicates polybaric crystallization from 200 MPa (7.5 km) to 30 MPa (w1 km) (Esposito et al., 2018). Clinopyroxene was the dominant separating phase in the shoshoniteelatite compositions, whereas alkali feldspar fractionated in the trachyte-phonolite magmas. Scattering of element distribution, linear trends observed in some diagrams, and radiogenic isotope variability testify to a role for additional processes, such as magma mixing and assimilation of crustal rocks (e.g., Pappalardo et al., 2002; Di Renzo et al., 2011). Radiogenic isotope behavior, especially 87Sr/86Sr in the rocks younger than 15 ka, is intriguing. Positive trends of 87Sr/86Sr versus MgO are the opposite than normally observed for assimilation processes. They imply higher amounts of crustal contamination in mafic than in felsic magmas. Such a process has been recognized elsewhere (e.g., at Alicudi, Aeolian arc; Peccerillo et al., 2004) and has been explained as an effect of the capability of hot and fluid mafic melts to incorporate and dissolve higher amounts of crustal rocks than the cooler and more viscous felsic magmas. However, isotopic variation might also testify arrival of new type of magmas within the volcano plumbing system. Pappalardo et al. (2002) highlight time-related geochemical variations through the entire Campi Flegrei activity and suggest evolution within two magma reservoirs, respectively hosted by the Hercynian lower crust and by the shallow arenaceous sedimentary cover. Early erupted magmas were less contaminated by crustal material than the younger ones because of the shorter time spent inside the deep reservoir. However, the emplacement during latest activity stages of a compositionally distinct type of primary magma with higher Sr- and lower NdePb isotope signatures than older products cannot be excluded. Recognizing primary compositions at Campi Flegrei is even more difficult than at SommaeVesuvio. Rocks with high MgO are lacking and the most primitive samples probably suffered heavy crustal contamination, as it has been discussed above. Yet, incompatible element patterns of the most mafic rocks are strikingly similar to those from SommaeVesuvio (Fig. 5.7), suggesting similar compositions for primary melts. The derivation of Campi Flegrei and SommaeVesuvio from a single parental magma raises the question about the absence of highly undersaturated leucite-rich rocks in the former. However, if silica undersaturation is the effect of carbonate assimilation, the scarcity of highly undersaturated rocks at Campi Flegrei could

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

be simply explained by a limited or no role for such a process. This conclusion agrees with the model of Pappalardo et al. (2002) who suggest that magma chambers are sited within the Hercynian basement and the siliceous sedimentary substratum and not inside carbonate sequences as at SommaeVesuvio.

Ischia Ischia consists of dominant trachytes, minor phonolites, and latites and rare shoshonites (Fig. 5.10). Basaltic rocks are absent; felsic rocks are sometimes peralkaline (Poli et al., 1987; Crisci et al., 1989; Civetta et al., 1991; Brown et al., 2008, 2014; Melluso et al., 2014; Iovine et al., 2017; Casalini et al., 2018). Rock mineralogy is made up of variable relative amounts of alkali feldspar, plagioclase, clinopyroxene, biotite, and FeeTi oxides phenocrysts; olivine occurs in the shoshonites. Sodalite-group minerals are observed in some trachytes and phonolites. Apatite and titanite are common accessories; aenigmatite, amphibole, aegirine, and ZreCaeNaeREEeF silicates have been found in the groundmass of peralkaline trachyphonolites (Melluso et al., 2014). Variation of selected major and trace elements (Fig. 5.11) show considerable scattering in the felsic compositions and smooth trends in the shoshonite-latite field. Mantle normalized incompatible element patterns are fractionated with negative spikes of

Figure 5.10 (A) Total alkali versus silica (TAS) classification diagram of Ischia and ProcidaeVivara rocks; compositions of basaltic lithics from Procida are also plotted; (B) DQ versus K2O/Na2O diagram. The shaded area is the field of mafic rocks (MgO > 3.0 wt%). For additional explanation on the diagrams, see caption of Fig. 5.3. Ischia data are from Poli et al. (1987), Crisci et al. (1989), Civetta et al. (1991), Brown et al. (2008, 2014), Melluso et al. (2014), Iovine et al. (2017), Casalini et al. (2017, 2018). ProcidaeVivara data are from DAntonio and Di Girolamo (1994), De Astis et al. (2004), Mazzeo et al. (2014), and references therein.

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Figure 5.11 Variation diagrams of Ischia and ProcidaeVivara rocks. Juvenile and lithic lasts at Procida are indicated with asterisks and crosses, respectively. Source of data as in Fig. 5.10.

HFSE and positive anomalies of Pb and LILE (Fig. 5.7C). Overall, they resemble Campi Flegrei and SommaeVesuvio patterns, although abundances of some LILE are slightly lower, in spite of more evolved compositions at Ischia.

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Radiogenic isotope data are variable (Fig. 5.6; 87Sr/86Sr ¼ 0.70538e0.70703; 143Nd/144Nd ¼ 0.51264e0.51249; 176Hf/177Hf ¼ 0.28283e0.28293; 206Pb/204Pb ¼ 18.94e19.23; 207Pb/204Pb ¼ 15.65 e15.71; 208Pb/204Pb ¼ 39.05e39.37) suggesting interaction between magmas and wall rocks and/or occurrence of different types of primary melts (e.g., D’Antonio et al., 2013; Casalini et al., 2018). There is a variation of radiogenic isotopes with time, a relationship that is particularly significant for Pb isotopes (Fig. 5.12). Oxygen isotope compositions on olivine and clinopyroxene phenocrysts range from d18OSMOW ¼ 5.5e6.5&, indicating little interaction with crustal rocks (D’Antonio et al., 2013). Ischia rocks mostly represent evolved compositions. These were likely derived from mafic parents with moderately potassic alkaline affinity. Magma evolution was dominated by fractional crystallization, with separation of mafic minerals joined by plagioclase and alkali feldspars in the intermediate and felsic compositions. Fractional crystallization was accompanied by mixing among compositionally different but comagmatic melts (Melluso et al., 2014). Interaction with the crust was moderate as indicated by oxygen and radiogenic isotope ratios in most of the rocks (D’Antonio et al., 2013; Casalini et al., 2018). Moretti et al. (2013) envisage that major fractionation events occurred in a magma chamber sited at about 8e10 km depth. There is also geochemical and isotopic evidence for fluid enrichments in the

Figure 5.12 Variation diagram of 206Pb/204Pb versus age (in 1000 years, ka) for Ischia volcanics. Crosses are the Monte Epomeo pyroclastic rocks. The stars with arrows point to 206Pb/204Pb ratios (not the age) of the Tyrrhenian Mid-Ocean Ridge Basalt (MORB) (206Pb/204Pb w18.60) and Etna Ocean Island Basalts (OIB) (206Pb/204Pb w19.70e20.10). For data of Etna and Tyrrhenian MORB see Peccerillo (2017) and references therein. Ischia data are from Casalini et al. (2017, 2018) and references therein.

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most evolved rocks and for repeated episodes of magma mixing (e.g., Poli et al., 1987; Civetta et al., 1991; D’Antonio et al., 2013 and many others). Recognizing the nature of primary melts at Ischia is even harder than at other centers. Rocks are more evolved than at any other Campania volcano, and primitive compositions are, in fact, absent. This is also true for melt inclusions in mafic phases that show maximum MgO contents around 4.0 wt% (Moretti et al., 2013). Casalini et al. (2018) show, however, that there is no significant relationship between SreNdeHfePb isotope signatures and the degree of evolution for most rocks, concluding that the observed isotopic variation reflect heterogeneities of mantle sources. These authors also seem to suggest that the parental magmas of Ischia might be represented by the most primitive rocks from Procida, which would imply crustal assimilation in the transition from Procida to Ischia magmas. Mantle-normalized incompatible element patterns of the least evolved rocks are strikingly similar to those of Vesuvio and Campi Flegrei, except for a slightly lower abundance of several incompatible elements (Fig. 5.7C). This is an indication that the Ischia magma sources may have similar trace element ratios as the other Campania volcanoes but lower incompatible element abundances.

Procida Procida and the nearby islet of Vivara consist of pyroclastic rocks (scoriae, hyaloclastites, pumices, and lithics) and a small lava dome. Juvenile materials are potassic alkaline and range from trachybasalt to trachyte (Fig. 5.10A). Mafic scoriae contain phenocrysts of diopside, plagioclase, and some olivine; sanidine phenocrysts occur in the trachytes, along with minor green clinopyroxene and andesine plagioclase (Di Girolamo and Stanzione, 1973; D’Antonio and Di Girolamo, 1994; De Astis et al., 2004, 2006; Fedele et al., 2006). Lithic clasts include silica undersaturated basalts with calcalkaline alkali abundances and ratios (Fig. 5.10B), which are not observed among the juvenile materials. These clasts and the samples from the buried volcanoes beneath Campi Flegrei are the only calcalkaline rocks in the Campania area. Calcalkaline basaltic clasts are porphyritic with phenocrysts of Mg-rich olivine and diopside, set in a matrix containing plagioclase, Ti-magnetite, rare alkali feldspar, and glass. Some olivine crystals contain inclusions of MgeCr-spinel.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

The ProcidaeVivara juvenile clasts show decreasing TiO2, MgO, FeO, ferromagnesian trace elements, and Sr and increase for alkalies and incompatible elements with increasing silica (Fig. 5.11). There is some scattering for several elements, especially among mafic rocks. Incompatible element patterns of the most primitive samples are fractionated and have a shape that resembles closely shoshonites from Ischia (Fig. 5.7C and D). However, absolute element enrichment is lower at ProcidaeVivara also because of more primitive compositions. SreNd isotope ratios show the most primitive compositions among Campania volcanics (87Sr/86Sr ¼ 0.7052e0.70733; 143 144 Nd/ Nd ¼ 0.5125e0.5127), whereas Pb isotopes overlap Ischia values (Fig. 5.6). He isotope ratios of olivine show R/RA ¼ 4.76e5.21, significantly higher than at other Campania volcanoes (R/RA ¼ 2.5e3.5) and partially overlapping rocks from Stromboli (R/RA ¼ 2.7e4.8) (Martelli et al., 2004, 2008). Basaltic lithics show high MgO, Ni, and Cr, which nearly fall in the compositional range of mantle-equilibrated melts. These samples also have the lowest incompatible element abundances and Sr isotope ratios in the Campania Province. 206Pb/204Pb ratios show relatively unradiogenic compositions and are shifted toward the Tyrrhenian MORB and the EM1-type (Enriched Mantle 1) basalts erupted by the Plio-Quaternary volcanoes in Sardinia (e.g., Gasperini et al., 2000, 2002; Lustrino et al., 2000). Geochemical variation suggests that fractional crystallization was a main evolutionary process at ProcidaeVivara. Radiogenic isotope variability also requires interaction with the crust (D’Antonio et al., 1999). There is an overlap of elemental variation trends of ProcidaeVivara and Ischia, which supports the Procida magmas as parental to Ischia (Casalini et al., 2018 and references therein). Procida hosts the only primitive rocks occurring in Campania. High MgO concentrations are also found among melt inclusions in olivine phenocrysts of juvenile clasts (Esposito et al., 2011, 2018 and references therein), suggesting a direct feeding from the upper mantle for these centers. Compared with other Campania volcanoes, ProcidaeVivara juvenile mafic rocks have similar patterns of incompatible elements but lower elemental abundances (Fig. 5.7). The lithic clasts have much less enriched compositions as well as lower LILE/HFSE ratios than juvenile equivalents. Therefore, two types of primary magmas can be recognized at ProcidaeVivara. The occurrence of two types of basaltic composition has also been

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demonstrated among olivine-hosted melt inclusions from Procida juvenile clasts (Esposito et al., 2011, 2018).

Petrogenesis of Campania magmas The Campania volcanoes are built up by a wide variety of rock types, ranging from mafic to felsic and from slightly oversaturated to strongly undersaturated in silica. Petrological and geochemical evidence suggests the occurrence of a single type of parental magma with a broadly trachybasaltic composition for all the centers. However, complex evolution processes generated the wide ranges of compositions observed among the erupted products.

Large regional magma chambers beneath Campania The complexity of evolution processes of trachybasaltic parental magmas at regional scale is best summarized by variations of radiogenic isotopes against any evolution parameter. A plot of 87 Sr/86Sr versus MgO is reported in Fig. 5.13A. It is obvious that the data, although much scattered, roughly fall in a triangularshaped area whose base is occupied by mafic magmas. In other words, mafic rocks show a larger range of compositions than felsic

Figure 5.13 (A) Variation diagram of 87Sr/86Sr versus MgO for the Campania Province. Arrows indicate possible evolution (mixing) trends of mafic magmas. Samples with Sr lower than 10 ppm have not been plotted to avoid compositions that are too readily modifiable by negligible assimilation or alteration; (B) La versus 87Sr/86Sr variation of mafic rocks. Samples with MgO >3.0 wt% have been plotted with the aim of including a significant number of samples from all volcanoes. Source of data as in Figs. 5.3, 5.8, 5.10.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

ones, but all converge toward a common, though wide, field defined by trachyte-phonolites. Such an array highlights the occurrence of isotopically different types of both mafic and felsic magmas, with the former showing larger variation. Moreover, convergence toward the trachytic-phonolitic field suggests an interaction of mafic melts with felsic magmas at the regional scale, implying the occurrence of a large phonolitic-trachytic reservoir (or a system of reservoirs), with which mafic melts coming from the source or from deeper reservoirs interacted (mixed) before being erupted at the surface. Seismic tomography suggests that a partially melted sill occurs beneath the active volcanoes of Campania at a depth between 7 and 14 km (e.g., Zollo et al., 2008; Fowler, 2019, this book and references therein). Moreover, Nunziata et al. (2019, this book) find a level with low S-wave velocity that starts from a depth of about 14e15 km and reaches the Moho. Such a layer extends continuously from the Roccamonfina volcano in the north to Vesuvio and Gulf of Naples, occupying the intermediate lower crust beneath the entire Campania Province. These authors conclude that geophysical data are consistent with the occurrence of a large regional magma reservoir (or a system of adjoining reservoirs) fed by mantle-derive melts. Therefore, a two-layer regional magma ponding system is suggested by geophysical evidence. Such a conclusion fits particularly well geochemical data. It is beyond the objective of this chapter discussing the complex issue of the plumbing system of Campania volcanoes (see Fowler, 2019, this book; Stabile and Carroll, 2019, this book). However, the model that best explains isotopic data is that of an upper reservoir (or various adjoining reservoirs) filled with trachyte-phonolite magmas derived from trachybasalt parents by dominant fractional crystallization and showing a more restricted range of isotopic compositions than mafic magmas ponding in a deeper reservoir(s). Different batches of mafic magmas ascending from depth cross and mix with evolved magmas sitting in the upper reservoir(s), modifying their isotopic signatures toward the trachyte-phonolite compositions. Large range of isotopic ratios of mafic melts may reflect stronger crustal assimilation in the deep magma chambers. However, this does not explain low Sr isotopic ratios of mafic magmas at Procida, suggesting that source heterogeneity must be assumed for Campania magmas.

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Compositions of primary melts The effects of evolutionary processes on the compositions of mafic rocks cannot be considered as fully understood. Therefore, compositions of primary melts are still rather speculative. However, it has been amply demonstrated that much of the trace element and isotopic variation of mafic rocks cannot be simply accounted for by evolutionary processes and likely reflects mantle source heterogeneity (e.g., Iovine et al., 2018 and references therein). Incompatible element patterns of mafic rocks support this conclusion. In spite of the complex evolutionary history described above, they show remarkable similar shapes for the different centers (Fig. 5.7), suggesting these represent pristine features. There is only a variation of incompatible trace element abundances, which decrease from SommaeVesuvio and Campi Flegrei to Ischia and ProcidaeVivara, in parallel with variations of SreNd isotope ratios (Fig. 5.13B). Therefore, geochemical evidence suggests heterogeneous mantle sources showing variable degrees of enrichments but similar distribution patterns of incompatible elements. Such a compositional array can be obtained by variable degrees of metasomatism by a single type of fluid or melt, which modified, with more intensity, the mantle source at Campi Flegrei and SommaeVesuvio than at the western centers of Ischia and Procida. Alternatively, one may hypothesize that a homogeneously metasomatized source underwent late mixing with a depleted source such as the Tyrrhenian MORB-type mantle, a process that was more significant in the western sector of the magmatic province.

Nature of mantle sources and metasomatism Fractionated incompatible element patterns with positive spikes of LILE, especially Pb, and negative anomalies of HFSE for the Campania Province are obvious arc signatures and strongly support an origin in a mantle that had been modified by subduction-related processes (Di Girolamo, 1978; Serri, 1990; De Astis et al., 2000; Peccerillo, 1999, 2001 and many others). SreNdePb isotope ratios of mafic rocks show that Campania volcanoes plot on a continuous trend between mantle and upper crust compositions, along with all the other orogenic volcanics from CentraleSouthern Italy (Fig. 5.14). Such an array clearly demonstrates an interaction between mantle and crustal components (Hawkesworth and Vollmer, 1979; Peccerillo, 2017

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Figure 5.14 (A) SreNd isotope diagram for mafic rocks (MgO > 3%) from Campania. Curved lines are mixing trends between Ocean Island Basalts (OIB)etype mantle and upper crustal rocks (marls and siliceous rocks). Note that the magmatic provinces plot along distinct mixing curves, suggesting variable roles of siliceous and marly sediments in source contamination; (B) 87Sr/86Sr versus 206Pb/204Pb diagram. Large arrows indicate trends of Procida mafic clasts and Pontine Islands (Ventotene) toward Sardinia EM1-type compositions. Compositions of mantle endmembers FOZO (Focus Zone), DMM (Depleted MORB Mantle) and Enriched Mantle 1 (EM1), and Tyrrhenian Mid-Ocean Ridge Basalt MORB (star) are also reported. Compositional fields of other magmatic province in the Tyrrhenian Sea area are reported for comparison (Peccerillo, 2017 and references therein). Source of data as in Figs. 5.3, 5.8, 5.10.

and references therein). Various amounts of siliceous and carbonate sediments are believed to be involved in the mantle metasomatism (e.g., Peccerillo, 1999; Mazzeo et al., 2014; Iovine et al., 2018). Premetasomatic mantle endmembers may have had FOZO-type (Focus Zone) OIB or MORB-type compositions (e.g., Serri, 1990; Morris et al., 1993; Ayuso et al., 1998; Casalini et al., 2018; Iovine et al., 2018). Both compositions are widespread in the Mediterranean area and are well represented by the Etna FOZOeOIB and by the Tyrrhenian Sea MORB (e.g., Lustrino and Wilson, 2007). The Campania Province plots in the middle of the trend between Etna and the upper crust, indicating moderate contamination of an FOZOeOIB source by sediments. Similar isotopic compositions as Campania are shown by the Stromboli volcano (Fig. 5.6) and to a much minor extent by Vulture, pointing to a common origin for all these magmas (De Astis et al., 2000; Peccerillo, 2001). Interaction between sediments and mantle components is also supported by low He isotope ratios, high B, and low d11B of Central Italy and Campania volcanics (e.g., Martelli et al., 2004, 2008; Tonarini et al., 2004, 2009). Geochemical modeling carried out by various authors (e.g., D’Antonio et al., 2007, 2013; Mazzeo et al., 2014; Iovine et al., 2018) suggests that subduction-related fluids released from an

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oceanic-type slab and associated sediments are able to explain the geochemical and isotopic signatures of Campania volcanoes. Sediment contribution ranges from 2% to 10%. Regional variations of incompatible trace element and radiogenic isotope ratios suggest that the sediment signature is stronger at SommaeVesuvio and Campi Flegrei than at Procida and Ischia. Such a variation could be attributed to the arrival of variable amounts of metasomatic fluids from the slab. However, it cannot be excluded that heterogeneity is a postmetasomatic feature, related to mixing between metasomatized Campania mantle and Tyrrhenian MORB, as recalled earlier in this discussion. Note that Ischia and Procida are sited nearest to the Tyrrhenian back-arc basin and, therefore, are more readily affected by MORB-type mantle from the west. The decrease of Pb isotopic ratios with time at Ischia (Fig. 5.12) may record an increasing role of depleted MORB-type components from earlier to latest activity. Combined LILE and HFSE and radiogenic isotope evidence can shed some further light on these issues. HFSE (Ta, Nb, Zr, Hf, Ti) are known to be relatively immobile during arc metasomatism (e.g., Kessel et al., 2005). Therefore, their abundances and ratios in mafic rocks furnish information on pristine mantle compositions. By contrast, LILE (Cs, Rb, Ba, K, Pb, LREE) are easily transferred by subduction-related fluids. Therefore, they cannot tell much on premetasomatic mantle compositions but give indications on the nature and degree of enrichment processes. HFSE abundances of Campania volcanoes are close to average OIB of Sun and McDonough (1989), whereas other Central Italy volcanoes such as Colli Albani (Alban Hills) have compositions close to E-MORB (Fig. 5.15A). Moreover, HFSE/HFSE ratios (e.g., Nb/Zr) in Campania are midway between OIB-type rocks of Etna and the Tyrrhenian MORB; Stromboli and Vulture basically plot in the same field of Campania, although Vulture is closer to Etna. In contrast, Colli Albani volcano plots with the Tyrrhenian MORB (Fig. 5.15B). Ernici-Roccamonfina falls between Campania and Colli Albani. These data suggest a role for both MORB- and OIB-type mantle pre-metasomatic sources along the Italian peninsula. MORB-type components dominated beneath the Roman Province; instead, OIB-type component contributed significantly to Campania, Vulture, and Stromboli magmatism. Ernici and Roccamonfina represent somewhat mixed compositions between Campania and Roman Provinces (Peccerillo, 2002, 2017). Moreover, LILE abundances and ratios and radiogenic isotope ratios indicate that metasomatism had different nature and much higher intensity for Roman than for Campania volcanoes. In conclusion, the Roman and the Campania volcanoes differ for both pristine

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Figure 5.15 (A) Mantle normalized incompatible element patterns of mafic rocks (MgO > 3.5%) from Campania (shaded area) compared with Colli Albani (Alban Hills) and Stromboli mafic potassic samples; (B) Nb/Zr versus 206 Pb/204Pb diagram for mafic rocks (MgO > 3.0%) from Campania. Ischia samples with MgO >2.0 wt% have been plotted because of the scarcity of mafic compositions. The fields of other volcanic areas are shown for comparison. Source of data as for Fig. 5.14.

mantle compositions and for compositions and degrees of metasomatism, strongly arguing against the commonly held view that Campania is a continuation of the Roman Province. PbeSr isotopic ratios furnish some additional information on a role of another mantle endmember, at least for the older activity (Fig 5.14B). While the Italian volcanics, including the Campania rocks, plot along a mixing trend between Etna (FOZOeOIB) and the upper crust, the basaltic lithics from Procida depart from the main trend pointing toward low 206Pb/204Pb compositions. A similar trend, but at higher Sr isotope values, is observed in the Pontine Island (Ventotene, 0-8e0.1 Ma old), offshore the coast of Campania. Pb isotope data, therefore, support a role for a third component in the origin of some older Campania magmas and for Ventotene. This endmember has lower 206Pb/204Pb than Tyrrhenian MORB, a feature that is only shown by EM1-type Plio-Quaternary volcanics from Sardinia (e.g., Gasperini et al., 2000, 2002; Lustrino et al., 2000). Such a component may have played a role in the older magmatism offshore the Campania Plain but seems absent or negligible in the more recent volcanism. In conclusion, the complex evolution of mantle source beneath Campania could be summarized as follows. An OIB-type premetasomatic mantle was affected by contamination by fluids coming from a subduction zone. Both sediments and a basaltic oceanic-type slab contributed to composition of

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metasomatic fluids. These affected at variable degrees the Campania mantle sources and were stronger beneath SommaeVesuvio and Campi Flegrei than at Procida and Ischia. Alternatively, metasomatism was homogeneous, but geochemical variations at the regional scale were generated by a postmetasomatic interaction of Campania mantle with a depleted mantle source such as that of Tyrrhenian MORB. An EM1 component might have played a role in the older magmatism in Campania and Pontine Islands.

Geodynamic implications The geodynamic significance of the volcanism in Central Italy has been the subject of a longstanding and still active debate. Most authors suggest that the entire volcanism occurring from Southern Tuscany to the Aeolian arc is subduction-related and results from mixing at the regional scale between mantle and upper crust. Two main mantle components, essentially MORB- and OIB-types, and various amounts and types of terrigeneous to marly sediments are believed to participate in the mixing (e.g., Peccerillo, 1999, 2017 with references; Conticelli et al., 2010 and many others). Regional variation of trace element and radiogenic isotope signatures along the peninsula has brought to recognize a number of magmatic provinces (Fig. 5.2). These result from different intensity and composition of the sedimentary contaminant, as well as from distinct premetasomatic mantle sources (Peccerillo, 2017 and references therein). Petrologicalegeochemical variation of magmatism, in turn, speaks for a complex and variable geodynamic setting along the Apennine subduction zone. Although this general picture is widely, though not unanimously, accepted, several aspects remain controversial. The occurrence of strongly undersaturated leucite-rich rocks at SommaeVesuvio has led to consider the Campania volcanoes as a district of the Roman ultrapotassic alkaline magmatic province (e.g., Conticelli et al., 2010; Melluso et al., 2014). However, it has been argued in the previous discussion that the strong degree of silica undersaturation at SommaeVesuvio may not reflect the compositions of primary melts but rather the effect of assimilation of carbonate wall rocks (e.g., Pichavant et al., 2014 and references therein). This hypothesis implies that strongly undersaturated ultrapotassic primary melts as those occurring in the Roman Province are lacking in Campania. Trace element and radiogenic isotope signatures also militate against a close genetic relationship between the Roman and

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

Campania provinces and rather demonstrate compositional affinities between Campania and Stromboli and, to a less extent, Mount Vulture (De Astis et al., 2000; Peccerillo, 2002). The close compositional similarity between Campania volcanoes and Stromboli requires a single type of contaminant superimposed over the same type of mantle material. Contamination could be provided by the Ionian plate that is actively subducting beneath the southern Tyrrhenian Sea (e.g., Orecchio et al., 2014 and references therein).

A possible geodynamic scenario The geodynamic scenario that best explains petrologicale geochemical variations of volcanism along the Tyrrhenian border of the Italian peninsula is that while Roman volcanoes are related to subduction of the Adriatic plate and contamination by marly sediments of a MORB-type premetasomatic mantle, a distinct subduction process of the Ionian plate affected an OIB-MORB type source beneath Campania, the eastern Aeolian arc, and Vulture. The Adriatic plate is of continental type, whereas the Ionian plate is believed to be oceanic or thinned continental in nature (Speranza et al., 2012 and references therein). It is obvious, therefore, that the type and amounts of upper crustal material brought into the mantle had strikingly different compositions for the two subduction systems. The limit between the two plates runs in an NW-SE direction south-west of Apulia (e.g., Sani et al., 2016; Pierantoni et al., 2019, this book). The evolution of the Adriatic-Ionian subduction system is discussed by Pierantoni et al. (2019, this book). A continuous plate was initially subducting beneath the Apennine chain. Eastward migration of the subduction system brought to fragmentation of the both the Apennine chain and of the Adriatic-Ionian foreland. The northern Adriatic sector collided earlier and possibly underwent slab break-off. Collision in the southern sector of the Adriatic plate (i.e., Apulia) occurred about 0.8 Ma (Patacca and Scandone, 2001), shortly before the onset of Vulture activity at about 0.75 Ma (Villa and Buettner, 2009). In contrast, the oceanic-type Ionian sector continued sinking into the mantle beneath the southern Tyrrhenian Sea. Collision in the Apulia sector generated an along-strike tearoff of the subducting slab, as suggested by Wortel and Spakman (2000), Spakman and Wortel (2004), and Panza et al. (2007). In other words, there was a slab breakoff in Apulia, whereas in the south, the slab remained attached to the Ionian foreland, continuing its sinking into the upper mantle while retreating

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south-eastward (e.g., Gvirtzman and Nur, 1999; Rosenbaum and Lister, 2004; Panza et al., 2007; Peccerillo, 2017 with references). It is suggested that dehydration of the Ionian oceanic slab and associated sediments produced mantle contamination and melting both beneath the eastern Aeolian arc and Campania (Fig. 5.16). Pierantoni et al. (2019, this book) show a somewhat distinct model in which a slab coming from Apulia occurs beneath Campania, whereas the Ionian slab is subducting beneath the Aeolian arc. According to this model, two distinct slab sectors, respectively, coming from Apulia and the Ionian Sea, should be responsible for mantle contamination and magmatism in Campania and the Aeolian arc. Such a hypothesis, however, is at odds with geochemical data, which require the same type of source contamination for Campania and Stromboli, related to the same type of fluids. It is unlikely that compositionally homogeneous fluids were released from two distinct slabs; geochemical data are better explained by a common origin of fluids from a single Ionian-subducting zone, though fluids might originate at different depths along the slab. Slab tear-off along the subduction hinge and rollback can furnish an explanation for the origin of the OIB- and MORBtype mantle components beneath CampaniaeStromboli. OIB-type material could be provided by asthenospheric mantle

Figure 5.16 Schematic model for the evolution of the Ionian Sea subduction system. (A) Subduction of a continuous slab from AdriaeApulia to the Ionian Sea. (B) Apulia collision at about 0.8 Ma and onset of along-strike slab break-off, with opening of a window through which foreland asthenosphere is suctioned onto the subducting slab (red arrow). (C) Present situation with a narrow Benioff zone extending from the eastern Aeolian arc to Campania. Red arrows indicate asthenospheric mantle inflow from the foreland and possible input from the Tyrrhenian Sea area.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

inflow from the foreland onto the subducting Ionian slab. Southeastern slab rollback could have suctioned asthenospheric mantle from the Apulia-Ionian foreland thus involving OIB-type components in the subduction factory (Peccerillo and Frezzotti, 2015 and references therein). Asthenospheric material from the foreland had a similar characteristic as the Etna magma source, which has an almost pure FOZO-type composition. Access to the subduction zone for the asthenosphere from the foreland occurred through the window opened by the along strike slab tear-off of the Apulia-Ionian plate. Rollback may have attracted additional mantle material from the west, i.e., from the Tyrrhenian Sea, thus justifying the MORB-type component at Ischia and Procida. In conclusion, the geochemistry of Campania magmas may result from the contribution of OIB- and MORB-type materials. Both these components are allochthonous and, respectively, come from the foreland and from the Tyrrhenian Sea area. OIB-type asthenospheric mantle migrated from the foreland onto the Ionian subduction zone and was contaminated by fluids delivered by the Ionian slab. A distinct mantle inflow occurred form the west and only affected the westernmost centers of Ischia and Procida. The same type of contamination hypothesized for Campania and Stromboli may also have affected the Vulture source. In the latter case, however, the role of OIB was stronger because of Vulture position close to the Apulia foreland, i.e., to the source of OIB component (De Astis et al., 2000).

Conclusions The main conclusions on the origin, evolution, and geodynamic significance of the Campania Province can be summarized as follows: 1. The Campania volcanoes have a wide range of compositions that were generated by complex evolution processes. These involved fractional crystallization, mixing, and assimilation of different types of wall rocks. Magmas with broadly trachybasaltic compositions were parental to all the volcanic suites in Campania. Evolution followed distinct trends at various volcanoes or also at different stages of single centers because of modification of the chemicophysical conditions of magma chambers and the nature of wall rocks. Heavy carbonate assimilation occurred at SommaeVesuvio, generating strongly undersaturated compositions that are absent at other centers.

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2. The Campania volcanoes are petrologically and geochemically distinct for other magmatic provinces in Central Italy. In particular, they differ from the Roman volcanoes by showing lower LILE abundances, lower LILE/HFSE ratios, lower Sr and higher Nd isotope ratios, and much more variable and overall higher Pb isotopic ratios. Moreover, primary ultrapotassic-undersaturated compositions that are common in the Roman Province are absent in the Campania volcanoes, as the leucite-bearing rocks at SommaeVesuvio are related to carbonate assimilation by a trachybasalt parent. By contrast, the Campania volcanoes show close geochemical similarities with Stromboli volcano, indicating similar source compositions and geodynamic setting. 3. The sources of Campania and Stromboli volcanoes consist of a mixture of premetasomatic FOZOeOIB-type mantle similar to Etna and MORB. MORB-type component is more evident beneath the western volcanoes of Ischia and Procida than at Campi Flegrei and SommaeVesuvio. 4. Mantle metasomatism beneath the eastern Aeolian arc and Campania was accomplished by fluids released by the subducting oceanic Ionian slab and associated sediments. The common nature of premetasomatic source and of the contaminating materials generated geochemically similar magmas in Campania and the eastern Aeolian arc, supporting a single slab as a source of metasomatic fluids. 5. The geodynamic model that best explains petrological and geochemical evidence suggests that the OIB-type component of the eastern Aeolian arc and Campania volcanoes was provided by inflow from the IonianeApulian foreland. Mantle probably inflow also occurred from the Tyrrhenian area and mainly affected Ischia and Procida. Inflow from the foreland onto the Ionian subduction zone took place through the along-strike tear-off of the Ionian slab and was favored by suctioning during rollback toward the southeast.

Acknowledgment The data used in this chapter come from many research articles, mostly carried out in the last two decades. Citing all the papers is impossible. A complete list of the data and their sources is reported by Peccerillo (2017) and supplementary material. Constructive comments by Gianfilippo de Astis (INGV) and Michael R. Carroll (University of Camerino) greatly contributed to improve the manuscript.

Chapter 5 Campania volcanoes: petrology, geochemistry, and geodynamic

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