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Compositional variations of magmas in the Aeolian arc: implications for petrogenesis and geodynamics

January 2013

Authors:

A. Peccerillo

University of Perugia

Gianfilippo De Astis

INGV Istituto Nazionale di Geofisica e Vulcanologia

Francesca Forni

University of Milan

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The volcanic rocks of the Aeolian arc exhibit important within-island and along-arc compositional variations that testify to both geochemical heterogeneous mantle sources and different roles and intensities of shallow-level magmatic evolution processes. Calcalkaline magmas are present on all islands, but dominate in the western arc and at Lipari and Panarea. Shoshonitic rocks are present on the central-eastern islands and are particularly abundant at Vulcano and Stromboli. Mafic and intermediate rocks comprise the bulk of older volcanic sequences for most islands. Rhyolites are restricted to younger activity of the central arc, and become particularly abundant at Lipari and Vulcano. Regional variations of incompatible trace element ratios and Sr-, Nd-, and Pb-isotope signatures in mafic-intermediate rocks document the variable composition of mantle sources, which were contaminated by different types of metasomatic fluids released from an oceanic slab in the western-central sectors and from oceanic slab plus sediments in the east. This metasomatism was superimposed over a heterogeneous mantle wedge, which had a mid-ocean-ridge basalt (MORB-) to ocean-island basalt (OIB)-type character passing from the centre to the margins of the arc. The OIB-type component in the external arc is attributed to asthenospheric mantle inflow from the Africa foreland, around the borders of a narrow slab during rollback.

Variation diagrams of some major and trace elements v. silica. Source of data and symbols as in Figure 15.2.

…

Regional variation of trace element ratios for the newly analysed Aeolian samples (Table 15.1). Average compositions of Tyrrhenian MORB (Dietrich et al. 1977), Etna (Viccaro & Cristofolini 2008) and Ionian sediments (De Astis, unpublished data) are also reported.

…

Schematic geodynamic setting of the Aeolian arc. A narrow Ionian plate is subducting beneath Calabria and the southern Tyrrhenian Sea. This is associated with deep seismicity and active volcanism, and is bounded to the west by the Tintari-Letojanni Fault (TLF) system. A detached and passively sinking oceanic slab is envisaged for the western Aeolian arc. Curved black arrows indicate asthenospheric mantle inflow from the foreland around the margins of the subducted slabs. Collision zones are indicated with a dashed line. For further explanation, see text.

…

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Geological Society, London, Memoirs

doi: 10.1144/M37.15 2013, v.37; p491-510.Geological Society, London, Memoirs

A. Peccerillo, G. De Astis, D. Faraone, F. Forni and M. L. Frezzotti

petrogenesis and geodynamics

Chapter 15 Compositional variations of magmas in the Aeolian arc: implications for

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Chapter 15

Compositional variations of magmas in the Aeolian arc: implications for

petrogenesis and geodynamics

A. PECCERILLO1*, G. DE ASTIS2, D. FARAONE1, F. FORNI3& M. L. FREZZOTTI4

Dipartimento di Scienze della Terra, Universita

`di Perugia, Piazza Universita

`1, 06100 Perugia, Italy

INGV (Istituto Nazionale di Geoﬁsica e Vulcanologia), Sezione di Sismologia e Tettonoﬁsica,

Via di Vigna Murata 605, 00143 Roma, Italy

Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum,

Universita

`di Bologna, Piazza Porta S.Donato 1, 40126 Bologna, Italy

Dipartimento di Scienze dell’Ambiente e del Territorio e di Scienze della Terra,

Universita

`di Milano – Bicocca, Piazza Della Scienza 4, 20126 Milano, Italy

*Corresponding author (e-mail: angelo.peccerillo@unipg.it)

Abstract: The volcanic rocks of the Aeolian arc exhibit important within-island and along-arc compositional variations that testify to

both geochemical heterogeneous mantle sources and different roles and intensities of shallow-level magmatic evolution processes. Calc-

alkaline magmas are present on all islands, but dominate in the western arc and at Lipari and Panarea. Shoshonitic rocks are present on the

central-eastern islands and are particularly abundant at Vulcano and Stromboli. Maﬁc and intermediate rocks comprise the bulk of older

volcanic sequences for most islands. Rhyolites are restricted to younger activity of the central arc, and become particularly abundant at

Lipari and Vulcano. Regional variations of incompatible trace element ratios and Sr-, Nd-, and Pb-isotope signatures in maﬁc-intermedi-

ate rocks document the variable composition of mantle sources, which were contaminated by different types of metasomatic ﬂuids

released from an oceanic slab in the western-central sectors and from oceanic slab plus sediments in the east. This metasomatism

was superimposed over a heterogeneous mantle wedge, which had a mid-ocean-ridge basalt (MORB-) to ocean-island basalt (OIB)-

type character passing from the centre to the margins of the arc. The OIB-type component in the external arc is attributed to astheno-

spheric mantle inﬂow from the Africa foreland, around the borders of a narrow slab during rollback.

Aeolian arc magmatism (Fig. 15.1) exhibits strong within-island

and regional variations in elemental and isotopic compositions.

These are the integrated effects of a variety of different processes

that include heterogeneity of the mantle sources, variable physico-

chemical conditions during magma formation and complex geo-

chemical evolution during magma ascent to the surface (e.g.

Keller 1982; Francalanci et al. 1989, 2004, 2007; Peccerillo 2005).

Intra-crustal magma compositional evolution was the latest

process to occur and therefore left the best evidence in the petrolo-

gical and geochemical signatures of subaerial volcanic rocks. Much

more difﬁcult to understand are the compositional characteristics

and conditions of melting within mantle wedge. This is generally

accomplished by studying the compositions of maﬁc magmas

erupted along the arc, based on the assumption that these are

reliable proxies of their mantle sources. However, it has been

demonstrated that complex evolution processes in the Aeolian arc

also affected maﬁc magmas which, in some cases, are more

heavily contaminated by wall rocks than the coexisting intermedi-

ate magmas (see Peccerillo & Wu 1992; Peccerillo et al. 1993,

2004; Santo et al. 2004; Lucchi et al. 2013a). This makes the under-

standing of source composition and evolution processes a parti-

cularly challenging problem, which is still a subject of debate.

This paper is a critical review of the petrology and geochemistry

of the Aeolian arc magmatism and of current ideas regarding the

origin and evolution of magmas, mantle source compositions

and their geodynamic signiﬁcance. The paper consists of two

parts. The ﬁrst part is based on literature data and summarizes

the volcanological and structural setting of the arc, describes the

ﬁrst-order compositional variation of rocks in the single islands

and at the regional scale and discusses the nature and effects of

magma evolution processes. The second part deals with regional

variations of trace elements and radiogenic isotope compositions

of magmas and their mantle sources and discusses the most

popular hypotheses regarding mechanisms and effects of mantle

metasomatism, conditions of formation of shoshonitic and

calc-alkaline magmas and the geodynamic setting of the Aeolian

arc. Along-arc geochemical variations are examined based upon

new LAICPMS (Laser Ablation Inductively Coupled Plasma

Mass Spectrometry) trace element analyses for a large number of

representative samples from across the Aeolian arc. Intermediate

rocks are considered along with maﬁc rocks, since andesites

from some islands show the most primitive isotopic compositions

across the arc and therefore represent more reliable proxies of

mantle sources than maﬁc rocks. The new analyses provide an

internally consistent set of data that overcomes the problems of

inter-laboratory analytical bias, a main limitation of data in the lit-

erature. These data offer a better insight into ﬁne-scale regional

geochemical zoning, thus providing a foundation for development

of a comprehensive model of the mantle source composition and

its geodynamic signiﬁcance.

Structural, volcanological and petrological outlines

The Aeolian volcanism consists of seven main islands (Alicudi,

Filicudi, Salina, Lipari, Vulcano, Panarea and Stromboli) making

up a volcanic arc and several seamounts (Marsili, Eolo, Enarete,

Sisifo, Lametini, Alcione, and Palinuro). These have formed

around and inside the Masili basin (Fig. 15.1), a rapidly expand-

ing back-arc basin (Nicolosi et al. 2006) ﬂoored by basaltic

rocks and characterized by thin lithosphere and crust (Trua et al.

2004). The arc exhibits strong lateral variation of structural,

volcanological and petrological characteristics, which make the

Aeolian volcanoes an important case study for subduction-

related volcanism.

From:Lucchi, F., Peccerillo, A., Keller, J., Tranne,C.A.&Rossi, P. L. (eds) 2013. The Aeolian Islands Volcanoes. Geological Society, London, Memoirs, 37,

491–510. http://dx.doi.org/10.1144/M37.15 #The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

Stuctural and volcanological setting

The Aeolian volcanoes are composite structures formed by the

superposition of multiple centres and recurrent volcanic and tec-

tonic events, with many sector and central collapses. Rocks

exposed above the sea level are younger than c. 270 ka (Gillot

1987; Leocat 2011). Vulcano and Stromboli are presently active,

but Lipari and Panarea have also erupted or demonstrated

intense submarine degassing during historical time. Of the sea-

mounts, Marsili and Palinuro are considered active. Marsili rises

for more than 3000 m over the sea ﬂoor of the Marsili basin, and

is the best studied among Aeolian seamounts (Trua et al. 2011).

The Aeolian islands are constructed upon the Calabro – Pelori-

tano basement, a block of the European continent which detached

from Sardinia– Corsica and migrated south-westwards during the

Miocene– Quaternary opening of the Tyrrhenian Sea. Crustal

thickness beneath the Aeolian arc is c. 15 – 25 km, and increases

westwards. The Aeolian arc is cut by a complex pattern of fault

systems (Ventura 2013). The NW – SE-trending Tindari –Leto-

janni Fault (TLF) is the most important tectonic lineament in the

area, running from the Salina – Lipari –Vulcano alignment to the

Malta escarpment (Fig. 15.1). In mainland Sicily, the TLF cuts

the Calabro– Peloritano basement near the boundary with the post-

Miocene accretionary prism and the Iblei continental block to the

west (Grasso 2001). It is likely that these geometric relationships

continue in the Aeolian arc. This implies that distinct types of base-

ment rocks are present across the Aeolian archipelago, that is, the

Calabro– Peloritano basement in the central-eastern sectors and

the accretionary prism rocks under the western islands. Such a

hypothesis is supported by the increase in crustal thickness west

of the Tindari– Letojanni Fault (Ventura 2013).

Traditionally, the Aeolian arc has been divided into three main

sectors – the western, the central and the eastern arcs – which are

characterized by ﬁrst-order volcanological, magmatic and struc-

tural differences (Peccerillo 2005; Ventura 2013). The western

arc is formed by Alicudi and Filicudi, which are situated along

east– west- to WNW –ESE-striking fault systems. A NNW –SSE

compressive strain ﬁeld due to the Africa – Eurasia convergence

is active in this sector (Ventura 2013). The central islands of

Vulcano and Lipari are located along the TLF, where a strike-slip

strain regime is active. Salina is sited at the intersection between

the east– west-trending structures of the western arc and the

Tindari– Letojanni Fault. Panarea and Stromboli are situated

along SW– NE-trending faults. An extensional tectonic regime

affects this sector of the arc.

Active volcanism occurs along the Tindari – Letojanni Fault and

east of this tectonic line. The compressive tectonic regime in the

western sector inhibits upraise and eruption of magmas, whereas

extensional and strike-slip strain regimes in the central-eastern

arc generate vertical faults that are pathways along which

magmas ascend and erupt at the surface (Ventura 2013).

Geophysical studies (e.g. Panza et al. 2003) indicate that deep

seismicity (up to 550 km) only occurs east of the Tindari – Leto-

janni Fault. This is a consequence of the Ionian slab subduction

beneath the Calabro – Peloritano basement and the southern Tyr-

rhenian Sea. Active Aeolian volcanism is therefore located

above or at the margin of the deep seismicity zone.

Magma compositions

Key geochemical data from the literature are shown in Figures

15.2– 15.6. The important information contained in these diagrams

can be summarized as follows.

(1) Calc-alkaline (CA) and high-K calc-alkaline (HKCA) rocks

occur throughout the arc but dominate at Alicudi, Filicudi,

Salina, Lipari and Panarea (Fig. 15.2). In contrast, shosho-

nites (SHO) are spatially restricted to the central-eastern

islands, where they generally appear during the mature to

late stage of volcanic activity. The Marsili seamount has a

CA basalt to basaltic andesite composition, with a few ande-

sites (Trua et al. 2011). A single sample has ocean-island

basalt (OIB)-type afﬁnity and is not plotted in the diagrams.

The small number of analyses available for the other Aeo-

lian seamounts (not shown) indicates that rocks are predomi-

nantly of calc-alkaline maﬁc to intermediate composition,

with a few shoshonites (Eolo, Enarete) and arc tholeiites

(Marsili basin margin; Trua et al. 2004; Peccerillo 2005).

(2) The degree of magma evolution increases from the external

to the central islands; rhyolitic volcanism (SiO

.70%) is

present at Panarea and Salina, and becomes abundant at

Lipari and Vulcano (Fig. 15.2). Rhyolites characterize the

younger stages of activity for all these volcanoes.

(3) Abundances of elements that are incompatible with main

magmatic minerals (e.g. Th, U, Nb, Ta and Light Rare

Earth Elements - LREE) increase with silica for all the islands

and seamounts (Fig. 15.3). The exception observed is for

Ba, which decreases in the rhyolites of Vulcano and Lipari,

but not in the rhyolites of Salina and Panarea (Fig. 15.3d).

(4) Incompatible trace element (ITE) abundances increase from

CA to SHO volcanics for the maﬁc-intermediate compo-

sitions (Fig. 15.4). This is observed for both the large-ion

lithophile elements (LILE: Rb, Ba, La, Th, etc.) and for the

high-ﬁeld-strength elements (HFSE: Nb, Ta, Hf, Zr).

However, there are several differences between islands.

These have important petrogenetic implications, and will

be discussed later (see “Isotope and trace element compo-

sition of mantle sources”).

(5) Incompatible element patterns normalized to primordial

mantle for basalts and basaltic andesites from the Aeolian

islands and Marsili seamount display the typical features of

arc volcanics worldwide, with enrichments in LILE and rela-

tive depletion in HFSE (Fig. 15.5). Most of these features are

also shown by the Calabro – Peloritano basement and the

Ionian Sea sediments (Fig. 15.5d). The Aeolian seamounts

(not shown) show similar patterns as the other Aeolian

rocks, with fractionation and abundances of ITE increasing

from CA to SHO rocks.

(6) Sr-isotope ratios of maﬁc – intermediate rocks increase from

the western island of Alicudi to the central and eastern

islands, reaching maximum values at Stromboli (Fig.

15.6a). Sr– Nd isotopic ratios display the well-known

Palinuro Smt.

Glauco Smt.

(Pliocene)

Eolo Smt.

Sisifo Smt.

Lametini Smt.

Tyrrhenian

Sea

Marsili

Smt.

MARSILI BASIN

Alicudi Filicudi

Stromboli

Panarea

Lipari

Vulcano

Sicily

Salina

AEOLIAN ARC

Calabria

Tyrrhenian

Sea

Alcione Smt.

Enarete Smt.

Fig. 15.1. Location map of Aeolian islands and seamounts. TLF is the Tindari –

Letojanni Fault system.

A. PECCERILLO ET AL.492

negative correlation. However, a slightly steeper slope

characterizes the western-central islands. Marsili shows a

large Sr– Nd isotope variation that overlaps the western-

central arc domain. Panarea has a variable Sr-Nd isotopic

composition, with CA rocks falling within the ﬁeld of

western islands and SHO rocks plotting with Stromboli.

At Stromboli there is a considerable increase of Sr- and a

concomitant decrease of Nd-isotopic ratios from calc-alka-

line to shoshonitic rocks (Francalanci et al. 1988, 1989,

2013), which is not observed at Vulcano (De Astis et al. 2000).

Normalized

He/

He (R/R

) ratios (not shown) range from

7.07 (Alicudi) to 2.51 (Stromboli) (Martelli et al. 2008).

(7) Pb-isotope ratios have variable and overlapping values for

most islands except for Stromboli, which has a distinctively

less radiogenic Pb-isotope composition. Overall, Pb-isotope

ratios fall between the highly radiogenic Etna OIB-type

basalts and the continental crust of the Calabro – Peloritano

basement (Fig. 15.6b). Etna is close to the so-called FOZO

(¼FOcus ZOne; Hart et al. 1992) mantle composition,

which is extremely common in anorogenic settings of

Europe and has been termed the European Asthenospheric

Reservoir (EAR) by Wilson & Downes (1991). The

Pb-isotope composition of Marsili overlaps Stromboli and

some of the western-central islands.

(8) Stromboli shows similar radiogenic isotope signatures as

Vesuvio (De Astis et al. 2000, 2013; Peccerillo 2001) and

other volcanoes from Campania. Such a similarity is also

observed for several incompatible trace element ratios, and

led Peccerillo (2001) to conclude that Vesuvio and other

Campania volcanoes represent the northern end of the

Aeolian arc rather than the southern sector of the Roman

Magmatic Province, as generally acknowledged.

Shallow-level magma evolution

Fractional crystallization, crustal assimilation, magma mixing or

some combination of these processes has been documented for

the Aeolian volcanoes. These have been extensively discussed

within individual chapters of this volume, so are only summarized

brieﬂy here.

Fractional crystallization

Fractional crystallization was the predominant process of magma

evolution at several centres. This process was much more

intense for the volcanoes of the central islands, where rhyolitic

compositions were reached. This outcome is likely related to

local tectonics associated with the Tindari – Letojanni transcurrent

fault, where the development of pull-apart basins favoured the for-

mation of large reservoirs (Barberi et al. 1994) in which magmas

ponded and fractionated. Maﬁc minerals plus plagioclase were

main fractionating phases, as demonstrated by curvilinear trends

for many major and trace elements, especially MgO, Ni, Cr but

also Al

and Sr, against SiO

(Fig. 15.3). A decrease of Ba in

the rhyolites of Vulcano and Lipari, but not at Panarea and

Salina, indicates signiﬁcant separation of alkali-feldspar late in

the evolution stages of the two former islands. Alkali-feldspar

crystallization is related to the HKCA to SHO afﬁnity of late

erupted magmas at Lipari and Vulcano. Fractional crystallization

modiﬁes major and trace element abundances of magmas, slightly

modiﬁes d

O‰, but leaves radiogenic isotope compositions and

incompatible trace element ratios unaffected. The values of these

parameters measured in evolved rocks can therefore be used to

infer compositions of primary melts and their mantle sources.

However, the main problem is that magma evolution rarely (if

ever) occurs simply by closed-system fractional crystallization;

wall-rock assimilation and magma mixing usually accompany

fractional crystallization in most cases.

Magma mixing/mingling

Magma mixing/mingling is widespread in the Aeolian volcanoes.

The most striking evidence of this process is seen in the occurrence

of abundant maﬁc enclaves in many intermediate and silicic lavas.

These enclaves are blobs of maﬁc magmas that were present within

the volcanic system and were intermingled with the silicic melts

during eruption. The best examples are observed for some Lipari

and Vulcano rhyolites (e.g. De Rosa & Sheridan 1983; Gioncada

et al. 2005; Perugini et al. 2007; De Astis et al. 2013; Forni

et al. 2013), for Panarea dacites and rhyolites (Calanchi et al.

K2O %

50 55 60 65 70 75 80

K2O %

SiO2 %

SHO

K2O %

Alicudi

Filicudi

Salina

Lipari

Vulcano

Panarea

Stromboli

Marsili

Eastern arc

Western arc

Central arc

(a)

(b)

(c)

Fig. 15.2. K

O v. SiO

classiﬁcation diagrams for the Aeolian arc volcanics.

Lines dividing arc tholeiitic (TH), calc-alkaline (CA), high-K calc-alkaline

(HKCA) and shoshonitic (SHO) series are from Peccerillo & Taylor (1976).

Data on Marsili are from Trua et al. (2011). For source of other data see

Peccerillo (2005).

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 493

2002; Lucchi et al. 2013d) and at Salina (Perugini et al. 2004;

Lucchi et al. 2013c). Mixing processes also affected most (if not

all) of the magmas however, although physical evidence is less

strong either because of the lack of compositional contrast

between end-members or because near-equilibrium conditions

were reached by hybrid magmas.

Mixing is a complex process of major geochemical and volcano-

logical interest. Detailed studies in the Aeolian arc are however

limited (e.g. De Rosa & Sheridan 1983; De Astis et al. 1997; Gion-

cada et al. 2003, 2005; Perugini et al. 2004, 2007; Davı

`et al. 2008;

Piochi et al. 2009), and the effects on magma compositions for

single eruptions, for individual volcanic centres and at the regional

scale, are still basically unexplored.

Magma contamination

Magma contamination by crustal wall-rocks in the Aeolian volca-

noes took place as a consequence of several different processes.

Assimilation plus fractional crystallization (AFC) is the most

common case, and has been recognized at several islands (e.g.

Salina, Vulcano and Lipari; Crisci et al. 1991; Esperanc¸a et al.

1992; De Astis et al. 2013; Forni et al. 2013; Lucchi et al.

2013c). This is clearly demonstrated by the positive correlations

Sr/

Sr and d

O‰ with silica observed for many Aeolian

islands by Ellam & Harmon (1990). More complex processes of

combined fractional crystallization, assimilation, reﬁlling of

magma chambers, mixing and frequent tapping by eruptions

(RFTA: reﬁlling, fractionation, tapping, assimilation) have been

recognized for the lowest exposed volcanic sequences of many

islands (e.g. De Astis et al. 1997; Di Martino et al. 2011; Lucchi

et al. 2013a,b, c). These rocks are generally maﬁc in composition

and display rather variable trace element and isotopic signatures,

which is typical of RFTA processes (O’Hara 1977). Finally, a par-

ticular type of assimilation is represented by incorporation of

different amounts of crustal rocks by basaltic and andesitic

magmas, with the former being able to assimilate greater

amounts of crustal rocks than andesites. Such a process has been

MgO%

0.0

0.4

0.8

1.2

TiO2%

l2O3 %

45 50 55 60 65 70 75 80

SiO2 %

100

200

300

400

500

Rb ppm

500

1000

1500

2000

Ba ppm

Ta ppm

45 50 55 60 65 70 75 80

100

150

La ppm

Marsili (a)(b)

(c)(d)

(e)(f)

(g)(h)

100

150

Ni ppm

SiO2 %

Marsili

Fig. 15.3. Variation diagrams of some

major and trace elements v. silica. Source of

data and symbols as in Figure 15.2.

A. PECCERILLO ET AL.494

0.5

1.0

1.5

2.0

2.5

Ta p pm

500

1000

1500

2000

Sr ppm

0 2 4 6

100

200

300

Zr ppm

K2O wt%

0 2 4 6

100

La ppm

K2O wt%

CA SHO

Alicudi

Filicudi

Salina

Lipari

Vulcano

Panarea

Stromboli

100

150

200

250

300

Rb ppm

500

1000

1500

2000

Ba ppm

2500

Marsili

CA SHO

(a)(b)

(c)(d)

(e)(f)

Fig. 15.4. Incompatible trace element

v. K

O diagrams for maﬁc-intermediate

rocks (SiO

,56 wt%) from the Aeolian arc

and Marsili seamount, showing increase of

element abundances from calc-alkaline to

shoshonitic rocks. Source of data as in

Figure 15.2.

100

1000

Rock/Primitive Mantle

100

1000

Rock/Primitive Mantle

100

1000

Ta K La

Y Yb

Rock/Primitive Mantle

100

1000

Ta K La

Y Yb

Rock/Primitive Mantle

Calabrian crust

Ionian sediments

Alicudi

Filicudi Lipari

Salina

Local MORB

Etna basalt

Marsili

Vulcano

Panarea

Stromboli

(a)(b)

(c)(d)

Fig. 15.5. Incompatible element patterns

normalized to primordial mantle

compositions for representative

maﬁc-intermediate rocks (SiO

,56 wt%)

from the Aeolian islands and Marsili

seamount (source of data as in Fig. 15.2).

Ionian sediments (average of two samples;

De Astis, unpublished data), averages of the

Calabro– Peloritano basement (Rottura

et al. 1991), Tyrrhenian MORB (Dietrich

et al. 1977) and Etna basalts (Viccaro &

Cristofolini 2008) are also shown.

Normalizing data are from Sun &

McDonough (1989).

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 495

well documented at Alicudi, where evolved andesites were less

affected by assimilation and, consequently, exhibit more primitive

isotopic compositions (i.e. lower Sr- and O- and higher Nd – Pb

isotope ratios) than associated basalts (Peccerillo & Wu 1992; Pec-

cerillo et al. 1993; Lucchi et al. 2013a). The same process has been

recognized, although less clearly, at Filicudi (Santo & Peccerillo

2008; Lucchi et al. 2013b).

Several studies on Aeolian volcanoes demonstrated that

magma– wall-rock interaction produced an increase in both

Sr/

Sr and d

O‰ (Ellam & Harmon 1990; Peccerillo et al.

2004; Santo & Peccerillo 2008). However, whereas O-isotope

ratios were increased from typical mantle values of d

O‰ c.

þ5.5 to values as high as d

O‰ c. þ8.5, Sr isotope ratios were

less strongly modiﬁed. Detailed studies of two contaminated

suites of maﬁc magmas from Alicudi and Vulcano (Primordial

Vulcano and Piano Caldera) have shown that extensive crustal

assimilation generated an increase in Sr isotope ratios by ﬁve to

six digits on the fourth decimal place (De Astis et al. 1997,

2013; Lucchi et al. 2013a). This is one order of magnitude lower

than the variation observed over the Aeolian arc. Some incompa-

tible element ratios, such as Rb/Ba, Rb/Sr and Ba/K, are signiﬁ-

cantly correlated with Sr-isotope variation, suggesting they were

modiﬁed by contamination. By contrast, other element ratios

such as Ba/La, Rb/Nb, U/Th, Sr/Nd and Tb/Yb do not show

any correlation with Sr isotope ratios, implying that they were

less affected or unaffected by contamination. Such different be-

haviour is related to the variable compositional contrast between

magma and wall rocks for various elements. This changes from

one volcanic centre to another however, and results found at

Alicudi and Vulcano cannot be considered as valid for the entire

Aeolian arc.

Conditions of magma ponding and ascent

Conditions of magma ponding, crystallization and ascent have

been examined using two different approaches. One is based on

measurements of crystallographic parameters of clinopyroxenes,

especially cell dimensions, under the assumption that these

depend on pressure of crystallization (e.g. Nazzareni et al. 1998,

2001). Other work has focused on ﬂuid inclusions in quartz-rich

xenoliths (Frezzotti et al. 2003, 2004; Zanon et al. 2003; Frezzotti

& Peccerillo 2004; Peccerillo et al. 2006; Di Martino et al. 2010,

2011).

Clinopyroxene studies have documented crystallization at

different pressures within the volcanic systems, suggesting the

occurrence of various depths of magma storage and fractionation

at the regional scale. Fluid inclusion studies provided additional

insight into magma evolution, conﬁrming polybaric mineral crys-

tallization and demonstrating that maﬁc to intermediate magmas

ponded in deep reservoirs sited at depths of 21–18 km in the

lower crust at the mantle-crust boundary. Here, magmas were sub-

jected to fractionation and assimilation processes, plus intensive

feeding by mantle-derived maﬁc melts (RFTA). At Lipari, long-

lived hot maﬁc magma reservoirs facilitated partial melting of

the lower continental crust, as testiﬁed by the eruption of

cordierite-, garnet-, and sillimanite-bearing lavas (Barker 1987;

Di Martino et al. 2011). By contrast, dacitic and rhyolitic

magmas were generated by dominant fractional crystallization of

maﬁc parental magmas in reservoirs located at depths of 15 –

12 km. Since felsic magmas are restricted to the younger stages

of activity at many Aeolian volcanoes, an overall upward

migration of the magma chambers with time has been suggested

(Peccerillo et al. 2006). The reasons for such a migration are

still poorly understood. A variation of local tectonic stress may

have allowed formation of mid-crustal reservoirs (Ventura

2013). Another possibility could be that there was a decrease in

the input of maﬁc magmas into the deep reservoirs during the

mature to latest (and vanishing?) stages of volcanism. This

would have allowed fractional crystallization to become dominant

with respect to input and mixing with fresh maﬁc magmas, favour-

ing the formation of evolved melts. These were able to rise more

readily than maﬁc magmas to shallow crustal levels because of

their lower density.

Mantle source composition, magma genesis

and geodynamic setting

Trace element and isotope data are crucial for understanding the

composition and evolution of mantle sources and for exploring

conditions of magma genesis and geodynamic evolution. Many

geochemical studies have therefore been carried out on the

Aeolian volcanoes. Much attention has been focused on maﬁc

magmas, under the assumption that they represent primary compo-

sitions. However, such a statement has been proven incorrect for

some maﬁc magma suites such as at Alicudi and Filicudi. The

possible effects of magma contamination have to be considered

before inferring compositions of primary melts and their

mantle sources.

Isotope and trace element composition of mantle sources

Regional variations of radiogenic isotope ratios for maﬁc rocks in

the Aeolian arc have long been recognized and attributed to

Marsili

Calabro-

Peloritano

basement

Calabro-

Peloritano

basement

Etna

0.703 0.704 0.705 0.706 0.707 0.708

0.5122

0.5124

0.5126

0.5128

0.5130

(a)

(b)

87Sr/86Sr

143Nd/144Nd

18.00 19.00 20.00

38.00

39.00

40.00

206Pb/204Pb

208Pb/204Pb

Etna

Vesuvio

Fig. 15.6. Sr–Nd–Pb isotopic compositions for maﬁc-intermediate rocks

(SiO

,56%) from the Aeolian arc and Marsili seamount. Source of data and

symbols as in Figures 15.2 and 15.4. Alicudi and Filicudi andesites

(SiO

¼56–62%) are also plotted, since these represent the least-contaminated

magmas in the Aeolian arc (see text). Average Etna basalts (Viccaro &

Cristofolini 2008) and compositions ﬁelds of Vesuvio (for source of data see

Peccerillo 2005) and Calabro–Peloritano basement (Rottura et al., 1991) are

also reported. NHRL (Northern Hemisphere Reference Line) is from Hart

(1984).

A. PECCERILLO ET AL.496

heterogeneities of the mantle wedge (e.g. Ellam et al. 1988; Ellam

& Harmon 1990; Francalanci et al. 1993; De Astis et al. 2000;

Peccerillo et al. 2004). However, the common occurrence of

magma– crust interaction raises the problem of how much of this

variation is due to magma contamination and how much to

source heterogeneity.

Combined O- and Sr-isotope studies can help to discriminate

magma contamination from source contamination processes.

Figure 15.7 represents a d

O‰ and

Sr/

Sr diagram for the

available data on Aeolian rocks and separated phases (Ellam &

Harmon 1990; Peccerillo et al. 2004; Santo & Peccerillo 2008;

De Astis, unpublished data). The solid line describes a model of

bulk mixing between a primordial mantle source and Ionian Sea

sediments. Only a small number of samples from Alicudi and a

few from Filicudi plot on or just above the mantle –sediment

mixing line. By contrast, most of the Filicudi samples are shifted

upwards and show high d

O‰, which is typical of contaminated

magmas. Well-deﬁned vertical trends are shown by Salina and

Vulcano samples, whereas Stromboli shows scattering and plots

away from the mantle – sediment mixing line.

Although the above model has to be considered as broadly quali-

tative because of the simplistic assumptions of simple bulk mixing

and uniform compositions for end-members, O – Sr isotope data

indicate that a few of the Alicudi and Filicudi magmas can be con-

sidered as near-primary in composition. Their different Sr-isotope

signatures at the same d

O‰ value suggest less radiogenic Sr

compositions for Alicudi magmas and their sources. The vertical

data arrays for Vulcano and Salina highlight strong variation of

O with a modest increase of

Sr/

Sr, typical of magma con-

tamination (Ellam & Harmon 1990). However, if these trends

are extrapolated back to the mantle – sediment mixing line,

Sr-isotope ratios similar to those at Filicudi are deduced (i.e.

Sr/

Sr slightly higher than 0.704). Stromboli does not show

typical magma contamination trends but no samples fall on the

mantle– sediment mixing line, suggesting that the Stromboli

magmas are also contaminated but that Sr-isotope compositions

are more variable and radiogenic than at other islands.

To summarize, the O– Sr isotope data suggest that there are few

uncontaminated magmas in the Aeolian arc. Magma contami-

nation processes had minor effects on Sr isotope ratios however,

in agreement with studies on Alicudi and Primordial Vulcano

discussed previously (see “Shallow-level magma evolution”).

This leads to the conclusion that ﬁrst-order Sr-isotope varia-

tion along the Aeolian arc is a direct manifestation of source het-

erogeneity. The same can be demonstrated for other radiogenic

isotopes.

Variations of Sr– Pb isotope ratios along the arc are shown in

Figure 15.8, to better highlight regional isotopic zoning. There is

an increase of the

Sr/

Sr ratio from Alicudi to Filicudi and

the central islands, where the lowest Sr-isotope values are slightly

above 0.704. Another increase in radiogenic Sr is observed at

Stromboli. Nd isotopic compositions exhibit a similar trend,

although anti-corrrelated with Sr-isotope variations. Ranges of

Pb-isotope ratios remain fairly constant across most of the arc,

but become less radiogenic at Stromboli. The back-arc Marsili sea-

mount has a rather wide range of Sr – Nd isotope compositions,

comparable to those observed over the entire western arc. A very

low

206

Pb/

204

Pb is observed for one sample from Lipari (Esper-

anc¸a et al. 1992).

Trace element abundances and ratios provide additional infor-

mation on mantle composition. Here, this issue is examined by

using a new set of trace element data (Table 15.1) for more than

90 maﬁc– intermediate rocks from different stratigraphic levels

on various islands. The new data have the advantage of minimizing

the inter-laboratory analytical bias that characterizes the data in the

literature, thus providing a conﬁdent picture of geochemical

zoning along the arc. Inferences on source composition are

based on trace element contents of both maﬁc and intermediate

rocks, since andesitic rocks at Alicudi have been shown to rep-

resent the least contaminated magmas across the entire arc (Pec-

cerillo et al. 1993; Lucchi et al. 2013a). Moreover, only trace

element ratios that have not shown systematic variation with

Sr-isotope ratios in the contaminated maﬁc rocks of Vulcano and

Alicudi are considered, under the assumption that they may

provide reliable information on mantle compositions. The

0.702 0.704 0.706 0.708

Sr/

2 4

Mantle contamination trend

Mantle

Fig. 15.7. d

Ov.

Sr/

Sr for Aeolian magmas. The solid line represents the

mixing trend between primordial mantle and Ionian sediments (mantle

contamination). Numbers along the line are the amounts of sediments involved

in the mixing. Arrows mimic effects of magma contamination by crustal wall

rocks: note strong oxygen isotope variation and modest increase of Sr isotope

ratios. Data for Filicudi, Alicudi and Vulcano have been determined on

separated clinopyroxene phenocrysts (Peccerillo et al. 2004; Santo & Peccerillo

2008; De Astis, unpublished data) and melt compositions have been calculated

considering high-temperature isotope fractionations. Data on the other islands

are bulk rock determinations (Ellam & Harmon 1990; Gertisser & Keller 2000).

Symbols as in Figure 15.4.

18.0

19.0

20.0

0.703

0.704

0.705

0.706

0.707

0.708

87Sr/86Sr

West East

Alicudi

Filicudi

Salina

Lipari

Vulcano

Panarea

Stromboli

206Pb/204Pb

West East

Alicudi

Filicudi

Salina Lipari

Vulcano

Panarea

Stromboli

(a)(b)

Marsili

Fig. 15.8. Regional variation of

Sr–Pb isotopic compositions for

maﬁc-intermediate rocks (SiO

,56 wt%)

from the Aeolian arc. Alicudi and Filicudi

andesites (SiO

¼56–62%) are also

plotted, since these represent the least

contaminated magmas in the Aeolian arc

(see text). Data of Marsili seamount are

shown as a dashed line on the left-hand side

of the diagrams. Source of data as in

Figure 15.2.

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 497

Table 15.1. Major and trace element data for representative rocks from Aeolian volcanoes. Major element data for Vulcano and Panarea are from De Astis et al. (1997) and Calanchi et al. (2002)

Sample A9 ALI A3 ALI A6 ALI A11 ALI A15 ALI A4 ALI A7 ALI A5 ALI FIL 95 FIL 90 FIL 9 FIL10 FIL 7 FIL 80 FIL101

Alicudi Alicudi Alicudi Alicudi Alicudi Alicudi Alicudi Alicudi Filicudi Filicudi Filicudi Filicudi Filicudi Filicudi Filicudi

SiO

51.10 51.42 54.03 55.07 56.27 56.32 56.99 58.84 48.78 50.20 50.58 50.62 50.96 50.99 51.43

TiO

0.69 0.72 0.77 0.69 0.92 0.72 0.66 0.77 0.72 0.75 0.77 0.77 0.72 0.83 0.81

16.93 16.98 17.84 16.49 18.94 18.68 18.35 18.86 18.92 18.65 18.47 19.44 18.05 19.30 18.78

3.96 7.71 1.96 3.24 3.31 2.12 2.27 4.71 9.40 9.84 9.06 8.88 8.73 9.91 9.61

FeO 3.82 0.87 5.26 3.74 3.30 4.19 3.79 0.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00

MnO 0.09 0.10 0.09 0.09 0.09 0.09 0.09 0.07 0.16 0.17 0.16 0.16 0.16 0.16 0.16

MgO 8.20 7.16 6.05 6.49 2.43 4.00 4.48 2.23 5.70 4.92 3.54 3.44 4.73 3.93 3.94

CaO 10.45 10.36 8.61 8.71 7.56 7.43 7.10 5.73 11.44 11.00 11.00 10.67 10.20 9.77 10.48

O 2.52 2.25 3.24 3.18 3.78 3.50 3.72 4.20 2.28 2.39 2.72 2.69 2.75 2.65 2.68

O 0.95 0.94 1.55 1.27 1.75 1.82 1.90 2.15 1.16 1.01 1.01 1.17 1.28 1.27 1.37

0.29 0.30 0.33 0.32 0.37 0.34 0.36 0.39 0.22 0.20 0.19 0.18 0.21 0.20 0.23

LOI 0.99 1.19 0.27 0.71 1.28 0.79 0.29 1.07 1.23 0.87 2.51 1.99 2.22 1.00 0.52

V 223 221 221 223 169 180 163 137 330 240 308 290 285 271 331

Ga 13 14 16 15 16 16 13 16 19 19 17 20 17 21 17

Rb 24 23 40 28 48 55 47 52 23 27 23 34 34 32 30

Sr 583 606 598 570 623 667 642 686 679 729 708 763 723 773 713

Y 171718 16 23 19182217181718181918

Zr 63 56 83 83 107 112 107 139 54 60 56 63 63 59 55

Nb 7.4 7.3 10.6 11.0 10.6 14.9 13.1 23.1 4.8 5.8 5.6 7.0 6.9 6.0 4.6

Cs 0.95 1.09 1.12 0.86 0.97 1.32 1.37 1.58 1.18

Ba 343 260 417 499 453 607 593 852 335 402 373 406 410 382 379

La 21 19 25 27 30 40 38 42 15 20 16 20 20 19 19

Ce 40 38 46 49 56 69 67 77 30 37 33 43 41 39 36

Pr 4.0 4.2 4.6 4.7 5.5 6.4 6.1 7.2 3.3 4.1 3.7 4.7 4.4 4.4 4.0

Nd 16 18 20 19 24 26 24 28 16 18 15 19 19 19 18

Sm 3.50 3.54 3.37 3.74 4.51 4.26 4.28 5.43 4.18 4.57 4.24 3.97 4.42 3.89 4.12

Eu 1.06 0.95 1.16 1.11 0.91 1.32 0.87 1.01 1.06 1.01 1.33 1.31 1.14 0.74 1.14

Gd 3.44 4.11 3.53 2.74 4.10 3.43 3.48 4.35 2.87 4.77 3.89 3.42 3.91 4.24 2.12

Tb 0.49 0.50 0.53 0.43 0.62 0.59 0.55 0.57 0.52 0.43 0.45 0.53 0.55 0.55 0.44

Dy 2.86 3.42 3.17 3.01 4.04 3.31 3.28 3.73 3.03 2.76 3.14 3.28 3.33 3.30 3.01

Ho 0.60 0.63 0.64 0.55 0.69 0.63 0.59 0.80 0.60 0.62 0.69 0.66 0.54 0.63 0.63

Er 1.70 1.78 1.83 1.54 2.43 1.80 1.83 2.29 1.62 1.80 1.71 1.75 1.96 1.91 1.50

Tm 0.23 0.26 0.25 0.26 0.36 0.28 0.28 0.32 0.36 0.34 0.37 0.24 0.25 0.40 0.26

Yb 1.48 1.53 1.79 1.30 2.08 1.92 1.47 2.28 1.93 2.16 1.68 1.73 2.11 1.92 1.61

Lu 0.24 0.28 0.20 0.29 0.27 0.25 0.28 0.31 0.30 0.41 0.35 0.30 0.29 0.53 0.27

Hf 1.64 1.34 1.87 1.57 2.26 2.26 2.30 2.99 1.87 1.76 1.24 1.45 1.40 1.67 1.28

Ta 0.44 0.36 0.48 0.50 0.65 0.65 0.67 1.34 0.28 0.26 0.34 0.37 0.35 0.30

Pb 5.1 3.3 5.6 4.9 5.5 5.7 6.1 6.9 3.8 2.9 5.8 6.6 6.8 4.1 4.6

Th 3.78 3.02 4.88 6.14 6.18 9.12 8.77 9.88 2.97 3.70 3.22 4.07 4.20 3.72 3.87

U 1.07 0.89 1.56 1.81 1.61 2.49 2.12 2.24 0.99 1.20 1.01 1.44 1.80 1.17 1.19

A. PECCERILLO ET AL.498

Sample FIL 40 FIL 29 FIL 24 SAL 98a SAL 28 SAL 40 SAL 48 SAL 55 SAL 79 SAL 27 SAL 82 SAL 88 SAL 1 SAL 76 A1 LIP

Filicudi Filicudi Filicudi Salina Salina Salina Salina Salina Salina Salina Salina Salina Salina Salina Lipari

SiO

52.38 52.68 53.28 49.50 49.53 49.79 50.02 50.76 50.93 51.03 51.46 51.81 52.03 52.15 52.17

TiO

0.70 0.78 0.77 0.73 0.65 0.73 0.74 0.65 0.69 0.74 0.67 0.74 0.65 0.66 0.68

19.56 18.17 17.00 17.84 19.13 17.87 19.77 17.85 20.09 19.32 18.53 17.50 18.07 17.36 17.30

8.87 9.66 8.30 11.44 9.82 11.56 11.31 10.15 9.83 10.62 9.91 10.95 9.63 9.88 9.58

FeO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

MnO 0.16 0.17 0.14 0.21 0.18 0.21 0.21 0.19 0.19 0.20 0.18 0.20 0.19 0.19 0.17

MgO 3.85 3.50 5.34 5.17 3.41 5.01 3.41 5.75 3.49 3.39 4.53 4.43 4.59 5.36 5.84

CaO 10.16 10.35 10.15 11.22 9.40 10.85 10.73 10.95 11.11 10.12 10.95 10.23 10.60 10.12 10.13

O 2.82 2.51 2.65 2.39 2.47 2.29 2.58 2.31 2.68 2.78 2.36 2.38 2.34 2.42 2.22

O 1.28 1.20 1.55 0.96 0.75 0.99 0.97 0.92 0.84 0.91 0.88 1.08 1.18 0.98 1.14

0.22 0.15 0.34 0.11 0.12 0.10 0.10 0.12 0.12 0.12 0.11 0.16 0.11 0.14 0.15

LOI 0.00 0.82 0.49 0.45 4.52 0.60 0.16 0.35 0.04 0.76 0.42 0.54 0.62 0.74 0.63

V 291 298 263 304 328 309 310 285 380 266 286 299 294 309 239

Ga 21 20 16 15 19 14 18 16 17 15 17 16 16 18 15

Rb 33 36 45 22 20 23 19 20 21 20 21 26 26 22 38

Sr 656 737 561 717 716 771 762 576 730 770 699 709 732 609 602

Y 17 18 16 15 2716161416171519161517

Zr 57 61 63 42 40 43 57 40 42 46 43 52 49 41 64

Nb 7.1 6.5 10.2 2.3 2.6 2.8 2.5 2.3 2.5 2.2 2.6 2.8 4.3 2.3 4.2

Cs 1.63 1.21 1.26 1.54 2.13 1.74 1.87

Ba 380 407 350 347 334 413 354 266 358 325 331 399 378 343 369

La 19 21 20 14 17 17 14 12 13 13 14 18 15 13 16

Ce 37 40 42 27 40 31 28 24 23 26 27 33 31 26 34

Pr 3.8 4.1 4.3 3.0 4.4 3.3 3.1 2.9 2.8 3.0 3.0 4.0 3.4 2.8 3.6

Nd 16 18 18 13 22 17 15 13 13 15 14 18 15 12 18

Sm 2.87 4.66 3.54 3.80 5.41 3.35 3.29 2.84 3.07 2.93 3.74 4.63 4.01 2.81 3.25

Eu 0.98 1.39 0.87 0.79 1.72 1.05 1.31 0.81 0.97 0.96 0.70 1.08 1.05 0.96 1.01

Gd 4.47 3.31 5.53 2.78 4.22 2.44 3.83 2.61 2.92 4.00 2.91 6.22 3.61 3.65 5.32

Tb 0.50 0.60 0.58 0.44 0.77 0.46 0.60 0.36 0.48 0.48 0.47 0.50 0.57 0.46 0.50

Dy 2.87 3.51 3.14 2.28 4.71 2.94 2.74 2.31 2.85 3.19 2.66 3.32 3.20 2.69 3.43

Ho 0.52 0.61 0.63 0.58 0.94 0.57 0.49 0.49 0.56 0.63 0.57 0.76 0.63 0.57 0.55

Er 1.70 2.03 1.73 1.24 2.78 1.61 1.60 1.56 1.60 1.44 1.40 1.65 1.50 1.33 1.54

Tm 0.28 0.28 0.30 0.31 0.45 0.29 0.23 0.28 0.29 0.25 0.32 0.36 0.37

Yb 2.10 1.85 1.50 2.12 2.76 2.28 1.60 1.51 1.27 1.75 1.55 2.12 2.17 1.48 1.89

Lu 0.25 0.30 0.32 0.30 0.37 0.30 0.24 0.33 0.28 0.25 0.32 0.29 0.39

Hf 1.76 1.58 1.48 1.29 1.18 0.93 1.09 0.89 0.95 1.48 0.86 1.68 1.50 1.14 1.45

Ta 0.30 0.34 0.52 0.21 0.13 0.23 0.21 0.29 0.40 0.23 0.27

Pb 7.4 5.9 4.7 5.8 5.7 6.6 6.2 3.9 4.5 4.0 5.6 5.8 5.5 5.2 7.4

Th 4.30 4.56 3.29 2.51 2.78 3.68 2.85 2.37 2.60 2.56 2.52 3.69 3.58 2.47 4.29

U 1.28 1.43 1.32 0.70 0.93 0.95 0.81 0.78 0.72 0.69 0.66 1.01 1.06 0.91 1.01

(Continued )

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 499

Table 15.1. Major and trace element data for representative rocks from Aeolian volcanoes. Major element data for Vulcano and Panarea are from De Astis et al. (1997) and Calanchi et al. (2002) (Continued)

Sample LIP 105 LIP 113 LIP 113B LIP 114 LIP 84 LIP 182 T17 A3 LIP LIP 180 A16 LIP MR6 LIP 122 LIP 143 T9 PN235

Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Lipari Panarea

SiO

52.31 52.64 52.64 53.38 53.53 53.54 53.59 53.76 53.82 54.08 54.94 55.19 57.05 59.27 47.83

TiO

0.55 0.67 0.67 0.68 0.73 0.69 0.77 0.68 0.67 0.81 0.71 0.83 0.62 0.79 0.56

14.90 14.95 14.95 14.97 16.56 17.19 17.00 16.72 17.80 17.25 17.81 16.28 17.41 16.18 17.50

8.62 9.16 9.16 9.13 9.17 8.99 9.60 9.35 8.59 8.67 9.01 9.35 8.33 8.14 8.94

FeO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

MnO 0.14 0.19 0.19 0.32 0.14 0.17 0.16 0.16 0.15 0.14 0.16 0.15 0.17 0.15 0.14

MgO 7.69 6.48 6.48 5.80 4.60 4.58 4.74 5.24 4.50 4.42 4.03 4.17 3.79 3.42 5.64

CaO 10.83 10.38 10.38 10.04 9.67 8.87 9.42 8.88 8.12 8.89 8.48 8.84 7.62 6.47 9.32

O 2.43 2.24 2.24 2.25 2.86 2.65 2.10 2.36 2.46 2.49 2.88 2.01 2.27 2.00 1.83

O 0.96 1.42 1.42 1.35 1.99 2.07 1.54 1.80 1.91 1.61 1.79 1.61 1.54 2.28 0.55

0.16 0.16 0.16 0.18 0.22 0.26 0.18 0.23 0.21 0.23 0.19 0.21 0.13 0.18 0.13

LOI 1.42 1.73 1.73 1.90 0.54 0.98 0.90 0.82 1.79 1.41 0.01 1.36 1.07 1.13 7.57

V 278 242 211 297 269 242 254 271 240 252 269 316 199 220 247

Ga 15 16 14 15 17 16 16 17 16 18 18 15 16 18 16

Rb 27 43 36 35 53 56 54 43 57 54 45 39 63 95 26

Sr 575 597 601 608 853 860 691 804 797 656 815 560 557 488 656

Y 15 20 19 1819 181917 19 21 1719 252319

Zr 45 64 67 62 86 81 90 71 78 91 77 67 75 120 58

Nb 2.3 4.4 3.9 4.0 7.1 6.6 6.1 5.2 6.6 6.2 5.1 4.3 5.8 8.8 4.1

Cs 1.02 2.73 1.31 1.70 1.53 1.35 3.00 2.51 2.09 3.62 0.76

Ba 316 329 344 356 526 481 392 464 444 555 478 366 373 620 281

La 13 17 18 18 24 24 22 22 23 23 20 18 25 27 17

Ce 25 35 36 37 49 48 46 43 45 48 41 37 48 56 33

Pr 2.8 3.7 3.8 4.3 5.3 5.2 5.2 5.0 5.2 5.4 4.7 4.1 5.3 5.9 4.0

Nd 13 17 18 19 23 23 23 21 23 23 21 19 22 26 19

Sm 3.11 3.75 4.14 3.43 5.75 5.14 4.60 3.34 4.85 5.07 3.94 4.83 5.55 4.97 4.20

Eu 0.80 1.16 0.98 0.96 1.14 1.47 1.13 1.03 1.31 1.43 1.23 1.35 1.32 1.17 1.08

Gd 4.01 4.25 3.47 3.83 4.00 4.36 4.67 4.19 4.00 4.60 4.11 3.44 4.35 4.23 3.89

Tb 0.48 0.58 0.61 0.55 0.58 0.58 0.67 0.63 0.59 0.61 0.51 0.43 0.62 0.60 0.51

Dy 2.61 3.50 3.59 3.58 3.81 3.56 4.21 3.63 3.38 3.96 3.26 3.57 4.25 4.15 3.33

Ho 0.55 0.66 0.67 0.61 0.62 0.65 0.89 0.55 0.65 0.83 0.67 0.64 0.74 0.80 0.68

Er 1.56 2.01 1.88 1.93 1.82 1.81 2.16 1.57 1.74 2.13 1.56 2.08 2.21 2.24 1.86

Tm 0.25 0.29 0.34 0.34 0.24 0.32 0.33 0.28 0.40 0.29 0.29 0.42 0.35 0.26

Yb 1.81 1.91 1.85 1.98 1.96 1.67 1.99 1.65 1.67 2.35 1.53 1.97 2.35 2.11 1.61

Lu 0.45 0.29 0.27 0.51 0.29 0.26 0.31 0.35 0.27 0.39 0.32 0.34 0.32 0.28

Hf 1.37 1.59 1.49 1.28 2.39 2.17 2.59 2.05 1.90 2.62 2.35 1.65 1.87 2.87 1.27

Ta 0.32 0.32 0.25 0.36 0.44 0.30 0.54 0.41 0.34 0.53 0.40 0.36 0.52 0.73 0.23

Pb 5.1 4.3 2.4 13.4 4.4 9.8 7.5 6.8 9.2 10.0 6.7 7.1 7.0 16.3 5.0

Th 2.80 3.89 3.85 4.02 5.44 5.70 5.79 6.03 5.45 5.95 5.05 4.28 4.94 8.70 3.90

U 0.86 1.16 0.99 1.25 1.80 1.47 1.61 1.66 1.63 1.54 1.53 1.66 1.41 2.27 0.56

A. PECCERILLO ET AL.500

Sample PF1 PS 11A VL168-10 VL250 VLPC1 VL229/1a 1b VL143-1S VL145/2 VL272 VUL508 VL189/1 VL157/2 VL139-6 VL259/1 VL90/1

Panarea Panarea Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano

SiO

51.16 52.25 48.54 49.13 49.23 49.81 50.10 50.93 51.21 51.23 51.40 52.27 52.33 52.70 52.88

TiO

0.62 0.92 0.77 0.66 0.68 0.68 0.76 0.76 0.67 0.81 0.69 0.70 0.80 0.71 0.71

17.12 17.79 12.51 16.33 15.81 14.27 14.73 17.40 16.49 17.54 15.77 17.53 16.96 15.38 16.20

9.69 9.20 5.42 5.90 5.18 5.73 6.17 5.19 4.66 6.59 4.52 5.81 5.30 3.81 4.59

FeO 0.00 0.00 6.02 3.79 3.82 4.68 4.33 4.42 4.55 3.59 4.74 3.26 4.81 5.76 3.96

MnO 0.16 0.16 0.21 0.18 0.19 0.19 0.18 0.21 0.15 0.23 0.17 0.18 0.18 0.18 0.13

MgO 6.25 4.23 8.65 6.85 5.56 7.29 6.28 4.09 5.49 3.83 6.00 3.86 3.17 5.38 3.54

CaO 10.24 9.06 12.49 10.51 9.65 11.39 10.50 9.39 8.82 8.57 9.15 8.45 7.23 9.46 7.04

O 2.54 2.50 2.20 2.31 3.10 2.40 1.77 2.44 2.83 3.33 2.69 3.13 3.32 2.71 4.35

O 0.90 2.45 2.08 1.75 3.78 2.04 2.23 2.52 2.47 2.72 2.56 2.63 3.67 2.46 3.36

0.08 0.58 0.21 0.25 0.48 0.22 0.22 0.28 0.27 0.28 0.26 0.29 0.40 0.21 0.39

LOI 1.24 0.85 0.90 2.33 2.53 1.30 2.72 2.37 2.39 1.29 2.06 1.89 1.82 1.23 2.83

V 251 341 264 260 228 237 245 208 253 326 245 213 251 211 195

Ga 16 20 15 15 18 19 12 16 20 16 17 18 17 16 16

Rb 21 82 46 17 115 47 58 58 35 51 57 50 113 60 125

Sr 593 893 1135 986 1619 1229 1077 1340 953 1293 1048 1249 1320 913 1303

Y 1321172517 16 17 23152016 303115 21

Zr 40 127 72 67 104 76 74 105 76 94 90 104 138 86 155

Nb 3.1 22.2 6.5 5.6 11.6 5.5 5.2 8.3 8.4 6.7 8.3 12.6 17.5 8.5 16.9

Cs 0.64 3.92 1.25 2.42 2.27 1.97 2.06 1.04 1.01 2.71 9.23 2.14 6.08

Ba 319 1199 578 567 1060 765 638 889 614 816 797 865 1150 630 1137

La 11 38 26 29 42 33 27 41 25 34 35 46 54 28 56

Ce 23 71 52 58 80 62 53 85 50 67 67 84 104 55 108

Pr 2.6 7.4 5.9 6.6 8.0 6.5 5.8 9.3 5.2 7.4 7.3 9.5 10.9 5.8 10.3

Nd 12 34 27 30 34 30 25 41 22 32 30 41 49 24 41

Sm 3.20 6.49 6.21 6.47 6.67 6.46 5.41 8.28 4.38 5.88 5.64 7.78 9.16 4.75 7.68

Eu 0.84 1.74 1.41 1.71 1.57 1.28 1.15 1.85 1.15 1.47 1.52 1.83 1.96 1.25 1.47

Gd 1.68 5.15 4.80 5.47 4.73 2.51 4.10 5.37 3.98 4.17 3.54 6.64 6.73 3.69 6.11

Tb 0.34 0.76 0.66 0.83 0.67 0.55 0.53 0.83 0.51 0.69 0.57 0.87 0.99 0.50 0.74

Dy 2.35 3.87 3.34 4.19 3.46 2.88 3.29 4.44 3.14 3.62 3.21 5.06 5.47 2.80 4.34

Ho 0.46 0.73 0.53 0.77 0.60 0.54 0.63 0.72 0.57 0.67 0.60 0.93 0.96 0.50 0.76

Er 1.41 2.03 1.61 2.08 1.48 1.66 1.62 2.00 1.57 1.96 1.65 2.73 2.66 1.30 1.88

Tm 0.22 0.27 0.23 0.31 0.27 0.38 0.25 0.25 0.27 0.20 0.45 0.33 0.23 0.36

Yb 1.26 1.64 1.19 1.80 1.66 1.16 1.29 1.69 0.97 1.55 1.34 2.17 2.01 1.27 1.87

Lu 0.25 0.26 0.29 0.18 0.23 0.21 0.29 0.30 0.30 0.22 0.40 0.37 0.22 0.30

Hf 1.02 3.16 1.81 1.46 2.01 1.95 2.06 2.25 1.94 2.41 2.37 2.60 3.01 1.99 3.49

Ta 0.16 0.91 0.32 0.27 0.51 0.29 0.23 0.48 0.42 0.47 0.39 0.63 1.14 0.48 1.23

Pb 5.2 13.9 8.3 7.1 13.2 9.3 7.7 13.4 9.5 9.1 11.6 13.7 18.0 11.5 17.9

Th 2.14 11.96 5.92 5.57 10.88 8.35 6.80 9.14 5.85 7.40 9.66 10.14 20.30 7.34 22.14

U 0.61 3.13 1.47 1.62 2.52 2.42 1.77 2.19 1.51 2.26 2.43 2.51 4.97 2.12 6.27

(Continued )

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 501

Sample VL345/1 VL283/10 VL273/1 VL149/1 VL144/2 VL356/20 SC1 LS6 T2a At1 STR 13 LR 5 STR 11 STR 5 LS4

Vulcano Vulcano Vulcano Vulcano Vulcano Vulcano Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli

SiO

53.24 53.35 53.44 53.78 54.00 54.62 48.15 48.88 49.40 50.06 50.33 50.64 50.86 50.91 50.94

TiO

0.86 0.67 0.63 0.69 0.75 0.66 0.93 0.84 0.99 0.95 0.81 1.00 0.91 0.90 0.97

16.76 16.36 17.60 16.42 14.58 14.23 18.17 17.86 18.38 16.77 17.15 17.54 15.31 17.88 17.22

4.26 4.45 5.05 6.92 4.47 4.58 7.69 6.97 3.92 3.02 1.49 3.34 2.61 2.63 2.85

FeO 4.90 4.12 2.85 2.14 5.19 4.82 0.73 0.68 4.36 4.91 7.43 4.72 6.16 5.41 4.93

MnO 0.16 0.16 0.13 0.15 0.17 0.17 0.13 0.12 0.13 0.13 0.15 0.13 0.17 0.15 0.13

MgO 4.01 3.61 3.59 4.07 4.18 5.04 5.99 5.82 6.88 7.57 5.95 5.21 6.69 5.71 6.03

CaO 7.60 7.25 7.76 7.45 7.37 8.30 10.89 10.66 10.22 9.19 10.90 9.42 10.95 10.55 8.97

O 2.63 4.17 4.38 3.35 2.98 2.84 2.31 2.38 2.77 2.19 2.55 2.59 2.23 2.45 2.49

O 2.83 4.36 2.53 3.59 4.57 3.39 1.82 1.72 1.81 3.63 2.33 3.53 3.23 2.33 3.77

0.27 0.36 0.34 0.30 0.36 0.25 0.48 0.44 0.40 0.63 0.60 0.61 0.65 0.53 0.67

LOI 2.49 1.14 1.70 1.14 1.38 1.11 2.71 3.65 0.74 0.95 0.31 1.26 0.23 0.55 1.05

V 220 199 194 238 231 199 220 220 258 220 262 247 257 247 221

Ga 18 16 15 15 15 15 14 14 13 15 15 15 17 15

Rb 68 144 79 102 136 136 62 60 50 117 70 124 108 64 101

Sr 1115 1162 1275 1041 1345 980 783 707 643 792 674 894 745 662 749

Y 202116232425 242322242227262124

Zr 109 139 100 104 143 145 151 145 106 165 140 168 145 136 165

Nb 11.7 17.4 9.9 12.3 14.2 10.0 17.5 16.2 13.0 19.3 21.5 23.8 27.1 24.3 20.5

Cs 2.57 5.60 1.97 2.04 5.07 5.58 4.91 5.65 2.09 5.44 3.18 4.39 7.30 4.36 7.13

Ba 701 993 862 746 980 600 1030 953 815 1660 995 1851 1553 891 1707

La 32 51 34 41 51 53 43 42 36 47 42 54 53 45 45

Ce 63 95 62 82 99 98 92 86 75 101 91 110 111 88 95

Pr 6.6 9.6 6.2 8.5 10.2 10.0 9.9 9.2 7.5 11.2 9.9 11.5 12.5 9.4 10.5

Nd 29 38 29 37 42 33 40 41 32 47 41 51 49 39 47

Sm 5.70 7.73 5.29 7.22 8.27 7.50 6.90 8.22 6.36 9.95 8.79 10.14 11.36 7.41 9.10

Eu 1.45 1.63 1.44 1.51 1.60 1.39 1.88 1.59 1.50 1.79 2.22 1.87 2.77 2.12 2.04

Gd 4.18 5.41 3.32 4.98 5.68 4.00 5.43 5.90 4.98 7.08 4.78 8.10 8.61 5.71 7.36

Tb 0.65 0.67 0.55 0.76 0.90 0.78 0.89 0.78 0.81 0.99 0.79 1.05 1.15 0.78 0.88

Dy 3.61 3.83 2.90 4.16 4.67 3.95 4.55 4.69 4.34 5.33 4.24 5.47 5.50 4.39 4.91

Ho 0.66 0.64 0.49 0.75 0.77 0.69 0.83 0.80 0.78 0.87 0.94 1.04 1.02 0.86 0.81

Er 1.83 1.81 1.30 1.91 2.20 1.83 2.17 2.16 1.88 2.28 2.35 2.47 2.61 2.05 2.18

Tm 0.28 0.26 0.22 0.25 0.31 0.29 0.27 0.37 0.40 0.32 0.32 0.39 0.36 0.31 0.33

Yb 1.91 1.97 1.18 1.50 1.98 2.20 2.52 2.06 2.08 1.95 2.02 2.12 2.56 2.28 1.48

Lu 0.25 0.25 0.23 0.29 0.29 0.33 0.32 0.26 0.26 0.31 0.34 0.35 0.40 0.30 0.30

Hf 2.91 3.26 2.01 2.51 3.83 3.60 3.40 3.41 2.43 4.11 2.57 3.49 3.87 3.29 3.54

Ta 0.66 0.97 0.42 0.81 0.95 0.90 1.11 1.11 0.52 1.15 0.66 1.52 0.98 0.86 1.32

Pb 12.6 17.4 11.3 16.8 18.7 16.0 26.0 39.5 20.5 23.3 18.3 25.2 25.7 15.8 23.5

Th 8.27 21.06 8.30 14.03 19.73 18.00 15.16 14.69 11.03 19.20 14.48 18.29 15.43 13.58 18.49

U 2.40 6.20 2.26 4.20 5.55 5.30 3.52 3.14 3.08 5.23 3.90 4.96 3.52 3.72 5.14

A. PECCERILLO ET AL.502

Sample STR 9 LS3 STR 12 STR 16 L2e STR 7 STR 6 STR 1 STR 2 STR 4 STR 3 STR 15 T3b1 STR 77 STR 17 STR 10 STR 8

Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli Stromboli

SiO

50.99 51.10 51.12 51.20 51.31 51.31 51.33 51.70 51.81 52.05 52.32 52.43 52.57 52.63 52.63 53.66 55.36

TiO

0.96 0.93 0.89 0.88 0.78 0.95 0.95 0.95 0.83 0.91 0.72 0.90 0.88 0.93 0.95 0.7 0.63

17.92 17.63 16.93 16.70 18.57 18.39 17.33 17.78 17.66 17.88 18.00 16.56 17.43 16.58 16.59 15.45 15.33

2.55 2.56 2.00 8.99 2.04 2.17 2.55 3.03 1.18 1.90 1.33 8.24 4.35 2.70 2.57 3.01 2.23

FeO 7.11 4.76 6.33 0.00 4.99 7.37 5.91 5.07 6.07 5.53 5.91 0.00 2.93 5.09 6.02 6.11 5.63

MnO 0.18 0.13 0.13 0.16 0.12 0.17 0.16 0.16 0.15 0.16 0.15 0.15 0.13 0.15 0.15 0.19 0.17

MgO 4.10 6.09 5.43 6.30 7.12 3.75 4.28 4.77 5.82 5.10 6.69 4.92 6.18 5.71 4.89 5.88 6.23

CaO 10.21 8.66 9.59 11.24 9.62 8.99 9.32 8.80 8.88 9.00 10.09 9.08 9.17 9.11 9.16 10.2 9.86

O 2.43 3.02 2.33 2.47 2.61 3.15 2.55 2.51 2.23 2.43 2.11 2.59 2.89 2.39 2.55 2.31 2.3

O 2.00 3.43 3.91 2.30 1.69 2.83 4.09 3.49 4.57 3.72 1.77 3.75 2.00 3.63 3.79 1.5 1.55

0.32 0.61 0.63 0.52 0.29 0.50 0.71 0.71 0.53 0.62 0.25 0.59 0.36 0.59 0.55 0.15 0.16

LOI 1.23 1.08 0.70 0.23 0.87 0.43 0.83 1.03 0.27 0.71 0.66 0.22 1.11 0.48 0.16 0.83 0.55

V 219 242 242 250 227 227 219 226 225 233 217 243 212 242 246 218 238

Ga 17 14 15 18 13 16 17 16 14 16 13 19 15 16 21 13 16

Rb 59 108 112 68 55 88 113 104 126 113 50 128 56 110 126 44 58

Sr 663 805 848 812 482 709 729 806 627 755 429 741 636 692 764 516 553

Y 21 25242619 242123182216 3324 25281618

Zr 138 159 163 164 95 164 163 173 142 152 85 204 139 161 197 91 106

Nb 19.6 23.2 33.2 22.5 10.8 27.4 28.2 36.8 27.1 30.3 12.3 28.0 13.9 20.1 27.4 10.1 17.7

Cs 3.48 6.73 5.47 3.13 3.65 3.48 7.68 7.72 6.16 7.60 3.48 3.89 1.67 2.07 6.23 2.15 3.28

Ba 757 1722 1815 1226 725 1206 1570 1825 1360 1611 656 1682 812 1450 1683 465 648

La 45 50 57 48 25 50 49 58 43 57 25 54 42 44 54 27 33

Ce 90 102 122 99 52 96 101 116 89 120 49 119 82 89 112 52 62

Pr 9.4 10.8 13.3 10.5 5.2 10.5 11.2 12.5 9.4 13.3 5.5 12.5 8.2 9.7 11.9 5.6 6.9

Nd 38 49 52 47 23 40 47 52 42 53 22 55 35 44 49 22 27

Sm 6.85 9.13 10.08 8.33 4.40 7.95 10.05 9.86 8.02 10.44 4.64 9.95 6.65 8.60 10.12 3.72 5.16

Eu 1.71 2.16 2.48 1.96 1.21 2.10 2.35 2.60 2.39 2.56 1.36 2.40 1.36 1.98 2.39 1.11 1.59

Gd 5.50 7.19 7.25 6.72 4.39 6.75 7.63 7.21 6.71 7.51 4.04 7.54 4.83 5.30 6.54 3.71 4.23

Tb 0.72 1.00 0.97 1.04 0.62 0.81 0.91 0.97 0.83 1.00 0.59 1.20 0.71 0.87 1.11 0.5 0.63

Dy 4.40 5.28 4.89 4.98 3.69 4.52 4.48 5.22 4.14 4.83 3.14 6.82 4.79 5.14 5.09 2.84 3.35

Ho 0.83 0.99 0.98 0.93 0.71 0.87 0.85 0.95 0.69 0.88 0.65 1.15 0.85 0.89 0.94 0.56 0.66

Er 2.30 2.31 2.17 2.28 1.69 2.31 2.11 2.29 1.86 2.27 1.66 3.19 2.15 2.47 2.80 1.6 1.72

Tm 0.35 0.29 0.32 0.51 0.28 0.30 0.28 0.28 0.26 0.31 0.23 0.69 0.38 0.32 0.44 0.25 0.3

Yb 2.32 1.86 2.07 2.04 1.92 2.39 2.05 2.15 1.83 1.80 1.53 2.49 1.99 1.99 2.44 1.68 1.84

Lu 0.33 0.28 0.26 0.38 0.22 0.32 0.25 0.30 0.24 0.32 0.28 0.56 0.39 0.40 0.48 0.26 0.28

Hf 3.19 3.85 4.08 3.30 2.04 3.68 4.09 3.84 3.27 3.51 2.10 5.19 2.77 3.77 4.43 2.51 2.51

Ta 0.72 1.30 1.33 0.79 0.56 0.84 0.91 1.23 0.83 1.06 0.46 1.10 0.89 1.16 1.19 0.34 0.47

Pb 13.3 23.4 29.5 22.0 12.8 19.1 27.5 29.8 19.1 26.1 12.8 21.3 11.2 16.5 25.4 9.9 15.2

Th 12.65 16.17 16.94 17.64 10.34 17.58 18.96 17.85 16.02 15.70 9.19 20.42 14.10 17.43 20.69 7.02 9.51

U 3.06 4.39 5.24 3.96 2.96 4.31 5.63 4.93 5.29 3.86 2.37 5.96 2.98 4.49 5.58 2.04 2.71

Analyses have been carried out by LA-ICPMSat the Department of Earth Sciences, University of Perugia, using a New Wave UP213 LA system coupled with a Thermo Electron X7 (Thermo Electron Corporation, Waltham, USA)

ICP-MS. A 60 micrometres laser beam has been used. Details on analytical methods are reported by Petrelli et al. (2007, 2008). Precision expressed as standard relative deviation is better that 5% foralmost all elements, except Cr

and Ho (.7%).

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 503

along-arc variation of some ITE ratios is reported in Figure 15.9.

The predominant features observed on diagrams are as follows.

(1) There is an evident increase of Rb/Nb and several other

LILE/HFSE ratios (e.g. La/Nb, Ba/Nb, U/Nb and, to a

lesser extent, Rb/Ta) from the marginal islands of Alicudi

and Stromboli to the central islands, where a large scattering

is observed for Vulcano.

(2) LILE/LILE ratios also show considerable variation along the

arc. For instance, Ce/Pb decreases eastwards and exhibits a

large scattering at Lipari. Sr/Nd and Sr/Th (not shown)

ratios are lower at the arc margins, especially at Stromboli,

than in the central islands (Fig. 15.9c). Ba/La increases

from Alicudi to Filicudi and other central islands, reaching

a maximum at Stromboli which also shows a large range of

values (Fig. 15.9d).

(3) HFSE/HFSE ratios Nb/Zr (Fig. 15.9e), Zr/Ti and, to a lesser

extent, Nb/Ta (not shown) decrease from marginal to central

islands. Nb and Zr abundances, but also LREE abundances

and La/Yb ratios, show the same type of distribution (not

shown).

(4) Th/LREE ratios (Fig. 15.9f) remain fairly constant in the CA

rocks of the western-central arc and increase in the Vulcano

shoshonitic rocks and at Stromboli.

(5) The Marsili volcano, sited in a back-arc position NW of the

Aeolian archipelago, shows a wide range of compositions but

is close to the western island of Alicudi for many ITE ratios.

Most trace element ratios of Figure 15.9 are not affected by frac-

tional crystallization since they are equally incompatible in the

main igneous rock minerals. Also, they do not show signiﬁcant

correlation with Sr isotopes in the contaminated Alicudi and

Primordial Vulcano maﬁc suites. It is therefore reasonable to con-

clude that the observed along-arc variations reﬂect a compositional

zoning of the mantle source. Understanding the processes that gen-

erated these variations is crucial for clarifying key aspects of the

Aeolian subduction factory.

Mantle metasomatism

At least three different end-members are considered to have con-

tributed to the source composition of the Aeolian magmas.

These include the pre-metasomatic mantle, the Ionian subducted

crust and the Ionian Sea sediments. The composition of each end-

member is internally variable and poorly known. The upper mantle

beneath the southern Tyrrhenian Sea has a mid-ocean-ridge basalt

(MORB-) to OIB-type composition, based on geochemistry of

magmas erupted in and around the Tyrrhenian Sea basin (Trua

et al. 2004, 2011). Subducted Ionian crust has been hypothesized

to have an oceanic to thinned continental character, and a lateral

variation in composition has been suggested (Doglioni et al.

2001). Sediments are abundant on the Ionian seaﬂoor, but inade-

quately characterized compositionally. For this reason, a geochem-

ical study of Ionian sediments has been undertaken and

preliminary data are reported as a spider-diagram in Figure 15.5d.

The concomitant increase of Sr- and decrease of Nd-isotope

ratios from the western to eastern Aeolian arc have been inter-

preted as evidence for eastwards increasing contamination of the

mantle source by subducted upper crustal material, likely

Rb/Nb

Ce/Pb

0.0

0.1

0.2

0.3

Nb/Zr

Etna basalts Ionian sediments Tyrrhenian MORB

Ba/La

Sr/Nd

West East West East

Alicudi

Filicudi

Salina

Lipari Vulcano

Panarea

Stromboli

Marsili

Alicudi

Filicudi

Salina

Lipari

Vulcano

Panarea

Stromboli

0.1

0.2

0.3

0.4

0.5

Th/La

(a)(b)

(c)(d)

(e)(f)

Fig. 15.9. Regional variation of trace

element ratios for the newly analysed

Aeolian samples (Table 15.1). Average

compositions of Tyrrhenian MORB

(Dietrich et al. 1977), Etna (Viccaro &

Cristofolini 2008) and Ionian sediments (De

Astis, unpublished data) are also reported.

A. PECCERILLO ET AL.504

sediments (e.g. Ellam et al. 1988, 1989; Francalanci et al. 1993,

2004, 2007; De Astis et al. 2000; Peccerillo 2005). The new ana-

lyses of Ionian sediments show Sr concentrations of c. 200 ppm

and

Sr/

Sr of c. 0.711. Assuming a bulk mixing between a

primordial-type mantle and such sediments, an addition of less

than 2% contaminant is sufﬁcient to explain the entire range of iso-

topic variation along the western-central Aeolian arc (Fig. 15.7).

Much higher amounts of c. 4– 10% are necessary to explain the

composition of the Stromboli mantle sources. These are

maximum values because shallow-level magma contamination

likely contributed to increase Sr isotope ratios of Aeolian

magmas, including the maﬁc magmas. Moreover, bulk mixing is

not a viable mechanism of mantle contamination, and hydrous

ﬂuid or melts from sediments have been suggested as the likely

carriers of incompatible elements into the mantle wedge

(Hermann & Rubatto 2009). These are much richer in Sr than

the source rocks because of low solid/ﬂuid partition coefﬁcients

for Sr at high pressures (Hermann & Rubatto 2009). This consider-

ably decreases the amount of contaminant that would be necessary

to explain the Sr-isotope ratios observed along the arc. For

instance, if a melt formed by 30 – 50% sediment melting is

assumed as metasomatic agent, Sr concentration in the melt

would be 2– 3 times higher than the source rock. This reduces

the amount of mantle contaminant by a factor of 2 –3, and less

than 1% melted sediment is sufﬁcient to explain Sr-isotope ratios

of the western-central arc and only 2 – 5% would be needed at

Stromboli.

In conclusion, two types of metasomatic agents, likely ﬂuids, are

suggested by Sr-isotope modelling in the Aeolian arc. One type of

ﬂuid, operating in the western-central arc, had low Sr isotope ratios

and was likely released from an oceanic slab with little or no sedi-

ment involvement. Another ﬂuid was enriched in radiogenic Sr and

requires an important contribution from sediments in the eastern

sector of the arc. Following Hermann & Rubatto (2009), the

term ‘ﬂuid’ is used here in its broadest sense, that is, to indicate

aqueous ﬂuids (water-rich ﬂuid containing low amount of

solute), H

O-rich silicate melts and supercritical H

O-silicic

ﬂuids (intermediate between the two).

The hypothesis of two compositionally distinct metasomatic

ﬂuids is supported by incompatible trace element ratios such as

Ba/La, Th/Sr, Th/Pb, Th/U, Ba/La, Ti/Zr and Sr/Nd, which

all show diverging trends for Stromboli and for the central-western

islands (e.g. De Astis et al. 2000). Variations for some of these

ratios are reported in Figure 15.10

The nature of metasomatic ﬂuids and the efﬁciency of element

transfer from slab to the mantle wedge is controversial. This is

true not only for the Aeolian arc, but for subduction magmatism

at a global scale (Brenan et al. 1995; Elliot et al. 1997; Becker

et al. 2000; Kessel et al. 2005; Hermann & Rubatto 2009).

Investigation of MORB-type rocks (Kessel et al. 2005) demon-

strated that the capacity of elemental transport increases with

increasing temperature and pressure from aqueous ﬂuids to

supercritical ﬂuids and melts. LILE/LILE ratios such as Rb/Sr,

Ba/La and Ba/Rb are more easily fractionated by aqueous ﬂuids

than by high-temperature supercritical ﬂuids and melts.

However, hydrous melts and supercritical ﬂuids more efﬁciently

fractionate other element ratios such as Sr/REE and La/Yb.

LILE/HFSE are fractionated by all types of ﬂuids, but low-

temperature aqueous ﬂuids are less able to transfer large

amounts of trace elements than high-temperature supercritical

ﬂuids and melts. High LILE/HFSE ratios coupled with low ITE

abundances (e.g. Th) have therefore been suggested as useful cri-

teria to recognize aqueous ﬂuid metasomatic modiﬁcations (Kessel

et al. 2005).

Hermann & Rubatto (2009) suggested that subducted sediments

are the most important sources of incompatible elements for meta-

somatic ﬂuids in subduction zones. The involvement of sediments

in the subduction processes considerably complicates the process

of slab to mantle element transfer however, due to the possible

occurrence of a large variety of major and accessory residual

phases such as phengite, rutile, allanite/monazite and zircon.

Their stability or breakdown at various pressure/temperature (P/

T) conditions inﬂuences the composition of ﬂuids emitted from

the slab and hence the ﬂux of incompatible trace elements into

the overlying mantle wedge. For instance, two- to ﬁve-fold Ba/

La variations can be generated in melted sediments and transferred

to the mantle wedge from these, depending on the occurrence or

absence of phengite and monazite in the residue. Note that high

Ba/La is traditionally considered a typical signature of low-

temperature metasomatic aqueous ﬂuids (Brenan et al. 1995;

Elliott et al. 1997).

The intrinsic complexities of element transfer from slab to

mantle wedge, along with the poorly known compositions of end-

members involved in the Aeolian subduction processes, make it

difﬁcult to understand mechanisms of element mobilization and

the contribution of various components to mantle wedge compo-

sition. This has fed much speculation and debate; for example,

Tonarini et al. (2004) suggested an increase of both aqueous

ﬂuid ﬂow and sediment input from west to the east, on the basis

of an eastwards increase of B/Nb and d

B of lavas. This is sup-

ported by an eastwards decrease of Ce/Pb, typical of aqueous

ﬂuids, and an increase in Th/La, which is high in the sediments

(Fig. 15.9f). However, LILE/HFSE show a decrease from

central arc to Stromboli, that is, the opposite to that expected for

aqueous ﬂuid metasomatism.

Francalanci et al. (1993, 2007) argued that an increase of LILE/

HFSE from external to central islands was related to a stronger role

of metasomatism by aqueous ﬂuids in the central arc. However,

this idea only holds if a homogeneous composition of pre-

metasomatic mantle wedge is assumed for LILE/HFSE. More-

over, high mobile/immobile element ratios (e.g. Rb/Th) should

be coupled with low immobile element (e.g. Th) enrichments

(Kessel et al. 2005). This is not observed in the central Aeolian

arc, except perhaps at Salina. Finally, variations of HFSE/HFSE

Etna basalts Ionian sediments Tyrrhenian MORB

10 20 30 40

0.703

0.704

0.705

0.706

0.707

0.708

87Sr/86Sr

Ba/La

Sr/Nd

10 30

Ba/La

(a)(b)Fig. 15.10. Ba/La, Sr/Nd and

Sr/

variation diagrams for the newly analysed

rocks. Sr isotope data are from the literature

(source of data as in Fig. 15.2) and have been

determined either on the same rocks

analysed in this study or on different rock

samples from the same outcrops.

Composition of the Tyrrhenian MORB,

Etna and Ionian sediments are also reported.

Arrows indicate effects of metasomatic

ﬂuids derived from oceanic crust (grey

arrow) and from sediments (white arrow).

Symbols as in Figure 15.4.

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 505

ratios (Fig. 15.9e) are also difﬁcult to explain, in that this group of

elements is immobile during aqueous ﬂuid transfer. Therefore,

aqueous ﬂuid transfer may have been present in the central

Aeolian arc, but it cannot be the only process responsible for the

observed trace element variations.

Many of the issues mentioned above are overcome if a hetero-

geneous OIB- to MORB-type starting mantle composition is

assumed for the Aeolian arc (Ellam et al. 1988). An OIB-type com-

ponent under the external islands could explain enrichment in Nb

and LREE, as well as the relatively high Nb/Zr and low Rb/Nb

and Sr/Nd ratios. By contrast, a MORB-type composition for

the central arc better explains the low Nb/Zr and Zr/Ti.

However, several issues still remain unresolved. For instance,

variations of Ba/La (Fig. 15.10) cannot result from any shallow-

level magmatic evolution process. By contrast, Sr/Nd ratios

can change during crystal fractionation if plagioclase is involved;

however, the positive correlation with Ba/La in the western-

central islands excludes this possibility (Fig. 15.10a). The covari-

ation of Ba/La and Sr/Nd in the central-western arc is therefore

a reproduction of source heterogeneity, and can be attributed to

metasomatic ﬂuids from an oceanic slab (grey arrows in

Fig. 15.10). The slight positive trend between Sr/Nd and

Sr/

Sr could indicate modest sediment involvement, but

might also reﬂect a variably altered oceanic crust as source of

ﬂuids. Positive correlation between Ba/La and

Sr/

Sr at Strom-

boli ﬁts well with the hypothesis of metasomatism by low-

temperature (about 700– 800 8C) hydrous melts from sediments

(white arrows in Fig. 15.10), which have high Ba/La because of

residual LREE-rich accessory phases (Hermann & Rubatto

2009). However, experimental data clearly show that these melts

also have high Sr/Nd, and a positive correlation between the

two ratios should be observed. Instead, the almost ﬂat trend for

Stromboli rocks (Fig. 15.10a) requires a selective Ba enrichment

that increases Ba/La but not Sr/Nd and other ITE ratios. Tomma-

sini et al. (2007) suggested a two-stage enrichment process for the

Stromboli mantle an hypothesis supported by Schiavi et al. (2012)

on the basis of trace element and Pb-B-Li isotope data on melt

inclusions. Early high-P/T supercritical ﬂuids from basalts and

sediments produced a general enrichment in all lithophile

elements, with little element fractionation. An aqueous ﬂuid at

lower P/T selectively enriched the mantle wedge in Ba (see Fran-

calanci et al. 2013). However, other element ratios that are strongly

affected by ﬂuid transport (e.g. U/Nb, Rb/Th, U/Ta, U/Th, etc.)

should be correlated with Ba/La, a feature that is not observed in

the Stromboli rocks.

Conditions of mantle melting and the origin of calc-alkaline and

shoshonitic magmas

The distribution of calc-alkaline and shoshonitic magmas in space

and time has received considerably less attention in the literature

than trace elements and isotope geochemistry. Calc-alkaline rocks

have comparable composition as shoshonites for several major

and trace elements (Fig. 15.3), but shoshonites have higher con-

centrations of K, P and all incompatible trace elements. Some

shoshonites are undersaturated in silica, with up to 10% of nor-

mative nepheline, whereas calc-alkaline rocks are saturated to

oversaturated in silica. These differences can depend either on a

heterogeneous source and/or on variable degrees and physico-

chemical conditions of partial melting.

REE geochemistry can help to clarify this issue. Light REE frac-

tionation (i.e. La/Sm) of primary magmas depends on the degree

of melting and/or on the La enrichment of the source. Heavy

REE (HREE) fractionation (i.e. Tb/Yb) depends essentially on

the presence or absence of residual garnet during mantle

melting. Garnet is a high-pressure mantle mineral that retains

HREE with respect to the light and mid REE. Its occurrence as

residual phase during partial melting therefore results in high

Tb/Yb (and La/Yb) in the magmas. La/Sm increases slightly

with magma evolution; only maﬁc rocks should therefore be con-

sidered for constraining source processes.

The La/Sm v. K

O diagram for the most maﬁc among the ana-

lysed rocks (MgO .4 wt%) shows that Filicudi, Salina and

Lipari have similar La/Sm ratios, but higher values are observed

at Alicudi and in some CA samples from Stromboli (Fig. 15.11a).

Since all these rocks have the same petrological characteristics, it

is reasonable to assume an origin by comparable degrees of

mantle melting. Higher La/Sm ratios in the CA rocks of the

two external islands therefore point to a stronger enrichment of

LREE in their mantle sources. At Vulcano, there is an increase

of La/Sm from CA to SHO rocks at fairly constant Sr-isotope

ratio (De Astis et al. 1997). By contrast, La/Sm ratios do not

change signiﬁcantly from CA to SHO rocks at Stromboli,

whereas

Sr/

Sr ratios increase strongly (Francalanci et al.

1988). These data suggest that HKCA and SHO magmas at

Vulcano could be related to variable degrees of partial melting

of a homogeneous source, whereas CA and SHO magmas at

Stromboli are generated by similar degrees of partial melting of

a isotopically heterogeneous source that was variably contami-

nated by subducted sediments. The obvious conclusion is that

SHO magmas are generated by different processes in the

Aeolian arc as already suggested by Ellam et al. (1988) and De

Astis et al. (2000). Finally, Tb/Yb ratios are generally high in

all shoshonites. This points to the occurrence of residual garnet

in the source during melting and, hence, to a deeper origin for

SHO than the associated CA magmas.

The physical conditions that generated variable degrees of

melting for CA and SHO magmas in the central Aeolian arc are

of interest for petrology and geodynamics. It is well known that

water is crucial to promote partial melting in the subduction

environments (e.g. Ulmer 2001; Grove et al. 2012). Variable

degrees of melting in the Aeolian arc could therefore be related

to different ﬂuxes of water from the slab. These were higher

MgO > 4%

0 1 2 3 4 5

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Tb/Yb

0 1 2 3 4 5

La/Sm

K2O wt% K2O wt%

(a)(b)

Fig. 15.11. La/Sm and Tb/Yb v. K

diagrams for the most maﬁc among the

analysed samples (MgO .4 wt%). Plots

are restricted to maﬁc compositions to

minimize effects of La/Sm variation related

to fractional crystallization. For further

explanation see text. Symbols as in

Figure 15.4.

A. PECCERILLO ET AL.506

during calc-alkaline magma activity, and were less abundant in

the zones and times of shoshonitic magma formation. Variable

water ﬂuxes could be tentatively attributed to different stages of

subduction process. Noting that shoshonitic magmas appear

during mature to late stages of volcanism, it is reasonable to pos-

tulate a decrease of water ﬂux with time.

Pre-metasomatic mantle composition

Gaining insight into the original composition of the upper mantle

beneath the Aeolian Islands is difﬁcult, due to extensive modiﬁ-

cation produced by metasomatic processes. This is however an

important step to a better understanding of mantle source evolution

and geodynamic setting in the southern Tyrrhenian Sea. Ellam

et al. (1988) hypothesized an OIB- to MORB-type composition

for pre-metasomatic mantle, and suggested that HFSE enrichment

in some islands was evidence for the occurrence of the OIB com-

ponent in the sub-arc mantle. Such a hypothesis also explains the

linear Pb-isotope arrays between the Calabro – Peloritano base-

ment and the OIB-type Etna volcano (Fig. 15.6b), which suggest

contamination of an OIB-type source by subducted crustal

material. By contrast, Francalanci et al. (2007) and Tommasini

et al. (2007) envisage a homogeneous MORB-type pre-

metasomatic mantle along the entire arc, and explain the regional

geochemical and isotopic variations as entirely related to variable

roles of aqueous and supercritical ﬂuids or melts from an altered

oceanic crust and associated sediments. Accordingly, radiogenic

Pb-isotope signatures observed in some islands were explained

as the result of metasomatism by ﬂuids released from sediments

and aged Ionian oceanic crust.

The data and discussion presented in this paper support the

hypothesis of a zoned OIB- to MORB-type pre-metasomatic

mantle for the Aeolian arc. In particular, an OIB-type component

in the marginal islands would explain both high HFSE contents and

LREE abundances and fractionation. Variable HFSE ratios are also

better explained by pre-metasomatic mantle heterogeneities, since

these elements behave as immobile during metasomatism.

Francalanci et al. (2007) argued that the OIB-type nature of the

external islands conﬂicts with the low Pb-isotope ratios of Alicudi

and Stromboli, as compared to those of the central island of Salina.

However, relatively unradiogenic Pb compositions at Stromboli

are an effect of contamination of the mantle source by sediments,

which completely altered its original Pb-isotope signature. A

decrease of

206

Pb/

204

Pb ratios from Salina to Alicudi is only

observed if the Alicudi basalts are considered as the most primitive

compositions in the island. However, it has long been demon-

strated that the Alicudi basalts are more contaminated than the

associated andesites (Peccerillo & Wu 1992; Lucchi et al.

2013a). Therefore, if more evolved but uncontaminated andesites

are considered, Pb-isotopic values at Alicudi are similar to those at

Salina.

Geodynamic implications

There are important relationships between magma and mantle

compositions and the geodynamic setting of the Aeolian arc. The

diversity of the mantle contamination processes in the western-

central and eastern sectors suggests a different nature for the

subducted material. A basaltic slab, with little or no sediment invol-

vement, is indicated by geochemical data as a source of metaso-

matic ﬂuids in the western-central islands, whereas an important

contribution by subducted sediments or other upper crustal

materials is required for metasomatism at Stromboli. The

Tindari– Letojanni Fault therefore represents the boundary that

divides two distinct compositions of the subducted material. Such

a conclusion is also suggested by Doglioni et al. (2001), although

these authors propose a continental-type crust in the west and an

oceanic-type crust in the east, a conclusion that strongly contrasts

with radiogenic isotope signatures of the Aeolian magmas.

Metasomatic ﬂuids activated extensive modiﬁcation of the

upper mantle beneath the Aeolian volcanic arc. However, some

geochemical signatures of the pre-metasomatic mantle were pre-

served, and indicate a depleted MORB-type source in the central

sector and a more fertile OIB-type component for the external

islands.

Peccerillo (2001) argued that the OIB-type component at Strom-

boli could have originated by inﬂow of asthenospheric mantle from

the Africa foreland around the margins of the retreating slab. Trua

et al. (2004, 2011) envisaged the same type of process to explain

the occurrence of MORB and OIB components at Marsili. Franca-

lanci et al. (2007) and Tommasini et al. (2007) consider the

hypothesis of mantle ﬂow as unrealistic, a statement that does

not take into account the particular geodynamic setting of the

Aeolian arc. Here, a narrow Ionian slab is subducting beneath

the southern Tyrrhenian Sea (Fig. 15.12) and is retreating toward

the SE (Gvirtzman & Nur 1999), generating deep seismic activity

beneath the eastern Aeolian arc. In contrast, deep seismicity is

lacking beneath the western Aeolian arc, a feature that could be

related to collision and slab break-off in this sector where a frag-

ment of oceanic slab is suggested to passively sink into the

upper mantle (see Peccerillo 2005; Panza et al. 2007 for further

details).

It is well known that the Benioff zone rollback requires mantle

ﬂow to replace the space left by the retreating slab. Such a replace-

ment can occur by mantle ﬂow from the back-arc area. However,

for a narrow slab such as that in the southern Tyrrhenian Sea

most of the asthenospheric inﬂow likely occurs from the foreland,

moving around the margins of the retreating slab (Fig. 15.12). The

mantle sources at the margins of the slab are therefore the most

heavily affected by inﬂow and consequently show the clearest evi-

dence of OIB-type components. It should be recalled that all vol-

canoes situated on the margin of the African plate (e.g. Etna,

Iblei, Linosa, etc.) have an OIB-type composition.

Fig. 15.12. Schematic geodynamic setting of the Aeolian arc. A narrow Ionian

plate is subducting beneath Calabria and the southern Tyrrhenian Sea. This is

associated with deep seismicity and active volcanism, and is bounded to the

west by the Tintari– Letojanni Fault (TLF) system. A detached and passively

sinking oceanic slab is envisaged for the western Aeolian arc. Curved black

arrows indicate asthenospheric mantle inﬂow from the foreland around the

margins of the subducted slabs. Collision zones are indicated with a dashed line.

For further explanation, see text.

COMPOSITIONAL VARIATIONS OF MAGMAS IN THE AEOLIAN ARC 507

Conclusions

The overall petrological and geochemical features of the Aeolian

arc and the relationships with petrogenesis and geodynamics can

be summarized as follows.

(1) CA and HKCA rocks make up all the western islands and the

largest part of Lipari and Panarea, whereas HKCA and SHO

rocks are dominant at Vulcano and Stromboli. Shoshonitic

rocks from these islands have similar compositions for

many major and many trace elements, but exhibit strong

differences for radiogenic isotopes (Sr– Nd –Pb) and some

trace element abundances and ratios. This suggests that

shoshonitic magmatism in the Aeolian arc is polygenetic. In

particular, decreasing degrees of partial melting of a homo-

geneous source at various depths generated the transition

from high-K calc-alkaline to shoshonitic magmatism at

Vulcano. At Stromboli, calc-alkaline and shoshonitic mag-

mas are related to polybaric melting of heterogeneous man-

tle sources that were variably contaminated by subducted

sediments.

(2) There are distinct Sr-, Nd- and Pb-isotope signatures in

different sectors of the arc. Some incompatible trace

element ratios also show diverging variation trends. Differ-

ent types of mantle metasomatic processes have been respon-

sible for these features. Metasomatic ﬂuids affecting the

western-central arc originated from a subducted basaltic

crust, whereas upper crustal material (likely oceanic-type

crust plus sediments) was a main source of metasomatic

ﬂuids under Stromboli.

(3) Modiﬁcation by metasomatic ﬂuids was superimposed on a

heterogeneous OIB- to MORB-type pre-metasomatic

mantle wedge. An OIB-type component in the source is

recognized for the external islands of Alicudi and Stromboli

and for the Marsili seamount, but not in the central Aeolian

arc where a depleted MORB-type mantle composition is

suggested by rock chemistry. The OIB-type component

was provided by asthenospheric inﬂow from the Africa fore-

land, around the edges of the slab during rollback.

(4) Aeolian arc magmas were affected by complex evolution

processes which drove parental basalts towards intermediate

and acidic compositions. The degree of magma evolution

was much more extensive in the central islands of Lipari

and Vulcano, where abundant rhyolites were erupted

during the latest activity stages. This is related to the trans-

tensional tectonics along the Tindari – Letojanni transfer

fault, which favoured the formation of large intra-crustal

magma chambers where magmas ponded and fractionated

for a long time to give abundant rhyolitic melts.

(5) Geobarometric investigations revealed polybaric magma

evolution processes for the Aeolian volcanoes. Early basaltic

activity, which characterized the lowest exposed sequences

on most islands, was fed by deep magma chambers in

which magmatic evolution was dominated by fractional crys-

tallization and assimilation plus continuous mixing with

fresh maﬁc melts from the source. Younger andesitic and

rhyolitic activity was fed by shallower magma chambers,

where magmatic evolution was dominated by fractional crys-

tallization. An overall upwards migration for magma

chambers of the Aeolian volcanoes is therefore suggested

by geobarometric investigations.

Research on Aeolian orogenic magmatism has been ﬁnanced by MIUR,

PRIN2008. The authors thank J. Hermann, ANU, R. Harmon and an anonymous

referee for constructive reviews.

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Characterization of an undocumented CO2 hydrothermal vent system in the Mediterranean Sea: Implications for ocean acidification forecasting

Article

Full-text available

Feb 2024
PLOS ONE

A previously undocumented shallow water hydrothermal field from Sicily (Southern Tyrrhenian Sea, Italy) is here described, based on a multidisciplinary investigation. The field, covering an area of nearly 8000 m² and a depth from the surface to -5 m, was explored in June 2021 to characterise the main physico-chemical features of the water column, describe the bottom topography and features, and identify the main megabenthic and nektonic species. Twenty sites were investigated to characterise the carbonate system. Values of pH ranged between 7.84 and 8.04, ΩCa between 3.68 and 5.24 and ΩAr from 2.41 to 3.44. Geochemical analyses of hydrothermal gases revealed a dominance of CO2 (98.1%) together with small amounts of oxygen and reactive gases. Helium isotope ratios (R/Ra = 2.51) and δ¹³CCO2 suggest an inorganic origin of hydrothermal degassing of CO2 and the ascent of heat and deep-seated magmatic fluids to the surface. Visual census of fishes and megabenthos (mainly sessile organisms) allowed the identification of 64 species, four of which are protected by the SPA/BIO Protocol and two by the International Union for Conservation of Nature. The macroalgae Halopteris scoparia and Jania rubens and the sponge Sarcotragus sp. were the dominant taxa in the area, while among fishes Coris julis and Chromis chromis were the most abundant species. This preliminary investigation of San Giorgio vent field suggests that the site could be of interest and suitable for future experimental studies of ocean acidification.

Melt inclusion formation during olivine recrystallization: Evidence from stable isotopes

Article

Full-text available

Aug 2022
EARTH PLANET SC LETT

Melt inclusions are often used to infer melting processes or to determine source magmas that are usually overprinted in bulk rocks due to late stage mixing or near surface contamination. Here we present the first investigation of oxygen (O) isotope equilibrium between melt inclusions and their host olivines from arc samples. Olivines in all but one sample record either magma mixing or fractional crystallization. All six melt inclusions from Vulcano, 83% of seven from Sukumoyama, 44% of 21 from St Vincent, 37% of four from Iwate, and 21% of 13 from Aoba are not in isotopic equilibrium with their olivine host, despite the other major elements being in apparent equilibrium. A detailed study of some of the olivines shows that only a small volume around the melt inclusions is in equilibrium with its host. This strongly suggests that in these olivines melt inclusions are trapped in partly recrystallized olivines, highlighting the importance of magma mixing and crystal recycling in the magmatic plumbing system of these volcanoes. Oxygen isotope fractionation between melt inclusions and their host olivines, as well as phosphorus-δ18O systematics, could be used to better understand the formation of melt inclusions and crystal history. It could also provide valuable information to help characterize the magmatic plumbing system that the inclusions and their olivine hosts formed in (e.g., crystal rich-mush versus crystal poor melt lenses).

The use of mineral interfaces in sand-sized volcanic rock fragments to infer mechanical durability

Article

Full-text available

Aug 2020

The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at a modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea (Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli Island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural (e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47,386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl (Plagioclase)/Glgr (Glassy groundmass) > > Px (Pyroxene)/Glgr > > Ol (Olivine)/Glgr > > Op (Opaque)/Glgr > > Hbl (Hornblende)/Glgr> > Bt (Biotite)/Glgr > > Idd (Iddingsite)/Glgr > > Rt (Rutile) / Glgr; b) stable interfaces, categorized as Pl/Migr (Microlitic groundmass) > > Op/Migr > > Px/Migr > > Ol/Migr; c) moderately stable interfaces, categorized as Op/Px > > Op/Hbl > > Px/P > > Ol/Pl> > Bt/Op; and d) unstable interfaces, categorized as Pl/Pl > > Px/Px > > Ol/Ol > > Op/Op > > Hbl/Hbl > > Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass, Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.

Volcanism and Tectonic Setting: The Modern Global Tectonic Framework, and an Approach for Evaluating Ancient Tectonic Settings, including the Hadean and Archean

Chapter

Jun 2024

Since publication of Cas and Wright (1987), the relationship between volcanism and tectonic setting has expanded into an enormous and multidisciplinary topic. In this chapter, we provide an updated review of the known tectonic settings in which volcanism occurs today and the relatively recent past, and the overall geological characteristics of these settings using the plate tectonic model as a global framework for Phanerozoic and Proterozoic times. However, there is little evidence that plate tectonics operated earlier during the Hadean and Archean, which represents almost 50% of geological time, and so we will also consider what the tectonic paradigm for volcanism was during the early history of the Earth. Initially, during the two billion years prior to when plate tectonics developed, the Earth was a magma ocean. This evolved into a single mafic–ultramafic crustal shell (stagnant lid) as the Earth cooled and was affected by mantle plume activity that influenced most volcanism. Buoyant diapiric granitoid plutonism resulting from anatexis of mafic lower crust allowed the Earth’s crust to evolve and “felsify”, leading to cratonic nuclei. Localised, limited subduction (mobile lid) commenced in the late Archean, but global plate tectonics probably didn’t develop as we know it until the Proterozoic (<2,500 Ma). In the post-Proterozoic plate tectonic framework, the first-order division of settings for volcanism is based on the overall prevailing regional tectonic regime: divergent, oblique/strike-slip, “passive or hot spot” (i.e. plume-related), or convergent settings. We describe the styles of volcanism typically found in the various plate margin and intraplate tectonic settings, incorporating information on crustal setting, magma generation, as well as the potential for the formation of Large Igneous Provinces (LIPs), providing examples from ancient terrains. In this discussion we will also introduce some of the more recent geodynamic concepts and their relationship to magmatic and volcanic activity. In particular, seismic tomography has evolved as one of the most powerful tools for studying the structure and dynamics of subduction zones and convergent plate margins. Finally, guidelines are given for the evaluation of the tectonic context in ancient volcanic and mineralised terrains. This chapter provides a dynamic framework to accompany our concluding chapter (Chap. 18) on volcanic-hosted resources.

From the mantle wedge to the shallow crust: Magmas, fluids, and mineralizations in the Aegean subduction system

Thesis

Full-text available

Jan 2021

Anna Grosche

Subduction zones are places of voluminous material transport and element recycling between the Earth’s surface and its interior. Magmatism and hydrothermal activity at subduction zones are the surface expression of the complex physical and chemical interactions between the subducted crust and the mantle wedge. Large amounts of volatiles get dragged down within the hydrated oceanic crust and are released at increasing pressures and temperatures, starting their way back to the surface. The interaction of mantle rock with fluids and other slab-derived components causes partial melting of the mantle wedge, followed by magma ascent, evolution, and interaction with the overriding plate. The emplacement of magmas in the shallow crust is accompanied by the exsolution of volatiles that react with the surrounding rocks resulting in the formation of magmatic-hydrothermal ore deposits, which are significant metal resources for our society. Complex models of subduction dynamics have been established by geophysical and geochemical studies over the past decades, however, some questions remain open and a better understanding of the processes that control the formation and evolution of arc magmas and related mineralizations is still needed. The Aegean region, located in the eastern Mediterranean, was affected by subduction since the late Cretaceous and provides vast opportunities to study subduction zone processes. Northwards subduction and accretion of oceanic and continental fragments beneath Eurasia led to slab rollback, southward trench retreat, and extension of the overriding plate during the past ~35 million years. Subduction-related magmas and associated porphyry-epithermal ore deposits are spread over the entire region and thus, the Aegean is an ideal target to study the element transport via magmas and fluids from the mantle wedge to the shallow crust. This thesis shall investigate (i) the contribution of subducted sediments to arc magmatism in a migrating subduction system, (ii) the formation and evolution of subduction-related potassic magmas, (iii) the magmatic preconditions that promote porphyry-epithermal-style mineralization, and (iv) the hydrothermal processes that control the metal enrichment in the shallow crust. To approach these questions, we compiled a comprehensive geochemical data set of Aegean magmas to develop a new tectono-magmatic model for the Aegean (chapter 3). Furthermore, we analyzed whole rock, mineral, and ore samples from two focus areas, the shoshonitic Maronia pluton in northeast Greece (chapter 4), and the volcanic and hydrothermally active Milos Island (chapter 5), highlighting different depths and time windows of the Aegean subduction system. The compiled geochemical and geochronological data of Aegean magmas along two age-progressive profiles provides evidence for the migration of the magmatic arc due to the Aegean slab rollback. The strong variation of magma compositions can be linked to the subduction of heterogeneous sedimentary and continental material during the past 30 million years. The transfer of sediment components from the slab to the sub-arc magma source can be best explained by the mixing of mantle rock with bulk sediment and the ascent of this mélange material in buoyant diapirs causing focused arc magmatism. Temporal changes in the isotope and incompatible element composition of the magmas are correlated with the subduction of different sedimentary and continental material at variable subduction rates. To study the genesis of potassic magmas in detail, we use major element, trace element, and Sr-Nd-Pb isotope data of monzodioritic to granitic rocks from the shoshonitic Maronia pluton. Our findings imply that shoshonitic magmas can be produced in arc settings by low-degree partial melting of a mantle source, that has been enriched by slab-derived crustal material. In Maronia hydrous melting of the subduction-modified mantle was followed by magma ascent, fractional crystallization, and magma emplacement at a depth of 5 to 6 km. Microanalytical data of apatite implies the exsolution of Cl- and metal-rich, but S-poor fluids from late-stage granitic magma leading to porphyry Cu-Mo ± Re ± Au mineralization and associated formation of sulfide-bearing miaroles. The Pb-Zn-Ag vein mineralization on Milos Island records the conditions and processes that control the transport and precipitation of metals in the shallow crust of an arc volcano. We use S-Sr-Pb isotopes of sulfides and sulfate to identify the fluid and metal sources of the system. The mineralization formed by circulation and heating of seawater, leaching of metals from the volcanic and metamorphic host rocks, and subsequent precipitation of sulfides at decreasing temperatures during fluid ascent along major fault zones. Based on in-situ trace element and S isotope data of sulfides, we can show that boiling and fluid-seawater mixing in the subseafloor control the vertical distribution of metals and metalloids in shallow-marine hydrothermal systems. Altogether, this thesis provides important new insights into the processes that control the element transfer in subduction zones from the mantle wedge to the shallow crust. In contrast to previous studies, we can show that the subduction of variable sedimentary and continental material accounts for the large range of Cenozoic magma compositions including K-rich magmas in the Aegean. The shallow emplacement of oxidized, volatile-rich magmas and the interplay of mafic and felsic magmas facilitates the formation of magmatic-hydrothermal mineralizations in the thinned arc crust. Additionally, the physicochemical conditions during boiling and fluid mixing control the transport and precipitation of metal(loid)s in shallow-crustal hydrothermal systems.

Migration of Arc Magmatism Above Mantle Wedge Diapirs With Variable Sediment Contribution in the Aegean

Article

Full-text available

Jun 2021
GEOCHEM GEOPHY GEOSY

Compiled data show the age progression of magmatic centers along two approximately linear profiles from NE Greece and NW Turkey to the South Aegean Volcanic Arc (SAVA). The age progression reveals the southwestward migration of arc magmatic activity from Oligocene to present, perpendicular to the Hellenic Trench. This is in accordance with the migration of the Aegean subduction zone due to the collision of oceanic and continental blocks, trench retreat, mantle flow, and coeval extension. We suggest that the subduction of large volumes of sediments and their contribution to the sub-arc magma source controlled the composition of calc-alkaline to high-K calc-alkaline and shoshonitic arc magmas during the past 30 Ma. The magma geochemistry and the approximately linear age-progressive migration of magmatic activity suggest focused ascent of mixed material from the subducted slab into the mantle wedge, most likely in the form of mélange diapirs. Geochemical data along the profile reveals increasing Sr and decreasing Nd isotopes during Upper Miocene in agreement with the ongoing subduction of continental blocks, low subduction rates, and development of an accretionary wedge. The different K-rich arc magmas reflect the variable subduction of sediments, whereas crustal assimilation often plays a minor role. Magmas with variable 87Sr/86Sr, P/Nd, and Ba/La indicate a variable contribution of clastic, phosphate-, and barite-bearing sediments. Low-degree partial melting in sediment-dominated mélange diapirs causes the formation of shoshonitic magmas with high Sr and P2O5 contents and high La/Yb in the northern Aegean.

The Geotraveller. Chapter 8: Mediterranean Basins and Italian Island Volcanoes: Active Volcanoes, Earthquakes, Microplates, and Greek Mythology

Chapter

Feb 2021

Roger Scoon

The Ancient GreeksAncient Greeks settled many of the coastal areas in southern ItalyItaly and the Italian IslandsItalian Islands. Well known archaeological sites of Magna GraeciaMagna Graecia include PaestumPaestum, near NaplesNaples, which includes three well-preserved temples, and SyracuseSyracuse in SicilySicily. MythologyMythology was an important part of the Ancient World and the difficulties that OdysseusOdysseus experienced on his return voyage from TroyTroy (western TurkeyTurkey) to his home island of IthacaIthaca (northwest GreeceGreece), as recounted by the Greek poet HomerHomer, Greek poet, contain descriptions of the perils of navigating the Mediterranean SeaMediterranean Sea. The historical (and mythological) record includes geological catastrophes such as earthquakesEarthquakes, volcanic eruptionsVolcanic eruption, tsunamisTsunami, and tidal whirlpoolsWhirlpool. The Stromboli VolcanoStromboli Volcano has been described as the world’s oldest lighthouse as the glow of the vent can be seen from many kilometres at night. The Mediterranean is comprised of multiple interlocking basins, each of which contains a sea identified by the ancient geographers. The Adriatic SeaAdriatic Sea, the Aegean SeaAegean Sea, the Ionian SeaIonian Sea, and the Tyrrhenian SeaTyrrhenian Sea each have different physical and chemical characteristics. Large parts of the central and eastern Mediterranean remain tectonically active. The Alpine OrogenyAlpine Orogeny is a long drawn out process of continental collision associated with the northward-migrating African PlateAfrican Plate and the Eurasian PlateEurasian Plate. Tectonism peaked in the Oligocene-Miocene with formation of multiple chains of fold mountainsFold Mountains. The collision is ongoing and includes subductionSubduction of oceanic crustOceanic crust associated with the ancient Tethys OceanTethys Ocean. The complexity of the tectonic setting is illustrated by the recognition of microplates, as well as the curvilinear nature of the Hellenic TrenchHellenic Trench, the current location of the plate boundary. The compressional tectonism was displaced in the PliocenePliocene by localized regions of crustal extension. Crustal extension associated with development of fore-arc and back-arc basinsBack-arc basin has resulted in some regions being subjected to frequent and relatively shallow, earthquakesEarthquakes. Catastrophic events between 1169 and 1908 resulted in the destruction of the cities of CataniaCatania and MessinaMessina. The Italian IslandItalian Island volcanoes are related to the convergent plate boundaries. There are several potentially hazardous volcanoes in the Aeolian Islands, including StromboliStromboli Island and the Fossa coneFossa cone, associated with aVolcanic island arcvolcanic island arcIsland arc (Volcanic island arc). The StrombolianStrombolian, volcanism style of volcanismVolcanism is characterized by relatively small eruptions constrained to discrete cratersCrater. The Fossa coneFossa cone on the island of VulcanoVulcano, island (named after VulcanVulcan, Roman god of fire, the Roman god of fire) is characterized by short-lived, yet violent eruptions. The Etna VolcanoEtna Volcano in northeast SicilySicily is one of the largest stratovolcanoesStratovolcano on Earth and also one of the most active. Historical activity includes the 1669 eruption during which lava flowed into the city of CataniaCatania. EtnaEtna Volcano is a major tourist attraction and the volcanic coneVolcanic cone is protected in a national park. Recent eruptions of EtnaEtna Volcano are generally restricted to the upper parts of the cone, but can be sufficiently hazardous as to restrict tourist visits. The small island of PantelleriaPantelleria, island is part of an active volcanic system associated with a transform faultTransform fault on the plate boundary between SicilySicily and North Africa.

Mush cannibalism and disruption recorded by clinopyroxene phenocrysts at Stromboli volcano: New insights from recent 2003–2017 activity

Article

Feb 2020
LITHOS

The Present-day (<1.2 kyr) activity of Stromboli (Aeolian Islands, Southern Italy) is fed by a vertically-extended mush column with an open-conduit configuration. The eruptive products are the result of periodic supply of mafic magma (low porphyritic or Lp-magma) from depth into a homogeneous shallow reservoir (highly porphyritic or Hp-magma). Clinopyroxene phenocrysts from the 2003–2017 activity exhibit marked diopside-augite heterogeneities caused by continuous Lp-Hp magma mixing and antecryst recycling. Diopsidic bands record Lp-recharge injected into the shallow Hp-reservoir, whereas resorbed diopsidic cores testify to the continuous disruption and cannibalism of relic antecrysts from the mush. The transition between diopside (∼1175 °C) and augite (∼1130 °C) takes place at comparable P (∼190 MPa) and H2O (0.5–2.4 wt%) conditions. Short timescales (∼1 year) for diopsidic bands from the 2003 paroxysm document restricted temporal intervals between mafic injection, magma mixing and homogenization in the Hp-reservoir. Longer timescales (∼4–182 years) for diopsidic cores indicate protracted antecryst remobilization times. By comparing clinopyroxenes from the Present-day and Post-Pizzo eruptions, we argue a distinct phase in the life of Stromboli volcano is evident from the 2003 paroxysm onwards. More efficient mechanisms of mush disruption and cannibalism involve diopsidic antecrysts remobilized and transported by Lp-magmas permeating the mush, in concert with gravitational instability of the solidification front and melt migration within the shallow Hp-reservoir. Magmatic injections feeding the persistent Present-day activity are more intensively mixed and homogenized prior to eruption, reflecting small recharge volumes and/or a more mafic system in which the mafic inputs are less pronounced.

Modern Iron Ooids of Hydrothermal Origin as a Proxy for Ancient Deposits

Article

Full-text available

May 2019

We constrained the origin and genetic environment of modern iron ooids (sand-sized grains with a core and external cortex of concentric laminae) providing new tools for the interpretation of their fossil counterparts as well as the analogous particles discovered on Mars. Here, we report an exceptional, unique finding of a still active deposit of submillimetric iron ooids, under formation at the seabed at a depth of 80 m over an area characterized by intense hydrothermal activity off Panarea, a volcanic island north of Sicily (Italy). An integrated analysis, carried out by X-ray Powder Diffraction, Environmental scanning electron Microscopy, X-ray Fluorescence and Raman spectroscopy reveals that Panarea ooids are deposited at the seafloor as concentric laminae of primary goethite around existing nuclei. The process is rapid, and driven by hydrothermal fluids as iron source. A sub-spherical, laminated structure resulted from constant agitation and by degassing of CO2-dominated fluids through seafloor sediments. Our investigations point the hydrothermal processes as responsible for the generation of the Panarea ooids, which are neither diagenetic nor reworked. The presence of ooids at the seawater-sediments interface, in fact, highlights how their development and growth is still ongoing. the proposed results show a new process responsible for ooids formation and gain a new insight into the genesis of iron ooids deposits that are distributed at global scale in both modern and past sediments.

Chapter 8 Volcanism, magmatism, volcano-tectonics and sea-level fluctuations in the geological history of Filicudi (western Aeolian archipelago)

Article

Full-text available

Jan 2013

Chapter 8 Volcanism, magmatism, volcano-tectonics and sea-level fluctuations in the geological history of Filicudi (western Aeolian archipelago)

Article

Full-text available

Jan 2013

Chemical and isotopic systematics of ocean basalts: Implications for mantle composition and processes, in Magmatism in the Ocean Basins

Article

Full-text available

Dec 1989

SUMMARY: Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (≤1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (≤2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type (eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by

Chapter 13 Eruptive, volcano-tectonic and magmatic history of the Stromboli volcano (north-eastern Aeolian archipelago)

Article

Full-text available

Oct 2013

Stromboli is famous for its persistent volcanic activity consisting of periodic discrete explosions alternating with lava effusion and more violent explosions. This paper presents a detailed reconstruction of the geological history of Stromboli and description of the characteristics and distribution of the volcanic units and structural features. Six main growth stages (Eruptive Epochs 1–6), in addition to the c. 200 ka activity of Strombolicchio, are recognized between c. 85 ka and the present day, displaying a magma composition ranging from calc-alkaline to potassic series which usually varies with changing Eruptive Epochs. The Epochs are subdivided into sequences of eruptions and characterized by dominant central-vent summit activity with episodic phases of flank activity along fissures and eccentric vents. The activity was repeatedly interrupted by erosional and destructive phases driven by recurrent vertical caldera-type (cc1–5) and sector (and flank) collapses (sc1–7) and generally associated with significant quiescences. The different serial character of the Stromboli rocks is associated with largely variable trace element contents and isotope ratios. These petrochemical characteristics together with our new stratigraphy indicate that magmas, generated in a heterogeneous mantle wedge, underwent complex differentiation processes during their ascent. Magmas are characterized by polybaric evolution residing in small magma reservoirs that are alternatively tapped by the different collapses. DVD The 10 000 scale geological map of Stromboli is included on the DVD in the printed book and can also be accessed online at http://www.geolsoc.org.uk/Memoir37-electronic . Also included is a full geochemical dataset for Stromboli.

Spatially resolved and bulk trace element analysis by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS)

Article

Apr 2008
PERIOD MINERAL

In this contribution, the analytical capabilities of the Laser Ablation - Inductively Coupled Plasma - Mass Spectrometer (LA-ICP-MS) instrumentation installed at the Earth Sciences Department of Perugia University are evaluated. The instrumental set up and the analytical protocols for single-phase spatially-resolved and bulk trace-element analyses are presented. Spatially-resolved analysis allow 'in situ' trace element determinations with lateral resolutions ranging from less than 20 mu m to more than 80 mu m. Precision (expressed as relative standard deviation) is better than 10% with the only exception of Cs (14% with a 20 mu m laser beam diameter) whereas accuracy (expressed as relative deviation from the reference value) is better than 11%. Precision and accuracy increase as increasing the laser beam diameter. The extreme versatility of the instrument permits to analyze with excellent results compositions of crystals, melt inclusions, ceramics, archaeological, and environmental samples. Bulk configurations are utilized to perform whole-rock trace-element determination on samples prepared as fusion beads. Both flux-free and lithium tetraborate fusion sample preparation for whole rock trace element determination are investigated. Results show that the lithium tetraborate fusion produces beads with higher degrees of homogeneity compared to the flux-free method, resulting in more precise and accurate trace-element determinations. In detail, for the lithium tetraborate fusion precision is better than 10% for elements with concentrations above 2 mu g/g with the only exception of Ph (similar to 15%). For elements with concentrations below 2 mu g/g the precision decreases to about 15%. Accuracy values are always better than 10% with the only exception of Pb.

Petrological and geochemical characteristics of the Alicudi volcano, Aeolian Islands, Italy: Implications for magma genesis and evolution

Article

Jan 1993

Structural and chemical variations in clinopyroxenes from the Island of Alicudi (Aeolian arc) and their implications for conditions of crystallization

Article

Mar 1998
EUR J MINERAL

The crystal chemistry of clinopyroxenes from calc-alkaline volcanic rocks from the island of Alicudi (Aeolian Arc) was studied by single-crystal X-ray diffraction and microprobe techniques, in order to explore the relationships between clinopyroxene structural and chemical parameters and the physicochemical conditions of their crystallization. Crystal chemical data indicate considerable differences between clinopyroxenes from early eruptive stages and those from the latest volcanic activity. Early-stage clinopyroxenes are characterized by smaller cell volumes and a more closely packed structure than late clinopyroxenes, suggesting a higher pressure of crystallization for the early clinopyroxenes. The crystal chemical pattern of clinopyroxene follows an overall trend of rock composition, which is basaltic and andesitic-basaltic for the earliest products and becomes slightly more acidic at the end of volcanic activity. This geochemical and petrologic evolution is also found in other Aeolian islands and may be explained by assuming the increasing role of crystal fractionation with respect to mixing with primary mafic melts. The variations in crystal chemical parameters of clinopyroxenes at Alicudi, which indicate decreasing pressure of crystallization with time, lend support to the hypothesis of polybaric evolution of the Alicudi magmas.

The Apenninic-Maghrebian orogen in southern Italy, Sicily and adjacent areas

Article

Jan 2001

Mario Grasso

The Apenninic—Maghrebian orogen or Southern Apenninic (SA) arc in the central Mediterranean region developed as the product of convergence between the Europe and Africa—Adria plates, mostly during Tertiary times. The European plate margin is represented by the Sardinian block, split from the main plate during the late Oligocene following the opening of the Balearic basin (Cohen et al., 1980; Cherchi and Montadert, 1982a,b; Dewey et al., 1989; Carmignani et al.,1995). The African foreland includes the continental areas of both the Pelagian block (Burollet et al., 1978), and the Adria (Apulian) block, which have been separated, during Jurassic or earlier times, by the growing Ionian oceanic basin (Ben Avraham et al., 1992; Vai, 1994; Finetti et al., 1996). The deposits of the foreland consist of Mesozoic—Cenozoic carbonates up to 10 km thick (Burollet et al., 1978; Patacca et al., 1979; Bianchi et al., 1989; Mostardini and Merlini, 1988), whereas the oceanic Ionian crust underlies thin Mesozoic—Cenozoic, deep-sea to oceanic sediments (Finetti et al., 1996).

A west-east geochemical and isotopic traverse along the volcanism of the Aeolian Island arc, southern Tyrrhenian Sea, Italy: Inferences on mantle source processes

Chapter

Jan 2007

The Aeolian Island arc, emplaced on continental lithosphere, is composed of seven islands and several seamounts, which have evidence of magmatic activity from 1.3 Ma (Sisifo seamounts) to present time (Vulcano, Stromboli). The rock compositions belong to different magmatic series and show a large silica range (48-76 wt%). Calc-alkaline and high-K calc-alkaline volcanics are present in all the islands, except for Vulcano. Shoshonitic rocks are only lacking at Alicudi, Filicudi, and Salina. Potas- sic magmas have been erupted at Vulcano and Stromboli. The different parental magmas originated in a heterogeneous mid-ocean-ridge basalt (MORB)-like mantle wedge, variously metasomatized by subduction-related components (oceanic crust + sediments, released as either fluids or sediment melts). Trace-element and Sr-Nd isotopic ratios show clear geographical west-east variations among calc-alkaline rocks. The composition of the mantle source of Stromboli is strongly influenced by the addition of a sedimentary component recycled into the mantle wedge; it shows evidence of a higher amount (∼2%) than in all the other islands (<0.5%). Furthermore, the islands from the central sector of the arc are characterized by a higher proportion of slab-derived fluids, which promotes a higher degree of melting. In this frame, the high Pb isotopic ratios (HIMU-like [high μ-like]) of the rocks of the central and western branch of the arc are explained with the high 206Pb/204Pb carried from a fluid component derived from the dehydration of the ancient subducting Ionian oceanic crust. On the contrary, the low Pb isotope signature of Stromboli magmas is dictated by the sediment input, as for Sr and Nd isotopes.Parental shoshonitic magmas of Vulcano are generated by low melting degrees of a MORB-like mantle wedge, metasomatized by crustal contaminant with high fluids/sediment values, whereas Vulcano potassic magmas are interpreted as deriving from the shoshonitic magmas by refilling, tapping, fractionation, assimilation (RTFA) processes. At Stromboli, potassic to calc-alkaline magmas are generated by increasing melting degrees of a heterogeneous veined mantle. The involvement of K-micas in the genesis of potassic magmas (during partial melting of mantle wedge and/or subducted sediments) is also suggested. U-Th disequilibria confirm the higher fluid versus melt proportion in the central than in the western islands. At Stromboli, the 238U excesses measured in calc-alkaline volcanics suggest a consistent addition of slab-derived fluids in the source, also promoting higher degrees of melting. The shift to the consistent 230Th excesses in shoshonitic and potassic rocks requires dynamic melting processes capable of producing in-growth of 230Th. Quantitative modeling suggests lower melting rates for shoshonitic and potassic rocks, which are consistent with the lower melting degree proposed for these magmas.

Mediterranean island arcs

Article

Jan 1982

J. Keller

There are two areas of island-arc volcanism in the Mediterranean Sea: the Aegean arc to the south of Greece and the Aegean Sea, and the Tyrrhenian Sea S of Italy. The petrography and geochemistry of the two areas are discussed, particularly the former. In both provinces the volcanic products are assigned to a calc-alkaline high-alumina basalt-andesite-dacite association. -A.H.

Plio-Quaternary Volcanism in Italy: Petrology, Geochemistry, Geodynamics

Article

Jan 2005

A. Peccerillo

Central-Southern Italy and the Tyrrhenian Sea are the sites of extensive Plio-Quaternary magmatic activity. The rock compositions include crustal anatectic granites and rhyolites, tholeiitic, calc-alkaline, shoshonitic volcanics, and potassic to ultrapotassic and Na-alkaline volcanics. This very wide compositional variation makes Italian magmatism one of the most complex petrological issues, the understanding of which is a challenge for modern petrology and geochemistry. This book summarises the petrological, geochemical and volcanological characteristics of Italian Plio-Quaternary volcanism, and discusses petrogenetic hypotheses and possible geodynamics settings. The book is written for petrologists and geochemists, but fundamental geochemical information is well presented and the use of excessive jargon is avoided, making the book readable to a wide audience of Earth scientists.

Compositional variations of magmas in the Aeolian arc: implications for petrogenesis and geodynamics

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