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ORIGINAL PAPER

Shoshonite and sub-alkaline magmas from an ultrapotassicvolcano: Sr–Nd–Pb isotope data on the Roccamonfina volcanicrocks, Roman Magmatic Province, Southern Italy

Sandro Conticelli Æ Sara Marchionni Æ Davide Rosa ÆGuido Giordano Æ Elena Boari Æ Riccardo Avanzinelli

Received: 7 February 2008 / Accepted: 3 June 2008 / Published online: 27 June 2008

� Springer-Verlag 2008

Abstract The Roccamonfina volcano is characterised by

two stages of volcanic activity that are separated by vol-

cano-tectonic caldera collapses. Ultrapotassic leucite-

bearing rocks are confined to the pre-caldera stage and

display geochemical characteristics similar to those of

other volcanoes in the Roman Province. After the major

sector collapse of the volcano, occurred at ca. 400 ka,

shoshonitic rocks erupted from cinder cones and domes

both within the caldera and on the external flanks of the

pre-caldera Roccamonfina volcano. On the basis of new

trace element and Sr–Nd–Pb isotope data, we show that

the Roccamonfina shoshonitic rocks are distinct from

shoshonites of the Northern Roman Province, but are very

similar to those of the Neapolitan volcanoes. The last

phases of volcanic activity erupted sub-alkaline magmas as

enclaves in trachytic domes, and as lavas within the Monte

Santa Croce dome. Ultrapotassic rocks of the pre-caldera

composite volcano are plagioclase-bearing leucitites char-

acterised by high levels of incompatible trace elements

with an orogenic signature having troughs at Ba, Ta, Nb,

and Ti, and peaks at Cs, K, Th, U, and Pb. Initial values of87Sr/86Sr range from 0.70926 to 0.70999, 143Nd/144Nd

ranges from 0.51213 to 0.51217, while the lead isotope

rations vary between 18.788–18.851 for 206Pb/204Pb,

15.685–15.701 for 207Pb/204Pb, and 39.048–39.076 for208Pb/204Pb. Shoshonites show a similar pattern of trace

element depletions and enrichments to the earlier ultra-

potassic leucite-bearing rocks but have a larger degree of

differentiation and lower concentrations of incompatible

trace elements. On the other hand, shoshonitic rocks have

Sr, Nd, and Pb isotopes consistently different than pre-

caldera ultrapotassic leucite-bearing rocks. 87Sr/86Sr ranges

from 0.70665 to 0.70745, 143Nd/144Nd ranges from

0.51234 to 0.51238, 206Pb/204Pb ranges from 18.924 to

19.153, 207Pb/204Pb ranges from 15.661 to 15.694, and208Pb/204Pb ranges from 39.084 to 39.212. High-K calc-

alkaline samples have intermediate isotopic values between

ultrapotassic plagioclase leucitites and shoshonites, but the

lowest levels of incompatible trace element contents. It is

argued that ultrapotassic magmas were generated in a

modified lithospheric mantle after crustal-derived meta-

somatism. Interaction between the metasomatic agent and

lithospheric upper mantle produced a low-melting point

metasomatised veined network. The partial melting of the

veins alone produced pre-caldera leucite-bearing ultra-

potassic magmas. It was possibly triggered by either post-

collisional isotherms relaxation or increasing T�C due

Communicated by T.L. Grove.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s00410-008-0319-8) contains supplementarymaterial, which is available to authorized users.

S. Conticelli � S. Marchionni � D. Rosa � E. Boari �R. Avanzinelli

Dipartimento di Scienze della Terra, Universita degli Studi di

Firenze, Via Giorgio La Pira, 4, 50121 Florence, Italy

S. Conticelli (&)

Consiglio Nazionale delle Ricerche, Istituto di Geoscienze

e Georisorse, Sezioni di Firenze, Via Giorgio La Pira,

4, 50121 Florence, Italy

e-mail: [email protected]

G. Giordano

Dipartimento di Scienze Geologiche, Universita di Roma III,

Largo San Leonardo Murialdo, 1, 00100 Rome, Italy

Present Address:

R. Avanzinelli

Bristol Isotope Group, Department of Earth Sciences,

Wills Memorial Building, University of Bristol,

Bistol BS8 1RJ, UK

123

Contrib Mineral Petrol (2009) 157:41–63

DOI 10.1007/s00410-008-0319-8

http://dx.doi.org/10.1007/s00410-008-0319-8

increasing heat flow through slab tears. Shoshonitic mag-

mas were generated by further melting, at higher

temperature, of the same metasomatic assemblage with

addition 10–20% of OIB-like astenospheric mantle mate-

rial. We suggest that addition of astenospheric upper

mantle material from foreland mantle, flowing through slab

tearing after collision was achieved.

Keywords Sr–Nd–Pb isotopes � Plagioclase leucitite �Shoshonite � Sub-alkaline basaltic andesite �Roccamonfina volcano � Roman Magmatic Province �Orogenic magmas � Slab tearing � Asthenospheric inflow

Introduction

Roccamonfina was the first volcano on the Italian Penin-

sula to be investigated in detail (i.e. Appleton 1972;

Ghiara et al. 1973; Cox et al. 1976; Carter et al. 1978;

Taylor et al. 1979). Detailed petrographic and volcano-

logic studies defined the volcanic succession and the

eruption styles (e.g. Giannetti and Luhr 1983; Luhr and

Giannetti 1987; Cole et al. 1992, 1993; Valentine and

Giannetti 1995; De Rita and Giordano 1996; Giannetti

1996a, b; Giordano 1998a, b), and discussed the nature of

the xenolith assemblage (Giannetti and Luhr 1990). Roc-

camonfina mafic volcanic rocks have been used to address

the issue of the genesis of Italian Potassic and ultra-

potassic magmatism (e.g. Hawkesworth and Vollmer

1979; Vollmer and Hawkesworth 1980; Ellam et al. 1989;

Beccaluva et al. 1991; Conticelli and Peccerillo 1992;

Giannetti and Ellam 1994; D’Antonio et al. 1996; Conti-

celli et al. 2002, 2007; Peccerillo 2005a), however, there

have been no detailed studies of the distribution of major

and trace elements and Sr–Nd–Pb isotopes in the various

phases of the Roccamonfina volcano since the study of

Appleton (1972).

Conticelli et al. (2004) showed that low potassium series

of Appleton (1972) is better defined as a shoshonitic series.

Shoshonitic rocks are leucite-free and are characterised by

lower K contents than ultrapotassic lavas. In Italy, shos-

honitic rocks generally post-date the ultrapotassic

magmatism (i.e. Tuscany, Vulsini, Vico; Conticelli et al.

1991, 2007; Perini et al. 2000, 2003, 2004), except in the

Neapolitan area, where the present activity at Vesuvius is

ultrapotassic.

Geochemical and isotopic variations in the high-MgO

rocks of the Roman Magmatic Province have been

described by several authors (Beccaluva et al. 1991;

D’Antonio et al. 1996; Conticelli et al. 2002; Peccerillo

2005a). Recently Avanzinelli et al. (2008) have shown that

the Neapolitan volcanoes are consistently different in their

U–Th disequilibria with respect to the volcanoes of Latium

(i.e., Vulsini, Vico, Sabatini, Colli Albani). Thus, Rocca-

monfina together with the Middle Latin Valley district

(Boari and Conticelli 2007; Frezzotti et al. 2007; Boari

et al. 2008a, in press), represents a key area for the

understanding the nature of the geochemical and isotopic

transition from the Latian to the Neapolitan sector of the

Roman Magmatic Province (Conticelli et al. 2004, 2007;

Peccerillo 2005a). In the present study, major and trace

element concentrations, together with Sr, Nd, and Pb iso-

tope ratios have been determined for Roccamonfina

volcanic rocks with the aim of elucidating the genetic

relationships between ultrapotassic leucite-bearing rocks

and shoshonitic lavas.

Geological and volcanological background

The Roccamonfina volcano is part of the Auruncan District

of Washington (1906). The volcano lies at the intersection

of important NE–SW, NW–SE and N–S tectonic linea-

ments cut the Mesozoic–Cenozoic Apennine carbonatic

sequences (Accordi 1963; Incoronato et al. 1985; Accordi

and Carbone 1988; Mattei et al. 1993; Giordano et al.

1995). The Roccamonfina volcanics are located in the NE-

trending Garigliano graben, filled by transgressive marine

sedimentary sequence (Ippolito et al. 1973; Watts 1987;

Giordano et al. 1995).

The Roccamonfina composite volcano is made up by

lavas and pyroclastic rocks erupted in three main periods of

activity, which accompanied the formation of the poly

phased summit caldera (De Rita and Giordano 1996).

Volcanic activity begun at 630 ka (Ballini et al. 1989a)

with a phase dominated by leucite-bearing lava flows inter-

bedded to minor ash fall and mud-flow deposits (Fig. 1).

Peripheral dikes and eccentric monogenetic volcanoes

were also emplaced in the area surrounding the volcano (Di

Girolamo et al. 1991).

The formation of the summit caldera sector collapse

marked the passage to the second period of activity (De

Rita and Giordano 1996).

The second period is characterised by plinian paroxistic

volcanic activity between 385 and 230 ka (Luhr and

Giannetti 1987), with the eruption of five main, caldera

forming pyroclastic flow units (Giannetti and Luhr 1983;

Luhr and Giannetti 1987; Ballini et al. 1989b; Cole et al.

1993; Bosi and Giordano 1997; Giordano 1998a, b) that are

the Brown Leucitic Tuff and the succession of the White

Trachytic Tuffs (De Rita et al. 1998).

The third and last period of post-caldera activity spans

between 155 and 50 ka (Cortini et al. 1973; Fornaseri

1985; Radicati di Brozolo et al. 1988). Leucite-free lavas

have been poured out in the form of intra- and peri-caldera

exogenous trachytic domes but small leucite-free mafic

42 Contrib Mineral Petrol (2009) 157:41–63

123

lava flows are also found within the caldera (Cole et al.

1992), and in some final monogenetic parasitic vents on the

flank of the volcano (Fig. 1).

For the purposes of this paper, the first period of activity

at Roccamonfina (630–400 ka) is named hereafter ‘‘pre-

caldera period’’, whereas the following two periods, the

paroxysm (385–230 ka) and the final one (155–50 ka), are

collectively named ‘‘post-caldera period’’.

Samples and analytical techniques

Forty-nine fresh samples representative of the two stages of

activity at the Roccamonfina volcano have been selected

for the present study. Their petrography, together with

sample localities, is reported in Table 1.

Major and trace elements on whole rocks were deter-

mined at the DST of Firenze University using XRF and wet

Volcanic districts (composite volcanoes)

Monogenetic volcano, dykes, hypabissal body

LuMP

RMP

TMP

Lucanian Magmatic Province

Roman Magmatic Province

Tuscan Magmatic Province

Limit of the Apennine front

Position and depth of present-day benioff zone

Cenozoic to present time Withinplate rocksexternal to Apennine-Tyrrhenian system

Aeolian Arc - calc-alkalic volcanoes

LEGEND:

Pietre Nere (70 Ma)

Vulture

Etna

Iblei

Aeolian Arc

Middle Latin Valley

Phlegrean

Roccamonfina

VesuviusIschiaPontine Is.

TMP

Pantelleria

Ustica

LuMP

Euganei (50 Ma)

Linosa

38° 38°

40° 40°

42° 42°

44° 44°

08° 10° 12° 14° 16° 18°

18°

20°

10° 12° 14° 16°

250

350

450

150

LD-RMP

ND-RMP

Pescosansonesco (70 Ma)

inflow

CMP

Fig. 1 Distribution of volcanism in Italy and geological sketch map

of Roccamonfina (redrawn after: Taylor et al. 1979; Cole et al. 1992;

Conticelli et al. 2007). Inset shows the location of the Roccamonfina

Volcano with respect to the rest of the Roman Province and the

definition of the Latian Districts of the Roman Magmatic Province

(RMP-LD) and the Neapolitan District of the Roman Magmatic

Province (RMP-ND). Note that the CMP represent the Corsica

Magmatic Province as defined by Conticelli et al. (2008, in press).

1 Campanian Ignimbrite (erupted from Campi Flegrei caldera at 39 ka),

late phase of post-caldera activity (Vezzara synthem; 155–50 ka),

2 HKCA final lavas, 3 Shoshonitic mafic lava and pyroclastics from

monogenetic centres, 4 Shoshonitic domes, 5 Yellow Trachytic Tuff,

early phase of post-caldera activity (Riardo synthem; 385–230 ka),

6 White Trachytic Tuffs, 7 Teano pyroclastic succession, 8 Brown

Leucitic Tuff, 9 pre-caldera activity Leucite-bearing lava and

pyroclastics (plagioclase leucitites) (Roccamonfina synthem; 630–

385 ka), 10 Mesozoic–Cenozoic pre-orogenic carbonatic-terrigenous

succession; 11 main extensional faults, 12 caldera rim, 13 scoria

cones

Contrib Mineral Petrol (2009) 157:41–63 43

123

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x+

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+P

lg+

Cp

x

+O

p+

Bio

RM

N3

0M

on

teS

anta

Cro

ce4

1�1

70 5

900 N

13

�570 4

300 E

SH

OD

om

eP

orp

hy

riti

c,m

icro

cry

stal

lin

eg

dm

Plg

+C

px

+B

io[r

es]

+O

p+

Plg

+O

p

+C

px

+B

io

RM

N4

2M

asse

ria

San

t’A

nto

nio

41

�180 3

000 N

13

�590 4

000 E

SH

OL

ava

Po

rph

yri

tic,

mic

rocr

yst

alli

ne

gd

mP

lg+

Cp

x+

Bio

[res

]+

Olv

[co

r]+

Op

+P

lg

+C

px

+B

io+

Ga

RM

N1

5N

ear

Mo

nte

Ata

no

41

�170 0

400 N

13

�580 5

300 E

SH

OD

om

eP

orp

hy

riti

c,p

ylo

tax

itic

gd

mP

lg+

Bio

[res

]+

Cp

x+

Op

+O

lv+

Plg

+C

px

+O

p+

Ph

l

RM

N2

1M

on

teL

atta

ni

41

�170 5

900 N

13

�590 0

700 E

SH

OD

om

eP

orp

hy

riti

c,p

ylo

tax

itic

gd

mB

io[r

es]

+P

lg+

Cp

x+

Op

+P

lg+

Cp

x

+B

io+

Op

RM

N2

2M

on

teL

atta

ni

41

�170 5

600 N

13

�590 0

400 E

SH

OD

om

eP

orp

hy

riti

c,p

ylo

tax

itic

gd

mP

lg+

Cp

x+

Bio

[res

]+

Op

+P

lg+

Cp

x

+O

p+

Op

x(?

)

RM

N2

0M

on

teL

atta

ni

41

�180 0

10000 N

13

�580 5

800 E

SH

OD

om

eS

tro

ng

lyp

orp

hy

riti

c,cr

yp

tog

dm

Plg

+B

io[r

es]

+C

px

+O

p+

Plg

+B

io

+C

px

+O

p

RM

N1

3N

ear

Mo

nte

Ata

no

41

�170 0

200 N

13

�580 3

800 E

SH

OD

om

eS

ub

-po

rph

yri

tic,

trac

hy

tic

gd

mS

d+

Cp

x+

Sp

h+

Sd

+P

lg+

Cp

x+

Op

RM

N2

9M

on

teS

anta

Cro

ce4

1�1

70 2

600 N

13

�570 2

000 E

HK

CA

En

clav

eS

ub

-po

rph

yri

tic,

py

lota

xit

icg

dm

Olv

(Ch

r)+

Cp

x+

Plg

+O

lv+

Cp

x+

Op

+G

lass

Po

st-C

ald

era

stag

e,fi

nal

ph

ase

(\1

55

ka)

RM

N3

1M

on

teS

anta

Cro

ce4

1�1

80 0

400 N

13

�580 2

000 E

HK

CA

Sco

riac

eou

s

red

lav

a

Su

b-p

orp

hy

riti

c,g

lass

yg

dm

Cp

x+

Olv

(Ch

r)+

Plg

+C

px

+G

lass

+X

eno

lith

of

Do

me

RM

N3

2M

on

teS

anta

Cro

ce4

1�1

80 0

400 N

13

�580 2

000 E

HK

CA

Fin

alla

va

at

the

ven

t

Po

rph

yri

tic,

vis

icu

lar,

gla

ssy

gd

mO

lv+

Cp

x+

Plg

+O

px

(?)

+P

lg+

Cp

x

+O

lv+

Gla

ss

RM

N3

9C

ian

nem

aie

41

�180 3

500 N

13

�570 5

200 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,m

ycr

ocr

yst

.g

dm

Olv

[id

d](

Ch

r)+

Plg

+C

px

+B

io+

Plg

+C

px

+O

lv[i

dd

]+

gl

RM

N4

1C

ian

nem

aie-

Ro

bet

ti4

1�1

80 4

100 N

13

�580 0

300 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,g

lass

yg

dm

Olv

(Ch

r)+

Cp

x+

Plg

+O

lv+

Cp

x+

Gla

ss

RM

N4

0C

ian

nem

aie-

Ro

bet

ti4

1�1

80 4

400 N

13

�580 1

300 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,g

lass

yg

dm

Olv

[sk

el](

Ch

r)+

Plg

+C

px

+P

lg+

Cp

x

+O

lv+

Gla

ss

RM

N3

7C

ian

nem

aie

41

�180 3

100 N

13

�570 5

900 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,p

ylo

tax

itic

gd

mO

lv(C

hr)

+P

lg+

Cp

x+

Plg

+C

px

+O

lv+

Gla

ss

RM

N3

3P

og

gio

Mo

lara

41

�180 0

800 N

13

�580 2

400 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,g

lass

yg

dm

Olv

(Ch

r)+

Cp

x+

Plg

+P

lg+

Olv

+C

px

+G

lass

RM

N3

4P

og

gio

Mo

lara

41

�180 1

200 N

13

�580 2

800 E

HK

CA

Fin

alla

va

Su

b-a

ph

yri

c,cr

yp

tocr

yst

alli

ne

gd

mO

lv(C

hr)

+P

lg+

Cp

x+

Gla

ss


123

chemical methods. MgO and Na2O were determined by

AAS, FeO by titration (after Shapiro and Brannock 1962),

and LOI gravimetrically. XRF data were corrected for

matrix effects following the methods of Franzini et al.

(1972) for major elements, and that of de Vries and Jenkins

(1971) for trace elements. REE, Ta, Hf, Th, Co, and Sc

were analysed by INAA (DST, Firenze University) fol-

lowing the procedure described by Poli et al. (1977) and by

ICP-MS (ACTLAB). Errors for trace elements are better

that 10% for Co, Sc, Nd, Lu, Tb, and Th, and better than

5% for the other elements. Bias between INAA and ICP-

MS was evaluated using international reference samples as

unknown, and was found to be within the range of ana-

lytical error.

Sr, Nd, and Pb isotopes were analysed at the DST of the

Firenze University following the procedures outlined by

Avanzinelli et al. (2005). Digested rocks solutions were

used for Sr and Nd purification through standard liquid

chromatographic techniques. Sr and Nd isotopic ratios

were measured by thermal ionisation mass spectrometry

(TIMS) using a Thermofinnigan Triton TI in a triple

jumping multi-dynamic mode (Thirlwall 1991; see also

Avanzinelli et al. 2005 for further details). Mass fraction-

ation of Sr and Nd isotopes has been exponentially

corrected with 86Sr/88Sr = 0.1194 and 146Nd/144Nd =

0.7219, respectively. 87Sr/86Srtriple average value for NBS

987 reference sample was 0.710251 ± 12 (2r, n = 70):143Nd/144Ndtriple average value for La Jolla reference sam-

ples was 0.511845 ± 7 (2r, n = 25). Pb was purified

following the method described by Deniel and Pin (2001)

using 100–150 lm Sr-spec resins in quartz fibres micro-

columns. The Pb separation efficiency was evaluated to be

about 97%. Pb samples were loaded onto zone-refined Re

filaments, with addition of 0.5 ll of silica gel and 1 ll of

high-purity H3PO4 and measured in static mode with a

Thermofinnigan Triton TI�; average runs were measured at

1,400�C and yielded *1.5 V of 208Pb. Mass bias was

monitored with repeated measurements of SRM 981 refer-

ence standard and we obtained a mass discrimination

factor (e) of 0.15% per a.m.u. The external reproducibility

of the international reference standard SRM 981 was:208Pb/204Pb = 36.495 ± 23; 207Pb/204Pb = 15.423 ± 7;206Pb/204Pb = 16.888 ± 6; 207Pb/206Pb = 0.91328 ± 15;208Pb/207Pb = 2.3662 ± 4; 208Pb/206Pb = 2.1610 ± 7

(2r, n = 45).

Petrography and geochemistry

Pre- and post-caldera volcanic rocks from Roccamonfina

are distinct in terms of their mineralogy and petrography

(Table 1). Pre-caldera rocks are leucite-bearing with

clinopyroxene and plagioclase ubiquitously present asTa

ble

1co

nti

nu

ed

Sam

ple

Lo

cali

tyL

atit

ud

eL

on

git

ud

eS

erie

sR

ock

typ

e

Tex

ture

Pet

rog

rap

hy

RM

N3

5P

og

gio

Mo

lara

41

�180 1

200 N

13

�580 2

800 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,p

ylo

tax

itic

gd

mC

px

+O

lv(C

hr)

+P

lg+

Plg

+O

lv+

Cp

x

RM

N3

6S

elle

tta

41

�180 2

100 N

13

�580 0

900 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,m

ycr

ocr

yst

.g

dm

Plg

+C

px

+O

lv+

Plg

+C

px

+O

lv+

Op

RM

N0

2C

ian

nem

aie

41

�180 2

600 N

13

�570 4

400 E

HK

CA

Fin

alla

va

Su

b-a

ph

yri

tic,

cry

pto

cry

st.

gd

mP

lg+

Cp

x+

Olv

+O

p

RM

N1

2P

og

gio

Mo

lara

41

�170 0

100 N

13

�580 3

300 E

HK

CA

Fin

alla

va

Su

b-p

orp

hy

riti

c,g

lass

yg

dm

Plg

+C

px

+O

lv+

Plg

+C

px

+O

p

+G

lass

En

trie

sw

ith

inb

rack

ets

are

min

eral

sen

clo

sed

inth

ep

rece

edin

gm

iner

al;

wit

hin

squ

ared

bra

cket

sar

ete

xtu

ral

feat

ure

of

the

min

eral

:re

sre

sorb

ed,

idd

idd

ing

site

d;

inb

old

are

the

ph

eno

cry

sts;

in

ital

ics

and

un

der

lin

edar

eth

ex

eno

cry

sts

HK

Sp

lag

iocl

ase

leu

citi

te,

SH

Osh

osh

on

ite,

HK

CA

hig

h-K

calc

-alk

alin

e,O

lvo

liv

ine,

Ch

rch

rom

ite,

Cp

xcl

ino

py

rox

ene,

Leu

leu

cite

,B

iob

ioti

te,

Plg

pla

gio

clas

e,O

po

paq

ue,

Ap

aap

atit

e,

Gl

gla

ss,

Ga

gar

net

,S

dsa

nid

ine,

Sp

hsp

hen

e


123

phenocrysts, and olivine only in the most mafic members.

Apatite and opaque phases are ubiquitous in the ground-

mass. Resorbed biotite and titanite also occur in the most

felsic samples. These rocks are ultrapotassic and range in

composition from basanite to phonolite (Fig. 2). Foley

(1992a) referred to Italian leucite-bearing rocks as plagio-

clase leucitites to distinguish them from within-plate

leucitites in which Al2O3 is extremely low (e.g. Rogers

et al. 1992, 1998).

Post-caldera rocks are leucite-free, with ubiquitous

clinopyroxene phenocrysts. Different phenocrysts are

present with clinopyroxene depending on the degree of

differentiation: olivine in the most mafic samples, plagio-

clase and biotite in the intermediate to felsic products and

sanidine, often as a megacryst, is restricted to the most

felsic samples along with rare titanite. On the basis of

chemical characteristics and temporal succession, the post-

caldera lavas can be further divided into two groups. The

early post-caldera lavas (400–155 ka) are shoshonitic in

composition and range from basalt to trachyte (Fig. 2a).

The final lavas (155–50 ka) have the lowest total alkali and

K2O contents, at comparable silica, of the entire Rocca-

monfina sequence (Fig. 2). They are sub-alkaline basaltic

andesites (Fig. 2a), that straddle the boundary between the

shoshonite series and High-K calc-alkaline series (Fig. 2b).

Pre- and post-caldera rocks show distinct trends in major

and trace element variation diagrams with MgO (Fig. 3).

Pre-caldera plagioclase leucitites show the highest levels of

K2O, FeO, TiO2, Rb and most of the incompatible elements

contents, and they increase with decreasing MgO contents

(Fig. 3).

Among post-caldera rocks, the final sub-alkaline lavas

(HKCA) have fairly homogeneous MgO contents

(Table 2), whereas early post-caldera rocks (i.e. shosho-

nites) are enriched in SiO2, Na2O, and Nb at comparable

MgO contents (Table 2; Fig. 3).

Small differences are shown on spider diagrams nor-

malised to primordial mantle between pre- and post-caldera

rocks (Fig. 4). Plagioclase leucitites have large peaks at Cs

and Pb, and small one at U and Sr; large through are

present at Ba, Ta, Nb, and Ti, with minor through at Nd, P,

and Hf (Fig. 4). Normalised Ta/Nb is \1. Early post-cal-

dera leucite-free rocks (i.e., shoshonites) have large peaks

at Cs and Pb, but still smaller than those shown by pla-

gioclase leucitites (Fig. 4). Thought at Ta, Nb, and Ti are

shown, with minor ones at Ba, Nd, and P. Normalised Ta/

Nb is variable from \1 to [1. The final post-caldera lavas

(i.e., HKCA), show the smallest peak and through magni-

tudes. Significant differences are shown by disappearance

of Ba through and inversion of the normalised Ta/Nb

values which are [1 (Fig. 4).

A twofold behaviour is also shown by isotopic compo-

sitions (Table 3). Plagioclase leucitites (i.e. pre-caldera)

have the highest initial 87Sr/86Sr (0.70926–0.70999) and

the lowest initial 143Nd/144Nd values (0.51213–0.51217),

respectively (Fig. 5). Little or no variation of initial87Sr/86Sr with decreasing MgO are shown by within either

plagioclase-leucitites of pre-caldera phase or leucite-free

post-caldera rocks (0.70665–0.70745), with final sub-

alkaline lavas intermediate (0.70748–0.70749) between

pre- and post-caldera rocks (Fig. 5). On the whole 87Sr/86Sr

and 143Nd/144Nd of Roccamonfina rocks show a clear

negative covariation straddling the fields of rocks from the

Latian districts (RMP-LD) and the Neapolitan one (RMP-

ND) of the Roman Magmatic Province (Fig. 6). The same

covariation is observed for 208Pb/204Pb, 87Sr/86Sr, and143Nd/144Nd vs. 206Pb/204Pb diagrams (Fig. 7), with

shoshonites showing the highest 206Pb/204Pb (18.924–

19.153) and 208Pb/204Pb (39.084–39.212) values and pla-

gioclase leucitites the lowest 206Pb/204Pb (18.788–18.851)

and 208Pb/204Pb (39.048–39.076) values (Table 3).

Discussion

The origin of the extremely enriched trace element com-

position of Italian potassic and ultrapotassic volcanoes

their fractionated LILE/HFSE and their isotopic signature

has been thoroughly discussed in many studies about Ita-

lian magmatism (e.g. Conticelli et al. 2004; Peccerillo

2005a, for reviews). To briefly summarise the genetic

scenario, Italian magmas in general, and Roccamonfina in

UltrapotassicSeries(HKS)

Shoshonitic Series(SHO)

High-K Calk-alkalicSeries

Calk-alkalic

Tholeiitic Series

A BFig. 2 Classification diagrams,

K2O + Na2O versus SiO2 (total

alkali silica; Le Bas et al. 1986)

and K2O versus SiO2 (Peccerillo

and Taylor 1976), for

ultrapotassic rocks of

Roccamonfina volcano. Note

that data are plotted on a

volatile-free basis


123

particular, have been generated in a sub-continental litho-

spheric mantle, enriched by the addition of crustal material,

recycled probably as sedimentary melts via subduction

(Peccerillo 1985, 2005a, b; Conticelli and Peccerillo 1992).

Silica saturation of ultrapotassic has been controlled by

XCO2during partial melting of the metasomatised mantle

source partial melting (Wendlandt and Eggler 1980a, b). In

this scenario, the CO2-rich component might have been

released during partial melting of CaCO3-rich subducted

marly sediment (Conticelli et al. 2004; Avanzinelli et al.

2008). Then de-volatilisation of CaCO3 sedimentary com-

ponent might provide the CO2 to increase the XCO2and to

provide the necessary CaO to re-fertilise the lithospheric

refractory mantle source. High-flux of CO2, with typical

crustal-derived oxygen isotopic values, has been recorded

in the Roman Magmatic Province (e.g. Bertrami et al.

1990; Chiodini and Frondini 2001; Beaubien et al. 2003).

In addition Conticelli et al. (2002, 2007) have shown that

initial 87Sr/86Sr and 143Nd/144Nd for Roman Magmatic

Province anticorrelate pointing to a crustal reservoir with

the isotopic composition intermediate between those of

shales and limestones. Leucite-bearing rocks from Rocca-

monfina volcano fall along this trend, with isotopic values

typical of leucite-bearing rocks (plagio-leucitites, leuci-

tites, and kamafugites) of the Roman Magmatic Province

but slightly less enriched in radiogenic Sr (Fig. 6).

Previous studies, however, have shown that Neapolitan

ultrapotassic volcanoes (RMP-ND) display clear differ-

ences in many geochemical (Beccaluva et al. 1991) and

isotopic (Peccerillo 2005a, and references therein) tracers

respect with ultrapotassic volcanic rocks belonging to the

northern district of the Roman Magmatic Province (RMP-

LD). The process responsible for this variation is still

matter of debated and it might involves several different

factors, such as: (1) the influence of an asthenospheric

component prior to metasomatism (Beccaluva et al. 1991;

Fig. 3 Differentiation diagrams

for some major (wt.%) and trace

(ppm) elements versus MgO

wt.%. Note that leucite-bearing

and leucite-free rocks plots

along different trends


123

Table 2 Representative chemical analyses of Roccamonfina rocks

Series Pre-caldera: leucite-bearing Post-caldera: leucite-free shoshonites

Sample RMN 44 RMN 18 RMN 46 RMN 45 RMN 43 RMN 11 RMN 14 RMN 09 RMN 16 RMN 04

Number 1 2 3 7 8 12 13 14 15 17

SiO2 46.3 48.2 49.0 50.8 52.6 47.3 47.7 48.2 48.1 51.1

TiO2 0.97 0.89 0.78 0.69 0.58 0.91 0.91 0.82 0.80 0.82

Al2O3 15.3 16.6 19.9 19.9 20.1 15.8 17.0 17.6 17.0 18.6

Fe2O3 4.73 3.99 1.70 3.12 1.32 2.48 3.29 3.57 2.99 3.79

FeO 4.10 4.01 5.70 3.48 3.98 5.96 5.80 5.08 5.96 4.03

MnO 0.15 0.15 0.16 0.17 0.12 0.15 0.16 0.15 0.16 0.14

MgO 6.61 5.78 2.80 1.78 1.75 9.35 8.94 7.10 8.67 5.87

CaO 12.6 10.2 7.64 7.02 5.16 12.1 12.0 11.2 12.4 9.15

Na2O 1.60 1.99 2.67 2.69 2.41 1.32 1.36 1.75 1.68 2.17

K2O 6.63 7.29 8.10 8.65 10.41 1.29 1.86 3.16 1.62 3.41

P2O5 0.62 0.51 0.42 0.37 0.36 0.30 0.27 0.37 0.27 0.31

LOI 0.58 0.76 1.07 0.93 1.01 3.22 0.74 1.14 0.58 0.67

Sum 100.18 100.27 99.90 99.65 99.74 100.11 100.00 100.09 100.11 100.05

Mg–V 62.38 61.46 44.81 37.25 41.54 70.53 68.15 64.23 67.76 62.33

Alk 8.23 9.28 10.77 11.34 12.82 2.61 3.22 4.91 3.30 5.58

Sc nd 29.6 nd nd nd 43.8 31.9 32.7 45.5 26.9

V 312 267 239 228 141 nd nd nd nd nd

Cr 164 154 bdl bdl 3 350 330 313 330 240

Co 34.5 30.6 24.4 14.6 15.4 43 40 39 47 36

Ni 72 54 21 6 11 74 76 56 74 47

Cu 109 nd 40 17 43 nd nd nd nd nd

Zn 83 nd 86 112 85 nd nd nd nd nd

Ga 18 nd 21 21 19 nd nd nd nd nd

Rb 322 345 358 511 606 189 177 191 153 152

Sr 1,784 1,842 1,890 2,190 1,670 819 777 1,152 784 882

Y 38.9 40.0 39.3 39.7 38.4 30 24 30 31 32

Zr 226 255 279 289 256 146 157 157 156 166

Nb 10.5 10.4 10.3 19.5 18.2 16 16 13 16 15

Cs 31.0 36.0 25.1 25.5 46.3 18.0 9.0 9.0 4.0 4.0

Ba 1,460 1,706 1,460 1,450 1,280 841 600 604 594 693

La 105.4 96.3 122.0 134.8 98.3 40.7 44 43.7 27.3 43.6

Ce 210.8 185.0 244.4 258.6 185.1 77 91 87 50 80

Pr 24.9 23.8 24.5 28.3 19.6 nd nd nd nd nd

Nd 90.0 93.0 90.0 97.2 65.5 36 44 42 26 38

Sm 18.4 17.6 16.0 17.4 11.5 7.66 9.29 9.06 6.04 7.70

Eu 3.70 3.50 3.29 3.51 2.31 1.88 2.27 2.03 1.63 1.77

Gd 12.9 12.5 11.1 10.8 7.44 nd nd nd nd nd

Tb 1.81 1.80 1.49 1.59 1.08 0.7 1.0 0.9 0.7 0.8

Dy 7.32 7.05 6.82 6.94 4.82 nd nd nd nd nd

Ho 1.19 1.17 1.18 1.21 0.82 nd nd nd nd nd

Er 2.96 3.14 3.28 3.30 2.33 nd nd nd nd nd

Tm 0.367 0.403 0.448 0.453 0.323 nd nd nd nd nd

Yb 2.16 2.22 2.71 2.80 2.02 1.73 1.88 1.92 1.64 2.33

Lu 0.311 0.320 0.389 0.406 0.292 nd nd nd nd nd

Hf 6.38 5.99 5.83 6.61 4.3 2.8 4.1 3.8 2.8 4.3

Ta 0.54 0.58 0.52 0.91 0.87 0.90 0.35 0.75 0.38 0.81


123

Table 2 continued

Series Pre-caldera: leucite-bearing Post-caldera: leucite-free shoshonites

Sample RMN 44 RMN 18 RMN 46 RMN 45 RMN 43 RMN 11 RMN 14 RMN 09 RMN 16 RMN 04

Pb 50.6 51.5 61.7 71.6 52.3 8.71 8.11 12.9 5.67 16.9

Th 36.7 43.0 47.9 46.3 40.4 7.8 7.5 7.6 4.3 13.0

U 8.68 9.21 11.5 11.4 9.8 1.7 2.3 2.0 1.0 3.3

Series Post-caldera: leucite-free shoshonites Post-caldera: leucite free HKCA

Sample RMN 17 RMN 48 RMN 24 RMN 01 RMN 30 RMN 42 RMN 22 RMN 29 RMN 39 RMN 33 RMN 12

Number 18 19 25 26 28 29 32 35 38 42 47

SiO2 51.1 51.7 54.4 54.4 55.2 55.2 58.0 52.3 52.3 53.4 53.9

TiO2 0.85 0.73 0.73 0.78 0.73 0.69 0.62 0.83 0.80 0.80 0.80

Al2O3 17.4 18.4 18.3 18.8 19.0 19.2 18.7 19.0 19.2 18.6 18.8

Fe2O3 3.49 2.21 2.09 1.45 4.14 1.89 2.86 2.13 1.90 1.92 2.16

FeO 3.54 4.60 4.37 5.04 2.46 4.10 2.60 6.21 6.17 6.09 5.84

MnO 0.14 0.15 0.14 0.15 0.16 0.14 0.13 0.16 0.15 0.15 0.15

MgO 7.76 5.91 3.14 3.54 3.04 2.96 2.68 4.67 4.63 4.44 4.31

CaO 10.1 8.08 7.25 7.53 6.24 6.51 5.57 8.67 8.25 8.58 8.15

Na2O 2.07 2.22 2.86 2.53 2.89 3.04 2.97 2.08 2.18 2.16 2.10

K2O 2.94 4.10 4.93 5.06 4.45 5.24 4.86 2.86 2.99 3.00 2.98

P2O5 0.25 0.24 0.30 0.24 0.24 0.28 0.20 0.18 0.20 0.18 0.17

LOI 0.55 1.68 1.75 1.58 1.36 0.76 0.83 0.88 1.22 0.63 0.57

Sum 100.19 100.06 100.18 101.10 99.86 100.00 100.00 100.00 100.00 100.00 99.90

Mg–V 70.90 65.29 51.30 53.92 50.76 51.70 52.08 54.65 55.20 54.36 53.73

Alk 5.01 6.32 7.79 7.59 7.34 8.28 7.83 4.94 5.17 5.16 5.08

Sc 35.6 nd nd 13.4 nd nd nd nd nd nd 18.6

V nd 201 205 nd 189 195 159 199 212 202 nd

Cr 300 254 14 25 9 14 20 38 37 43 24

Co 35 24.7 20.3 16.4 19.9 19.1 15.2 26.2 25.2 23.8 24.4

Ni 66 51 10 14 11 9 12 14 16 17 14

Cu nd 59 43 nd 51 36 21 30 26 15 nd

Zn nd 61 68 nd 81 69 64 75 93 99 nd

Ga nd 16 19 nd 20 20 19 19 21 19 nd

Rb 132 146 207 153 162 230 188 120 118 132 152

Sr 806 723 1,060 909 898 1,070 773 857 910 892 944

Y 28 35.4 32.0 32 30.8 33.8 31.8 25.3 28.1 26.2 30

Zr 174 150 205 155 199 228 211 128 136 139 151

Nb 9 11.9 16.2 16 16.6 18.4 19.3 10.2 11.0 10.6 10

Cs 5.0 3.67 10.8 nd 4.98 14.4 7.06 7.14 6.62 7.67 nd

Ba 581 630 752 587 656 792 561 561 626 580 572

La 36.5 70.5 63.0 62 53.2 69.0 64.6 37.0 42.0 39.0 42

Ce 67 100.1 128.6 114 108.9 138.4 120.9 78.0 81.9 78.7 71

Pr nd 13.2 13.4 nd 11.2 14.4 12.0 8.34 9.27 8.72 nd

Nd 31 50.4 52.5 49 42.7 55.2 44.5 32.9 36.5 34.1 38

Sm 6.45 9.89 10.5 8.40 8.65 10.7 8.57 6.91 7.44 6.91 7.60

Eu 1.60 2.23 2.40 1.92 1.97 2.45 1.91 1.63 1.69 1.65 1.58

Gd nd 8.30 8.12 nd 6.85 8.11 6.67 5.59 6.05 5.72 6.0

Tb 0.8 1.27 1.21 1.0 1.07 1.26 1.06 0.86 0.94 0.91 0.8

Dy nd 6.10 5.92 nd 5.44 6.15 5.33 4.44 4.83 4.59 nd

Ho nd 1.13 1.08 nd 1.06 1.14 1.04 0.90 0.97 0.90 nd


123

Peccerillo and Panza 1999); (2) variation in the composi-

tion of the metasomatic agent; (3) the presence of a further

metasomatic event in the Neapolitan area (Peccerillo

2005a; Avanzinelli et al. 2008). In this context the Roc-

camonfina volcano has many characteristics, in addition to

geographic position, to represent a key point to solve this

issue. Differently from the northermost Roman Volcanoes

(RMN-LD) at Roccamonfina volcano occur shoshonitic to

high-K calc-alkalic rocks following silica undersaturated

plagioclase leucitites. This shoshonitic volcanism is coeval

to the appraisal and building up of the Neapolitan volca-

noes (RMP-ND) (Conticelli et al. 2004, and references

therein). On the basis of the incompatible trace element and

Sr, Nd, and Pb data (Tables 2, 3) it is clear that Rocca-

monfina shoshonites have many geochemical and isotopic

similarities with Neapolitan shoshonites (RMP-ND),

whereas pre-caldera plagioclase leucitites still fall well

within the geochemical and isotopic field of other ultra-

potassic Roman volcanoes (RMP-LD) (Fig. 7). Boari and

Conticelli (2007) have shown that coeval shoshonites also

occur in the Middle Latin Valley monogenic volcanic field,

few km north of Roccamonfina, associated to plagioclase

leucitites, kamafugites and calc-alkalic magmatism. In that

case extensive detailed studies on fresh rocks have shown

that incompatible trace elements and isotopic characteris-

tics of shoshonites and calc-alkalic magmas from Middle

Latin Valley are not different from those of northernmost

Roman magmas (RMP-LD) and therefore significantly

different from those of the Neapolitan volcanoes (RMP-

ND) (Boari et al. 2008a, in press).

Shallow level differentiation processes

Before tackling any source process, it is necessary to

investigate the effect of shallow level processes. The aim

of this section is not to reproduce or model the evolution of

the magmas in the shallow reservoir of Roccamonfina

volcano, but to evaluate the possibility that the different

series were cogenetic and related one to the other by crystal

fractionation, crustal assimilation, or a combination of both

(AFC).

There is no doubt that pre-caldera and post-caldera

volcanic rocks at Roccamonfina volcano follow distinct

differentiation trends (Fig. 3). Post-caldera leucite free

rocks can be further divided into two groups: the early

post-caldera shoshonitic rocks, and the late post-caldera

high-K calc-alkalic rocks. Low pressure differentiation

processes are then required for modelling the composi-

tional variations within each group of rocks recognised.

Small Sr and Nd isotopic variations with MgO decreasing

are shown within each trend (Fig. 5), indicating that dif-

ferentiation at low pressure of each trend is mainly driven

by either fractional crystallisation (FC) or fractional crys-

tallisation plus contamination (AFC). Post-caldera rocks

with high-K calc-alkaline affinity have Sr and Nd isotopes

intermediate between the plagioclase leucititic samples and

the shoshonitic ones, but closer to the latter (Fig. 5), sug-

gesting a possible derivation from shoshonites through

either AFC or mixing plus crystal fractionation (MFC).

Major element mass balance calculation performed on

pre-caldera leucite-bearing rocks having similar initial87Sr/86Sr (from RMN 44 to RMN 45) has provided at the best

an R2 = 1.1 for a fractionation of clinopyroxene (37.9

vol.%) + leucite (15.6 vol.%) + apatite (2.5 vol.%) +

magnetite (13.5 vol.%). This assemblage is compatible with

modal mineralogy of the choose end members, and is con-

firmed by trace element enrichment factors calculated.

A plagioclase (7.7 vol.%) + clinopyroxene (9.2 vol%) +

apatite (0.73 vol.%) + magnetite (6.9 vol.%) assemblage

(R2 = 0.45) is argued to achieve the composition of the most

evolved rocks at MgO levels lower than 2 wt.% (RMN 43),

but differences in the 87Sr/86Sr and 143Nd/144Nd isotopes

argue for open system processes. AFC does not model the

isotopic composition of the most differentiated plagioclase

Table 2 continued

Series Post-caldera: leucite-free shoshonites Post-caldera: leucite free HKCA

Sample RMN 17 RMN 48 RMN 24 RMN 01 RMN 30 RMN 42 RMN 22 RMN 29 RMN 39 RMN 33 RMN 12

Er nd 3.15 3.08 nd 3.10 3.23 3.13 2.61 2.84 2.61 nd

Tm nd 0.439 0.441 nd 0.441 0.464 0.455 0.368 0.405 0.378 nd

Yb 2.06 2.73 2.84 2.86 2.80 2.90 2.91 2.34 2.48 2.51 2.84

Lu nd 0.405 0.414 nd 0.424 0.426 0.435 0.347 0.373 0.373 nd

Hf 3.5 3.88 5.20 5.3 5.04 5.50 5.14 3.47 3.65 3.72 3.5

Ta 0.50 0.70 0.94 1.07 0.96 1.03 1.06 0.70 0.70 0.70 0.69

Pb 9.90 20.6 22.5 23 25.3 33.5 23.6 17.1 20.0 17.8 15

Th 8.9 12.9 18.6 20 19.1 21.1 21.2 8.8 9.5 9.2 9.7

U 2.7 2.7 5.3 6 5.6 6.0 7.1 2.1 2.2 2.2 2

Major elements have been determined by XRF; trace elements by ICP-MS; when in italic they have been determined by XRF and INAA


123

leucititic sample (RMN 43), whereas it might be explained

by either bulk mixing or mixing plus crystal fractionation

(MFC) between plagioclase leucitites and mafic shoshonites

(Fig. 8).

Shoshonitic rocks show the largest differentiation range

covering the entire MgO spectrum of Roccamonfina

rocks, from trachybasalts to trachytes (Fig. 2). Differen-

tiation occurs with small but significant isotopic variation

suggesting that crystal fractionation plus assimilation

dominated. The differentiation pathways followed by

the0shoshonitic rocks are governed mainly by crystal

fractionation of an assemblage made up by olivine

(4.9%) + clinopyroxene (29.6%) + plagioclase (19.9%) +

magnetite (9.7%) ± biotite and sanidine in the most dif-

ferentiated steps. Applying partition coefficients of

Francalanci et al. (1987) and Foley and Jenner (2004)

AFC has been modelled to account for Sr and Nd isotopic

variations (Fig. 8). According to the geology of the area a

limestone has been taken as contaminant (Mattei et al.

1993; Giordano et al. 1995). In Fig. 8 the AFC modelling

(DePaolo 1981) for Sr/Th versus initial 87Sr/86Sr is

reported. Starting from a mafic parental magmas the entire

trend of shoshonites can be modelled with an r (i.e.

assimilation/crystallisation mass proportions) = 0.2. On

the other hand, it is not possible to derive any plagioclase-

leucititic composition with an AFC process starting from

a mafic shoshonitic end member (Fig. 8).

Regarding late post-caldera leucite-free rocks (HKCA),

they distinctively plot on a further different trend. AFC

starting from a mafic shoshonitic composition does not

account completely for their genesis. In fact an r value

[0.5 is needed (Fig. 8), which would results a far too high

proportion of assimilated material. On the other hand a

mixing process between mafic shoshonite and some pla-

gioclase leucitite magma might account for their genesis.

The possibility of generating such enrichment in the

incompatible trace element contents by crustal assimilation

has been thoroughly discussed and discounted in previous

works (e.g. Conticelli 1998; Murphy et al. 2002). Fur-

thermore, the role of crustal contamination of such

protoliths does not match with the strong degree of silica

undersaturation of ultrapotassic leucite-bearing rocks.

Recently Iacono Marziano et al. (2007) have called for

strong involvement of sedimentary carbonate assimilation

in the Italian rocks to justify the derivation of ultrapotassic

leucite-bearing rocks from shoshonite. This general picture

was already arise by several authors in the early twentieth

century (e.g. Daly 1910; Rittmann 1933) and discounted by

Savelli (1967). On the other hand, Iacono Marziano et al.

(2007), on the basis of experimental data, justify the pas-

sage from shoshonite to either leucititic or plagioclase

leucititic magmas through limestone assimilation plus

clinopyroxene crystallisation. Our calculations (Fig. 8)

clearly show that AFC is an important process in gene-

rating the geochemical and isotopic variation in post-

caldera shoshonitic rocks but cannot reproduce the

transition from post- to pre- caldera products, or vice versa.

Other characteristic of Roccamonfina volcano rocks

argues against such a process. Analogously to Savelli

(1967) we have found that ultrapotassic leucite-bearing

rocks are enriched in incompatible trace elements respect

with leucite-free (i.e. shoshonite and high-K calc-alkaline)

ones, with limestones characterised by the lowest concen-

tration levels (Fig. 9). In addition limestones from

Apennine (Melluso et al. 2003, 2005a, b; Conticelli et al.

2002, 2007, 2008, in press; Boari et al. 2008a, in press)

Fig. 4 Patterns of incompatible trace elements normalised to the

primordial mantle (Sun and Mc Donough 1989) for ultrapotassic

rocks of the Roccamonfina volcano. Element order in the abscissa

follows the increasing compatibility of the elements according to

Hoffman (1996). Note that pre-caldera plagioclase leucitites and post-

caldera leucite-free rocks have similar normalised patterns, but Nb/Ta

values are inverted passing from pre- to post-caldera ones


123

Ta

ble

3S

r,N

d,

and

Pb

iso

top

eso

nre

pre

sen

tati

ve

sam

ple

fro

mR

occ

amo

nfi

na

Sam

ple

87S

r/86S

r

mea

sure

d

2si

gm

a87S

r/86S

r

init

ial

143N

d/1

44N

d

mea

sure

d

2si

gm

a143N

d/1

44N

d

init

ial

206P

b/2

04P

b207P

b/2

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b/2

04P

b

Pre

-cal

der

a;le

uci

te-b

eari

ng

ult

rap

ota

ssic

rock

s

RM

N4

40

.70

95

33

±0

.00

00

07

0.7

09

52

90

.51

21

52

±0

.00

00

03

0.5

12

15

21

8.7

88

15

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93

9.0

48

RM

N1

80

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98

37

±0

.00

00

05

0.7

09

83

40

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±0

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00

05

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71

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23

15

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83

9.0

52

RM

N4

60

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99

91

±0

.00

00

06

0.7

09

98

7n

dn

dn

dn

dn

dn

d

RM

N4

50

.70

98

56

±0

.00

00

07

0.7

09

85

20

.51

21

71

±0

.00

00

04

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17

11

8.8

51

15

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13

9.0

76

RM

N4

30

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92

61

±0

.00

00

07

0.7

09

25

50

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34

±0

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53

9.0

48

Po

st-c

ald

era;

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yp

has

e,sh

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on

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rock

s

RM

N1

10

.70

66

63

±0

.00

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06

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20

.51

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±0

.00

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07

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9.1

53

15

.68

03

9.1

99

RM

N1

40

.70

66

88

±0

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07

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06

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70

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23

59

±0

.00

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09

0.5

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91

9.0

26

15

.66

13

9.1

23

RM

N0

90

.70

67

88

±0

.00

00

04

0.7

06

78

60

.51

23

50

±0

.00

00

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0.5

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01

8.9

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9.0

84

RM

N1

60

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00

03

0.7

06

65

40

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±0

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35

6n

dn

dn

d

RM

N0

40

.70

68

13

±0

.00

00

04

0.7

06

81

20

.51

23

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±0

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03

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34

2n

dn

dn

d

RM

N1

70

.70

67

62

±0

.00

00

04

0.7

06

76

1n

dn

dn

dn

dn

dn

d

RM

N4

80

.70

68

92

±0

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00

07

0.7

06

89

1n

dn

dn

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dn

dn

d

RM

N2

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55

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9.2

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RM

N0

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55

±0

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08

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05

4n

dn

dn

dn

dn

dn

d

RM

N3

00

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70

31

±0

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07

0.7

07

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20

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±0

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dn

dn

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dn

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d

RM

N2

20

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77

±0

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00

07

0.7

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50

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±0

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2n

dn

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has

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cks

RM

N2

90

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03

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±0

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05

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71

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15

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RM

N3

90

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±0

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RM

N3

30

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N1

20

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±0

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2n

dn

dn

dn

dn

dn

d

Init

ial

val

ues

hav

eb

een

calc

ula

ted

on

ages

fro

mli

tera

ture

(Co

rtin

iet

al.

19

73;

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rnas

eri

19

85

;R

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see

tex

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nat

ion


123

have intermediate Sr isotope ratios between plagioclase

leucitites and shoshonitic rocks, precluding any possibility

to derive one from the other by limestone assimilation. It

has been shown indeed, that limestone assimilation by ultra-

potassic magmas has the effect of diluting incompatible

trace elements (Peccerillo 1998, 2005b) due to their

extremely low K and incompatible trace elements contents

(Fig. 9). In addition sedimentary carbonate assimilation

would also modify trace element signature of magmas

imparting extremely high U/Th, which is not observed

(Avanzinelli et al. 2008). By contrast, due to the very low

REE contents, and then of Nd and Pb contents of lime-

stones the trends observed for REE and 143Nd/144Nd and206Pb/204Pb should be the opposite of what observed at

Roccamonfina (Figs. 5, 6).

In summary, the post-caldera MgO-rich leucite-free

magmas, either shoshonitic or high-K calc-alkalic, cannot

represent the parental magma of the entire Roccamonfina

succession. Geochemical and petrographic characteristics

suggest that ultrapotassic plagioclase leucititic magmas and

leucite free magmas, erupted, respectively, during pre- and

post-caldera stages, are not cogenetic and they derive from

different events of partial melting of a variably meta-

somatised upper mantle source.

Origin of ultrapotassic parental magmas

In the light of the above discussion we can safely assume

that the strong fractionation between LILE and HFSE

(Fig. 4) is a primary characteristics of Roman ultrapotassic

leucite-bearing rocks, which has also been observed in

volcanic island arcs where the budget of incompatible trace

elements is clearly dominated by sediment addition (e.g.

Aeolian Arc, Francalanci et al. 1993, 2007; Banda Arc,

Vroon et al. 1993; Sunda arc, Whitford et al. 1979;

Hoogewerff et al. 1997). Depletion of HFSE except Th

(Fig. 4) with respect to LILE is attributed either to the

original fractionation in the sedimentary reservoirs (Fig. 9)

Fig. 5 143Nd/144Nd and initial 87Sr/86Sr versus MgO wt.% for

Roccamonfina rocks

Mafic enclaves in TAP

Tuscan Province

Tuscan Anatectic Province

Apennine Crustal Rocks

Vulture (LuMP)

Pietre Nere

Tyrrhenian Sea Floor

RMP-LD(Latian Districts)

Aeolian Arc RMP-ND(Neapolitan District)

Fig. 6 143Nd/144Nd versus

initial 87Sr/86Sr isotopic

composition for the Italian

potassic and ultrapotassic rocks.

Fields have been drawn on the

basis of data from Conticelli

et al. (1992, 1997, 2002, 2007,

2008, in press), Conticelli

(1998), Pappalardo et al. (1999),

Perini et al. (2004), Avanzinelli

et al. (2008), Boari et al. (2008a,

b, in press) and author’s

unpublished data (e.g., Vulture,

Vesuvius). A blow up of the

inset is reported at the top-righthand side. Symbol size is larger

than analytical error (2r)


123

recycled into the mantle (Plank and Langmuir 1998) or to

retention of Ta, Nb, Hf, Zr and Ti by a residual phase

during recycled sediment partial melting (Nicholls et al.

1994; Elliott et al. 1997). Th is not readily partitioned into

slab-derived fluids, but can be efficiently enriched in the

metasomatising agent via partial melting of recycled sedi-

ments (Johnson and Plank 1999). Also Pb is efficiently

enriched within the mantle wedge by sediment-derived

metasomatism. The high Th/Nb values shown by plagio-

clase leucititic pre-caldera rocks (Fig. 10) are clearly

suggestive of melt dominated subduction component

(Elliott et al. 1997; Plank 2005). Shoshonites, on the other

hand, show a linear decreasing of this ratio, with values\1,

pointing towards the composition of the within plate alkali

basalts of Pietre Nere (PN end member in Fig. 10) in the

Adriatic foreland (Fig. 1).

Production of silica-undersaturated melts (i.e. leucite-

bearing pre-caldera volcanic rocks) is thought to be due

either to extremely high-P partial melting or to partial

melting under extremely high XCO2conditions of a meta-

somatised mantle source. Most of the geochemical and

mineralogical characteristics of Roccamonfina leucite-

bearing rocks are compatible with partial melting of a

modally metasomatised lithospheric upper mantle similarly

to other volcanic fields of the Roman region (i.e., RMP-

LD; Boari and Conticelli 2007; Boari et al. 2008a,

in press). The same holds true for their extreme enrichment

in Al2O3 which is also testified by the occurrence of modal

plagioclase (Table 1). In this scenario, the CO2-rich com-

ponent might have been acquired during partial melting of

CaCO3-rich subducted marly sediment. Then devolatilisa-

tion of CaCO3 component might provide the CO2 for

increase the XCO2and the necessary CaO to refertilise the

lithospheric refractory source, whereas melts from the

silicoclastic components would have enriched in K and

incompatible elements the mantle source of Roccamonfina

magmas. In Fig. 6 it is clear the decoupling between initial87Sr/86Sr and 143Nd/144Nd with Roman Magmatic Province

pointing to a crustal reservoir with the isotopic composition

intermediate between those of shales and limestones.

Leucite-bearing rocks from Roccamonfina volcano fall

Fig. 7 143Nd/144Nd, and initial 87Sr/86Sr versus 206Pb/204Pb isotopic

compositions for the Italian potassic and ultrapotassic rocks (in

colour) with reported data for the Roccamonfina Volcano (black,

white and grey). Data sources Conticelli et al. (1992, 1997, 2002,

2007, 2008, in press), Conticelli (1998), Pappalardo et al. (1999),

Perini et al. (2004), Avanzinelli et al. (2008), Boari et al. (2008a, b,

in press) and author’s unpublished data (e.g., Vulture, Vesuvius).

TMP Tuscan Magmatic Province, RMP-LD Latian Districts of the

Roman Magmatic Province, RMP-ND Neapolitan District of the

Roman Magmatic Province, LuMP Lucanian Magmatic Province, PSPescosansonesco dykes, PN Punta delle Pietre Nere dykes, LMPlamproites, SHO shoshonites, HKCA high-K calc-alkalic, KAMkamafugites, HKS plagioclase leucitites and leucitites

Fig. 8 Sr/Th versus 87Sr/86Sr for the Roccamonfina volcanic rocks

with reported simulation pathways for AFC and bulk-mixing

differentiation models. Lines for AFC refers to r = 0.2 and p 0.5,

respectively. F = Mm/Mo (final volume of magma/initial volume of

magma); r = assimitared/crystallased rate. Partition coefficient used

are after Francalanci et al. (1987) and Foley and Jenner (2004). Note

that AFC with r = 0.2 is able to model the entire shoshonitic trend,

whereas AFC is not able to model the differentiation within

plagioclase leucitites


123

along this trend, with isotopic values typical of leucite-

bearing rocks (plagio-leucitites, leucitites, and kamafugi-

tes) of the Roman Magmatic Province but slightly less

enriched in radiogenic Sr (Fig. 6). Avanzinelli et al. (2008)

focussing attention of the southern Roman Province and

using new Sr and Nd isotopes and U–Th disequilibria

modelled the observed compositional variation of MgO-

rich mafic magmas of Southern Roman Province with the

addition to the mantle wedge of a ‘‘marl’’ subducting

sediment assemblage, estimated as a 50:50 mixing between

the clay- and carbonate-rich components. Given the esti-

mated composition of sediment melts, the authors

calculated that less than 5% of recycled sediments melts is

able to reproduce the Sr–Nd isotope variation of the Roman

Province. Roccamonfina high-Mg plagioclase leucititic

rocks from Roccamonfina fit perfectly this simulation. In

Fig. 12 the plot of 208Pb/204Pb versus 206Pb/204Pb varia-

tions is reported for the entire set of Neogene to Quaternary

rocks of the Italian Peninsula and in particular for the

Roccamonfina volcanic rocks. D-DMM, OIB, and CaCO3-

rich bulk sedimentary components with several different

simulations are also reported (Fig. 12). Focussing attention

on ultrapotassic rocks (plagioclase leucitites), the Rocca-

monfina ones fall well within the field of northern volcanic

district of the Roman Province (RMP-LD). Taking into

account a D-DM mantle on one hand, and a bulk sedi-

mentary component enriched in CaCO3, on the other one,

less than 3–5% of recycled sediments melts is able to

reproduce the Pb isotopic isotope variations of the ultra-

potassic rocks of Roccamonfina volcano, but also of the

RMN-LD portion of the Roman Province (Fig. 12).

Transition from ultrapotassic to shoshonitic magmas

The two major issues that remain the centre of debate,

when Roccamonfina volcano is concerned, are the coex-

istence of ultrapotassic leucite-bearing and shoshonitic

rocks in the same volcano, and the link between this shift in

composition and the overall southward chemical variation

observed in Italian volcanism jumping from the Latian

districts (RMP-LD) to the Neapolitan one (RMP-ND) of

the Roman Magmatic Province.

As outlined in other papers (e.g. Peccerillo 2005a;

Avanzinelli et al. 2008) Neapolitan rocks (RMP-ND)

clearly differs from Latian districts rocks (RMP-LD) in at

least three main features: they have (1) lower Sr and higher

Nd and Pb isotope ratios (Peccerillo 2005a, and references

Fig. 10 Th/Nb versus Ta/Nb for the Roccamonfina rocks. Data fields

for Tuscan Magmatic Province (TMP), Roman Magmatic Province

north of Roccamonfina (RMP-LD), Roman Magmatic Province South

of Roccamonfina (RMP-ND), and Lucanian Magmatic Province

(LuMP) are also reported in colour, as well as values for the Punta le

Pietre Nere (PN) and Pescosansonesco (PS) within plate magmatic

rocks from Adriatic plate. Data Sources Conticelli et al. (1992, 1997,

2002, 2004, 2007, 2008, in press), Conticelli (1998), Pappalardo et al.

(1999), Perini et al. (2004), Avanzinelli et al. (2008), Boari et al.

(2008a, b, in press) and author’s unpublished data (e.g., Vulture,

Vesuvius, Middle Latin Valley)

Fig. 9 Patterns of incompatible trace elements normalised to the

primordial mantle (Sun and Mc Donough 1989) for Apennine crustal

rocks (top) and comparison among the compositions of high-Mg

plagioclase-leucitites (pre-caldera), shoshonites (post-caldera), and

limestone from Lepini Mounts (bottom). Note that limestone have

strongly lower normalised values than volcanic rocks, and different

distributions. Assimilation of limestone plus crystal fractionation of

clinopyroxene starting from the shoshonite would have affected

dramatically U/Th, Nb/Ta, Ce/Pb, and Sr/Nd values, which are not

fractionated by clinopyroxene


123

therein); (2) 238U excess testifying a recent U-enriched

metasomatic event which is not present in the other Latian

volcanic districts (i.e. Avanzinelli et al. 2008); (3) higher

Nb suggesting the involvement of a rather fertile end

member (e.g. OIB pre-metasomatism mantle wedge?—

Beccaluva et al. 1991).

The Roccamonfina volcano is the only volcanic district

where both geochemical and isotopic signatures occur but

temporarily separated. Pre-caldera plagioclase leucitites

(HKS) have compositional and isotopic characteristics

similar to those of the Latian districts (Figs. 10, 11, 12) of

the Roman Magmatic Province (RMN-LD). Post-caldera

shoshonites, on the other hand, have Nd (143Nd/144Nd =

0.512342–0.512382) and Pb (e.g., 206Pb/204Pb = 18.924–

19.153) higher than those of pre-caldera rocks and over-

lapping those of Neapolitan rocks (RMN-ND). Therefore,

we believe it is important to relate the regional shift in the

composition of Italian volcanism with that occurring in the

different phases of the Roccamonfina volcano in order to

make the most of the clues that Roccamonfina volcano

might provide on the overall Italian volcanism. It is clear in

Figs. 7 and 11 that the shoshonitic and the sub-alkaline

basaltic andesitic rocks from Roccamonfina fall always

within the field of Neapolitan rocks (RMP-ND) pointing

towards the composition of Punta Pietre Nere volcanic

rocks, though those of Monte Vulture (Lucanian Magmatic

Province). However, few U–Th isotope data on shoshonites

and sub-alkaline lavas (authors’ unpublished data) show

near equilibrium isotopic composition and no sign of the238U excess characteristic of the Neapolitan region. This

suggests that the recent addition of the U-enriched com-

ponent affecting the Neapolitan region seems not to be

effective beneath Roccamonfina.

The transition from plagioclase leucitites rocks to

shoshonites has to be explained in terms of the general

decrease in incompatible element, the change in Sr–Nd–Pb

isotope and the increase in Nb content (Figs. 10, 11). Two

hypotheses has been proposed to explain this transition: (1)

increasing country rock-vein interaction within the mantle

wedge with increasing contribution of a within plate

Fig. 12 208Pb/204Pb vs. 206Pb/204Pb isotopic compositions for the

Italian potassic and ultrapotassic rocks (in colour) with reported data

for the Roccamonfina Volcano (black, white and gray); for symbols

about Italian rocks see Fig. 7. Data sources Conticelli et al. (1992,

1997, 2002, 2007, 2008, in press), Conticelli (1998), Pappalardo et al.

(1999), Perini et al. (2004), Boari et al. (2008a, b, in press) and

author’s unpublished data (e.g., Vulture, Vesuvius). TMP Tuscan

Magmatic Province, RMP-LD Latian Districts of the Roman

Magmatic Province, RMP-ND Neapolitan District of the Roman

Magmatic Province, LuMP Lucanian Magmatic Province, PS Pesco-

sansonesco dykes, PN Punta delle Pietre Nere dykes. A marlstone has

been taken as the sediment end member (see Avanzinelli et al. 2008

for a thorough discussion). Due to the lack of Pb data on Italian

sediments we used the Pb isotopic composition of sediments

subducting under Sunda arc (Plank and Langmuir 1998) as a proxy;

indeed, the lithologic assemblage subducting under Sunda is made up

by an alternation of limestone and clays, resembling subducting under

Italy. The isotopic composition of Punta Pietre Nere (PN) has been

taken as the within plate component fluxed through slab tearing into

the mantle wedge of the Italian Peninsula. Roccamonfina plagioclase

leucitites samples lie along with other Roman magmas (RMP-LD) on

a mixing curve between D-DMM bulk and Marlstone sediments

(dashed line with crosses). Shoshonites compositions can be repro-

duced by adding to the source of plagioclase leucitites magmas a

variable amount (7–20%, dashed line with dots) of within plate

asthenospheric component. On the contrary, the simple addition of

marlstone sediments to the within-plate astenospheric mantle (dashedline with stars) does not fit the isotope composition of Roccamonfina

shoshonitic rocks

Fig. 11 Zr/Nb vs. 206Pb/204Pb isotopic compositions for the Rocca-

monfina Rocks Data fields for Tuscan Magmatic Province (TMP),

Roman Magmatic Province north of Roccamonfina (RMP-LD),

Roman Magmatic Province South of Roccamonfina (RMP-ND), and

Lucanian Magmatic Province (LuMP) are also reported in colour, as

well as values for the Punta le Pietre Nere (PN) and Pescosansonesco

(PS) within plate magmatic rocks from Adriatic plate. Data sources

Conticelli et al. (1992, 1997, 2002, 2007, 2008, in press), Conticelli

(1998), Pappalardo et al. (1999), Perini et al. (2004), Avanzinelli et al.

(2008), Boari et al. (2008a, b, in press) and author’s unpublished data

(e.g., Vulture, Vesuvius)


123

component from slab tears (Foley 1992b; Conticelli et al.

2002, 2007); (2) partial melting in different mantle wedge

levels (Peccerillo and Panza 1999).

Metasomatism within the upper mantle usually occurs

along the main flow pathways of metasomatic agents.

Reaction between metasomatic agents and the upper

mantle produced a new mineralogy accommodated in a

vein network (Foley 1992b). In the case of ultrapotassic

magmatism vein network is established within the litho-

spheric portion of the mantle (e.g. Mitchell 2006). The

metasomatic mineralogical assemblage has lower melting

point than surrounding upper mantle (Foley 1992b). When

veined mantle is within a mantle wedge at a destructive

continental plate margin and collision come to end, in the

back of the orogen extension brought to isotherms relaxa-

tion. Upraise of isotherms brought to partially melt the vein

network, which has the lowest melting point of the mantle

wedge; further isotherms relaxation brings also the sur-

rounding mantle to melts and then interaction with pure-

vein melt continuously change the composition of the

produced magmas. An increasing diminution of the alka-

line degree of the magmas and therefore of the total

metasomatic signature within the incompatible trace ele-

ment distribution is observed in some alkaline-ultrapotassic

to potassic associations (i.e. Tuscan Magmatic Province,

Conticelli et al. 2007; Trans Mexican Volcanic Belt, Maria

and Luhr 2008) with increasing melting degree and thus

increasing proportions of country rock over vein-mantle.

In the case of Roccamonfina Volcano we observe a

decreasing alkaline degree and total abundance of incom-

patible elements passing from pre-caldera, leucite-bearing

magmas, to early post-caldera, shoshonitic magmas, till

late post-caldera, high-K calc-alkalic magmas (Figs. 2, 4).

All these characteristics are consistent with the process of

increasing interaction proportion of melts from surrounding

mantle with respect to vein melts (i.e. leucite-bearing

magma). Problems arise, however, when we consider the

large variation in Sr–Nd–Pb isotopes, for simple mass

balance reasons. Given the difference in Sr, Nd and Pb

content of the vein and the surrounding depleted mantle

(Sun and Mc Donough 1989), the isotopic composition of

any resulting melt would be strongly dominated by that of

the vein. Higher degrees of melting and thus higher pro-

portion of country rock would dilute the absolute

concentration of those elements, but hardly change the

isotopic composition of the melt. Another problem arises

from the expected isotopic composition of the surrounding

mantle: its low Sr and high Nd isotope ratios, respectively,

would suite the versus of variation in the shoshonites;

however, a depleted mantle is expected to have developed

low U/Pb and Th/Pb and thus to have an unradiogenic

signature, rather than the radiogenic one necessary to

explain the increase in Pb isotopic ratios towards the

shoshonites (Figs. 10, 11). A high 206Pb/204Pb mantle

component could be envisaged only suggesting the mantle

wedge with an OIB signature prior to metasomatism

(Beccaluva et al. 1991). A fertile OIB-like surrounding

mantle would also have higher trace element composition,

and thus potentially more leverage on the mass balance

proportions of elements between vein and country rock, but

more importantly it would bear high Nb concentration

producing the Nb enrichment observed in the post-caldera

shoshonites. This has been found recently in mantle

xenoliths from Eifel volcanic field.

An OIB-like mantle wedge, however, cannot be sug-

gested also for the ultrapotassic (plagioclase leucitites) pre-

caldera rocks, which clearly follow a mixing trend between

a D-DMM and marlstone sediment (Figs. 7, 12). In the

frame of a veined mantle, it could be argued that the

decrease in Zr/Nb in post-caldera rock reflects their lower

proportion of vein to country rock in the ultrapotassic pre-

caldera rocks, but if mantle wedge had an OIB signature

prior to the metasomatism, it is conceivable that this sig-

nature would be at some extent preserved also within the

vein (Fig. 12).

More information can be obtained from the mineral

chemistry of separated phases in other Italian volcanoes.

Cr-spinel inclusions in olivine crystals from Italian volca-

nic rocks (Boari et al. 2008b, in press) have given clues on

the degree depletion of the pre-metasomatism mantle

beneath Italy. Although no such data are available for

Roccamonfina, olivine-spinel pairs from the ultrapotassic

leucite-bearing rocks from the Latian districts (Perini and

Conticelli 2002; Boari and Conticelli 2007), comparable

with pre-caldera rocks, suggest a highly depleted mantle;

on the opposite a more fertile one is suggested by olivine-

spinel pairs measured in the Neapolitan districts volcanic

rocks (e.g. Conticelli et al. 2004), which can be related to

the post-caldera shoshonites.

In summary trace element ratios, such as Zr/Nb, Th/Nb,

and isotopic values all points to the OIB component similar

to Punta Pietre Nere in the Adriatic foreland (Figs. 7, 10,

11, 12); therefore it is argued that an asthenospheric

component with the trace element and isotopic composi-

tions similar to the source of the Punta Pietre Nere magma

is involved in the genesis of the post-caldera shoshonites.

As outlined, earlier the presence of an astenosperic OIB-

like component in the genesis of the southernmost Italian

magmas (i.e. RMP-ND) had been claimed in previous

studies (Beccaluva et al. 1991; Ayuso et al. 1998; Pecce-

rillo and Panza 1999). According to the interpretation of

Peccerillo and Panza (1999) the OIB-like signature of post

caldera magmas could be interpreted with a metasomatised

source within the mantle wedge located at a different,

deeper and thus asthenospheric, level than that of pre-cal-

dera ones, which would be instead located in the


123

lithosphere. Here we propose a slight different interpreta-

tion when the asthenospheric, high Zr/Nb and radiogenic

Pb-isotope component is added to the source of ultrapot-

assic plagioclase leucitites successively to their genesis to

generate shoshonites. In the 208Pb/204Pb versus 206Pb/204Pb

diagram (Fig. 12) Roccamonfina shoshonitc rocks do not

plot on a hypothetic mixing line between the PN end-

member and the sedimentary component as expected if

metasomatism occurred at different mantle levels. Instead,

post caldera mixing trend start directly from the pre-caldera

ones moving away toward the PN component, within a

range of 10 and 20% of an OIB-like component added to

the source of plagioclase leucitites. The fact that the OIB-

like component is recorded late in the history of the Roc-

camonfina volcano we might argue for its late arrival

within the mantle wedge after the caldera formation. This

agree also with the chronological differences within the

Roman Magmatic Province being the Nepolitan volcanoes

(RMP-ND) much younger than those of the Latian Districts

(RMP-LD). The oldest shoshonitic event at Roccamonfina

volcano has been dated at 327 ± 24 ka (40Ar/39Ar per-

formed by M.A. Laurenzi 2006 personal communication),

an age comparable to the beginning of magmatism in the

Neapolitan Area (Brocchini et al. 2001).

In summary all the available data on Roccamonfina

volcano suggest similar surrounding mantle for pre- and

post-caldera rocks, but with an increasingly asthenospheric

component late arrival. This would imply that partial

melting occurs within the mantle wedge under high XCO2to

produce ultrapotassic leucite bearing rocks. The subsequent

arrival of the OIB-like astenospheric component changed

the geochemical isotopic compositions of the mantle

source. In addition it increases also heat flow triggering

larger degrees of partial melting that exhaust the sedi-

mentary-derived CO2 providing magmas under low XCO2

partial melting conditions.

The physical processes responsible for the arrival of

asthenospheric material into the metasomatised mantle

wedge can be discussed in relationship with the complex

geodynamics of the Italian area.

The peculiar arcuate morphology of the slab beneath

the Italian peninsula following the south-eastward slab

retreat (Lucente et al. 1999; Wortel and Spakman 2000)

brought to the formation of ruptures of the downgoing slab

(e.g. Faccenna et al. 2001). This phenomenon induces

small slab tears to large plate windows, which might allow

the inflow of sub-slab asthenospheric mantle. U/Th dis-

equilibria measured on Monte Vulture (Lucanian

Magmatic Province; Fig. 1) have shown that influx of hot

asthenospheric mantle material, undergoing adiabatic

melting, invaded the Southernmost sector of the Italian

Mantle wedge in recent times (\350 ka; Avanzinelli et al.

2008). Monte Vulture volcano is part of the Lucanian

Magmatic Province (LuMP) and is located offset with

respect to the Apennine chain (Fig. 1) just at the edge of

the present day Calabrian Arc, site of the still active

subduction beneath the Aeolian Arc (e.g., Francalanci

et al. 2007, and references therein). This suggests that hot

asthenospheric material from the mantle behind or beneath

the subducted slab enters the mantle wedge from the

north-eastern corner of the Ionian subduction (Mattei et al.

2004). The arrival of sub-slab asthenospheric hot material

through slab tears at Monte Vulture is testified by the

composition of Lucanian magmatic rocks, which are

characterised by intermediate geochemical and isotopic

signatures between mantle wedge and within plate (e.g.

Beccaluva et al. 2002; Downes et al. 2002; authors’

unpublished data). Carbonatites with transitional signa-

tures, between within plate and arc magmatism, are also

found at Monte Vulture volcano (D’Orazio et al. 2007).

Here, oblique upraise of the mantle pierced the slab tears

formed as a consequence of the strong bending of the

Adriatic slab during rolling back (Faccenna et al. 2001).

The proximity of Monte Vulture to the trench and thus the

limited vertical extension of the mantle wedge, makes it

the volcano to be interested to higher extent by the by the

asthenospheric flow.

The trace elements and isotopic data of Roccamonfina,

however, are not as extreme as those of Monte Vulture

(Figs. 8, 9). In addition, Monte Vulture plate-window is far

away from the Roccamonfina volcano. However, Lucente

et al. (1999) have shown the presence of a slab tear also in

correspondence of the Ortona-Roccamonfina lineament

(Fig. 1), which might has acted as a preferential way for

sub-slab asthenospheric mantle influx into the mantle

wedge. Then heating provided by the influx might have

triggered larger partial melting of the mantle wedge.

Conclusion

Roccamonfina volcano is a composite volcano character-

ised by a two stage activity: a pre-caldera period

characterised by leucite-bearing rocks (plagioclase-leuci-

tite, HKS) and a post-caldera period with exclusively

leucite-free shoshonites and sub-alkaline basaltic andesites.

Magmas of each period of activity are not genetically

related to those of the other one. Shoshonites and sub-

alkaline basaltic andesites are not comagmatic with pla-

gioclase leucitites (HKS). Within each period of activity

shallow level differentiation mainly driven by crystal

fractionation with minor crustal assimilation occurred.

Leucite-bearing ultrapotassic magmas have been gene-

rated by partial melting of a metasomatised lithospheric

mantle wedge, where a vein network of modally modified

peridotite after metasomatism has been established.


123

Metasomatic agent is clearly derived from melting and

dehydratation of recycled carbonate-rich sediments.

High-MgO shoshonites and sub-alkaline basaltic ande-

sites have been generated from the interaction between the

lithospheric mantle wedge and an asthenospheric OIB-like

mantle component with very high 143Nd/144Nd,206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, but consistently

lower Zr/Nb and 87Sr/86Sr than original metasomatised

lithospheric mantle wedge.

The most feasible process capable to add a within plate

asthenospheric OIB component within the sub-italian

mantle wedge is influx from slab tears, from the adjacent

area, as shown by tomographic studies.

Acknowledgments We sincerely appreciate Sergio Chiesa, Angelo

Peccerillo, and Piero Manetti for helps and discussions during the first

field campaign in the late 1980s, Alice Farinelli for helps during the

second field campaign in the early new millenium, Lia M Todaro for

help with AAS analyses, Lorella Francalanci for handling INA

analyses on some samples, and at last but not the least Leone Melluso,

Lorella Francalanci, Simone Tommasini, Giampiero E. Poli, and

Angelo Peccerillo for stirring and focusing discussions. Maurizio

Ulivi provided technical support for isotope analyses. Thoughtful

reviews made by two anonymous peer-reviewers greatly improved the

original manuscript. Editorial managing by Tim Grove is greatly

appreciated. Financial support was provided by Firenze-Perugia Ph.D.

consortium during the early field campaign (1986–1987), by FIRB

2001 (grant # RBAU01FX8M_003) for the final field campaign

(2003) and analytical work, and PRIN 2007 (grant #

2007NS22NZ_005), for the final modelling.

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