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90 G. Corti et al.

bated problem. On the basis of petrological, geochemical, and 100
isotopic data, two main processes are competing, i.e., a crystal
fractionation starting from a transitional mildly alkaline basalt 50 Pantelleria
versus partial melting of an alkaline gabbro formed in a rela-
tively shallow magma chamber (Ferrara and Treuil, 1974; Ma-
hood and Baker, 1986; Lowenstern and Mahood, 1991; Civetta Rock / Primordial Mantle
et al., 1998; Avanzinelli et al., 2004). 10
The island of Linosa is much smaller than Pantelleria,
2
~6 km ; it was built up through three main stages of volcanic ac- 5
tivity developed between 1.06 and 0.53 Ma (Lanzafame et al.,
1994) with either submarine or subaerial eruptions. Indeed, the
eruptive activity was characterized by the emission of hydro-
magmatic tuffs, locally palagonitized, and by the construction 1
of tuff rings associated with scoria cones, spatter cones, and lava Rb Th Ta K Ce Pr P Hf Sm Ti Dy Y Yb
Ba U Nb La Pb Sr Nd Zr Eu Gd Ho Er Lu
flows forming a small lava field. In some volcanic centers, one
can observe a transition from hydromagmatic to strombolian ac-
tivity, which produced the ejection of hydromagmatic tuffs
followed by basaltic scorias as the eruption advanced (Rossi 100
et al., 1996). The emitted products are mildly alkaline, scarcely Linosa
evolved rocks; they are dominated by alkali basalts and trachy- 50
basalts. Rare trachyandesites and trachytes are mainly found as
xenoliths in pyroclastic rocks erupted during the oldest stage of
activity (Fig. 8).
The submarine volcanic centers sampled in Adventure Rock / Primordial Mantle 10
plateau and in Graham and Nameless Banks (Carapezza et al.,
1979; Beccaluva et al., 1981; Calanchi et al., 1989) are also 5
characterized by the eruption of scarcely evolved Na-alkaline
products represented by alkali basalts and hawaiites. Only some
basic samples collected by Carapezza et al. (1979) and consid-
ered erupted by Foerstner volcano show Na O ≤ K O.
2 2 1
Overall, the volcanic products erupted in the Strait of Sicily Rb Th Ta K Ce Pr P Hf Sm Ti Dy Y Yb
Ba U Nb La Pb Sr Nd Zr Eu Gd Ho Er Lu
constitute a bimodal sodic, moderately alkaline association. The
basic rocks, alkali basalts and hawaiites, are largely predomi- Figure 9. Primordial mantle-normalized incompatible element dia-
nant, and in many volcanic areas, as on the island of Linosa and grams for selected basalts from Pantelleria and Linosa. Data sources:
Civetta et al. (1998); Avanzinelli (2004). Ocean island basalts pattern
in the submarine volcanoes of Adventure plateau and Graham
(gray line) and normalizing values from Sun and McDonough (1989).
and Nameless Banks, are the only products found. Therefore,
the bimodal compositional distribution of the erupted products
is essentially due to the conspicuous presence of pantellirites,
pantelleritic trachytes, and trachytes outcropping only on the is- aly of Hf and K; the latter has been thought to reflect the pres-
land of Pantelleria. The general petrologic features of the vol- ence of a residual K-bearing phase (mica or amphibole) in the
canism of the Strait of Sicily point to an anorogenic magmatism mantle source (Wilson and Bianchini, 1999).
akin to that found in continental rift areas (Corti et al., 2003).
The trace element distribution is comparable with that observed ANALOGUE MODELING
in intraplate basalts or ocean island basalts. This is well illus-
trated in Figure 9, where primordial mantle-normalized multi- Experimental Set-up
element patterns are plotted for representative basalts from
Linosa and Pantelleria and compared with the pattern of ocean Analogue modeling was used to investigate the structural
island basalts. Even if the trace element patterns are similar in pattern resulting from interaction between two coeval distinct
the two islands, the basalts from Pantelleria display higher geodynamic processes, namely compression with a superim-
contents of incompatible trace elements compatible with their posed orthogonal extensional regime. Experiments were per-
relatively more evolved character; in fact, the Mgv (i.e., Mg/ formed in the Tectonic Modeling Laboratory of the CNR-IGG
+
+
(Mg Fe2 ) atomic ratio) of Pantelleria basalts varies between [AQ1] (Consiglio Nazionale delle Richerce–Instituto di Geo-
50 and 53, whereas in Linosa it ranges between 69 and 76. It is scienze e Georisorse) settled at the Earth Sciences Department
worth noting that all the samples exhibit a slight negative anom- of Florence University (Italy). Models with dimensions of 40 cm