Page 7 - Corti_2006

Coexisting geodynamic processes in the Sicily Channel 89

Noto has a more northerly azimuth than Lampedusa. This dif- of Plio-Pleistocene age (Calanchi et al., 1989). Historic activity
ferent trend generates extension between the two GPS sites. took place in the nineteenth century close to Pantelleria. On
Computing the relative motion of the NOTO station relative to Graham Bank, in A.D. 1831 a submarine volcano was con-
a fixed LAMP, the estimated rifting rate is v = (1.556 ± 0.800) structed at a depth of ~200 m, giving rise to an ephemeral island
rel
mm/yr with a northeastern direction (Fig. 7). This confirms ~65 m above sea level named Foerstner volcano. This volcano
the coexistence of the two presently active tectonic settings of erupted again in 1863. The youngest eruptions of the region took
a northwest-southeast-directed compression and a northeast- place in 1891 ~5 km northwest of Pantelleria, where a subma-
southwest-oriented extension in the same area. rine volcanic eruption was recorded (Washington, 1909), and in
Calculations of the strain rate field from the GPS data con- 1941 at the Pinne Marine Bank at the southeastern wedge of
firm the northeast-directed extension in the Sicily Channel rift- Graham Bank, where emissions of gases were observed (Cara-
ing system (Hollenstein et al., 2003). Dextral shear strains were pezza et al., 1979; Imbò, 1965).
2
observed only on faults trending oblique to the regional stress Pantelleria, with its 83 km of surface area, represents the
fields; this component of movement can be a result of the obliq- largest extent of emerged volcanic rocks of the Sicily Channel;
uity of fault segments to the regional extension direction (e.g., they were erupted between 0.324 and 0.003 Ma (Mahood and
Corti, 2004). Hidreth, 1983; Civetta et al., 1998). The structure of the island
is dominated by two nested calderas (Mahood and Hidreth,
VOLCANISM IN THE SICILY CHANNEL 1983). Several tens (~40) of volcanic centers have been recog-
nized in and around the caldera structures: they are composed of
In the Sicily Channel, volcanic activity is concentrated pyroclastic cones, domes, and cinder cones (Villari, 1974; Orsi
mainly on the islands of Pantelleria and Linosa. Minor subma- et al., 1991). The volcanological and structural evolution of the
rine volcanism took place in Adventure plateau and in Graham island is considered an expression of the occurrence of small
and Nameless Banks. The oldest products have been found in a magma reservoirs at shallow depths (Mahood and Baker, 1986).
submarine volcanic seamount located eastward of Nameless The erupted products show an alkaline to peralkaline affinity
Bank, where hawaiitic dredged samples gave a K-Ar age of 9.5 and consist mainly of alkali basalts, hawaiites, trachytes, and
± 0.4 Ma (Beccaluva et al., 1981). However, the climax of the peralkaline trachytes to peralkaline rhyolites (pantellerites). The
volcanism occurred during the Pleistocene on the islands of volcanic association is typically bimodal, with the evolved rocks
Linosa and Pantelleria; the volcanic centers recognized in Ad- largely dominant (more than 95% of the outcropping materials)
venture plateau (Anfitrite and Tetide) are also considered to be (Fig. 8). The genesis of peralkaline-evolved rocks is still a de-

1 4

12

10
Figure 8. Total alkali silica diagram for
volcanic rocks from the Strait of Sicily.
Classification grid from Le Maitre
8 (2002). Dividing gray line between al-
kaline and subalkaline fields taken
from Irvine and Baragar (1971). Data
6 sources: Barberi et al. (1969); Villari
(1974); Carapezza et al. (1979); Becca-
luva et al. (1981); Mahood and Baker
4 (1986); Calanchi et al. (1989); Esper-
ança and Crisci (1995); Rossi et al.
(1996); Civetta et al. (1998); Prosperini
2 et al. (2000); Bindi et al. (2002);
Avanzinelli (2004).
0

Linosa Foerstner Vocano
Pantelleria Submarine volcanic centres
(Adventure Bank, Nameless Bank)