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Fig. 1 I. Line G-37 showing one of the contractional structures seen in the previous figure. Contraction was active in the early stage of basin
formation. The tie with line G-69 is shown by the triangle. See Fig. 3 for location.
Line INVO-7 (Fig. 9) shows the ES in a position characterized by opposite dip of the main extensional
where no main boundary faults are present. The faults. Therefore, half grabens along the axis of the
major feature displayed is a large anticline located at basin show altemation of the dip of the main bound-
the basin centre. The geometry of reflections sug- ing fault. Contractional structures are widely present
gests that this anticline is due to contractional reacti- within the basin infill; some of them seem to reacti-
vation of a previous extensional fault. This contrac- vate previous extensional faults and their geometries
tional episode acted for a limited amount of time closely resemble those obtained by analogue mod-
during the basin filling although a recent reactivation elling on basin inversion (McClay and Buchanan,
is likely, as shown by the sea-floor topography. At 1992). Hence, inversion tectonics (Letouzey, 1990)
the southern margin of the basin (Fig. 10) a large- occurred within this basin. In the WS, contractional
scale NE-SW-trending contractional fault affects the stmctures trend about NE-SW, perpendicular to the
basin sediments and has been active until Recent basin axis, and were formed early during the basin
time. Within the basin, an early contractional stmc- evolution. On the other hand, the ES presents con-
ture can be obsewed (Fig. 10). This strutture is best tractional structures with variable trends, but mainly
seen on line G-37 (Fig. 111, perpendicular to the parallel to the basin axis, and with different age of
previous one, and trends almost parallel to the basin activity; some of these structures have been active
axis (Fig. 4). until Recent time.
6. Discussion and conclusions Large-scale inversion structures affecting the
Neogene extensional basins of the peri-Tyrrhenian
The INVO-2 basin, located on top of the Egadi area have been reported (Trincardi and Zitellini,
FTB, was formed by a set of mainly NW-SE- and 1987; Argnani and Trincardi, 1991; Bartoie et al.,
NNW-SSE-trending extensional faults that produced 1991; Torelli et al., 1991) and, in addition, field
two subbasins (WS and ES). These subbasins are analysis of meso-stmctures in the Neogene Tuscan
comparable, in size and thickness of their sedimen- basins has allowed to recognize small-scale contrac-
tary infill, to the Neogene extensional basins located tional events that punctuated the extensional tecton-
on top of the Northem Apennines (Mariani and ics (Boccaletti et al., 1991, 1992). However, the
Prato, 1988; Bossio et al., 1992; Keller et al., 1994) INVO-2 basin presents a higher degree of stmctural
and along the eastem and southem Tyrrhenian mar- complexity, so far not reported elsewhere.
gins (Fabbri et al., 1981).
In contrast to the other extensional basins super-
Both the WS and ES are divided into sub-areas posed on top of the Apennine-Maghrebian fold-
and-thrust belt, where the main boundary faults par-
alle1 the thmst directions. the INVO basins trend
