Structural framework and crustal characteristics of theSardinia Channel Alpine transect in the central Mediterranean
Attilio SulliDepartment of Geology and Geodesy, University of Palermo, Via Archirafi 26, 90123 Palermo, Italy
Received 13 January 2000; accepted 28 January 2000
Abstract
The submerged area located between the Sardinia Channel and the western Sicily offshore has been investigatedbased on deep crustal and conventional seismic lines with the aim of illustrating the relationships between the crustand its overlying crystalline and sedimentary thrust wedge. Analyses of seismic attributes and reflector pattern,supported by dredge hauls, also provided data in areas where stratigraphic and lithologic control is absent. Crustalgeometries, tectonic processes and timing of the deformation are discussed here.
North of the Elimi chain (central Sardinia Channel ) the reflecting body consists of superposed tectonic wedges ofcrystalline rocks and their Meso-Cenozoic carbonatic and terrigenous cover (Sardinian and Kabilian–Calabrian units).The Kabilian–Calabrian units overthrust the Maghrebian–Apenninic units along the Drepano thrust front (Elimichain), which is traceable on-land in eastern Sicily (Nebrodi–Peloritani Mountains). This lineament roots on thecrustal–mantle discontinuity, where the local superposition of two different crusts occurs. The thrust front of thecrystalline Kabilian–Calabrian units marks the boundary between thick-skinned and thin-skinned tectonics in the chain.
1. Introduction of a submerged segment of the Alpine collisionalbelt. This belt is believed to develop along theAfrica–Europe plate boundary (Bellon et al., 1977;The study region located between Sicily,Channell et al., 1979; Dercourt et al., 1986) andSardinia and Tunisia (Figs. 1 and 2) is a key arealinks the African Maghrebides with Calabria andto understanding the geological framework of thethe Apennines. In the central Mediterranean threecentral Mediterranean, because of the occurrencemain tectonic elements mark the submergedaccretionary wedge (Fig. 3): (a) foreland area,
* E-mail address: [email protected] located in the Sicily Channel; (b) Plio-Pleistocene
Fig. 1. Tectonic sketch of the central Mediterranean: 1, Sardinian units; 2, Kabilian–Calabrian units; 3, Apenninic–Maghrebian units;4, foreland; 5, areas with superimposed extension; 6, Plio-Quaternary volcanoes.
Fig. 2. Location map of the study area, showing the morphology of the Sardinia Channel, northwestern Sicily offshore and Straitsof Sicily.
foredeep, partly buried by the nappe front in the from internal to external, of the Sardinian belt,the Kabilian–Calabrian belt and the Apenninic–central southern Sicily offshore; (c) complex chain,
thrust towards the east and south-east, consisting, Maghrebian units.
323A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 3. Structural map of the Sardinia Channel–Sicily Straits area constructed on the basis of the reflection seismic lines (modifiedfrom Catalano et al., 1996): 1, main thrust fronts; 2, thrusts; 3, strike–slip faults; 4, structural axes; 5, normal faults. (a) Front ofthe Apenninic–Maghrebian submerged basinal units. (b) Egadi thrust front. (c) Belice thrust front. (d) Sciacca thrust front. STF:Sardinia thrust front; DTF: Drepano thrust front; ETF: Egadi thrust front.
Previous studies, based mainly on seismostrati- $ the mechanism and timing of the overthrust ofthe Kabilian–Calabrian units and Apenninic–graphic analysis, described the sector of the chain
developing between Sardinia and Sicily (Section 4). Maghrebian units.Nevertheless, very little information has been avail-able until now on deep crust and its mutualrelations with the overlying chain. New deep 2. Physiographyseismic reflection profiles (Italian CROP line9423), together with a reinterpretation (Sulli, 1996) The main morphological and topographic fea-
tures occurring in the Sardinia Channel areof multichannel seismic lines (AGIP, OGS), pro-vided new information on the main crustal charac- described here in order to illustrate the physiogra-
phy of the study area (Fig. 2).teristics (geometry, thickness, depth of theMoho, etc.). In the southern sector of the study area a
widespread continental slope (from −200 toSeismic facies analysis, calibrated by dredges,well and outcrop data, supported by geophysical −1000 m deep) drops down from the Sicilian shelf
and is linked to the western prolongation of thedata, sheds light on some open problems such as:$ the geometry and structural style of the crust Tyrrhenian basin, where the depth exceeds 2000 m.
In this borderland slope some seamounts andbetween southern Sardinia and north-westernSicily; basins occur. The north-western Sicily offshore, an
indented continental shelf interrupted by canyons$ the geometry and deformation style of the crys-talline bodies north of the Elimi Chain (Fig. 2); related to morphodynamic and tectonic events,
324 A. Sulli / Tectonophysics 324 (2000) 321–336
merges southwards with the shallow-water (Rehault et al., 1987), such reflectors may beAdventure Bank. This sector is separated from the considered as associated with the crust–mantleTunisian platform by narrow deep-water areas discontinuity (Moho).(Sicily Straits), joined to the southernmost 2. Facies B is characterized by a transparent layerPantelleria and Malta basins. Towards the north, limited upwards by a group of high-amplitude,the Egadi valley divides the Egadi shelf from the high-frequency reflectors with good lateral con-Skerki Bank, a morphological high stretching from tinuity. The seismic fabric of this portion isthe Tunisian platform towards the NE. typical of the lower crust (Ponziani et al., 1995;
In the central part the Scuso Bank, a N–S- Barchi et al., 1998).trending morphological high, separates the 3. Facies C is characterized by high to mediumTrapani basin in the west from the Erice basin to amplitude, variable frequency and very highthe east. Westwards, a widespread morphological velocity, topped by a strong reflector. Theflat, between −300 and −600 m deep, occurs, seismic signal is discontinuous and often cov-interrupted by the Elimi chain and by small basins ered by diffraction effects. We associate thisand isolated morphological highs. facies with crystalline basement rocks or, gen-
Northward the SW–NE-trending Elimi chain is erally, with the upper crust.a widespread submarine (volcanic, carbonatic, 4. Facies D is topped by a reflector with highmetamorphic) belt that reaches tops between −600 amplitude and velocity, while the internaland −100 m, and crops out to the east, in the reflectors have low frequency and variable lat-Ustica Island. The Elimi chain bounds to the south eral continuity. Internal geometries are regularthe Cornaglia terrace, a flat area occurring between over wide areas. The signal refers to thick-−1000 and −2000 m, passing northwards to the bedded carbonate platform rocks, in agreement>2500 m deep Cornaglia basin. with Anselmetti and Eberli (1993), and is con-
firmed by well calibrations.5. Facies E shows reflectors with intermediate
3. Data setamplitudes and velocities, and high frequency.This signal, which is homogeneous but notThe data set used here is a dense grid ofcontinuous, was correlated to thin-beddedmultichannel seismic profiles (Fig. 4), integratedpelagic carbonates and marl successions.by a crustal line, at places calibrated by strati-Similar seismic facies has been found in thegraphic and geophysical data (seismic refraction,adjacent western Sicily (Catalano et al., 1998a),heat flow, gravimetry, magnetic anomalies). Thesewhere it is calibrated by well data.data have provided the basis for a reinterpretation
6. Facies F is characterized by discontinuous andof the seismic facies and geometries of the struc-non-homogeneous horizons, with alternation oftural edifice.high and low amplitude, high frequency andThere is little borehole controlled, stratigraphiclower velocity. This facies corresponds toand chronological data in the investigated area.coarser clastic and argillaceous successions.The analysis of seismic attributes and the reflector
7. Facies G shows very continuous reflectors, withpattern, compared with well-calibrated seismichigh amplitudes and velocities; it is known todata (Catalano et al., 1996; Sulli, 1996), made itbe representative of evaporitic horizons (hori-possible to distinguish several seismic facies thatzon M in the Messinian evaporites).were able to estimate the lithology and geometry
8. Facies H is represented by low-amplitude andof the reflecting body (Fig. 5). The main facies arehigh-frequency reflectors, with very low velocityreported here for the sake of information:and good lateral continuity, generated by Plio-1. Facies A is characterized by high-amplitude,Pleistocene sandy and marly successions.low-frequency reflectors; it is found at greatSequence stratigraphy methods have been useddepth, with poor lateral continuity. As a result
of comparison with refraction seismic data for the analysis of these deposits, taking into
325A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 4. Grid zone C and G seismic reflection lines of Minister of Industry of Italy and of CROP line and location map of dredgehauls (modified from Antonelli et al., 1991) and some commercial borehole drills. Dredge symbols: A, Quaternary–Upper Miocenerocks and volcanics; B, Lower Miocene–Oligocene flysches; C, Eocene–Upper Jurassic deep marine carbonates; D, Liassic shallowplatform carbonates; E, Upper Triassic deep marine shales and carbonates; F, Hercynian-type crystalline rocks.
account the chronostratigraphic scheme of the Colombi et al., 1973) where Recent magmaticbodies (Ustica to Aceste volcanic complexes), anddepositional sequences of the Plio-Pleistocene
marine record of the central Mediterranean crystalline rocks of the Sardinian and Kabilian–Calabrian units, as well as the thinned continental(Catalano et al., 1998b).crust, give higher anomalies. Low heat flow valuesare known from the southern Sardinia Channel,whilst the northern zone is characterized by higher4. Previously available dataheat flow (Della Vedova et al., 1984; Hutchinsonet al., 1985). The low-frequency magnetic anoma-4.1. Geophysicslies in the Elimi chain (AGIP, 1981) could berelated to a shallow basement (4–5 km), as wellGeophysical data, collected in the past by sev-
eral authors, has provided some information on as to discontinuities of the structural framework(Terdich, 1984).the crustal characteristics of the Sardinia Channel.
Seismic refraction data (Steinmetz et al., 1983;Recq et al., 1984; Duschenes et al., 1986; Rehault 4.2. Structural setting and stratigraphyet al., 1987) point out that the depth of the Mohoincreases from 10 km in the Tyrrhenian basin, to In the study area (Figs. 3 and 6) the most
elevated portions of the tectonic stack (Sardinian30–35 km towards Sardinia and Sicily.Gravity anomalies are fairly high over the whole units) override the Kabilian–Calabrian units
(Barbieri et al., 1984) in the Cornaglia areaSardinia Channel (Morelli and Finetti, 1973;
326 A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 5. Main seismic facies types observed on seismic profiles (see text).
(Catalano et al., 1985; Torelli et al., 1985; Catalano stacking above the Apenninic–Maghrebian unitsis believed post-Burdigalian (Beccaluva et al.,et al., 1989; Antonelli et al., 1991). The Kabilian–
Calabrian stack is represented by a pile of tectonic 1986). The thrust front can be observed at thesouthern escarpment of Mt. Drepano (Elimi chain)units of mostly crystalline rocks, covered by
Tertiary terrigenous successions and Plio- and is buried beneath the Plio-Pleistocene fillingof the Trapani basin (Agate et al., 1993). The rolePleistocene clastic and pelagic sediments (Catalano
et al., 1989; Compagnoni et al., 1989). Their of extensional tectonics, invoked by some authors
327A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 6. Interpretative geological cross-section (Catalano et al., 1996). G and C with relative numbers indicate seismic profiles crossingthe geological section.
(Tricart et al., 1990; Torelli et al., 1992) as respon- stratigraphy appears comparable with rocksoutcropping in westernmost Sicily. The Neogenesible for the crustal thinning in this area, is a
matter of debate. terrigenous deposits locally exhibit affinities withthose of the Tunisian offshore (Antonelli et al.,The Apenninic–Maghrebian units, seaward
extension of the Sicily chain (Catalano et al., 1989), 1991).are believed to be a thick tectonic body made upof several embricate units progressively overthrust-ing east- and south-eastward the foreland units 5. Description of data(Catalano et al., 1985, 1989; Antonelli et al., 1991).They originated from the Neogenic deformation The interpretation of the Italian CROP profile
(shown as a line drawing in Figs. 8 and 9), togetherof the Mesozoic–Tertiary basin and carbonateplatform rocks that have been correlated with with the reinterpretation of AGIP multichannel
seismic lines contributed to integrate previousthe Pre-Panormide, Imerese, Panormide andTrapanese units outcropping in north-western Sicily investigations (Catalano et al., 1989; Tricart et al.,
1990; Torelli et al., 1992; Sulli, 1996). The collected(Catalano et al., 1985; Antonelli et al., 1991). Inthe Apenninic–Maghrebian belt two main tectonic data yields information on the whole crust and on
the attitude and location of the Moho discontinu-elements can be distinguished, that contain anumber of genetically related thrust systems ity. It sheds light on the paleogeography and the
tectonic evolution of the area.(Catalano et al., 1996). The inner tectonic elementincludes tectonic units emplaced essentially duringthe Miocene; at sea it develops from Elimi chain to 5.1. The Cornaglia areaEgadi area. The outer tectonic element, deformedduring Tortonian–Pleistocene, occurs in the area The transition from the Algerian–Provencal
oceanic crust to the Sardinian continental crust isbetween the Egadi Islands and the Sicily Channel.The submerged sedimentary succession (Fig. 7) expected to take place in the western Cornaglia
terrace (Fig. 2). The reduced crustal thicknessconsists of Triassic–Lower Liassic carbonate plat-form deposits overlain by Jurassic–Paleogene sea- (around 15–20 km) and the occurrence of layered
reflectors in the lower crust (Fig. 8) are characteris-mount and slope-to-basin, marly and sandycarbonates, in turn unconformably covered by tics which denote, according to Meissner and
Kuznir (1987), a thinned continental crust. In theNeogene foredeep deposits (Pre-Panormide andTrapanese domain Auct.). As shown in Fig. 7, the Cornaglia basin the contact between the Sardinian
328 A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 7. Stratigraphy and facies domains of Sicily offshore (time scale according to Harland et al., 1990).
Fig. 8. Line drawing of the deep seismic profile (CROP) between the Algerian–Provencal Basin and the Cornaglia area.
crystalline body and the underlying Kabilian– basement, covered by a very thin sedimentaryveneer, appears strongly deformed.Calabrian stack corresponds to the overlap of
lower continental crustal levels on rocks of the Close to the Elimi chain (Fig. 2), the crust isabout 28 km thick. It consists of a stack of crystal-upper crust. Consequently the crust is thick up to
around 25 km. In the above-mentioned sector the line units, superposed on sedimentary deformed
329A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 9. Line drawing of the deep seismic profile (CROP) where crustal geometries and relationships between the Kabilian–Calabrianand the Apenninic–Maghrebian units are shown. B, crystalline basement. LC, top of lower crust. M, Moho discontinuity.
rock bodies pertaining to the Apenninic– indicates that the continental crust of this sector isalso thinned (Fig. 9). In turn the crystalline wedgeMaghrebian chain (Figs. 9 and 10). The superposit-
ion of the crystalline basement on the Apenninic– is overlain by duplexes with seismic characteristicsof pelagic successions that form an embricate fanMaghrebian units (platform carbonate thrusts) is
shown in Fig. 10. The layering of the lower crust with locally complex geometries (Fig. 10). The
Fig. 10. The seismic section shows, from the top, some thin layered (basinal ) thrust wedges forming a multiduplex structure (Tb)with its roof complex (CT). It overlies thick crystalline thrust sheets (KT) overthrusting in turn platform imbricates (Tp). Key: PP,Plio-Pleistocene deposits; CT, terrigenous deposits; Tb, top of the basinal carbonates; Tp, top of the platform carbonates; KT,crystalline units.
330 A. Sulli / Tectonophysics 324 (2000) 321–336
overlying Tertiary deep-sea arkosic turbidites of et al., 1986), underwent a reactivation, accordingto a ‘thrust envelopment’ geometry, which involvedAquitanian–Early Burdigalian age are here interpre-
ted as the roof thrust of the duplex systems. the basement after the Messinian. Fig. 9 shows howthe Messinian reflector plunges under the Kabilian–Seismic profiles do not reveal prominent exten-
sional structures related to negative tectonic inver- Calabrian tectonic wedge, whilst the Plio-Pleistocene basin filling is deformed in the lowersion (as claimed by Tricart et al., 1990; Torelli
et al., 1992). Neither listric normal faults nor part, where inversion tectonic structures occur. Theprogression of the deformation is ‘in sequence’, asthrust plane inversion in normal faults are visible
in our seismic lines. Furthermore growth struc- deeper levels are involved in more internal areas(Bally et al., 1985). This peculiarity is common totures, as well as large basins, are absent in the
Neogene–Quaternary successions. Crustal thin- other areas near the Sicilian mainland (Catalanoet al., 1998a) and seems to be linked to post-ning therefore appears to be mostly an inherited
geometry, which predates the orogenic stage. Miocene tectonics that modified the morphotectonicsetting of the area. On the whole the pre-MessinianThe Drepano thrust front (Fig. 3) is the tectonic
boundary between Kabilian–Calabrian units and tectonic transport exhibits a SE vergency, as pointedout by the NE–SW-trending thrust fronts (Fig. 11).Apenninic–Maghrebian units. It is traceable at
depth, where it also displaces some crustal reflectors The compressional post-Messinian features have ageneral SSE transport direction. NW–SE right-(Fig. 9), accounting for the partial overlap of the
‘Sardinian’ crust on the ‘Alpine’ crust. This front, lateral strike–slip movements cut off the main frontin several discrete portions (Fig. 11).considered to be Middle Miocene in age (Beccaluva
Fig. 11. Geological structural map of the study area.
331A. Sulli / Tectonophysics 324 (2000) 321–336
5.2. From the Elimi chain to the western Sicily mentary bodies. The carbonate platform rampsare separated by variably thick clastic deposits,offshoreprobably Tertiary in age. Shape, geometry andseismic characteristics well differentiate these struc-The Apenninic–Maghrebian chain (Fig. 3)
develops southeastwards from the Drepano thrust tures from the overlying stacked duplexes of thinlylayered bodies with acoustic characteristics offront toward the western Sicily offshore. It appears
as a strongly deformed sedimentary thrust stack, Mesozoic pelagic carbonates (Catalano et al., 1996;Sulli, 1996).which is clearly detached from the crystalline base-
ment (Fig. 9). The underlying crust, apparently The highest deformed units in the reflectingbody consist of clastics, recognized as Numidiannot deformed, is bounded by a fairly deep Moho
that dips to the north (Fig. 9). The basement lies or equivalent syntectonic terrigenuous deposits(Fig. 12), originally filling the foredeep of theat about 15 km, while the thickness of the whole
crust reaches about 25 km. Kabilian–Calabrian chain. Similar rocks occurwestward also in the La Galite Archipelago andFrom NW to SE the chain shows four main
embricate fans bounded by the Inner Maghrebian, on Skerki Bank (Fig. 2), where Numidian nappesoverlie Mesozoic–Eocene deep-water marly car-Egadi, Belice and Sciacca thrust fronts (respec-
tively a, b, c, d in Fig. 3). These thrust fronts face bonates which, in turn, overthrust Triassic evapo-rites and shallow-water carbonates (Tricart et al.,sedimentary basins filled by progressively more
recent foredeep deposits. 1993).In the study area the stack of basinal carbonatesInternal geometries of the inner sector of this
chain are well represented in Figs. 12 and 13 where and Numidian units override carbonate platformrock units (Fig. 12) through the Inner Maghrebianthe structural edifice shows from the bottom: (a)
fairly inclined carbonate platform thrust sheets; thrust front (a in Fig. 3).In the above-mentioned inner sector the reflect-(b) thinner pelagic carbonate nappes; and (c) a
stack of folded and thrust thick terrigenous sedi- ing body points out that the basement has a depth
Fig. 12. The seismic section shows from the top: roof complex of Numidian Flysch terrigenous successions, overlying a duplex wedgeof interpreted basin-type carbonates, in turn overthrust on carbonate platform units. Key: M, Messinian horizon; FN, NumidianFlysch; Tb, top of basinal successions; Tp, top of platform carbonates.
332 A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 13. NW–SE-trending seismic profile shows, between 8 and 5 s (twt), some strong reflectors interpreted as carbonate platformtops of deeper thrust which underlie duplexes of interpreted basin-type rocks and tectonic slices of terrigenous deposits (Numidianor equivalent Flysch roof-complex) (modified after Catalano et al., 1996; Sulli, 1996). Plio-Pleistocene sediments partly cover theMessinian (M ) reflector. FN, Numidian Flysch; Tb, top of basinal successions; Tp, top of platform carbonates.
of about 6–7 s/twt as confirmed by the multichan- Syn- and post-Messinian low-angle normalfaults gave rise to wide basinal areas linked to thenel seismic line of Fig. 13. In this area the crust
has the greatest thickness (about 35 km) of the opening of the Tyrrhenian sea (Fabbri et al., 1981;Kastens et al., 1988). The Pliocene–Pleistocenewhole chain.
The chain developing from Egadi to Adventure basin filling appears to be deformed by extensionalgrowth faulting, later affected by tectonic inversionBank consists of a 12 km thick fold and thrust
belt overlying a 25 km thick crust. (I in Fig. 17). The latter event is possibly relatedto a change in the stress field implying compressionThe main structural features are shown in
Figs. 14 and 15, where only stacks of carbonate along a N–S stress axis (Catalano and Milia,1990). Recent high-angle and high-throw normalplatform units occur. Basin-derived and Numidian
deposits nappes disappear south-eastwards in the faults point to extensional tectonics in the area,maybe due to the crustal isostatic response to theEgadi area.
The carbonate ramps are bounded by the Egadi emplacement of the tectonic edifice.thrust front that faces the Upper Tortonian fore-deep basins filled by clastic deposits. Also thisfront appears deformed and thrust south-eastward 6. Tectonic evolutionby a younger deformational event (Fig. 16).
The vergence of the chain, generally south- In the central Mediterranean, the deformationstarted after the collision of the Sardinia islandeastward directed, was modified by variously dip-
ping post-Messinian thrust planes (Oldow et al., arc with the African margin. Thrusting began inthe Late Paleogene–Early Miocene, with the1990) and Plio-Pleistocene strike–slip positive
structures. internal imbrication of the Sardinian and
333A. Sulli / Tectonophysics 324 (2000) 321–336
Fig
.14.
Seis
mic
line
show
ing
the
arra
ngem
ent
ofth
eA
penn
inic
–Mag
hreb
ian
unit
s.
Fig
.15.
Seis
mic
line
show
ing
the
over
thru
stof
Mar
etti
mo
unit
onF
avig
nana
unit
inth
eE
gadi
Isla
nds
offsh
ore.
334 A. Sulli / Tectonophysics 324 (2000) 321–336
Fig. 16. NW–SE seismic line shows in the Egadi thrust front area a tectonic wedge of mainly carbonate platform thrust units overlyingthe Trapanese-type carbonate units, covered by Miocene foreland basin deposits. Key: M, Messinian horizon; TV, Terravecchia Fmdeposits (Lower Messinian–Upper Tortonian); mLM, Middle to Lower Miocene marls; Tp, top of carbonate platform rocks.
Fig. 17. The seismic line shows Plio-Pleistocene deposits affected by inversion tectonics (I ) and unconformably covered by morerecent sediments.
Kabilian–Calabrian crystalline units. Their The decoupling and internal imbrication of theApenninic–Maghrebian element started in theemplacement above the Apenninic–Maghrebian
carbonate successions occurred during the Early Early Miocene and developed mostly duringSerravallian–Tortonian times. DeformationMiocene. The already formed chain and the related
main thrust front were then affected by compres- reached first the original basinal domains and laterthe carbonate platform embayment of the Africansional tectonics occurring after the Messinian.
Their NW-trending dissection by right-lateral continental margin (Catalano et al., 1996).According to the crustal data illustrated here, thesestrike–slip faults, during the Upper Pliocene–
Pleistocene, is believed linked to dextral lateral domains could grow on thinned continental crust.Deformation and internal imbrication occurredwrenching.
335A. Sulli / Tectonophysics 324 (2000) 321–336
with the detachment of both carbonate and clastic– a post-Messinian thrust envelopment deformation,marks the discontinuity between the internal thick-terrigenous cover throughout regional subhorizon-skinned part of the chain to the NW and the thin-tal surfaces. The bodies separated by these surfacesskinned external chain to the SE.formed superposed duplex levels. The geometry of
The chain, between the Elimi ridge and offshorethe thrust fronts (Figs. 3 and 11), from theSicily, is an embricate fan of sedimentary rocks,Cornaglia area to the Sicily offshore, points outwhose thrust planes root on the not involvedthe swinging of the transport direction trend fromAfrican crystalline basement.SE to ESE.
The African crust is 25–30 km thick, a lowerThe Upper Oligocene–Burdigalian terrigenousvalue than expected. The extensional structures dosuccessions (Numidian and equivalents) filled thenot appear significant in order to reduce originalforedeep of the Sardinian and Kabilian–Calabriancrustal thickness. As a consequence, it is suggestedchain (Fig. 9). These deposits were deformed ashere that most of the crustal thinning was inheritedroof thrust of the carbonate duplexes and emplacedfrom the Mesozoic Tethyan rifting.south-eastward over more external domains after
the Langhian (Fig. 12). The Numidian nappes didnot overpass the Egadi thrust front. In the outer
Acknowledgementssector younger foredeep clastics (Lower to MiddleMiocene) were stacked progressively south-eastward.
Many thanks to R. Catalano for constructivePost-Messinian high-angle thrusts dissected thediscussions, A.W. Bally for suggestions on theMiocene thrust embricates, reactivating or cross-structural setting, and to the reviewers for theircutting previous fault planes (Oldow et al., 1990),useful comments. Thanks also to S. Merlini andwith an in-sequence thrust envelopment. Pliocene–to ENI-AGIP for providing us with CROP andLower Pleistocene syntectonic basins later devel-commercial seismic profiles. This work has been
oped in the frame of Tyrrhenian opening. funded by CNR 96-98 (R. Catalano).
7. Discussion and conclusions References
The submerged Alpine–Apenninic chain,Agate, M., Catalano, R., Infuso, S., Lucido, M., Mirabile, L.,
between Sardinia and the Elimi ridge, exhibits Sulli, A., 1993. Structural evolution of the Northern Sicilystrongly deformed crystalline basement, with frag- continental margin during the Plio-Pleistocene. In: Max,
M.D., Colantoni, P. (Eds.), Geological Development of thements of both the lower and the upper crustSicilian–Tunisian Platform. UNESCO Report In Marineoccurring in the high levels of the chain. ThrustScience 58, 25–30.
surfaces can be followed down to deep crustal AGIP, 1981. Italia: carta magnetica. Anomalie del campo mag-levels, and somewhere they affect the crust–mantle netico residuo (scala 1:500.000). Thesis Attiv. Min. Direz.
Espl. Idrocarburi, Met. Appl. Geofis., S. Donato Milanese.interface. Duplex made up of crystalline and sedi-Anselmetti, F.S., Eberli, G.P., 1993. Controls on sonic velocitymentary units occurs in the southern part of the
in carbonates. Pageoph 141, 2–4, 287–323.inner chain. Antonelli, M., Franciosi, R., Pezzi, G., Querci, A., Ronco, G.P.,
The Moho discontinuity, very shallow in the Vezzani, F., 1991. Paleogeographic evolution and structuralsetting of the northern side of the Sicily Channel. Mem. Soc.Algerian–Provencal sector, where oceanic crustGeol. It. 41, 141–157.occurs, is still shallow in the Cornaglia area, where
Bally, A.W., Catalano, R., Oldow, J., 1985. Elementi di tetton-thinned continental crust has been recognized. ica regionale. Pitagora Editrice, Bologna. 276 pp.No significant extensional deformation is Barbieri, F., Cornini, S., Marchetti, F., Morlotti, E., Terdich,
P., Torelli, L., 1984. Geological investigations in the Sar-observed which can explain the shallow Moho;dinia Channel area: preliminary results. Acta Naturalia del-therefore we suspect that the crust was alreadyl’Ateneo Parmense 20, 117–207.thin in pre-orogenic times.
Barchi, M., Minelli, G., Pialli, G., 1998. The CROP03 profile:The Drepano thrust front, a late Miocene a synthesis of results on deep structures of the Northern
Apennines. Mem. Soc. Geol. It. 52, 383–400.in-sequence progressive contractional feature, with
336 A. Sulli / Tectonophysics 324 (2000) 321–336
Beccaluva, L., Morlotti, E., Torelli, L., 1986. Notes on the geol- Smith, A.G., Smith, D.G., 1990. A geologic time scale 1989.Cambridge University Press, Cambridge. 263 pp.ogy of the Elimi chain area (southwestern margin of the
Hutchinson, I., Von Herzen, R.P., Luoden, K., Sclater, J.G.,Tyrrhenian sea). Mem. Soc. Geol. It. 27, 213–232.Jemseck, J.P., 1985. Heat flow in the Balearic and Tyrrhen-Bellon, H., Coulon, C., Edel, J., 1977. Le deplacement de laian Basins, Western Mediterranean. J. Geophys. Res. 90,Sardaigne: synthese de donnees geochronologiques, mag-685–701.matiques et paleomagnetiques. Bull. Soc. Geol. Fr. 19,
Kastens, K., et al., 1988. ODP Leg 107 in the Tyrrhenian sea:825–831.insights into passive margin and back-arc basin evolution.Catalano, R., Milia, A., 1990. Late Pliocene–Early PleistoceneGeol. Soc. Am. Bull. 100, 1140–1156.structural inversion in offshore Western Sicily. In: Pinet, D.,
Meissner, R., Kuznir, N.J., 1987. Crustal viscosity and theBois, C. (Eds.), The Potential of Deep Seismic Profiling forreflectivity of the lower crust. Annal. Geophys. 5B (4),Hydrocarbon Exploration. Technip, Paris, pp. 445–449.365–374.
Catalano, R., D’Argenio, B., Montanari, L., Morlotti, E., Tor-Morelli, C., Finetti, I., 1973. Geophysical exploration of the
elli, L., 1985. Marine geology of the NorthWest Sicily off- Mediterranean sea. Boll. Geofis. Teor. Appl. 24 (96),shore and its relationships with mainland structures. Boll. 263–344.Soc. Geol. It. 104, 207–215. Oldow, J.S., Channel, J.E.T., Catalano, R., D’Argenio, B.,
Catalano, R., D’Argenio, B., Torelli, L., 1989. From Sardinia 1990. Contemporaneous thrusting and large-scale rotationsChannel to Sicily Strait. A geologic section based on seismic in the western Sicilian fold and thrust belt. Tectonics 9and field dataThe Lithosphere in Italy. Acc. Naz. dei Lincei, (4), 661–681.Atti dei Convegni Lincei 80, 109–127. Ponziani, F., De Franco, R., Minelli, G., Biella, G., Federico,
Catalano, R., Di Stefano, P., Sulli, A., Vitale, F.P., 1996. Paleo- C., Pialli, G., 1995. Crustal shortening and duplication ofthe Moho in the Northern Apennines: a view from seismicgeography and structure of the central Mediterranean: Sicilyrefraction data. Tectonophysics 252, 391–418.and its offshore area. Tectonophysics 260, 291–323.
Recq, M., Rehault, J.P., Steinmetz, L., Fabbri, A., 1984. Amin-Catalano, R., Franchino, A., Merlini, S., Sulli, A., 1998a.cissement de la croute et accretion au centre du Bassin Tyrr-Assetto strutturale profondo della Sicilia centro-occidentale.henien d’apres la sismique refraction. Mar. Geol. 55,In: Atti 79th Congr. Naz. Soc. Geol. It, 257–260.411–428.Catalano, R., Di Stefano, E., Infuso, S., Sulli, A., Vail, P.R.,
Rehault, J.P., Moussat, E., Fabbri, A., 1987. Structural evolutionVitale, F.P., 1998b. Sequence and system tracts calibrationof the Tyrrhenian back-arc basin. Mar. Geol. 74, 123–150.on high-resolution bio-chronostratigraphic scheme: the
1983. A 550 km long Moho traverse in the Tyrrhenian seaPaleontol. Mineral., Spec. Publ. 60, 155–177. from O.B.S. recorded Pn waves. Geophys. Res. Lett. 10
Channell, J.E.T., D’Argenio, B., Horvath, F., 1979. Adria, the (6), 428–431.African promontory, in Mesozoic Mediterranean paleoge- Sulli, A., 1996. Evoluzione geologica del Canale di Sardegna eography. Earth-Sci. Rev. 15, 213–292. dell’offshore della Sicilia occidentale. Analisi sismostrati-
Colombi, B., Gieze, P., Luongo, G., Morelli, C., Riuscetti, M., grafica e strutturale. Ph.D. Thesis, Palermo, 167 pp.Scarascia, S., Schutte, K.G., Stowald, J., De Visentini, G., Terdich, P., 1984. Geologia del Canale di Sardegna (Tirreno1973. Preliminary report on the seismic refraction profile sud occidentale). Tesi di laurea, Universita di Parma.Gargano–Salerno–Pantelleria. Boll. Geofis. Teor. Appl. 15 Torelli, L., Cornini, S., Marchetti, F., 1985. Seismic stratigraphy(59), 225–254. and tectonic–structural setting of the Sardinia Channel
(Western Central Mediterranean). In: Galson, D.A.,Compagnoni, R., Morlotti, E., Torelli, L., 1989. Crystalline andMueller, S. (Eds.), Proc. II EGT Workshop, ESF, 241–246.sedimentary rocks from the scarps of the Sicily–Sardinia
Torelli, L., Tricart, P., Zitellini, N., Argnani, A., Bouhlel, I.,trough and Cornaglia Terrace (Southwestern TyrrhenianBrancolini, G., De Cillia, C., De Santis, L., Peis, D., 1992.Sea): paleogeographic and geodynamic implications. Chem.Une section sismique profonde de la chaıne Maghrebides–Geol. 77, 375–398.Appennins, du bassin tyrrhenien a la platform pelagienneDella Vedova, B., Pellis, G., Foucher, J.P., Rehault, J.P., 1984.(Mediterranee centrale). C.R. Acad. Sci. Paris II 315,Geothermal structure of the Tyrrhenian Sea. Mar. Geol.617–622.55, 271–289.
Tricart, P., Zitellini, N., Torelli, L., De Angelis, Bouhlel, H.,Dercourt, J., et al., 1986. Geologic evolution of the Tethys belt
Creuzot, G., Morlotti, E., Ouali, J., Peis, D., 1990. La tec-from the Atlantic to the Pamirs since the Lias. Tectonophy- tonique d’inversion recente dans le Canal de Sardaigne:sics 123, 241–315. resultat de la campagne MATS 87. C.R. Acad. Sci. Paris II
Duschenes, J., Sinha, M.C., Louden, K.E., 1986. A seismic 310, 1083–1088.refraction experiment in the Tyrrhenian sea. Geophys. J. R. Tricart, P., Torelli, L., Bouillin, J.P., Rekhiss, F., Argnani, A.,Astron. Soc. 85, 139–160. Brancolini, G., De Santis, L., Peis, D., Zitellini, N., 1993.
Fabbri, A., Gallignani, P., Zitellini, N., 1981. In: Geological Structure and Neogene dynamics of the Northern Tunisiaevolution of the peri-Tyrrhenian sedimentary basins. Tecno- margin. In: Max, M.D., Colantoni, P. (Eds.), Geologicalprint, Bologna, pp. 101–126. Development of the Sicilian–Tunisian Platform. In:
UNESCO Report In Marine Science 58, 71–76.Harland, W.B., Armstrong, R.L., Cox, A.V., Craig, L.E.,
