The Liguride Complex of Southern Italy —a Cretaceous to Paleogene accretionary wedge
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Tectonophysics, 142 (1987) 217-226
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
The Liguride Complex of Southern Italy -a Cretaceous to Paleogene accretionary wedge
STEVEN D. KNOTT
Department of Earth Sciences, University of Oxford, Parks Road, Oxford OXI 3PR (Great Britain)
(Received March 25, 1986; revised version accepted January 1, 1987)
Knott, SD., 1987. The Liguride Complex of Southern Italy-a Cretaceous to Paleogene accretionary wedge.
Tectonophysics, 142: 217-226.
The ophiolite-bearing allochthonous flysch (Liguride Complex) of the Southern Apennines, Italy, has traditionally
been divided into two tectonic units: the metamorphic Frido Unit and the unmetamorphosed Cilento Unit. The two
units have hitherto been considered to derive from two distinct paleogeographic domains; however, the identification of
Cilento Unit sediments within Frido Unit successions implies that the sediments of both units were coeval deposits
within the same sedimentary basin. Cilento Unit sediments also occur as the sedimentary cover of kilometre-scale
oceanic slices within the Liguride Complex indicating deposition on oceanic basement and not continental basement as
was previously considered. Thrust transport directions and sediment provenance indicate that during Late Jurassic time
this ocean basin lay to the east of the Calabrian terrain and to the west of Apulia, Calabria and Apulia representing the
European and African margins of Neotethys respectively. Northwestwards subduction of oceanic crust beneath the
Calabrian terrain from Late Cretaceous time onwards produced an accretionary wedge which was later emplaced onto
the Apulian margin during the Burdigalian collision of Calabria and Apulia. The Liguride Complex represents the
abducted remains of this accretionary wedge.
This interpretation contains three important implications for pre-Tertiary plate tectonic reconstructions of the
western Mediterranean region, these are:
(1) The Calabrian continental terrain formed part of the Iberian Plate on the north margin of Neotethys, this may
have implications for the former location and continuation of the North Pyrenean Fault.
(2) The existence of a continuation of the Eo-Alpine belt through Calabria and the Kabylies is placed in doubt
thus requiring only one, constant polarity (NW-dipping) subduction direction to explain the structures now seen in
(3) The existence of a transform fault between the Europe-vergent structures of Corsica and the Africa-vergent
structures of Calabria. This transform must have been active from at least Late Cretaceous time in a position now
occupied by the Tyrrhenian Sea.
The Calabrian Arc (Fig. l), Southern Italy, can
be divided into three major tectonic elements. The
lowest element consists of thrust sheets of
carbonate sediments, originally deposited upon
the continental margin of Apulia, and now for-
ming the Apennine mountain chain (Scandone,
1979). Tectonically overlying this element is an
ophiolite-bearing allochthonous flysch which, in
the Southern Apennines, is known as the Liguride
Complex (Ogniben, 1969). The upper-most
tectonic element consists of thrust slices of con-
tinental basement with or without a Mesozoic
This sequence of tectonic elements is consid-
ered to be a remnant of the Eo-Alpine chain of
European vergence which was later thrust east-
0040-1951/87/$03.50 0 1987 Elsevier Science Publishers B.V.
Fig. I. Geologic map of Southern Italy and Sicily.
wards onto the Apennine domain in Late Tertiary time (Alvarez, 1976; Amodio-Morelli et al., 1976). In the most recent synthesis of Calabrian geology (Bonardi et al., 1982) the Liguride Complex was divided into the Frido Unit and the Cilento Unit each unit being derived from a different sedimen- tary basin, the former was situated upon Tethyan oceanic crust on which sedimentation commenced in Early Cretaceous time, the latter was situated upon the Apulian continental margin with deposi- tion commencing in Early Paleogene time.
The aim of this paper is to show that the Liguride Complex, including the Frido Unit and the Cilento Unit, represents the remains of a single ocean basin which originally lay between the Calabrian and Apulian terrains, was deformed by subduction-accretion processes and was finally emplaced onto the Apulian margin during the Neogene. The structure of the paper shall be to review the previous work on the Liguride Com- plex, present new structural and sedimentological data and finally to discuss the implications of this data and their interpretation to plate tectonic re- constructions of the western Mediterranean re- gion.
The Liguride Complex has been divided by Amodio-Morelli et al. (1976) into three tectonic units, the Frido Unit, the Cilento Unit and an ophiolite unit (Fig. 2).
The Frido Unit includes the Frido Formation of Vezzani (1969) and is roughly equivalent to the flysch ar~lloso-filladi~o of Ippolito and Lucini (1957) the flysch fillonitico of Cotecchia (1958) the flysch a quartzites of Caire et al (1960) and also the argillitico-quartzoso-calcareo flysch of Selli (1962). This unit is composed of weakly foliated shale, slate, talc-schist and quartz-arenite. In the Southern Apennines the Frido Unit is associated with kilometre-scale masses of con- tinental and oceanic crust. Figure 2 shows the extent of Frido Unit outcrops within the Southern Apennines. The age of the Frido Formation according to Vezzani (1969) is Neocomian to Ap- tian. However, Scandone (in Amodio-Morelli et al., 1976) identified Globotruncana sp. in Frido
Fig. 2. Geologic map of the Southern Apennines including the
region involved in this study. M-Timpa delle Murge,
P -Timpa Pietrasasso, T-Monte Tumbarino.
Formation shales from the Cilento area (Fig. 1)
suggesting a Late Cretaceous age.
Vezzani (1969) and Ogniben (1969) state that
the Frido Formation in the Southern Apennines
lies stratigraphically below the Crete Nere Forma-
tion (the oldest formation of the Cilento Unit).
Amodio-Morelli et al. (1976), however, state that
the two are separated tectonically by fragments of
an ophiolite unit and the Polia-Copanello base-
ment unit, and are therefore not in stratigraphic
contact. In the Calabrian Coastal Chain to the
west (Fig. 1) the Frido Unit is situated tectonically
beneath the ophiolitic Malvito, Diamante-Ter-
ranova and Gimigliano Units, and above Apen-
nine carbonate rocks of the Verbicaro and San
Donato Units (Amodio-Morelli et al., 1976).
The metamorphism of the Frido Unit within
the Southern Apennines is considered to be very
low, on the border between greenschist facies
metamorphism and diagenesis (Amodio-Morelli et
al., 1976). However, Lanzafame et al. (1979)
recognise high pressure/low temperature lawso-
nite-albite to incipient glaucophane schist facies
assemblages within this part of the Frido Forma-
tion. The latter authors and De Roever (1972)
distinguish true glaucophane schist facies assemb-
lages within outcrops of the Frido Unit in the
Calabrian Coastal Chain.
According to Amodio-Morelli et al. (1976) the
Cilento Unit belongs to a group of allochthonous
units of uncertain paleogeographic position and
lies tectonically above the Frido Unit.
The Cilento Unit comprises three sedimentary
formations. The oldest, the Crete Nere Formation
consists of black shale, quartz-arenite, calcarenite
and calcilutite, of Aptian to Albian age (Vezzani,
1968). The overlying Saraceno Formation consists
of calcarenite and calcilutite with occasional
volcaniclastic sediments of Middle to Late Eocene
age (De Blasio et al., 1978). Unconformably overlying both these formations is the Albidona
Formation which comprises conglomerate and
quartz-arenite of Late Oligocene to Burdigalian
age (Zuppetta et al., 1984) and contains two
laterally continuous calcilutite beds occasionally
reaching 50 m in thickness. The conglomerates of
the Albidona Formation contain boulders which
have been derived from the Calabrian continental
terrain (Zuppetta et al., op. cit.).
Various interpretations of the relationships be-
tween the tectonic units mentioned above and the
ophiolitic rocks have been suggested within the
literature. Dietrich and Scandone (1972) and
Amodio-Morelli et al. (1976) both consider that
the ophiolites belong to a tectonic unit distinct
from the Frido Formation, and that the latter is
the sedimentary cover to an oceanic basement not
yet recognised. Bousquet (1973) assigned the
ophiolite sedimentary cover to the Timpa delle
Murge Formation and stated that it is this for-
mation and not the Frido Formation which lies
stratigraphically beneath the Crete Nere Forma-
tion (cf. Vezzani, 1968), suggesting that the Cilento
Unit was deposited on the ophiolitic sequence.
Lanzafame et al. (1978) recognised a stratigraphic
continuity between the ophiolite sedimentary cover
and the overlying Crete Nere Formation and they
further suggested that this sedimentary cover lay
within a basin with an ophiolitic basement. In a
subsequent paper (Spadea et al. 1980) however,
the same authors stated that the relationship be-
tween the ophiolites and the sediments of the
Cilento Unit was still debated. (The ophiolites
of the Southern Apennines and Calabria are all
incomplete and dismembered and should really be
classed as disrupted oceanic slices following the
recommendation of the ophiolite Penrose Con-
ference (Conference Participants, 1972).
The present study was carried out within an
area situated in the region of Basilicata, Italy at
the northern extremity of the Calabrian Arc (Fig.
Kilometre-scale oceanic slices crop out to the
east of Monte Pollino at Timpa delle Murge,
Timpa Pietrasasso and Monte Tumbarino (Fig. 2).
At each of these localities serpentinite (c. 15 m
thick), gabbro (c. 20 m), basalt dykes (rare), pillow
lavas (40 m) and sedimentary cover (10 m of
pelagic limestone and ribbon radiolarite) are ex-
posed. Detailed mapping around the base of Timpa
delle Murge and Timpa Pietrasasso (Fig. 3) was
carried out to determine the nature of the contact
between the slices and the underlying material.
At Timpa delle Murge a southward-dipping
shear zone (c. 200 m wide) lies beneath the slice,
separating it from underlying pelitic schists of
Early Cretaceous age. Within the shear zone a
number of diverse hthologies display moderate to
intense ductile deformation. The upper part of the
shear zone contains tectonised serpentinite derived
from the oceanic slice above. Beneath the
serpentinite sheet is a tectonic slice of granite
surrounded by a foliated granite envelope. Defor-
mation gradually increases away from the unde-
formed granite core with undeformed granite
augen becoming smaller and more diffuse until
eventually minor shear zones within the foliated
granite become so pervasive that the lithology is
entirely mylonitic displaying no original igneous
texture in thin-section. Beneath the granite and
serpentinite sheet lie pelitic schists and deformed
calcarenite and quartz-arenite. Well-bedded sedi-
CR ET E N E A E F 0 R hi A T I 0 N m BASALT h GAEERO
m SHEAR ZONE
a APENNINIC IJNfT
- QEOLOGICAL BOUNDARY
- THRUST N tt-_
0.*.-O TRAVERSE 500m f
TIMPA OELLE MURGE
Fig. 3. Geologic map and cross-section of the Timpa delle Murge and Timpa Pietrasasso oceanic slices.
ments belonging to the Crete Nere Formation occur below and outside the shear zone, and these appear to be the less deformed equivalents of the schists and metasediments found within the shear zone.
At Timpa Pietrasasso (Fig. 3) a similar south- ward-dipping shear zone occurs below an oceanic slice comprising ribbon radiolarite, basalt, gabbro and a serpentinite thrust sheet containing frag- ments of granite, amphibolite, talc-schist and basalt. The serpentinite sheet is superposed tecton- ically above calcarenite of Late Cretaceous age belonging to the Crete Nere Formation which contain abundant calcite veins. Immediately to the north of the serpentinite sheet the strike of adjac- ent Crete Nere Formation bedding becomes paral- lel to the shear zone margin. Figure 3 shows a schematic section displaying the geometry of these imbricate oceanic slices.
Fig. 4. Geologic map of the San Severino Lucano area showing
the extent of Cilento Unit sediments (i.e. Crete Nere and
Saraceno Formations) previously considered to belong to the
Frido Formation (Frido Unit).
At Timpa delle Murge a traverse (Fig. 3) was carried out to determine the relationship between the sedimentary cover of the oceanic slice and the surrounding sediments. The traverse commenced at the conformable stratigraphic contact between the Crete Nere and Saraceno Formations and terminated at the base of the sedimentary cover exposed on top of Timpa delle Murge. The sedi- ments throughout the entire traverse were found to be in stratigraphic continuity from the basal contact of the Saraceno Formation, down succes- sion through the Crete Nere Formation to the pelagic limestone and ribbon radiolarite deposited above the pillow lavas. The sedimentary cover at Timpa delle Murge is lithologically identical to exposures already attributed to the Crete Nere Formation (e.g., Crete Nere Formation at Serra Scorzillo located on the border between Calabria and Basilicata, Foglio 221 I NO Terranova di Pollino). This suggests that the entire succession above the pillow lavas up to the base of the Saraceno Formation, should be assigned to the Crete Nere Formation.
Significance of the Frido Formation and the Frido
A re-evaluation of the Frido Formation type- area (Fig. 4) showed that all members of this formation were in fact moderately or intensely deformed rocks of the Crete Nere Formation or Saraceno Formation. The less deformed portions were lithologically and petrographically similar to Crete Nere Formation and Saraceno Formation sediments found within the eastern part of the area (i.e. Cilento Unit). Figure 5 shows the similar- ity between the sedimentary petrography of the Frido Formation (Frido Unit) and the Crete Nere and Saraceno Formations (Cilento Unit). Within the calcareo-scistoso member of the Frido Formation it was possible to recognise Saraceno Formation lithic arenites, the base of the beds containing the characteristic schist, limestone and quartz clasts commonly found in Saraceno Forma- tion sediments in the eastern part of the area (see Fig. 32; Vezzani, 1968a). The identification of
IRF Q mQn
MRF F L
0 FRIDO FORMATION QUARTZ-ARENITE 0 FRIDO FORMATION LITH-ARENITE l CRETE NERE FORMATION QUARTZ-ARENITE l SARACENO FORMATION LITH-ARENITE
Fig. 5. Petrography of the Frido Formation (Frido Unit) and t...