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

    217

    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)

    Abstract

    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

    these regions.

    (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.

    Introduction

    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

    sedimentary cover.

    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.

  • STROVILLARI

    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.

    Liguride Complex

    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).

    Frido Unit

    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.

  • 219

    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.

    Cilento Unit

    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.).

    Ophiolites

    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).

    Present study

    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.

    2).

    Oceanic slices

    Kilometre-scale oceanic slices crop out to the

    east of Monte Pollino at Timpa delle Murge,

  • 220

    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

    - FAULT

    - THRUST N tt-_

    0.*.-O TRAVERSE 500m f

    NORTH SOUTH

    TIMPA OELLE MURGE

    A S

    Fig. 3. Geologic map and cross-section of the Timpa delle Murge and Timpa Pietrasasso oceanic slices.

  • 221

    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).

    Sedimentary cover

    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

    Unit

    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

  • 222

    IRF Q mQn

    MRF F L

    C

    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...

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