RICERCA ITALIANA     

STRUCTURAL AND STRATIGRAPHIC STUDIES ON THE DINARIC (SERBIA-MONTENEGRO) HELLENIC (EPIRO-MACEDONIA-TESSALY) AND CRETE. COMPARISON WITH THOSE OF ALBANIDS AND SOUTHERN HELLENIDS.

Università degli Studi di Firenze

Abstract

The proposed research program focuses along three sections of the Dinarid-Hellenic Orogene to study the structural and stratigraphic characters, biostratigraphy, petrology, geochemistry and, possibly, paleomagnetism of the Jurassic-Cretaceous units of a key area in the frame of the Western Tethys evolution.
a)-In the first section, Dinaric, the operative unit (O.U.) of Florence will study the massifs of Varda-Zlatibor, while the Pise O.U. will study those of Ibar-Kopaonik. The attention will be devoted to the sedimentary successions covering the ophiolitic massif, to the peridotitic rocks, to the subophiolitic melange, to the amphibolitic soles and to the relationships between the ophiolitic units and the Pelagonian units of the Drina Ivanjica zone.
b)- In the second section, Hellenic, the O.U. of Florence will study the Pindos, Koziakas, Vourinos e Othrys ophiolitic massifs, while the O.U. of Pise will focus on the Guevgueli and Paikon vardarian units. Here a collection of petrological and biostratigraphic data in the ophiolitic series is necessary to complete previous studies. A special attention will be devoted to the Paikon units.
c)- In the third section, Cretan, the O.U. of Catania will work on the ophiolitic units of Arvi, Vatos and Miamou and on the Pelagonian Asterussia Unit.
The objective are:
- The definition of the number of ophiolitic basins;
- The stratigraphic reconstruction of the ophiolitic successions;
- The acquisition of structural data to reconstruct the tectonic evolution of the ophiolitic units;
- The lithologic definition of the blocks in the sub-ophiolitic melange;
- The investigation of the geometric and structural relationships between the ophiolitic and Pelagonian units;
- The study of the relationships between the regional kinematic and the geodynamic processes.
The final objective will be to reconstruct a general evolutionary model for the ophiolitic units of the Dinaric-Hellenic chains.
The program is organised in two years.
During the first year we will perform a revision of the available cartographic material and we will build a data-base to collect all the geological and structural data.
A preliminary excursion on the Dinarid ophiolitic massifs will be organized. Working missions will be carried out in the Zlatibor and Kopaonik massifs. Successively detailed studies will focus on the Koziakas, Othrys, Arvi, Vatos and Miamou. We will carry on mineralogical, geological and geochemical analyses on the ophiolites and biostratigraphic analyses on the sediments.
At the end of the first year we will organize a general excursion and the new data will be presented in a workshop.
In the second year the study will be focused on the northern Varda and Ibar massifs, and on the relations between the ophiolitic units and the Drina Ivanjica massif. In the Hellenic sector the data collection will be completed also for the Pindos-Vourinos ophiolitic successions as well as for the metamorphic Pelagonian and for the relationship between the ophiolitic units and the sub-ophiolitic mèlange. To the East the working target will be the study of the relations between the Paikon and Guevguele units. An important objective will be also the investigation on the amphibolitic soles.
In the Cretan sector the studies will extend to the Pelagonian Asterussia Unit.
At the end of the project we will produce cross sections of the three transects that will help define an evolutionary model for the sub-Pelagonian, Pelagonian and Vardarian units of the Dinarid-Hellenic chain.
The data will be presented and discussed in a final workshop. The results will be released in the project web page and published in international journals. <<<

Principal Investigator

Gianfranco Principi Università degli Studi di FIRENZE

Research Objectives

The goals of our project are:
1) the definition of the number and genetic features of the ophiolitic oceanic basements involved in the Dinaric-Hellenic orogenesis with particular focus on the Cretan section.
2) The reconstruction of the originary stratigraphy of the ophiolitic sequences including their sedimentary cover and coeval continental margin sequence.
3) The collection of sufficient structural data to reconstruct the tectonic evolution of the ophiolitic units from the early tectonic phases up their emplacement on the Adriatic continental margin
4) The lithologic classification of the various blocks occurring in the sub-ophiolitic mélange, the understanding of their relations and their provenance areas. The study of the amphibolitic soles intercalated between the ophiolitic units and the mélange will allowed to define the early emplacement process of the ophiolitic units themselves.
5) The understanding of the structural and geometric relations between the ophiolitic and Pelagonian units and their paleogeographic setting.
6) The interpretation of the regional kinematic processes and the large scale geodynamic events to reconstruct a structural model of the studied area.

The final goal will be to propose an evolutionary model of the ophiolitic units of the Dinaric-Hellenic orogenic chains, through a comparison between the studied sections and the available data on the Albanian and Greek units. <<<

Timescale

24 months

National and international background

The ophiolitic sequences formed in an oceanic ridge (MOR) or suprasubduction (SSZ) environment (Crawford et al., 1981; Beccaluva et al., 1983; Pearce and Parkinson, 1993) are deformed during subduction, obduction and continental collision processes.
To reconstruct the evolution of the oceanic lithosphere, until consumption, it is necessary to know its petrological and structural features together with the chronological (biostratigraphic and radiometric) data.
Knowing the ophiolites evolution in the orogens is fundamental to reconstruct the early orogenic phases, which constitute the starting point to understand the successive collisional and post-collisional chain evolution.
Along the Dinaric-Hellenic belt the ophiolites are preserved along two main alignments:
a- the western alignment (Subpelagonian or External Ophiolites Zone), including oceanic MOR type (Jones and Robertson, 1991; Beccaluva et al., 1994; Robertson and Karamata, 1994; Bortolotti et al., 1996, 2002a, 2004a; Robertson and Shallo, 200; Pamic et al., 2002), of Bania (Croatia), Varda-Zlatibor (Serbia), Mirdita (Albania), Pindo-Vourinos, Othrys, Eubea, Argolis and Creta Island (Greece).
b- the eastern (Vardar zone), which includes the ophiolitic rocks (MOR after Robertson and Karamata, 1994 and Trubelja et al., 1995; SSZ after Pamic et al., 2002 and Marroni et al., 2004) and the continental rocks of Bistrica (Croatia), Ibar-Kopaonik (Serbia), Guevgueli (Macedonia-Greece), Calcidican Peninsula (Greece) and continues northwards in the Apuseni Mts, Buck, Meliata and western Pienini Mts.(e.g. Bortolotti et al., 2002b, 2004a, Bortolotti and Principi, 2005).
After the Anisic rifting phases, the following Ladinian-Carnian oceanic is follows characterized by MOR magmas on a lherzolitic basement (e.g. Robertson and Karamata, 1994; Robertson and Shallo 2000; Bortolotti et al, 2002a, 2003; Pamic et al. 2002, Bortolotti and Principi, 2005 and referenced therein).
The Eurasia-Adria convergence started between Early and Middle Jurassic (e.g. Dimitrijevic and Dimitrijevic, 1973; Robertson and Karamata, 1994; Pamic et al., 1998; Dimitrijevic, 2001; Bortolotti et al., 2002a, 2004a,b; Bortolotti e Principi, 2005) producing suprasubduction oceanic basins and harzburgitic basements.
The Dinaric-Hellenic orogen began its development during the middle Jurassic, following the convergence between Eurasia and Adria, which caused the disappearance of the interposed oceanic crusts. Whether one or more oceans existed between the two plates is a still open question (Bortolotti et al., 2002a, 2004a; Bortolotti and Principi, 2005 cum bibl.).
The closure age varies between Late Jurassic-Early Cretaceous (Bortolotti et al., 1996, 2002a, 2004a) and Late Cretaceous-Tertiary (Pamic et al, 1998, 2002; Robertson and Shallo, 2000)
The collisional continental phases, with west-verging deformations and orogenic magmatism are mainly of Tertiary age.
About the orogenetic geodynamics there are various hypotheses:
- a subduction jump model (Robertson and Shallo, 2003;Smith and Rassios 2003), with an early western immersion, followed by an eastward one;
- two east-dipping, chronologically and spatially scattered subductions (Pamic et al., 2002);
- one west dipping (Dilek and Shallo, 2003; Beccaluva et al., 2004);
- only one east-dipping subduction (Bortolotti 2003, 2004a).
The scarcity of information on the structural frame of the Dinaric-Hellenic units, especially the internal units, and the varying degree of knowledge in the different areas, explains the coexistence of very different opinions.
Recently the ophiolitic units of the western belt (Mirdita, Pindos, Vourinos, Othrys, Argolis an, to a lower extent, those of the eastern belt as Guevgueli, Macedonia, Greece; Apuseni Mts., Romania) were studied by the Italian researchers of the UO of this project; the results of this work were published on international journals (Bortolotti et al., 1971, 1996, 2002a,b, 2003, 2004b; 2005a,b; Rassios et al., 1983; Chiari et al., 1994, 1996, 2002, 2003, 2004; Beccaluva et al., 1994; Marcucci et al., 1994; Bakalli et al., 1995; Aiello, 1996; Carosi et al., 1996a,b; Kodra et al., 1996; Gardin et al., 1996; Marcucci and Prela, 1996; Carras et al., 2004; Cortesogno et al., 1998;. Marroni et al., 2004; Aiello et al., 2005; Zelic et al., 2005).
The performed studies (Bortolotti et al., 2004a; Bortolotti and Principi 2005) revealed that in the western units, from Albanides (Mirdita) to Hellenides (Pindos. Vourinos, Koziakas, Othris, Argolis), both the spatial distribution and the structural position of the ophiolites (MORB and SSZ) are homogeneous and that the opening and closure times of the ophiolitic basins coincide.
In particular:
1- The presence of a sub-ophiolitic mèlange, including blocks with both ophiolitic and continental margin affinity, on the continental margin units (Adria).
2- The presence of Triassic (MOR) ophiolites usually interposed between the sub-ophiolitic mèlange and the ophiolitic Units.
3- The presence of middle Jurassic amphibolitic soles at the base of ophiolitic units which, given the absence of the orogenic metamorphism in the ophiolites, point to a “hot” obduction event active from Middle Jurassic to Early Cretaceous.
4- The presence, starting from Early Creetaceous, of neritic and carbonatic or silicoclastic pelagic deposits, which overlay unconformably on the ophiolitic units.
The researches within this project will be carried out mainly in dinaric and cretan ophiolites in three different transects:

A- Dinaric transect. In this sector the ophiolitic massifs are poorly studied (Bortolotti et al., 1971; Dimitrijevic e Dimitrijevic, 1973; Pamic, 1982, 1983; Pamic e Desmond, 1989; Robertson e Karamata, 1994; Dimitrijevic, 1997, 2001; Pamic et al., 2002; Marroni et al., 2004, Zelic, 2005).
The transect regards the ophiolitic units of the western zone (subpelagonian) (Varda and Zlatibor Massifs) and, passing through the Pelagonian unit of the Drina-Ivanjica Zone, it will reach the units of the Vardar eastern Zone (Ibar and Kopaonik Massifs).
Beneath the Ophiolitic Massifs, there is a subophiolitic mélange with elements of continental margin and ophiolites, that formed between Upper Jurassic and Lower Cretaceous (Pamic et al., 2002). Amphibolitic soles of the middle-lower Jurassic are present beneath the ultramafites (Pamic et al., 2002).
The ophiolitic massif of Varda (lherzolites and cumulates) – Zlatibor (harzburgites) are part of the Dinaride Ophiolite Zone (Pamic, 1983; Pamic and Desmond, 1989), considered as the northward edge of the Subpelagonian Zone.
To the western margin of Varda, the volcano-sedimentary covers of middle-upper Trias to lower Cretaceous age (Pamic, 1982), crop out (Radiolarite Formation after Pamic et al., 2002), forming isolated strips East of Zlatibo. To the west, all these units are superposed on the continental margin successions of the Budva Zone.
To the east, the subpelagonian units are thrust by the continental margin units of the Drina-Ivanjica Complex (Pelagonian). These, in their turn, are thrusted by the Vardar Zone unit, characterized by a pile of oceanic and continental tectonic units (Ibar and Kopaonik Massifs).
These units are overthrust by a tectonic unit made up of a Cretaceous turbidite sequence (paraflysch of the Central Vardar Subzone of Dimitrijevic, 2001). The contact with the Eurasian type units of the Serbian-Macedonian Massif is characterized by the interposition of a series of tectonic slices, including ophiolites, belonging once again to to the Vardar Zone (Internal Vardar Subzone, Dimitrijevic, 1997).
The ophiolite sequence, characterized by a very low metamorphic imprint, is mainly made up of serpentinized harzburgites, intruded by small gabbroic bodies and by boninitic sheeted-dike complex (Marroni et al. 2004) and covered by rare basalt flows .
In Robertson and Karamata, 1994 and Trubelja et al., 1995, the ophiolites are interpreted as MOR type while in Pamic et al. (2002) and Marroni et al. (2004) they are of SSZ type.
This tectonic unit overthrusts the Sub-ophiolitic Melange Unit, which is represented by discontinuous and thin slices of coarse-grained clastic complexes, associated with ophiolites and turbidites of unknown age.
The Subophiolitic Melange overthrusts the "Central Kopaonik Series" metamorphic complex, consisting of amphibolites, phyllites and Upper Triassic marbles (Sudar, 1986).
This is intruded by a Lower Oligocene magmatic complex (Kopaonik and Zeljic granodiorites and Ibar volcanics). This tectonic stack is known as “External Vardar Subzone” (Dimitrijevic 2001).
The relationships between these tectonic units and their structural evolution are almost unknown, as well as the stratigraphy of the ophiolitic unit. The possible presence of a cover series and of amphibolitic soles is another question.

B- Hellenic transect. This transect will cross the Epiran, Tessalic, Magnesian and Macedonian areas, in which the ophiolitic units of the western belt occur, and, eastwards, the Vermion, Paikon, Almopias and the Guevgueli Massifs, in which the units of the eastern ophiolitic belt crop out.
The subpelagonian ophiolitic massifs of Pindos, Vourinos, Koziakas and Othrys thrust westwards onto the Pindic terrains (Adria margin). The Pelagonian metamorphic rocks of western Macedonia are also thrusted by these units. Similar contacts are present N-E of the Othrys massif. To the east, the Subpelagonian and Pelagonian units are overthrusted by the Vermion and other internal (Vardarian) units.
In the Pindos Massif, the ophiolites are piled in several tectonic units and subunits. At the base there is a sub-ophiolitic mèlange (Avdella Mèlange), which is very similar to the Dinaric transect’s one and to that of Albanide sector (Rubik Mèlange). To the west, the ophiolitic units of Aspropotamos (MOR and SSZ, Saccani et al., 2004, Jones and Robertson, 1991; Capedri et al. 1982) and of Dramala (composed SSZ ophiolites, Saccani et al., 2004, Jones and Robertson, 1991) are tectonically superposed on the mélange. Amphibolitic soles (Jones and Robertson, 1991) of Jurassic age are interposed between the ophiolites and the mélange. The uppermost Dramala Ophiolitic unit is correlable with that of Vourinos (Ross and Zimmermann, 1996; Bortolotti et al., 2004a). A very similar tectonic and stratigraphic framework is documented in Koziakas (Saccani et al, 2003) and Othrys (Photiades et al., 2003; Capedri et al., 1985; Bortolotti et al, 2005).
The ophiolitic unit of Vourinos lies under a middle Jurassic to Cretaceous sedimentary succession. Cretaceous-Eocenic sediments cover all these rocks uncomformably. In the Pindos,Vourinos and Koziakas these sediments are unconformably overlapped or replaced by the Tertiary siliciclastic sediments of Mesohellenic Trough.
In the Guevgueli area, the Vardar pile of nappes is bounded to the west by the Paelagonian units and by the Serbo-Macedonian ones to the east.
In this area, the Vardar zone consists, from east to west, of Guevgueli ophiolitic units, which is thrusted upon the Paikon massif (Brown and Robertson, 2004).
The Guevgueli unit is made by a Middle Jurassic ophiolites sequence intruded by a Late Jurassic intrusive complex, mainly represented by granitoids (e.g. Bebien et al., 1987). This ophiolitic complex represents the best preserved oceanic sequence detectable in the Vardar zone. Both the ophiolites and the granitoid complexes are associated to a migmatitic complex (Bebien et al., 1986).
The Paikon Massif is located in the middle of the Vardar zone in northern Greece and is very important for the reconstruction of Neotethys in the E Mediterranean region. The massif is formed by a single tectono-stratigraphic unit of Jurassic to Early Tertiary age, that originated along the margin of a continental unit known as the Serbo–Macedonian Zone (Brown and Robertson, 2003). In this area, a Mesozoic oceanic basin opened in the Triassic between the Serbo–Macedonian continent to the NE and another continental unit, the Pelagonian Zone, to the SW. The Paikon Massif is characterized by a Jurassic Paikon Volcanic Group which comprises two volcanogenic units of island arc-type (Livadia and Kastaneri Formations). The arc developed along the SW margin of the Serbo–Macedonian continent in response to NE subduction of the Almopias Ocean (e.g. Brown and Robertson, 2004). However, the features of the Guevgueli ophiolites are poorly known and their geodynamic setting or its their relationships with the migmatites are still undetermined.

C- Cretan transect. In the Island of Crete, a segment of the Hellenic orogenic belt is exposed. The Hellenic paleodomains, in spite of significant differences both for the space-time evolution of the deformations and for the tectonic setting, are recognizable also in this belt. The lowermost structural element of the chain, represented by the carbonate sequences (Plattenkalk Series of Hall et al., 1984; Mt. Ida sequence of Bonneau, 1984) of the Ionian domain, is affected by HP/LT metamorphism (Fassoulas et al., 1994; Jolivet et al., 1996) and is considered as a core complex exhumed during Miocene (Fassoulas et al., 1994; Jolivet et al., 1996; Fassoulas, 1999; 2001).
An intermediate tectonic unit is represented by a carbonate platform succession (Tripolitza Nappe) with its metamorphic Permo-Triassic basement (Phyllite-Quartzite Nappe of the Gavrovo domain (Creutzburg and Siedel, 1975; Bonneau and Karakitsios, 1979; Bonneau, 1984; Hall et al., 1984).
The uppermost tectonic element of the belt is made up of a pile of allochthonous terraines represented by ophiolite-bearing nappes, tourbiditic sequences, basinal carbonate successions and by units deriving from a continental crystalline basement.
The ophiolitic units (Arvi, Vatos and Miamou nappes) are partially affected by HP/LT metamorphism (Vatos and Miamou units) and derive from the deformation of oceanic paleodomains, ranging in age from Jurassic to Cretaceous (Vardar and Pindos-Arvi domains), while the crystalline units (Asteroussia nappe) are probably related to the Pelagonian zone paleomargin (Bonneau, 1972; 1984; Seidel et al. 1976; Bonneau and Lys, 1978; Robert and Bonneau, 1982; Hall et al., 1984; Robertson 2002).
The sure recognition of the paleodomain is still a matter of debate, especially for the ophiolitic units. In fact, the age, the composition and structural position of these latter varies in the pile of nappes, making it very difficult to interpret their evolution in this sector (Robertson 2002).

Many questions are still open about these topics, as, for example:
-The chronological data of amphibolites: obtaining new data and perform a revision of old ones, especially of those derived by the K-Ar method.
-Composition and genetic mechanisms of the subophiolitic melanges.
-General sequence of the deformation phases, in particular for the Late Jurassic-Eocene time interval.
-The number of the ocean basins and their paleogeographic position.
-The geometric and structural relationships between the ophiolitic units and the Pelagonian successions.
-The correlation between the Pelagonian and the Adriatic successions in the Middle Triassic-Early Cretaceous time interval.
Others question are linked with local peculiar features, as:
-Structural and geometric relationship between the Drina-Ivanjica Complex and the Eastern and western ophiolitic units.
-The relationship between the Zlatibor ophiolites and the metamorphic unit at its eastern border.
-The relationship with the Cretian ophiolitic units and those of other Hellenic units.
-Age and geodynamic genetic event related to the HP-LT metamorphism of some Cretan ophiolites.
The attempt to fill up all these gaps is a real starting base for this project. If the results will satisfy the expectations, a remarkable contribution for a better understanding of the evolutional picture of the Dinaric-Hellenic chain will be obtained. <<<