04; DIA- Sion of Previous Assumptions on the Geometry, Kinemat- Ics and the Tectonic Evolution of This Part of Northern MANTOPOULOS, 2004; OCAKOGLOU Et Al., 2005)
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Geologia Croatica 59/1 85–96 8 Figs. ZAGREB 2006 Plio–Quaternary Geometry and Kinematics of Ptolemais Basin (Northern Greece): Implications for the Intra-Plate Tectonics in Western Macedonia Anastasios DIAMANTOPOULOS Key words: Progressive shear strain, Intra-plate tec- Western Macedonia in Northern Greece. New structural tonics, Ptolemais Basin, Western Macedonia, North- data, observed in the Ptolemais basin are presented in ern Greece. order to elucidate the principal deformation styles and mechanisms in this area (Fig. 1). Distribution of defor- mational structures, the geometry and kinematics of Abstract deformation, and a new kinematic model for the Ptol- An integrated structural study of the Ptolemais basin of Northern Greece allows assessment of deformation processes and their impli- emais basin are also addressed. Finally, an integrated cation in the Pliocene–Quaternary structural evolution of this part of evaluation of new data and their implications allows a Western Macedonia. Normal and reverse faults within Plio–Quater- new improved comprehension of intra-plate tectonics of nary sediments, NE–SW striking anticlines in both Plio–Quaternary Western Macedonia. sediments and pre-Tertiary basement-units, torsions and deforma- tion partitioning, highlight the particular characteristics of intra-plate deformation. Field investigations and drilling data infer the conclusion 1.1. Previous studies and that intra-plate processes were governed by progressive shear strain target of this work during the Plio–Quaternary. A new kinematic model for the develop- ment of the Ptolemais basin is proposed, showing the importance of Previous studies of the Ptolemais basin by PAVLIDES progressive shear strain. (1985), DOUTSOS & KOUKOUVELAS (1998), MOUNTRAKIS et al. (1999), and GOLDSWORTHY & JACKSON (2000) provided an insight into the impor- tance of active faults and their role in the geomorphol- ogy and seismology of this basin. Structural data pre- sented in these papers were mainly concerned with the 1. INTRODUCTION geometry and kinematic characteristics of the observed fault sets. According to PAVLIDES (1985) and MOUN- Geological evidence in the Hellenic orogenic belt of TRAKIS et al. (1999), multiple tectonic phases during eastern Mediterranean confirms complex Neogene– Miocene–Quaternary times were recognized, each char- Quaternary tectonic processes, both in the orogenic acterized by compressional or extensional structures. front of the Central and South Aegean, and in the back- arc domain of the North Aegean and Western Mace- New structural analysis of the Ptolemais basin in donia (STEWART & HANCOCK, 1991; PIPER & Western Macedonia presented in this paper, allows revi- PERISSORATIS, 2003; KREEMER et al., 2004; DIA- sion of previous assumptions on the geometry, kinemat- ics and the tectonic evolution of this part of Northern MANTOPOULOS, 2004; OCAKOGLOU et al., 2005). Greece (Fig. 1). This structural synthesis is based on These observations make evident the importance of het- data obtained by field analysis, drilling and geophysical erogenous strain, including co-existence of strike-slip, investigations, which document the main structural pat- rotational and ductile structures. Since deformation and tern within Plio–Quaternary sediments, the sub-surface strain outline three-dimensional quantities, structural geometry of the Ptolemais basin fill and also the re-acti- heterogeneity from the lithospheric-scale to the grain- vation of the pre-Miocene structures by Plio–Quaterna- scale of observation mark an essential constituent of ry tectonics. The study area is an open-pit lignite mine strain (JONES et al., 2005; DE PAOLA et al., 2005). exploited by the Public Power Corporation of Greece This work analyzes the Plio–Quaternary structures (PPC). and the deformation style in the Ptolemais basin of 2. GEOLOGY OF WESTERN MACEDONIA National Technical University of Athens, Department of Mining, Metallurgical & Engineering Geology, Section of Geosciences, 9 Herron Polytechniou Street, GR-15780, Zografou, Athens, Geological data, geophysical studies and GPS measure- Greece; e-mail: [email protected] ments in Western Macedonia denote on-going tectonic 86 Geologia Croatica 59/1 Fig. 1 Tectonic map of Western Macedonia. Three distinctive domains (dotted black boxes) with compressional field structures are illus- trated, see MOUNTRAKIS (1983), FOTIS (2004) and DIAMANTOPOULOS (2004). Inset map: The Hellenic orogenic arc in the Eastern Mediterranean, based on MARIOLAKOS et al. (2004) and DIAMANTOPOULOS (2004). Legend for inset map: AEP – Aegean plate; AFP – African plate; APMC – Apulia micro-continent; CFZ – Cephalonia Fault Zone; NAF – North Anatolia Fault; AFZ – Axios Fault Zone; STRMZ – Strymon Fault Zone; MNR – Morpho–Neotectonic Region; SA – Study area. activity (MOUNTRAKIS et al., 1999; FOUNTOULIS 3. GEOLOGY OF THE PTOLEMAIS BASIN et al., 2002; DRAKATOS et al., 2005; BURCHFIEL et al., 2005). Here, several tectonic basins of continental Sedimentary fill of the Ptolemais basin includes terres- origin developed during Miocene–Quaternary times trial and lacustrine sediments of Miocene up to Pleisto- (the Florina, Ptolemais, Kozani–Servia, Almopia basins cene age, abundant in lignite reserves (KOUKOUZAS – Fig. 1). The presence of Plio–Quaternary volcanism in et al., 2000; KVACEK et al., 2002). STEENBRINK the Almopia basin (VOUGIOUKALAKIS et al., 2004 (1998) studied distinctive sedimentary facies and con- cluded that the basin formation started during the Torto- and reference there in), also indicates re-arrangement of nian. DIAMANTOPOULOS & DIMITRAKOPOULOS the lithospheric material. The physiography of North- (2004a) by synthesis of tectono–sedimentary data, rec- western Greece is characterized by the two elevated ognized three distinctive lignite members of Miocene, domains of Pelagonian and Pindic Cordillera as well as Pliocene and Pleistocene age, intercalated with clas- by the two subsided domains of the Mesohellenic and tic sediments. The same authors also recognized two Axios basins (Fig. 1). The latter are interpreted as Ter- major unconformities within the sedimentary basin tiary (AUBOUIN, 1965) piggy-back basins with thick succession, i.e. the first one at the base of the Miocene, sedimentary accumulations. (between the first terrestrial sediments and the pre-Ter- Diamantopoulos: Plio–Quaternary Geometry and Kinematics of Ptolemais Basin... 87 A B Fig. 2 (A) Digital elevation model of Western Macedonia. Photos of Figs. 4 and 5 are depicted. (B) Simplified tectonic map of the southern part of the Ptolemais basin. Inset map shows the spatial distribution of the analyzed drillings in three domains I, II and III of Fig. 3. The location of the geological sections A–B–C of Fig. 7 is also illustrated. tiary basement units), and the second one between the Pre-Tertiary basement rocks of the Ptolemais basin Pleistocene strata and the Pliocene sediments. Arrange- can be subdivided into four distinctive tectonic units, ment and geometry of lignite layers of the Ptolemais (Fig. 2b). From the lowermost to the highest unit, they basin indicate a westward migration from the eastern are: (I) pre-Alpine Pelagonian Basement, separated into marginal domain (Vermion mountain) toward the west- Schist sub-unit, the Gneiss sub-unit, the granitoid mylo- ern marginal domain (Askion and Vernon mountains), nites and the granites (BRUNN, 1956; MOUNTRAKIS (DIAMANTOPOULOS & DIMITRAKOPOULOS, 1983; DIAMANTOPOULOS, 2005), (II) Almopia 2004a). Unit, with Triassic–Lower Jurassic marbles and meta- 88 Geologia Croatica 59/1 A B Fig. 3 (A) Quantitative thickness variation of the Pliocene lignite sequences; (B) Quantitative thickness variation of the Plio–Quaternary sedi- ments (overburden cover of Pliocene lignites). The spatial distribution of the domains I, II and III is depicted in the inset map of Fig. 2. sediments of Late Jurassic age (DIAMANTOPOULOS, also show a great difference in lithostratigraphic devel- 2005), (III) Ultramafic–Mafic Unit of Mesozoic age, opment and sedimentary evolution, which makes strati- and (IV) Cretaceous Unit, with platform limestones graphic correlation of Plio–Quaternary strata between and Maastrichtian flysch (MERCIER, 1968). Steep and these sub-basins difficult (DIAMANTOPOLOUS & low-angle shear zones, formed in brittle–ductile condi- DIMITRAKOLOPOUS, 2004a). tions, separate distinctive tectonic units. Recent struc- tural studies show that during the Oligo–Miocene, a 3.2. Quantitative and qualitative analysis strong orogen-perpendicular stretching re-arranged the of borehole data geometry of the pre-Tertiary sequences (MOUNTRA- KIS, 2004; DIAMANTOPOULOS, 2005). The NW–SE Borehole data, which include 720 boreholes that pen- strike of the Ptolemais basin is controlled by pre-exist- etrated the Plio–Quaternary basin fill and 50 boreholes ing shear zones in pre-Tertiary basement units, which that reached the pre-Tertiary basement have been taken accommodated Oligocene stretching of the Internal Hel- into account, and are distributed in 3 domains (Fig. 2b). lenides (DIAMANTOPOULOS, 2005). These inherited The thickness of the Pliocene lignite sequence and also structures correspond to several shear zones between the thickness of the Plio–Quaternary sediments (the pre-Tertiary basement sequences. overburden of the Pliocene lignite sequence) have been quantitatively analyzed. Diagrams A and B of Fig. 3 3.1. Morphotectonic units of shows the following thickness-variation pattern: the Ptolemais Basin a) Thicknesses of the lignite