Thrust faults and extensional detachment faults in Cretan tectono-stratigraphy: Implications for Middle Miocene extension

Tectonophysics 488 (2010) 233–247

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Thrust faults and extensional detachment faults in Cretan tectono-stratigraphy: Implications for Middle Miocene extension Dimitrios Papanikolaou, Emmanuel Vassilakis ⁎ Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Greece

a r t i c l e

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Article history: Received 1 July 2008 Received in revised form 27 April 2009 Accepted 29 June 2009 Available online 6 July 2009 Keywords: Aegean Sea Crete Island Hellenides Detachment Crustal extension

a b s t r a c t The revised tectono-stratigraphy of Crete and especially of the “Phyllites–Quartzites” complex demonstrated the distinction of the probable Paleozoic low-medium grade metamorphic rocks of the Arna unit from the underlying Permo–Triassic phyllites and associated carbonate sediments (Trypali facies) of Western Crete unit as well as the overlying Permo–Triassic phyllites and associated sediments of the Tyros/Ravdoucha Beds at the base of the Tripolis unit. The pre-existing mixture of the above tectono-stratigaphic units in a single complex created a number of misinterpretations as far as stratigraphy, metamorphism and interpretation of low angle faults as thrusts or detachments. Especially in cases where the inferred tectonic contact concerns the transition between the Tyros Beds and the base of the Tripolis carbonate platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment. Based on the revised tectono-stratigraphic analysis the determination of the structural omission for each tectonic contact was possible and several detachments were described for the first time. Footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes. The detachment may separate not only metamorphosed units in the footwall (Mani, Western Crete, Arna) from non metamorphosed units in the hanging wall (Tripolis, Pindos and higher nappes) but also all other possible combinations from the Cretan nappe pile. Extension in Crete started in the Middle–Late Miocene with the formation of extensional detachment faults. The reported extensional structures of Oligocene to Early Miocene age do not correspond to crustal extension of Crete but to localized shear zones related to nappe stacking and the exhumation of metamorphic rocks. Extensional detachments in Crete form a tectonic horst through two oppositely dipping E–W-trending zones; one dipping north, related to the opening of the Cretan basin, and the other dipping south, related to the formation of the Messara supra-detachment basin. The deformation history of units within Crete can be summarized as: (i) compressional deformation producing arc-parallel east–westtrending south-directed thrust faults in Oligocene to Early Miocene time; (ii) extensional deformation along arc-parallel, east–west-trending detachment faults in Middle Miocene time, with hanging wall motion to the north and south; and (iii) Late Miocene–Quaternary transtensional deformation along high-angle normal and oblique normal faults that disrupt the older arc-parallel structures. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Low-angle faults separating different tectonic units have been usually interpreted as thrusts, resulting from compression within the nappe stacking process at the front of evolving mountain belts. Normal faulting was generally considered as a later deformation resulting from extension usually at the back-arc area of the orogenic arc. Normal faults were recognized in general as medium–high angle faults with dip angle more than 40°. It is only after the 1970s that low-angle faults have been interpreted also as normal faults resulting from extension and were

⁎ Corresponding author. Fax: +30 210 727 4096. E-mail addresses: [email protected] (D. Papanikolaou), [email protected] (E. Vassilakis). 0040-1951/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2009.06.024

separated from the rest low-angle faults representing compressive structures (Davis et al., 1980; Wernicke, 1981; Wernicke and Burchfiel, 1982; Burchfiel and Royden, 1985). Since the late 1990s the tendency is toward a generalized interpretation of low-angle faults as extensional detachments rather than thrust faults (Wernicke, 1995). The criteria used to interpret a low-angle fault as thrust or extensional detachment become crucial and there is a need for accurate determination of the kinematic and dynamic conditions during faulting. The usual occurrence of multi-phase deformation structures within subduction–exhumation processes with opposite dynamic and kinematic characteristics perplexes the overall final result with cases where the thrust component dominates and the extensional detachment remains a minor secondary component and vice versa. In every case, the simple criterion of either structural omission or structural duplication in a given tectonostratigraphic sequence gives the main argument about overall extension

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or compression. Nevertheless, the key point still remains on the tectonostratigraphic succession used as the reference model for determining omission or duplication. In simple cases where the tectono-stratigraphy involves only one column of several km thickness belonging to a certain domain (e.g. continental margin) the choice is easy. On the contrary, in cases where the succession involves several nappes of different paleogeographic and geodynamic settings within a given fold and thrust belt then there is a need for accepting the most “complete” succession including the maximum tectono-stratigraphic thickness of all nappes involved in the structure during the building up of the fold and thrust belt while compression is the dominating stress field. During the 1990s–2000s, several papers interpreted a number of the tectonic contacts between the Cretan tectonic units as extensional detachments, usually those separating the non-metamorphosed nappes from the underlying metamorphosed units (Fassoulas et al.,1994; Jolivet et al., 1996; Ring et al., 2001a; Rahl et al., 2005; Seidel et al., 2007). However, in several cases the amount of throw and the overall extensional deformation across the proposed extensional detachments were not clearly demonstrated. On the contrary, it is obvious that in some cases the tectonic surfaces interpreted as extensional detachments separate the Late Triassic beds of the Tripolis carbonate platform from its directly underlying Middle Triassic pre-platform volcano-sedimentary stratigraphic sequence and thus, they represent minor decollement sliding surfaces without any important structural omission. In the case of the East Peloponnesus detachment, developed within a similar tectonostratigraphy as Crete, it was shown that it has omitted 8–10 km of units above the Mani autochthon (Papanikolaou and Royden, 2007). Thus, it is important to examine the tectonic contacts and decipher whether they are thrusts, extensional detachments, minor ‘decollement’ type sliding surfaces due to disharmonic phenomena, or even more complex cases with opposite kinematic characteristics of primary thrusting followed by later extension. Additionally, the interpretation of several low-angle faults as normal faults and/or extensional detachments in the Aegean area since the 1990s has produced some confusion about the dynamic and kinematic evolution of the different segments of the Hellenic arc. Thus, the beginning of extension since the Late Oligocene–Early Miocene following the previous compressive deformation in areas like Crete proposed by some researchers (Jolivet et al., 1996; Thomson et al., 1998; Ring and Reischmann, 2002) implies that Crete should be already in the back-arc area during this early period. However, Crete occupied the front of the Hellenic arc in Oligocene time and present-day as well as this is shown by the well dated time of thrusting and nappe emplacement in the Late Oligocene (e.g. Aubouin et al., 1976; Bonneau, 1984) and by its present day position in the front of the Hellenic arc and trench system (e.g. Le Pichon et al., 1979) (Fig. 1). Nevertheless, the Miocene–Pliocene compressive belt of the Hellenic arc which is known to have been active all along western continental Greece and the Ionian Islands (e.g. Papanikolaou and Dermitzakis, 1981; Underhill, 1989) is hard to be located between Crete and the Hellenic trenches. In addition, tectonic transport directions deduced from micro-structural fabric analysis and dating of extensional detachment faults indicate opposite slip directions during the Miocene both to the south and to the north (Kilias et al., 1994; Ring et al., 2001a; Rahl et al., 2005; van Hinsbergen and Meulenkamp, 2006; Seidel et al., 2007). Nevertheless, it is not clear whether the Late Oligocene to Early Miocene kinematic indicators refer either to the tectonic emplacement of the metamorphic rocks, or to their internal deformation, or to the postulated extensional detachments (Xypolias et al., 2007). Our research provides a detailed analysis of the tectono-stratigraphic nappe pile of Crete with a re-interpretation of the available geological maps combined with new field observations. The result is a new map of the tectono-stratigraphic units of Crete at the scale of 1:200,000 (Fig. 2) and a revised tectono-stratigraphy which are presented at the first part of our paper. This material is the basis for our elaboration of tectonic profiles and palinspastic reconstructions. The re-interpretation of the

tectonic contacts between the tectono-stratigraphic formations as thrusts, extensional detachments, secondary disharmonic structures or re-activated thrusts during later extension, which is presented at the second part, is the primary scope of this paper. 2. Geological setting of Crete: a review of previous models The first detailed geological and tectonic data for Crete were presented by Papastamatiou and Reichel (1956) and Papastamatiou et al. (1959a,b,c) based on geological mapping at a scale of 1:50,000. The general picture was similar to that of western continental Greece and especially of Peloponnesus, with the two major geotectonic units being the Pindos nappe, characterized by pelagic sediments, overlying the Tripolis unit, characterized by a shallow-water carbonate platform together with its metamorphic basement. Both units belong to the external Hellenides as this was shown by their continuous Mesozoic– Early Cenozoic stratigraphic sequences deformed during Late Eocene– Oligocene after the deposition of their flysch formations (Renz, 1955; Aubouin et al., 1963, 1976). During the 1970s, several studies provided a more detailed tectonostratigraphic succession for the island of Crete by differentiating several nappes either at the base of the nappe pile below the Tripolis carbonate platform or at the top above the Pindos nappe. Below the Tripolis carbonate platform the discovery of Tertiary fossils within the autochthon metaflysch (Kalavros Beds by Fytrolakis, 1972) resulted in the recognition of the aforementioned unit as the metamorphic equivalent of the Ionian unit cropping out in western continental Greece (Epting et al., 1972; Bonneau, 1973a) instead of its initial interpretation as Paleozoic basement rocks at the base of the metamorphic succession below the Tripolis carbonate platform. Thus, a major thrust was recognized between the Tripolis platform and the autochthon unit, named the Mani unit by Fytrolakis (1980). Two additional tectonic units named Trypali and the Phyllites–Quartzites were also distinguished between Tripolis and the autochthon (Wachendorf et al., 1975; Seidel et al., 1976; Creutzburg et al., 1977; Fytrolakis, 1980; Krahl et al., 1983). The Trypali unit, comprising Late Triassic–Early Jurassic crystalline limestones, was initially considered to be a minor duplication of the base of the autochthon neritic sequence of carbonate rocks, whereas the Phyllites–Quartzites unit encompassed all of the schistose rocks below the Tripolis platform. Based on the distinction between the very low grade Permo– Triassic Tyros Beds at the base of the Tripolis upper Triassic–Eocene carbonate platform and the underlying low to medium grade metamorphic rocks of the Arna unit in Peloponnesus (Ktenas 1924; Lekkas and Papanikolaou, 1978; Papanikolaou and Skarpelis, 1987), a modified tectono-stratigraphic succession for the “Phyllites–Quartzites” unit of Crete was proposed by adding not only the unit of Western Crete (including the Trypali) between the autochthon basement and the Arna unit, but also including the Variscan age, Sitia metamorphic rocks within the Tyros Beds (Papanikolaou, 1988). The tectonic contacts separating the above tectonic units were generally considered to be thrusts of Oligocene to Early Miocene age, while the overall tectonic transport was from north to south. Above the Pindos nappe the higher tectonic units of Arvi, Miamou, Vatos, Asteroussia and the ophiolites were distinguished in several small outcrops all over Crete (Fig. 2). They are always overthrusting the Pindos flysch, representing more internal units within the paleogeography of the Hellenides with an Early Tertiary tectonism but also a Late Cretaceous history at the uppermost units (Tataris, 1964; Davis, 1967; Seidel et al., 1976; Bonneau et al., 1977; Creutzburg et al., 1977; Seidel et al., 1981; Bonneau, 1984; Koepke et al., 2002). The paleogeography of the external Hellenides and the resulting tectonic units during the Early Tertiary tectonic evolution of the Hellenic arc was revised after the understanding that much of the metamorphic rocks below the external and the medial metamorphic belts of the Hellenides were parts of the Metamorphic Hellenides, equivalent to the

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Fig. 1. (a) Location of Crete within the Hellenic arc and trench system. The main outcrops of the external terranes H1 (External carbonate platform) and H2 (Pindos–Cyclades oceanic basin) of the Hellenides are shown along with the distinction of the main outcrops of their metamorphosed units of Mani and the Cyclades. (b) Geographic map of Crete with the main names used in the manuscript.

classical non-metamorphosed Hellenides (Papanikolaou, 1984; Bonneau, 1984; Papanikolaou, 1986). Thus, the position of Mani unit should be located between Paxos and Ionian units whereas the position of the Cycladic metamorphic rocks should be located between Tripolis– Olympos and Pindos units (Papanikolaou, 1986) (Fig. 3). The distinction of tectono-stratigraphic terranes in the Hellenides (Papanikolaou, 1989, 1997, 2008) included: (i) all units bearing a shallow-water carbonate platform sedimentation in the Late Triassic–Eocene which belong to the terrane H1 of the External Carbonate Platform of the Hellenides, incorporating the Paxos, Mani, Ionian, Gavrovo, Tripolis, Amorgos, Olympos, Almyropotamos and Kerketeas units (Fig. 3). Paxos, Ionian, Gavrovo and Tripolis units are the classical non metamorphosed units whereas Mani, Amorgos, Olympos, Almyropotamos and Kerketeas units

are metamorphosed units during Late Eocene–Oligocene. The shallowwater carbonate sedimentation was interrupted in Late Lias–Dogger by pelagic sedimentation following a rifting episode observed in Mani, Ionian and Amorgos units; (ii) the Pindos unit and the metamorphosed during Early Tertiary Cycladic units characterized by pelagic–abyssal sedimentation during Mesozoic belong to the Pindos–Cyclades oceanic terrane H2 (Fig. 3); and (iii) the Parnassos unit and the more internal units belong to the terrane H3 of the Internal Carbonate Platform of the Hellenides and to more internal terranes (H4–H9). The resulting nappe pile of Crete was sliced by normal faults and created the post-Alpine sedimentary basins of Crete since the Middle Miocene (Meulenkamp et al., 1979; Fytrolakis, 1980; Angelier et al., 1982; ten Veen and Postma, 1999).

236 D. Papanikolaou, E. Vassilakis / Tectonophysics 488 (2010) 233–247 Fig. 2. Geological map of Crete indicating the main tectono-stratigaphic units, simplified after the original map elaborated at the 1:200,000 scale. This map was compiled by Papanikolaou and Vassilakis using the published literature (IGME maps, Creutzburg et al., 1977) and their own unpublished field observations. This is a digital dynamic map compilation created on a GIS platform; the geodatabase was designed especially for distinguishing the several tectono-stratigraphic units. The locations of photos and geological sections described in the text are also shown.

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Fig. 3. Paleogeographic section of the external part of the Hellenides during the Late Cretaceous and palinspastic tectonic model of the external carbonate platform and overlying more internal units (Papanikolaou, 1986, modified). The extension of the tectonostratigraphic terranes (H1, H2, H3) and the position of the Western Crete and Arna unit are also indicated.

3. Revised Cretan tectono-stratigraphy 3.1. The “Phyllites–Quartzites” unit within the external carbonate platform of the Hellenides H1 Special emphasis was given in our research to the distinction of the complex term “Phyllites–Quartzites” which has created a lot of confusion and misinterpretations and needs to be analyzed in several tectono-stratigraphic units. The term “Phyllites–Quartzites” is a purely petrographic term that can be found anywhere, whereas terminology of typical tectono-stratigraphic formations should follow the type locality name with a sufficient description, as in the case of the Tyros Beds (Ktenas, 1924; Papanikolaou and Skarpelis, 1987) and the Arna Unit (Skarpelis, 1982; Papanikolaou and Skarpelis, 1987). The term “Phyllites–Quartzites” does not correspond to a certain tectonostratigraphic unit and the way it is used in the literature as a very low grade metamorphic rock sequence but also as a low–medium grade metamorphic unit implies that it encompasses two different tectonometamorphic units as shown in Peloponnesus, where the distinction between the very low grade Tyros Beds at the base of Tripolis unit and the low–medium grade metamorphic rocks of the Arna unit was described by Papanikolaou and Skarpelis (1987). In addition, the generally-proposed Permo–Triassic age concerns only the very low grade metamorphic rocks, like the Tyros Beds in Peloponnesus (Ktenas, 1924; Fytrolakis, 1971) and their equivalent formations partly known also as Ravdoucha beds in several areas in Crete (Cayeux, 1902; Wurm, 1950; Papastamatiou, 1958; Papastamatiou and Reichel, 1956; Fytrolakis, 1967; Creutzburg and Seidel 1975). On the contrary, the low to medium grade metamorphic rocks belonging to the Arna unit are of Paleozoic age, with probably only one Carboniferous age determination from crystalline limestones cropping out at western Crete near Sfinari (Krahl et al., 1983; Papanikolaou, 1988) and another age determination from the Carboniferous granite of Kythira within the Arna unit (Danamos and Papanikolaou, pers. com. in Stampfli et al., 2003; Seidel et al., 2006; Xypolias et al., 2006). Another fossiliferous outcrop of Late Paleozoic age assumed to be part of the “Phyllites– Quartzites” in the area of Fodele on the northern slopes of Talea Ori (Kuss, 1963) has been proven to correspond to the base of the autochthon (Epting et al., 1972). The confusion still remains in western Crete where Permo–Triassic formations have been reported from a number of outcrops within the “Phyllites–Quartzites” unit (e.g. Krahl et al., 1983). This is due to the fact that a very low grade metamorphic Tyros type sequence of Permo–Triassic age occurs also below the Late Triassic–Liassic carbonate rocks of the Trypali unit which have been incorporated in the so-called unit of Western Crete (Papanikolaou, 1988). The existence of these phyllitic rocks in stratigraphic continuity to the Trypali carbonate rocks along with some fossiliferous sites was first reported by Tataris and Christodoulou (1965). The overall difficulty lies in the fact

that the low-medium grade metamorphic rocks of the Arna unit are sandwiched between the tectonically underlying Permo–Triassic phyllites of Western Crete and the tectonically overlying Permo– Triassic phyllites of Tripolis (Tyros Beds). Thus, from the tectonically deeper metamorphosed carbonate rocks of the relative autochthon unit of Mani (known also as Plattenkalk or Metamorphosed Ionian) to the shallower carbonate rocks of the Tripolis carbonate platform, there are at least four different tectono-stratigraphic formations within the schistose type formations that are usually named in the literature as “Phyllites–Quartzites” (Papanikolaou, 1988) such as (Fig. 4): (i) the metamorphosed flysch of the Mani unit (Oligocene in age, also known as the Kalavros Beds, Fytrolakis, 1972); (ii) the complex unit of Western Crete, comprising a Tyros-type low-grade metamorphosed volcano-sedimentary sequence of Permian to Middle Triassic age, followed by Middle to Late Triassic evaporites and Late Triassic– Early Jurassic crystalline limestones (the latter formation referenced as “Madara kalke” by Creutzburg, 1958 and later as the Trypali unit by Creutzburg et al., 1977, Kopp and Ott, 1977, Fytrolakis, 1980 and Krahl et al., 1983). This unit largely corresponds to the unit characterized by Tataris and Christodoulou (1965) as the “Triassic transgressive system of Western Crete” during their geological mapping of the Alikianou sheet (Tataris and Christodoulou, 1967); (iii) low to medium grade HP/LT metamorphic rocks of the Arna unit. The age of this unit is presumed to be Paleozoic as previously described, but its metamorphism is Tertiary (Seidel et al., 1982; Thomson et al., 1999); and (iv) The Permo–Triassic volcano-sedimentary base of the Tripolis carbonate platform, consisting of phyllites, meta-sandstones, volcanic rocks and some carbonate layers, equivalent to the Tyros Beds in Peloponnesus (partly known as the Ravdoucha Beds — Creutzburg and Seidel, 1975). Some important outcrops of the Variscan high-grade metamorphic rocks of the Sitia unit including Cambrian granitoids (Seidel et al., 1977; Krahl et al., 1986; Zulauf et al., 2002; Finger et al., 2002; Romano et al., 2004) occur within the Tyros Beds in eastern Crete and above the Permo–Triassic phyllites and evaporites of the Western Crete unit (in the area of Mochlos). The position of the Variscan Sitia metamorphics within the Tyros Beds is demonstrated by the occurrence of pebbles of these medium–high grade metamorphic rocks in the coarse clastics (Kopp and Wernado, 1983) as the characteristic outcrop in the area of Vai (Fig. 25 in Papanikolaou, 1988). The above four tectonic units belong to the External Carbonate Platform of the Hellenides (Terrane H1) (Papanikolaou, 1997), which was imbricated during its Early Tertiary deformation (Fig. 3). The main tectonic structure related to this deformation was the underthrusting of the Mani unit under the Ionian and Gavrovo–Tripolis units extending to the east, which remained unmetamorphosed, whereas Mani underwent a low-grade metamorphism (Papanikolaou, 1986). Thus, the Mani Autochthon represents, from the paleogeographic point of view, the more external part of the platform between the Paxos and Ionian units, while the Western Crete nappe represents

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Fig. 4. Tectono-stratigraphic column of the former “Phyllites–Quartzites” complex (Papanikolaou, 1988, modified).

part of the Ionian unit, mainly its lower part below the pelagic Middle Jurassic–Eocene sequence (Papanikolaou, 1979) (Fig. 3). Finally, Arna and the Tyros Beds at the base of the Tripolis platform represent the central part of the external platform, as the Tyros Beds occur stratigraphically beneath the platform and the Arna unit probably represents the pre-Alpine Paleozoic basement of this platform (see also Fig. 12b). The presumed unconformity between the Arna basement rocks and the Tyros Beds sequence has been used as a tectonic discontinuity surface and is the upper boundary of the individual tectonic unit of the Arna nappe. This tectonic process implies a first ‘decollement’ of Arna beneath the Tyros Beds and the stratigraphically overlying Tripolis platform, with subduction to deeper levels along the subduction zone during the Oligocene (phase 1a in Figs. 3 and 12b), followed by an exhumation process with the opposite sense of motion towards the more external units of Western Crete and Mani during the Early Miocene (phase 1b, Figs. 3 and 12b, two-fold kinematics of the Arna during the Oligocene–Early Miocene). The Tripolis nappe along with its base of the Tyros Beds was overthrusted to the more external parts of the platform during its first phase (2a) and later may have an opposite sense of movement with sliding backwards onto the Arna unit (2b in Figs. 3 and 12b). The tectonic contact between the Arna unit and the Tyros Beds can be observed in the area of Ravdoucha. The Tyros Beds form a layer of

volcano-sedimentary formations passing upwards to the base of the upper Triassic carbonate platform of Tripolis with the characteristic stromatolitic facies. The contact with the underlying metamorphic rocks of the Arna unit is sub-horizontal and there is a difference in the landscape produced by the quartzite layers forming linear rocky scarps along the abrupt slopes of the hill towards the seashore and the overlying smooth relief developed over the phyllitic rocks of the Tyros Beds (Fig. 5a). Another locality where the contact between the Tyros Beds and the metamorphic rocks of the Arna unit can be observed is in the area of Plakalona along the old road from Kolymbari to Kastelli (Papanikolaou, 1988) (Fig. 5b). The base of the Tyros Beds is generally characterized by cataclastic rocks, also known as corneule or rhauwackes (Fig. 5c) and the development of shear zones and transposition structures. Gypsum and graphite occurrences are common near the tectonic contact, as are some iron deposits. The thrusting of the Arna unit onto the Western Crete unit is a characteristic sub-horizontal tectonic surface bringing the low to medium grade metamorphic rocks of probable Paleozoic age over the very low grade metamorphic rocks of Permian–Lower Jurassic age. A characteristic outcrop occurs in the area of Sklavopoula village where the sub horizontal tectonic contact can be observed over several kms (Fig. 6a). The outcrops of the two units are easily detectable in the landscape from the massive rocky layers of the Arna quartzites and

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Fig. 5. (a) Landscape view towards the south of the Tyros Beds overlying the Arna unit in the area of Ravdoucha. (b) Close-up view of the tectonic contact between the Arna and Tyros beds in the area of Plakalona. (c) Detail of the cataclastic rocks (corneule type) from the base of the Tyros Beds above the thrust on Arna unit.

Fig. 6. (a) View of the subhorizontal Arna thrust over the Western Crete unit at the area of Sklavopoula. (b) Isoclinal recumbent folds of the Middle–Late Triassic very low grade phyllitic sequence of the Western Crete unit in the area south of Sklavopoula. (c) View from Elafonisi beach towards the east showing the Western Crete evaporites dipping to the east under the meta-sedimentary sequence of Fig. 6b.

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metavolcanic rocks contrasting the soft relief made by the phyllitic rocks of the Western Crete metasediments. Spectacular isoclinal folds are observed within the Western Crete phyllites below the Arna nappe (Fig. 6b). Papastamatiou (1958) reported Middle to Late Triassic age for these outcrops of the Western Crete unit. The intercalation of the evaporites within the phyllites and the dolomites/rhauwackes (Trypali facies) of the Western Crete unit crops out along the western coastline of Crete with nice view from Elafonisi area (Fig. 6c). In the area of Kandanos and between the Lefka Ori and Malaxa, the Arna thrust brings the metamorphic rocks along with a serpentinite body over the upper Triassic–lower Jurassic carbonates and evaporites of Western Crete. The structure in Kandanos represents a tectonic window of the Western Crete unit below the Arna nappe, whereas in Malaxa the Arna thrust dips to the north by 20°–30°. In other regions, the Arna nappe is observed directly on top of the autochthon unit of Mani without the intervention of the Western Crete nappe. This situation might be due to primary disharmonic phenomena during tectonic emplacement but may well be due to later extension that has omitted the Western Crete nappe. Thus, the metamorphic rocks of the Arna unit are interlayered between the Permo–Triassic formations of the Western Crete unit and the Tyros Beds of the Tripolis unit. This intermediate position creates a double tectono-metamorphic hiatus to both the lower and the upper very low grade sequences. Judging from the available data from petrologic studies in certain localities in Crete (Seidel et al., 1976; Theye et al., 1992; Jolivet et al., 1996; Thomson et al., 1998; Rahl et al., 2005) and from the available data from Peloponnesus (Papanikolaou and Skarpelis, 1987; Theye et al., 1992) the P/T conditions in the three successive units are: (i) 300 °C and 2–4 kbar for the Tyros Beds, (ii) 400 °C and 8–12 kbar for the metamorphic rocks of Arna, and (iii) 350 °C and 3–5 kbar for Western Crete. The main difference between the metamorphic conditions of the Arna unit and the two phyllite-bearing units of Western Crete and the Tyros Beds is the presence of chloritoid, which is exclusive in Arna. Typical lithologies of the Arna unit from Taygetos Mountain in Peloponnesus (Papanikolaou and Skarpelis,1987) can be found in several localities in Crete, like: (i) the metabasalts in Preveli and Aghia Pelagia, (ii) the meta-conglomerates in Almyros to the east of Aghia Pelagia and in Sitia, north of the airport and (iii) the serpentinized peridotites in Malaxa. In conclusion, the outcrops characterized as “Phyllites–Quartzites” comprise–besides the Oligocene metaflysch of the Mani autochthon– three different tectonic units (Fig. 4) representing the Permo–Triassic phyllitic base of the Western Crete/Ionian unit, the Permo–Triassic

phyllitic base of the Tripolis unit (Tyros/Ravdoucha Beds) and the Paleozoic basement (partly Carboniferous) Arna unit whose initial position was probably beneath the Gavrovo–Tripolis units of the External Carbonate Platform H1 (Figs. 3 and 12b). 3.2. The higher tectonic units of the Pindos–Cyclades oceanic terrane H2 and more internal units The higher tectonic units of Crete belong to the Pindos–Cyclades tectono-stratigraphic terrane H2 (Papanikolaou, 1989, 1997, 2009) which is characterized by the pelagic upper Triassic–Eocene Pindos unit, also known in Crete as the Ethia unit (in the Asteroussia Mountains) or as the Mangassa unit (in Sitia) (Renz, 1955; Papastamatiou et al., 1959a,b; Bonneau and Zambetakis, 1975). The main difference of the Cretan Pindos-type nappes from the typical Pindos unit of continental Greece is the later arrival of the flysch, which starts in the Eocene instead of the Late Maastrichtian–Danian. The Pindos nappe is observed on top of the Tripolis unit (usually overlying its Late Eocene– Oligocene flysch), together with several nappes with limited outcrops all around Crete Island, occurring at the higher positions of the Cretan nappe pile (Fig. 2). These higher nappes are: (i) Arvi unit, comprising Late Cretaceous basalts and pelagic sediments (Tataris, 1964; Bonneau, 1973b). The MORB affinities of these basalts (Robert and Bonneau, 1982) indicate that a mid-ocean ridge was active within the Pindos oceanic basin at least up to the Late Cretaceous–Paleocene (Bonneau, 1984; Papanikolaou, 1997); (ii) Miamou unit, comprising a Late Cretaceous wild-flysch with olistholites of Jurassic limestones (Bonneau, 1976); (iii) Vatos unit, comprising a Late Paleozoic–Jurassic sedimentary sequence (Bonneau, 1976); (iv) Asteroussia nappe, comprising highgrade metamorphic rocks and granites with a Late Cretaceous age of metamorphism (Davis, 1967; Bonneau, 1976; Seidel et al., 1976); and (v) the Cretan ophiolitic nappe, found at the uppermost position, although sometimes ophiolite bodies are also found intercalated within the Vatos and Asteroussia nappes (Bonneau, 1976; Seidel et al., 1976; Koepke et al., 2002 ). The aforementioned tectonic units belong to the oceanic basin of the Pindos–Cyclades tectono-stratigraphic terrane H2 (Papanikolaou, 1989, 1997, 2009) with the exception of the Asteroussia metamorphics, which may represent slices of the basement rocks of the Internal Carbonate Platform of the Hellenides, also known as the Pelagonian Terrane (H3) (Papanikolaou, 1997). In conclusion, the overall tectono-stratigraphic succession of Crete comprises 10 tectonic units with a total thickness of about 10–12 km (Fig. 7). This succession can be found complete in very few areas

Fig. 7. Tectono-stratigraphic diagram of Crete showing the Oligocene nappe pile made of 10 tectonic units and the two major Middle Miocene extensional detachments. Note that the vertical axis is exaggerated.

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where later extension has not thinned it. The usual case is to observe some higher parts of the pile resting on top of some lower ones, either because of detachment faults or large normal faults. In general, all the nappes above the Pindos are found in some limited outcrops and only in some geographic areas. This is due either to intense erosion throughout the Late Cenozoic that has eliminated most outcrops of the upper tectonic units especially at the neotectonic horst areas or to their burial by overlying Late Tertiary sediments that were deposited in the tectonic grabens formed during extensional faulting (Fytrolakis, 1980; ten Veen and Kleinspehn, 2003).

4. Re-interpretation of the tectonic contacts of the Cretan units: thrusts or extensional detachments? 4.1. Primary tectonic contacts The primary tectonic contacts between the above ten tectonic units are thrusts, which can be observed in numerous outcrops shown in our geological map of Crete (Fig. 2). The tectonic transport is from north to south following the geometry and asymmetry of the Hellenic arc from its interior in the North Aegean to its periphery in the Ionian Sea at the west and the Libyan Sea at the south (Fig. 1). This overall southward tectonic vergence is shown by spectacular isoclinal folds with east–west trending fold hinges (at the kilometer scale) observed in the autochthon marbles in the northern slopes of Dikti Mt (Fig. 8). The age of thrusting, as indicated by the syn-tectonic flysch formations of the nappes, ranges between Late Eocene in the higher nappes (e.g. Pindos/Ethia) to Late Oligocene–Early Miocene in the lower nappes (Mani autochthon) (Fytrolakis, 1980; Bonneau, 1984; Kilias et al., 1994). The thrust nature of each tectonic contact separating the tectonic units is additionally supported by the superposition of tectonic units bearing more internal paleo-geographic areas of the Hellenides onto more external ones with the older syntectonic flysch deposits occurring in the successively higher nappes. Furthermore, the tectonic emplacement of metamorphic units like the Arna or Asteroussia nappes over non-metamorphic units or units of much lower metamorphic degree shows the tectonic superposition. Finally, the overall tectonic superposition of Crete follows the geometry and evolution of the fold and thrust belt of the Hellenides in continental Greece, as all the tectonic units of Crete are also known along strike in continental Greece and/or the Dodecanese Islands (Aubouin et al., 1976) with the exception of the Asteroussia metamorphic rocks, which are, however, known in the Cyclades area further to the north (Seidel et al., 1976; Reinecke et al., 1982; Soukis and Papanikolaou, 2004). The primary thrust surfaces of the higher nappes and especially of the Pindos/Ethia unit over the Tripolis unit are well preserved in several areas with characteristic outcrops in central Crete around Kastelli and in Sitia around Ziros.

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4.2. Late tectonic contacts Late tectonic contacts representing extensional detachments in the upper crust occur in several places in Crete, but they generally form two zones of extensional detachments trending east–west and dipping 10°–30° either northwards under the Cretan Sea or southwards under the Libyan sea (Fig. 7). These two east–west-trending low-angle normal fault systems control the east–west orientation of Crete and have produced its general arc-parallel tectonic horst structure (Papanikolaou and Vassilakis, 2008). However, they do not follow a particular earlier tectonic contact, but instead follow several planes of anisotropy representing both primary thrusts and stratigraphic boundaries.

4.2.1. South dipping detachment The structural omission across these detachments varies. In some cases, the whole tectono-stratigraphic column of Crete with an average 10–12 km thickness is missing, like around the southern slopes of Psiloritis Mt., where ophiolites of the uppermost unit rest directly on the lowest unit of the autochthon marbles (Vassilakis, 2006) (Fig. 9a). The average dip of the Psiloritis detachment is 20–25° and thus, the overall displacement of the Psiloritis detachment to the south exceeds 25–30 km. This case is similar to the Peloponnesus regime (Papanikolaou and Royden, 2007), where the East Peloponnesus detachment at Parnon Mt. brings the uppermost internal units on top of the Mani unit in the footwall. In other cases, significant parts of the Cretan nappe pile are missing, like in the area east of Viannos, where the upper nappes of Arvi and Pindos occur at the hanging wall next to the Tripolis carbonates, which are located in the footwall (Fig. 9b). The detachments of both Psiloritis and Viannos belong to the southdipping detachment zone of Crete. A characteristic outcrop of the same detachment zone occurs in southwestern Crete, where along the southern coastline carbonate rocks belonging to the Tripolis and Pindos nappes are observed in the hanging wall, whereas formations of the Western Crete unit form the footwall. The section at Cape Krios involves the upper Triassic limestones and evaporites of the Western Crete unit in the footwall and the Pindos nappe overlying the Tripolis nappe in the hanging wall. Both the Tripolis and the Pindos nappes are tilted to the north against the detachment (Fig. 9c). A thin layer of 5– 10 m thick Tripolis upper Eocene flysch occurs below the upper Cretaceous pelagic limestones of the Pindos nappe whose flysch at the top dips 20°–30° towards the north. The section at Paleochora and Sougia shows mainly the Pindos nappe in the hanging wall, whereas the footwall comprises Permo–Triassic formations of the Western Crete unit, including the volcano-sedimentary sequence, the limestones and the evaporites below the thrust of the Arna nappe (Fig. 9d). In conclusion, the south dipping detachment zone of Crete comprises a number of detachment faults with different units participating in the footwall and the hanging wall structure respectively. Structural omission

Fig. 8. Recumbent isoclinal kilometric fold with asymmetry towards the south of the Mani autochthon marbles in the area SE of Kastelli, at the foothills of Dikti Mountain.

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Fig. 9. (a) View from the east (Aghia Varvara area) of the southern Psiloritis detachment. The low-angle fault surface dips below the ophiolites (uppermost tectonic unit) towards the Messara basin, whereas the Mani autochthon crops out at a higher elevation on the footwall. (b) View of the southern Cretan detachment at Arvi. The geometrical fault plane separates the Tripolis carbonates in the footwall from the Arvi volcanics in the hanging wall. (c) Tectonic sketch of the southern Cretan detachment in the area of Cape Krios. The northward tilt of the Tripolis and Pindos nappes in the hanging wall contrasts the south dipping detachment over the Western Crete footwall. (d) View of the southern Cretan detachment in the area NE of Paleochora. The Pindos unit lies directly on top of the Western Crete unit.

varies from a few km up to 10 km. The footwall comprises both metamorphosed and non-metamorphosed units and almost every tectonic unit of Crete can be observed either at the footwall or at the hanging wall of the detachments. 4.2.2. North dipping detachment The northern detachment zone is observed in northwestern Crete in the area of Platanos and Sfinari (Fig. 10a). The detachment dips 20°–25° to the north and the Tripolis and Pindos nappes are observed in the hanging wall dipping 5°–15° to the south against the detachment surface. A thin bed of 20–30 m of Tripolis flysch lies on top of the uppermost part of the platform (upper Cretaceous–Eocene), separating the Tripolis limestones from the Pindos nappe, while the footwall is comprised of metamorphic rocks of the Arna unit. Several kilometers to

the east of Sfinari in the area of Topolia, the detachment is observed again, but here the hanging wall comprises mainly breccias and conglomerates coming almost exclusively from Tripolis limestones (Seidel et al., 2007) (Fig. 10b). Some blocks of Tripolis limestones occur at the base of the breccias and the conglomerates, which are of Middle Miocene age (Meulenkamp et al., 1979). Sub-horizontal upper Miocene marine sediments unconformably cover both the Topolia formation and the detachment. Several kilometers north of Topolia and Platanos, in the areas of Falassarna and Ravdoucha, the Tripolis thrust can be observed on top of the Arna unit with parts of the Tyros Beds at the base of the Upper Triassic platform, which bears the characteristic stromatolitic limestones. In central Crete the north-dipping detachment zone is found in the area of Vatos and Spili, where the higher nappe of Vatos lies on the

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Fig. 10. (a) View from the west of the northern Cretan detachment at Sfinari. Thin slices of the Tripolis and overlying Pindos units directly overlie the Arna unit. (b) View from the SW of the northern Cretan detachment at Topolia. Blocks of Tripolis carbonate rocks occur along the base of the detachment below the Topolia breccias and conglomerates. (c) View of the northern Cretan detachment at Vatos. The units of Pindos and Arvi are omitted between the Tripolis limestones in the footwall and the Vatos formations in the hanging wall.

hanging wall, whereas the Arna and Tripolis units form the footwall (Fig. 10c). Ophiolitic rocks are observed at both the base and the top of Vatos unit with an overall thickness of more than 1 km. Structural omission across the detachment comprises the Pindos and Arvi nappes, which occur below Vatos in the hanging wall at some horizontal distance of 2–4 km east of the detachment. In conclusion, the north dipping detachment zone of Crete comprises detachment faults with the Tripolis unit found in the hanging wall but also in the footwall. Additionally, the timing of the detachment can be determined on the basis of the syntectonic clastic sediments (Middle Miocene Topolia Formation) and post tectonic marine Late Miocene– Pliocene sediments. 4.2.3. Disharmonic phenomena Some impressive sub-horizontal contacts observed between the upper Triassic Tripolis carbonates and the Tyros Beds are minor structures without any important structural omission. The sharp contact observed in several outcrops, especially around Sitia as in the area above Roussa Eklissia and at the base of the western margin of the Zakros basin, is due to disharmonic phenomena developed during the compressive primary and/or extensional late deformation (Fig. 11). The discontinuity surface has been developed at the transition between the stratigraphically lower volcano-sedimentary plastic layers of the Permo–Triassic Tyros beds and the 1–2 km thick competent massive carbonate rocks of the Upper Triassic–Eocene platform.

5. Discussion and conclusions The major tectonic contacts between the tectonic units of Crete can be distinguished in thrusts, extensional detachments and normal/strikeslip faults with kilometric order movements (Fig. 12a). The amount of slip can be determined at first approximation from the juxtaposition of the higher nappes (units 5–10 in Fig. 12b and d), belonging to the Pindos terrane H2 against the lower units of the external carbonate platform H1 (units 1–4 of Fig. 12b and c) and especially the relative autochthon Mani unit (unit 1 of Fig. 12b and c). Thus, the structural omission becomes more evident in each case of a detachment structure with: (i) detachments eliminating only part of the nappe pile within the external platform such as the case of Anogia–Idaion Andron in Psiloritis mountain (unit 1 at the footwall and unit 4 at the hanging wall) (Rahl et al., 2005) and circum-Lefka Ori detachments (unit 1 at the footwall and units 2, 3, 4 at the hanging wall) and (ii) detachments eliminating several nappes from the lower part as well as the upper part of the nappe pile as in the case of the southern slopes of Psiloritis (unit 1 at the footwall and units 5–10 at the hanging wall), Cape Krios (unit 2 at the footwall and units 4 and 5 at the hanging wall) and Vatos (unit 4 at the footwall and units 8, 9 and 10 at the hanging wall). The opposite tilt of the primary tectonic contacts against the dip of the detachments has been observed in several cases like the Psiloritis, Krios, Platanos–Sfinari and Vatos detachments (Fig. 12a). The east–west trending Middle Miocene extensional detachments of Crete represent arc-parallel extensional structures following the

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Fig. 11. (a) View of the disharmonic contact surface between the upper Triassic limestones of the Tripolis platform overlying the Tyros Beds (Middle Triassic) near the area of Roussa Eklissia. (b) View from the east of the planar subhorizontal contact of the top of the Tyros Beds (middle-upper Triassic) from the base of the Tripolis carbonate platform (upper Triassic) in the area of Zakros.

previous arc-parallel Oligocene–Early Miocene compressional thrusts and folds (Kilias et al., 1994). Oligocene to Early Miocene age determinations reported from the undivided “Phyllites–Quartzites” (Jolivet et al., 1996; Thomson et al., 1998, 1999) do not date the crustal extension of Crete but only some extensional shear zones within the tectono-stratigraphic units of this complex (analyzed in the stratigraphic column of Fig. 4). In particular, those data referring to the base of the Tripolis platform and the underlying schistose formations are mostly small-scale internal slip surfaces developed during nappe emplacement and nappe stacking. In the case of the Arna unit, these age determinations and slip directions in part show the exhumation process beneath the Tyros Beds and the overlying Tripolis carbonate platform (Figs. 3 and 12b). In fact, the Arna unit probably represents the Paleozoic basement originally lying below the Gavrovo and Tripolis segments of the external carbonate platform, which after subduction beneath the Tripolis and more internal parts of the platform (Olympus etc), was exhumed at its present position below the Tripolis unit (Figs. 3 and 12b; for a palinspastic model of the platform see also Papanikolaou, 1986). This tectonic process would explain its age, geometry, position and metamorphism, as well as its tectonic interlayering in between the very low grade Permo–Triassic formations of Western Crete (below) and the Tyros Beds (above). This timing fits with the Oligocene age of the metamorphosed flysch of the Mani autochthon and its consequent metamorphism during the Late Oligocene–Early Miocene. This age is also confirmed by the fact that in western continental Greece, the compressive deformation of the Gavrovo and Ionian units was still active during Oligocene and Early Miocene time, a conclusion that is based on age determinations of the upper stratigraphic horizons of the flysch and molasse deposits (IGSR and IFP, 1966; Fleury, 1980). The age of the extensional detachments is Middle Miocene, dated by the syn-tectonic breccias-conglomerates cropping out at Topolia (Meulenkamp et al., 1979) and Anogia (Moraiti and Alexopoulos, 2000). The overall neotectonic structure of Crete following the Middle Miocene extensional detachments is a tectonic east–west-trending horst (Papanikolaou and Vassilakis, 2008) (Fig. 7). The Cretan basin to the north seems to have opened during the Middle(?)–Late Miocene (Jongsma et al., 1977) following the extension of the north-dipping

detachment zone of Crete (Ring et al., 2001b). The East Peloponnesus detachment probably produced the western margin of the Cretan basin (Papanikolaou and Royden, 2007) in the Late or even Middle Miocene following the age determination of the Itea–Amfissa detachment at the northern end of the East Peloponnesus detachment (Papanikolaou et al., 2009). At Anafi Island just north of Crete across the Cretan Sea, a similar succession of tectonic events has been identified, with Oligocene to Early Miocene thrusting and folding post-dating the relative autochthon upper Eocene–Oligocene flysch, followed by Middle Miocene extensional detachment faults; consequently, extensional deformation continued since the Late Miocene with normal and oblique normal faults that caused the opening of the Cretan basin to the south (Soukis and Papanikolaou, 2004). A similar conclusion was driven also for the Ios detachment (Ring et al., 2001a) which lays a few tens of km to the west of Anafi along the same margin of the Cretan basin. Thus, the opening of the Cretan Basin in back-arc position of the Hellenic arc and trench system between Crete and the Cyclades has resulted from the activity of the two antithetic parallel detachments during Middle– Late Miocene. The south-dipping detachment of Crete produced the east–westdirected Asteroussia mountain chain in its hanging wall characterized only by outcrops of the higher Cretan nappes (Fig. 12a). Otherwise, the east–west-oriented southern coastline to both the west and the east of Asteroussia and Messara basin is controlled by the southern detachment zone. The Messara basin and its westward offshore prolongation in the basin between Gavdos and Crete are supra-detachment basins developed on top of the hanging wall of the southern detachment. The Middle to Late Miocene age of the Messara basin sediments (Meulenkamp et al., 1979) marks the onset of southward slip of the detachment. It is characteristic that Gavdos Island (the southernmost outcrop of the Hellenic arc) is made up of the Pindos nappe and relics of higher nappes along with ophiolitic rocks. High-angle normal and strike-slip faults dissect and disrupt the previous structure of thrusts and extensional detachments and form the tectonic margins of the Late Tortonian–Quaternary basins (e.g., the Iraklion basin) (Angelier et al., 1982). Most such faults are seismically active structures overprinting the previous tectonic fabric (Caputo et al., 2006). Nevertheless, some segments of the former detachments

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Fig. 12. (a) Simplified tectonic map of Crete showing the structure resulting from the superposition of the extensional detachments and other major normal/strike-slip faults in the previous nappe pile. This is facilitated by the distinction of the lower units (terrane H1) from the upper ones (terranes H2 and H3). The different shading of the Mani autochthon helps identify the magnitude of structural omission in each case. The paleogeographic organization of the Cretan units is schematically given in (d) and the schematic tectonic superposition of the nappes is indicated in (b) for the External carbonate platform (H1) in (c) for the more internal terranes (H2, H3).

are still active today through steeper normal faults disrupting the previous low-angle fault surfaces. The outcrops of Late Miocene– Pliocene marine sediments show the subsided blocks during this period (Figs. 2 and 12a). The general uplift of Crete during the Quaternary marks the present-day deformation, with half of the island being a recently emerged area from the previously submerged neotectonic grabens. Following the above described three groups of the major brittle tectonic structures of Crete (Fig. 12a) three deformational phases can be distinguished: (i) a first phase with compressional deformation producing arc-parallel east–west-trending south-directed thrust faults. This early phase was accompanied by isoclinal folding and other ductile deformation structures either with metamorphism at deep/middle tectonic levels or without at shallow tectonic level during Oligocene to Early Miocene time; (ii) a second phase with extensional deformation along arc-parallel, east–west-trending detachment faults during Middle Miocene time. This medial phase produced a tectonic horst structure with hanging wall motions driven to the north and south respectively; and (iii) a third phase during the Late Miocene– Quaternary with extensional deformation along younger high-angle normal and oblique normal faults that disrupt the older arc-parallel structures. In conclusion, the revised tectono-stratigraphy of Crete and especially of the “Phyllites–Quartzites” complex demonstrated the

distinction of the probable Paleozoic low-medium grade metamorphic rocks of the Arna unit from the underlying Permo–Triassic phyllites and associated sediments of Western Crete unit as well as the overlying Permo–Triassic phyllites and associated sediments of the Tyros/Ravdoucha Beds at the base of the Tripolis unit. The pre-existing mixture of the above tectono-stratigraphic units in a single complex created a number of misinterpretations as far as stratigraphy, metamorphism and interpretation of low angle faults as thrusts or detachments. Especially in cases where the inferred tectonic contact concerns the transition between the Tyros Beds and the base of the Tripolis platform there is no structural omission and therefore the contact represents a minor disharmonic sliding surface and not a detachment. Based on the revised tectono-stratigraphic analysis the determination of the structural omission for each tectonic contact was possible. Footwall rocks of the detachments comprised several tectonic units usually from the lower nappes and hanging wall rocks comprised several tectonic units usually from the upper nappes. The detachment may separate metamorphosed units in the footwall (Mani, Western Crete, Arna) from non metamorphosed units in the hanging wall (Tripolis, Pindos and higher nappes) but also all other possible combinations from the Cretan nappe pile. Extension in Crete started in the Middle–Late Miocene with the formation of extensional detachment faults. The reported extensional structures of Oligocene to Early Miocene age do not correspond to crustal extension of Crete but

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