Tectonophysics 568–569 (2012) 320–334

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The Cretan ophiolite-bearing mélange (Greece):A remnant of Alpine accretionary wedge

L. Tortorici ⁎, S. Catalano, R. Cirrincione, G. TortoriciDipartimento di Scienze Geologiche, University of Catania, C.so Italia 55, 95129 Catania, Italy

⁎ Corresponding author. Tel.: +39 0957195721.E-mail address: tortoric@unict.it (L. Tortorici).

0040-1951/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.tecto.2011.08.022

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 February 2011Received in revised form 19 August 2011Accepted 27 August 2011Available online 4 October 2011

Keywords:OphiolitesAccretionary wedgePaleogeneCreteGreece

New data collected in central Crete on the ophiolite-bearing units, result in a better understanding of therole and tectonic significance of these units in the construction of this segment of the Hellenides. Thesenappes are composed of three main tectonic units that, characterized by different metamorphic facies con-ditions, are represented by an un-metamorphosed lower unit, a greenschist to HP greenschist-facies inter-mediate unit and a blueschist-facies upper unit. These chaotic thrust-nappes include blocks of oceanic andcontinental deriving rocks and can be considered as a remnant of an accretionary complex. The lower unitrepresents the toe of the wedge whereas the intermediate and upper units refer to the innermost and dee-per subducted portions exhumed and superimposed on top of each other during the early stages of conti-nental collision. The structural evolution of the accretionary wedge was controlled by four maincontractional deformation events that, including distinct groups of structures developed at different crustallevels, were driven by SSE and SSW directions of tectonic transport. Our data strongly suggest that theophiolite-bearing tectonic wedge was accreted during the Paleogene subduction of a Late Jurassic–Creta-ceous oceanic realm beneath the continental margin of the Pelagonian domain and it was successively in-volved in the continental collision with the Adria Block. The greenschist to blueschist facies metamorphismand the subsequent exhumation and emplacement of the intermediate and upper units above the frontalportion of the wedge may mainly be due to deep duplexing marking the onset of continental collision.We thus suggest that the ophiolite-bearing units of Crete represent a single suture zone related to the clo-sure of a unique oceanic domain (Pindos-Cycladic Ocean) subducted beneath the Internal Hellenides Plat-form continental domains thus assuming the significance of a southern oceanic seaway of the largesteastern Neotethys developed since the Triassic between Eurasia and Africa.

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1. Introduction

The island of Crete represents a fragment of the perimediterraneanAlpine orogenic belt. It is located at the front of the Hellenic Arc andconnects the Hellenides to the northwest, with the Taurides to thenortheast. The orogenic belt consists of a pile of thrust-nappes deriv-ing from the deformation of Mesozoic to Cainozoic paleogeographicdomains related to the progressive Africa–Eurasia convergence. Thisfirstly caused the subduction of the northeastern oceanic domain(s),then it caused the continental collision with the Adria microplateand finally, the present northward-dipping subduction of the easternMediterranean oceanic realm.

1.1. Tectonic setting

The overall architecture of the island is characterized by a pile ofthrust-nappes grouped in two major structural elements (upper andlower tectonic units in Fig. 1) separated by a major shear zone (e.g.Chatzaras et al., 2006; Fassoulas et al., 1994; Jolivet et al., 1996;Seidel et al., 1982). This regional feature which bounds upwards theHP rock-units of the island of Crete, aswell as those occurring in the Ae-gean domain (e.g. Cycladic zone), is currently interpreted as being partof a large low-angle extensional detachment (the Cretan detachment)responsible for the crustal thinning of the southern Aegean and forthe exhumation of the HP/LT metamorphic rocks of the lower nappes(Fassoulas, 1999; Fassoulas et al., 1994; Jolivet et al., 1996; Listeret al., 1984; Papanikolaou and Vassilakis, 2010; Ring and Layer, 2003;Ring and Reischmann, 2002; Ring et al., 2001; van Hinsbergen et al.,2005). Alternatively, the Cretan detachment has also been interpretedas being the upper boundary of an extruding wedge developed abovethe Hellenic subduction zone during the Africa–Europe convergent pro-cesses, which involved oceanic domains and/or continental terranes be-longing to the fragmented margin of the Adria block (Ring et al., 2007

Spili

Agia Galini

Heraklion

N

Lendas

Asteroussian

mountai

Greece

Crete

Upp

er te

cton

ic u

nits

Low

er te

cton

icun

its

Uppermostunits

Pindos unit

Tripolitza unit

PhylliteQuartzite unit

Plattenkalkunit

Ophiolitic mélange

Deep water carbonates and flyschdeposits (Triassic-Oligocene ?)

Shallow water carbonates and flyschdeposits (Triassic-Oligocene)

Marbles, schists, dolomitic marbles,marbles with nodular cherts and flyschdeposits (Triassic-Middle Oligocene)

Phyllites, quartzites, marbles,metavolcanics (Carboniferous-Triassic)

a

Miocene-Quaternarydeposits

Upper tectonic units

Lower tectonic units

50 km

Pindos-Ethia nappe

(Triassic-U. Eocene)

Ophiolites

?

?

Bl o

c k yF l y s c h

cOphiolites

Miamou-Vatos nappe(Triassic-U. Jurassic)

Arvi nappe(U. Cretaceous-Palaeoc.)

Pindos-Ethia nappe(Triassic-Oligocene)

As

t e r o u s s i a n a p p e

b

Fig. 2

Fig. 3

Fig. 1. Simplified tectonic map of the island of Crete. Inset (a) shows a tectonostratigraphic scheme of the major tectonic units of Crete (modified from Chatzaras et al., 2006). Insets(b) and (c) illustrate the two major tectonostratigraphic interpretations of the uppermost ophiolite-bearing units. Inset (b) indicates the ophiolites and the associated rocks as dis-tinct tectonic units (from Bonneau et al., 1977; Bonneau, 1984) whereas inset (c) shows these rock-assemblages as olistoliths and/or olistostrome within the uppermost turbiditicsequence of the continental margin Pindos succession (from Hall et al., 1984).

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and referencewithin, Brun and Faccenna, 2008; Jolivet and Brun, 2010).The lower structural unit forms the backbone of the island and repre-sents the deepest and most external part of the Hellenides in Crete. Itconsists of a series of thrust sheets involving the neritic to pelagic car-bonate sequences of the Plattenkalk unit and the low-grade metamor-phic basement rocks of the Phyllite–quartzite nappe (inset a in Fig. 1)both affected by a Late Oligocene to Early Miocene HP/LT metamor-phism (Bonneau, 1984; Creutzburg and Seidel, 1975; Greilling, 1982;Hall et al., 1984; Jolivet et al., 1996; Seidel et al., 1982; Theye and Seidel,1991; 1993; Thomson et al., 1998). The upper structural unit (inset a inFig. 1) includes platform and pelagic carbonates of the Adria continentalpaleomargin forming the Tripolitza and Pindos units (Bonneau, 1984;Hall et al., 1984) tectonically covered by the so-called Uppermost Unit(Bonneau, 1984).

1.2. Geological setting of the ophiolite-bearing units

The Uppermost Unit is constituted by ophiolite-bearing nappeswithassociated continental basement rocks that, affected by Upper Creta-ceous HT/LP metamorphism (Langosch et al., 2000; Seidel et al.,1977), belong to the Pelagonian domain (Bonneau, 1984). Ophiolitesand associated rocks have been grouped in local and distinct tectonicunits (inset b in Fig. 1): the Asteroussia nappe (Bonneau, 1972), the Tri-assic–Upper Jurassic Miamou–Vatos units (Bonneau, 1984; Bonneauet al., 1974; 1977) and the Upper Cretaceous un-metamorphosed Arviunit (Bonneau, 1973; Robert and Bonneau, 1982). In contrast, the Cre-tan ophiolites and the Asteroussia continental basement rocks havebeen grouped together in a wide tectonic mélange (Langosch et al.,2000; Seidel et al., 1977, 1981) in which the ophiolite-bearing se-quences have been discerned in three major units represented by theVatos, Spili and Preveli groups, partially affected by greenschist toHP/LT metamorphism (Fassoulas, 1999; Krahl et al., 1982). However,both the ophiolitic and the continental basement rocks have been alsoconsidered as large exotic blocks (olistoliths and/or olistostrome) with-in the Upper Cretaceous–Eocene “Blocky Flysch” (inset c in Fig. 1) at thestratigraphic top of the pelagic paleomargin succession of the Pindos

unit (Hall et al., 1984). The apparent difference of interpretations ofstratigraphy and architecture of the Cretan ophiolite-bearing unitsmainly derives from the geological and structural complexity of theseunits, which including remnants of different portions of deformed oce-anic domains and continental paleomargins, underwent both oceanicand continental subduction processes. The distinct ages, the widerange of composition and the different structural position in the pileof nappes of Cretan ophiolites make it difficult to place these units inthe geodynamic models proposed for this segment of the eastern Med-iterranean orogenic belt. The ophiolitic sutures of the Hellenides haveindeed been related to the closure of a single large oceanic domaincharacterized by the occurrence of micro-continents or continentalpromontories separating different oceanic seaways (Bortolotti andPrincipi, 2005; Dercourt et al., 1986; Garfunkel, 2006; Ring and Layer,2003; Papanikolaou, 2009) or to the disruption of distinct oceanicbranches (Vardar, Pindos and Arvi oceans) separated by wide conti-nental microplates (Bonneau, 1984; Dilek et al., 1999; Golonka, 2004;Hall et al., 1984; Robertson, 2002, 2004; Stampfli and Borel, 2002). Inparticular, the Jurassic ophiolites extending on Crete have been inter-preted as the south-easternmost edge of the Dinaric–Hellenic ophioliticbelt deriving from the northern Neotethyan ocean while the UpperCretaceous ophiolites of the Arvi unit have been related to the Creta-ceous ophiolitic belt of the Taurides, Cyprus and Syria belonging tothe southern Neotethys (Koepke et al., 2002; Robertson, 2002).

In this paper, we present new geological, petrographic and struc-tural data from the ophiolite-bearing nappes cropping out on centralCrete. The study is mostly based on 1:20,000 scale field mappingwhich accompanied by detailed structural analyses contribute to defin-ing the geometric relationships between the distinct ophiolite-bearingunits and the geometry and sequence of the distinct sets of structuresformed at different crustal depths. These results combined with thosealready published and with the geological mapping of the Institute ofGeology and Mineral Exploration (I.G.M.E., 1982, 1984, 1985a, 1985b)contribute to the definition of a new architecture of the ophioli-tic nappes in the areas located in the Spili region, between theKedros massif to the north and the southern coast of the island

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(Fig. 2), and in the western part of the Asteroussia Mountainbelt, between Kali Limenes and Lendas (Fig. 3). In addition, ourdata also provide information on their structural and kinematicevolution in the light of the Alpine tectono-metamorphic evolu-tion of this segment of the Hellenides.

2. Tectono-stratigraphy of Cretan ophiolitic nappes

In central Crete, the ophiolite-bearing allochthonous nappes arerepresented by chaotic thrust-nappes that, as a whole, exhibit the pe-culiar features of a tectonic mélange (cf. Cowan, 1985; Hsu, 1968;Raymond, 1984). These assemblages of disrupted rocks, which corre-spond to the Cretan mélange (Langosch et al., 2000; Seidel et al.,1977, 1981) represent the highest tectonic nappe of the chain lyingabove both the Tripolitza and the Pindos units (see inset a in Fig. 1).The ophiolite-bearing nappes of the Cretan mélange can be subdi-vided into three main superimposed tectonic units defined by differ-ent metamorphism, the nature of the included blocks and by distinctgroups of structures developed at different crustal levels. Altogether,these units form an imbricate antiformal stack (inset a in Fig. 2)emplaced above the continental margin domains of the Adria Blockby a flat-lying sole-thrust of regional extent. This major detachmentis characterized by the occurrence of large-scale lens-shaped lithonsof fault-rocks deriving from shear deformation of portions belongingto both the hanging and footwall blocks, comparable with the “Thrustbreccia” described by Krahl (1982).

2.1. Lower unit

• The lower unit of the ophiolite-bearing allochthonous nappes is repre-sented by an un-metamorphosed to weakly metamorphosed chaoticunit made of a matrix that corresponds to portions of the Tertiary

Fig. 2. Structural sketch map of the Spili region in central Crete (see Fig. 1 for location). Insrelations with the continental margin tectonic units.

flysch of both the Tripolitza and thePindos nappes and to the turbiditicsequences of Vatos and Miamou units. This unit tectonically includesblocks of ophiolites with remnants of their sedimentary cover, pelagicand neritic carbonates and sequences of terrigenous and calcareousturbidites. The ophiolite-rocks partially correspond to the Vatos andMiamou units (Bonneau, 1984; Bonneau et al., 1974, 1977) and tothe Spili and Vatos groups described by Krahl et al. (1982). This unitalso includes several dismembered tectonic slices constituted by theophiolite-rocks with associated carbonate sediments belonging tothe Arvi unit (Bonneau, 1973; IGME, 1985a, 1985b; Robert andBonneau, 1982). The lower unit crops out extensively south of the vil-lage of Spili, along the tectonic depression located between the Kedrosand Assideroto ridges, in the area between Agia Galini, Melambes andAgios Pavlos (Fig. 2) and in the Asteroussia Mountain (Fig. 3).

The matrix is composed of seemingly chaotic sequences of shalesand/or metapelites affected by a penetrative foliation. It usuallylooks bright and shows different grades of fissility distributed in dis-crete domains separated by shear surfaces. Domains with relativelywell-preserved S–C-like fabric and abundant domains with dominantpervasive anastomosing foliation are recognizable, giving to therock-mass a typical appearance, which is usually described as scalyfoliation (Vannucchi et al., 2003). Despite the overall stratigraphicdisruption, coherent units are locally preserved as layered intervals,represented by sequences of brown claystone and marlstones withassociated fine-grained siliciclastic and calcareous turbidites whichshow ages ranging between the Late Cretaceous and the Eocene. Mi-cropaleontological analyses carried out on several samples indicate,in fact, nannofossil associations characterized by the occurrence ofArkhangelskiella cymbiformis, Micula spp., Stradneria crenulata andWatznaueria spp. (Late Cretaceous), Heliolithus kleinpellii, Prinsiusspp. and Toweius spp. (Paleocene) and Chiasmolithus solitus,

et (a) shows the tectonostratigraphic scheme of the Cretan ophiolitic nappes and their

Fig. 3. Structural sketch map of the western Asteroussia Mountain (see Fig. 1 for location; legend as Fig. 2).

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Coccolithus pelagicus, Ericsonia Formosa, Helicosphaera compacta andSphenolithus radians (Eocene).

The matrix wraps a multitude of lens-shaped blocks rangingin size from few centimeters up to about 1 km (Figs. 2, 3 and 4a).Ophiolite-blocks are mainly represented by extrusives composed ofaltered massive aphyric basalts and pillow lavas (Fig. 5a), rare gab-bros and gabbro-breccias and serpentinites containing slices of gab-broic rocks. In places, basalts show remnants of their sedimentarycover made up of reddish to brown siliciferous shales, radiolaritesand thin-layered pelagic marly limestones (Fig. 5b). However,inter-pillow pocket-sediments made of barren pinky to whitish calci-lutites have rarely been recognized (Fig. 5a). Ophiolite rocks exhibitgeochemical features of typical MORB and show a Middle Jurassic–Early Cretaceous age as constrained by absolute K/Ar and Pb/U dating(Koepke et al., 2002; Liati et al., 2004). Blocks of pelagic sediments aremainly represented by sequences attributed to the Arvi unit (Bonneau,1973; Robert and Bonneau, 1982). These bocks, well exposed to NE ofthe village of Melambes (Fig. 2) and along the coast of the AsteroussiaMountain from Kali Limenes and Lendas (Fig. 3), are made of red togreen calcareous mudstones, marlstones and calcareous marlstones,which grade upwards to pinky to white calcilutites (Fig. 5c). In places,these sediments contain rare nannofossil associations characterized bythe occurrence of Heliolithus kleinpellii, Prinsius spp. and Toweius spp.and Coccolithus pelagicus, Cyclicargolithus floridanus, Discoaster cf. barba-diensis, Discoaster deflandrei, Dictyococcites spp., Ericsonia formosa, Reticu-lofenestra spp. and Zygrhablithus bijugatus indicating a Paleocene to EarlyEocene age. Exotics of pink to red marly limestones and calcilutites arealso recognizable. Micropaleontological analyses carried out on severalsamples of these sequences which have been attributed to the UpperCretaceous (Bonneau, 1973; Robert and Bonneau, 1982), yielded a Pa-leocene nannofossils association characterized by the occurrence ofHeliolithus kleinpellii, Prinsius spp., Sphenolithus sp. and oweius spp.These sediments are frequently associated by well-exposed tectoniccontacts with bodies of pillow lavas and hyaloclastites defining distincttectonic slices within duplex horizons (Fig. 5d). WSW of the village ofMelambes (Fig. 2) and near the village of Lendas (Fig. 3), blocks of pe-lagic sediments, represented by Triassic to Cretaceous thin beddedwhite limestones and pink to red marly limestones, and by Cretaceousto Paleocene gray platy limestones and cherty limestones are often in-cluded. In places (e.g. E of the village of Vatos, Fig. 2), levels of turbiditicdebris flow constituted by poorly sorted breccias with clasts of

extrusives and white massive neritic limestones, gray glauconitic calcar-enites and Middle Eocene turbiditic biocalcarenites containing rests ofalgae, Nummulites sp., Assilina sp., Discocyclina sp. and Rotaliniidae, arerecognizable. Near the village of Melambes (Fig. 2), the different tecton-ic slices that dismember this chaotic complex are unconformably over-lain by a roughly 200 m thick siliciclastic turbiditic sequence made of amonotonous alternance of gray to brown mudstones and decimeter tometer thick beds of graded lithoarenites. Blocks of this turbidic se-quence are, in places, cannibalized within the matrix of the chaoticthrust-nappe.

2.2. Intermediate unit

This unit is composed of a polymetamorphosed and polydeformedsequence with associated blocks of oceanic and continental typerocks. The ocean-deriving nappes partially correspond to the Vatosand Miamou units (Bonneau, 1984; Bonneau et al., 1974, 1977), andto portions of the Vatos and Spili groups described by Krahl et al.(1982), whereas the continental basement rocks belong to the Aster-oussia unit (Bonneau, 1972, 1984; Langosch et al., 2000; Seidel et al.,1977, 1981). The intermediate unit is made up of prevalent phyllitesand schists with intercalations of metarenites, quartzites and mar-bles, and of sequences of calcschists and metalimestones (Fig. 4).The ophiolite-rocks are mainly represented by highly sheared serpen-tinites and serpentinized peridotite-breccias containing slices of gab-broic rocks partially rodingitized as well as remnants of metadiabasedykes. Serpentinites usually occur as lens-shaped bodies (Fig. 6a) thatmark the tectonic contact with the underlying un-metamorphosedophiolite-bearing nappe (Figs. 2 and 4a) or as slivers between the dif-ferent thrust-sheets that characterize the internal geometry of thisunit (Figs. 2 and 4). Ophiolite-rocks are also represented by raremetagabbros and metabasalts with remnants of their metasedimen-tary covers made up of metaradioralites, purple to red siliciferousschists, rare metahyaloclastites and calcschists. Metabasites, and inplaces their metasedimentary cover, show mineral assemblages indi-cating greenschist to HP greenschist conditions. The continental base-ment rocks are represented by blocks of different shapes and size thatconsist of sequences of phyllites and quartzites, amphibolites, schistsand marble and augen-gneisses with associated Upper Cretaceous in-trusive granitoid bodies (Langosch et al., 2000; Seidel et al., 1977,1981). Small, centimeters-sized, lithons of gneissic rocks are often

Fig. 4. Detailed maps showing the structural features and the relationships of the three ophiolite-bearing tectonic units of the Cretan mélange in the key-areas near Mourne (a) andPreveli (b). For location see Fig. 2.

324 L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

a b

c d

m

w

β

β

β

s

ml

s

ml

ml

ml

ml

Fig. 5. a) Ophiolite-block pillow-lavas with inter-pillow reddish marly sediments (ml) includedwithin the lower unit cropping out along the southern coast of the Asteroussia Mountain(see Fig. 3 for location). b) Tectonic slices of pillow-lavas (β) with remnants of sedimentary cover of siliciferous shale (s) grading upwards to reddish marly limestones (ml), embeddedwithin the lower unit of the Asteroussia Mountain. c) Block of pelagic sediments consisting of red calcareous mudstones (m) and white calcilutites (w) affected by NNE trending foldsexposed toNE of the village ofMelambes (see Fig. 2 for location). d) Block of red pelagic calcareousmudstones (m) including a tectonic slice of pillow lavas (β) exposed along the southerncoast of the Asteroussia Mountain (see Fig. 3 for location).

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sandwiched between both matrix (phyllites and calcschists) andmetabasites with a uniform pervasive tectonic foliation, whereasslivers ranging in size from a few to hundreds of meters are complete-ly wrapped in the matrix. Kilometric sized blocks of continental base-ment rocks, like those cropping out around the village of Melambes,are considered as exotics, tectonically embedded within this unit ofthe Cretan mélange (Fig. 2) as also stated by Seidel et al. (1981) andLangosch et al. (2000). Consequently, also the continental basementrocks that crop out on top of the Asteroussia Mountain range, fromKali Limenes to Lendas for a total length of about 12 km, could alsobe considered as large blocks contained within the Cretan mélange(Fig. 3). In this area continental rock-assemblages are in fact repre-sented by distinct rock-masses, which separated by lenses and sliversof highly-sheared serpentinites and serpentinized peridotite-breccias,form a tectonic stack completely sandwiched between the HP-greens-chist ophiolite bearing metamorphic rocks that crop out at its base,along the coastal region, and at its top in the area between the Miamouand Krotos villages (Fig. 3).

2.3. Upper unit

The uppermost unit of the Cretan mélange consists of theophiolite-bearing metamorphic sequence corresponding to the Preveligroup described by Krahl (1982) and to part of the Vatos unit (Bonneauand Lys, 1978; Bonneau et al., 1977). This unit tectonically overlies the in-termediate unit, which in turn overthrust the Tripolitza carbonates(Fig. 4). It is constituted by prevalent phyllites and micaceous schists al-ternating with quartzites and shaly-limestones, and by horizons of calcs-chistswith associatedmassive to gross-stratifiedmetalimestone (Fig. 4b).Lens-shaped blocks, ranging from a few centimeters to hundreds of me-ters in size, of massive marbles of Permian age (Bonneau and Lys, 1978;

Krahl, 1982) are also present as tectonic inclusionswithin themetapeliticmatrix (Fig. 4). Ophiolite-rocks are represented by rare metagabbros andmetabasalts with remnants of their metasedimentary covers made up ofmetaradiolarites, red siliciferous schists, pinkymetalimestones and calcs-chists (Fig. 6b). Small lens-shaped lithons of granitoid rocks, ranging froma few centimeters to tens of meters in length, are often sandwiched be-tween bothmatrix (phyllites and calcschists) andmetabasiteswith a uni-form pervasive tectonic foliation. The metabasites, with the associatedmetasedimentary cover, show mineral assemblages indicating a HP/LTmetamorphism. K/Ar absolute dating yielded ages around 148–150Ma(Seidel et al., 1981), which indicate an Upper Jurassic–Lower Cretaceousage for this metamorphic event, thus implying that this rock-assemblagemay represents the ophiolite suture zone of the internal Hellenides relat-ed to the closure of the Vardar–Axios ocean (Papanikolaou, 2009). Con-versely, these rocks have been correlated with the Cycladic blueschistsunits thus suggesting that the associated HP/LT metamorphic eventmay be related to a Paleocene–Eocene orogenic process (Fassoulas,1999; Fassoulas et al., 1994).

3. Petrographic features of the ophiolite rocks

The petrographic features of the ophiolitic rocks included withinthe Cretan mélange have been analyzed by studying 93 thin sections.

The ultramafic rocks are represented by serpentinites and serpen-tinized peridotite breccias, which mainly occur as tectonic slices be-tween the distinct ophiolite-bearing units. Serpentinites show anet-like texture with serpentine-minerals forming pseudomorphsafter olivine and pyroxene with large magnetite grains probably de-veloped as pseudomorphs after Cr-spinel. The dominant mineral as-semblage is represented by lizardite+bastite+magnetite+calcite+chlorite±crysotile. The massive serpentinites are locally affected by

a

b

s

l

r

β

β

Fig. 6. a) Slice of highly-sheared serpentinite (σ) enclosed within schists (s) andmeta-limestones (l) of the intermediate unit cropping out near the village of Vatos(see Fig. 2 for location). b) Glaucophane-bearing metabasalts (β) with remnants ofmetasedimentary cover of metaradiolarites (r) of the upper unit exposed near the Pre-veli Monastery (see Fig. 2 for location).

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brittle shear zones along which elongated serpentine fibers andcalcite±chlorite occur. The serpentinized peridotite breccias are co-hesive, disorganized, with highly angular ultramafic clasts of differentsizes showing a porphyroclastic texture. The ultramafic clasts varyboth in composition and in transformation degree ranging from ser-pentinized to relatively fresh lherzolites characterized by olivineand ortho- and clinopyroxene porphyroclasts. Alterated clasts aremainly composed of serpentine and magnetite, and display mesh,hourglass and bastite textures. Some clasts containing metamorphicminerals such as tremolite and chlorite frequently occur. The frag-ments of serpentinite cannot be clearly distinguished from the matrixor groundmass thus suggesting that the matrix was generated bycomminuting and alteration of the serpentinized peridotite porphyro-clasts. On the basis of the observed specific microscopic textures, theserpentinite peridotite breccias can thus be considered as cataclasites.

In the lower unit, extrusives are represented by metabasalts char-acterized by aphyric to porphyritic (P.I. from 5% to 25%) texture. Por-phyritic metabasalts are composed of euhedral plagioclase,pseudomorphic aggregates of chlorite, opaque and calcite. Hydrationof the primary ferromagnesian phases is common, often generatingtotal pseudomorphic textures; pyroxene and olivine relics are occa-sionally preserved. Plagioclase phenocrysts are totally albitized onlyin small irregular areas; an oligoclase composition has rarely been rec-ognized. Plagioclase phenocrysts, usually exhibiting cloudy surfaceswhich are covered by discontinuous flakes of sericite, frequentlyshow skeletal textures with the internal cavities, originally filledwith glass, characterized by aggregates of calcite±chlorite. Severalmicrolitic inclusions are commonly found along the primary cleavagesurfaces of the albitized plagioclase. Pseudomorphic textures are com-mon with the euhedral boundaries of such structure often consistingof opaques with fillings of calcite, chlorite and serpentine and/or mix-tures of iddingsite–bowlingite. Matrix varies from glassy, with low

amounts of spiky albitized plagioclase crystals, to microgranular withplagioclase, serpentine, patches of chlorite and opaques. Opaques areinhomogeneously distributed occurring in high (black matrix rocks),moderate and/or low amounts within the analyzed rocks. Flow align-ments of plagioclase microlites are locally present wrapping pseudo-morphs on mafic minerals. Subvariolitic textures made up of acicularplagioclase and/or chlorite-opaques aggregates have been often ob-served. Vesicles in the groundmass are usually filled with calcite, chal-cedony, or calcite associated with opaques and/or chlorite, and morerarely with zeolites. Gabbroic rocks show porphyroclastic texturewith magmatic gabbroic texture locally well preserved. The mineralassemblage is represented by clinopyroxene+actinolite+plagiocla-se+epidote+chlorite+opaques+calcite+white mica. The plagio-clase is totally albitized, whereas, the mafic phases are completelyreplaced by chlorite, actinolite, calcite and microcrystalline magnetite.The gabbroic breccias are made up of fragments of undeformedmicrogabbros mostly displaying equant textures. Both the texturaland the mineral assemblages observed in the ophiolites includedwithin this tectonic unit strongly indicate that these rocks were affect-ed by ocean-floor metamorphism and by metasomatic processes dur-ing subduction processes.

In the intermediate unit, metabasalts consist either of fine-grainedmassive and foliated rocks characterized by flow textures aroundquartz-feldspar, or of mafic augen-microdomains. Magmatic textures,preserved in microdomains, are represented by albitized magmaticplagioclase phenocrysts, frequently iso-oriented along the main folia-tion and often preserving “sieve textures”. The main foliation is de-fined by a greenschist facies assemblage represented by albite,chlorite, actinolite, epidote, titanite, opaques and rare biotite. Largeidioblastic amphiboles grew along the foliation. In some samples amineralogical association with riebeckite/crossite suggests an evolu-tion towards the HP greenschist facies. The metasedimentary coverconsists of schists, calcschists, and marbles often showing bandedtextures. In some schist specimens, high chlorite contents suggest avolcanoclastic component in the primary sediment. Schists and calcs-chists display a syn-kinematic crystallization of white mica, calcite,quartz and albite along the main foliation. This foliation is affectedby isoclinal folding which develops an axial plane foliation inquartz-feldspar-rich levels and a crenulation cleavage in the mica-r-ich levels (Fig. 7a). No blastesis evidence has been observed alongthis latter surface. Quartz grains within fractures show crystal pre-ferred orientation subparallel to the axial plane foliation. In the mar-bles, the polygonal texture developed during the first event, istruncated by brittle shear plane related to the second event. Thesefeatures define banded-amygdaloid structures consisting of an alter-nance of levels with different grain-size.

The ophiolitic-rocks of the upper unit consist of metabasalts, meta-volcanoclastic and metagabbros and metadolerites which underwent aprograde metamorphic path defined by relics of sub-greenschist faciesmineral assemblage and later albite and glaucophane overgrowth.Metabasalts and metavolcaniclastic rocks consist of fine-grained foliat-ed rocks defined by yellow-greenish bands alternating with deep-bluelayers. The blue bands show a HP/LT syn-kinematic blastesis of glauco-phane (Fig. 7b), chlorite, actinolite, titanite, epidote, albite and quartzwhereas, the yellow-greenish bands exhibit amineral assemblage of ep-idote, calcite, actinolite and subordinate glaucophane. The main folia-tion, frequently accompanied by rootless intrafolial folds (Fig. 7c), islocally affected by a late crenulation cleavage that developed withoutany syn-kinematic blastesis. In places the hinge zones are characterizedby the occurrence of chlorite and glaucophane with mimetic texture(Fig. 7d).Metagabbros andmetadolerites are characterized byweak an-isotropy and by subophitic texture with preserved plagioclase and py-roxene magmatic relicts. Metagabbros display mineral assemblages ofblueschist metamorphic grade constituted by albite and glaucophanegrowth on mafic minerals. In metapelites the main foliation is definedby white micas, quartz, albite and tiny glaucophane. Representative

a b

c d1 mm

1 mm

1 mm

3 mm

Fig. 7. a) Crenulation cleavagedeveloping on themain foliation inmetapelitic rocks of the intermediate unit (1 N). b) Syn-kinematic glaucophane inmetabasites of the upper unit (1 N). c)Rootless isoclinal fold hinge developed along themain foliation inmetabasites of the upper unit (1 N). d) Crenulation affecting themain foliation inwhite mica-glaucophane schist of theupper unit; both minerals show a syn-to-late kinematic growth displaying a mimetic texture (N+).

327L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

analyses of minerals of metabasites and metapelites (glaucophane andwhite micas) of the upper unit clearly indicate (Table 1) that whitemicas exhibit a high phengite content (3.65–3.74 Si p.f.u.). Accordingto the phengite geobarometry of Massonne and Schreyer (1987), min-eral assemblages together with the compositional features of phengiteand glaucophane, suggest a HP/LT metamorphism typical of blueschistfacies conditions characterized by values of pressure ranging from 12to14 kb and an estimated temperature of about 350°.

4. Structural data

The above-described ophiolite-bearing units show a wide spec-trum of structures whose development is strictly related to lithology,

Table 1Representative analyses of glaucophane (gl) and white mica (wm) in rocks of the upper unitron microprobe (Istituto di Geologia Ambientale e Geoingegnereia-CNR, Rome,) with silicalogiche, University of Catania) using a Tescan Vega LMU scanning electron microscope equBe window. Analyses were performed at 20 kV accelerating voltage and 0.2 nA beam curre

Samples 221ametabasite

221ametabasite

236metabasi

gl31 gl32 gl37SiO2 58.11 58.51 58.98TiO2 0.04 0.05 0.00Al2O3 7.14 7.66 7.41MgO 11.63 11.28 11.15CaO 1.49 0.81 0.51MnO 0.12 0.23 0.16FeO 13.16 12.68 13.23Na2O 6.57 6.80 6.76K2O 0.02 0.01 0.00P2O5 0.03 0.00 0.00F 0.00 0.01 0.04Cl 0.01 0.01 0.01Total: 98.31 98.03 98.25

as well as to the size and shape of the included blocks and to theirrheological contrast with the matrix. The rock-assemblages of Cretanmélange are characterized by distinct groups of structures that, hav-ing developed at distinct times and different structural levels, can beassigned to four major (DA–DD) deformation events. These eventshave been constrained by the structural geometry, the overprintingrelations between the distinct sets of the observed structures andby their statistic analysis (Fig. 4). The DA and DB events include allthe structural features generated during the building of the Cretanmélange from the oceanic subduction to the early stage of continen-tal collision, while the DC and DD events are characterized by thosestructures that, developed during the continent collision, uniformlyaffect all the units of Cretan mélange.

t. Mineral compositions were obtained using a WDS/EDS-equipped CAMECA SX50 elec-tes and oxides as standards, and by SEM–EDS analyses (Dipartimento di Scienze Geo-ipped with an EDAX Neptune XM4-60 micro-analyzer characterized by an ultra-thinnt. Precision of collected data is on the order of 5%.

te221bmetapelite

221bmetapelite

208metapelite

wm35 wm36 wm3851.45 51.84 51.680.12 0.08 0.14

25.62 26.10 26.663.90 3.78 3.530.01 0.04 0.030.03 0.01 0.003.58 3.06 2.840.31 0.38 0.49

10.41 10.53 10.490.05 0.00 0.000.17 0.00 0.000.00 0.01 0.02

95.66 95.83 95.86

328 L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

4.1. DA deformation event

The earliest recognizable structures of this event are related to thetectonic inclusions of the exotic blocks (mainly ophiolites) and to theformation of a tectonic mélange characterizing all three units.

In the un-metamorphosed unit, DA deformation is marked by stra-tal disruption and by the development of a bedding-parallel layeringdefined by a fissility and/or penetrative anastomosing foliation(SA1//S0). The SA1 is strictly associated with isoclinals, mainly recum-bent, rootless folds (FA1) and boudinage that affect the competentlayers, thus suggesting a total transposition of primary bedding relat-ed to layer-parallel extension (Fig. 8a). The SA1 is affected by discrete,decimetric to metric thick, shear zones that in the metapelitic matrixare characterized by S–C like fabric. This geometry frequently evolvesin an anastomized pattern, leading to the formation of lens-shapedmicrolithons bounded by shear surfaces thus defining a scaly foliation(SA2). The scaly foliation also defines an intersection lineation (LA2)mainly orientated along a NNE–SSW (Figs. 4a and 9a). Kinematic in-dicators and intersection lineations indicate a top to SE direction ofshear. Shear zones deflect around the distinct blocks involved in theshearing process, which are in places rotated with σ and/or δ geome-try (Fig. 8b). Shearing also produced a pervasive internal deformationof blocks, which are usually highly fractured and affected by roughlyE–W trending shear planes (TA2) which define lithons elongated ina SE direction. Tight to isoclinals folds (FA2) with axes orientedalong an N–S to NNE–SSW directions, in places accompanied byaxial plane cleavage, mostly developed in radiolarite and cherty lime-stone blocks (Fig. 5c). Kinematic data derived from the analysis ofshear bands, minor duplex structures, fold geometry and slickensidesurfaces with striae indicate a general top-to-the SSW sense of shear.

a b

c d

g

FA1

FB1

β

Fig. 8. a) Rootless recumbent fold (FA1) affecting fine-grained turbiditic sandstones of the uthe southern coast of the Asteroussia Mountain (see Fig. 3 for location). b) σ-type block shbearing unit near Agios Pavlos (see Fig. 2 for location). c) Rootless intrafolial fold in a smalaffected by a uniform pervasive tectonic foliation, exposed SSE of the Xiro ridge (see Fig.(see Fig. 2 for location).

In the overlying intermediate and upper metamorphic units, themélange formation was followed by a pervasive tectonic foliation(SA1) that affected both matrix (phyllites and calcschists) and blocks(ophiolites and continental type rocks). This planar fabric is charac-terized by metamorphic layering composed of greenschist and blues-chist facies mineral assemblages that developed in metabasites and inthe phyllites and micaschists in the intermediate and upper units, re-spectively. Minor rootless intrafolial folds (FA1) with a roughly NNW–

SSE to NE–SW trending axes, recognizable on metapelites and on oce-anic and continental basement blocks, are strictly associated with themain foliation, thus suggesting a large-scale transposition (Fig. 8c).Rare WNW–ESE to NNE–SSW trending stretching lineations (LA1) de-fined by alignments of feldspars, chlorite, micas and amphiboles inthe intermediate unit lithologies and of glaucophane and feldsparsin the upper unit, have been recognized (Figs. 4 and 9b).

4.2. DB deformation event

In the un-metamorphosed lower unit, the structures of this eventare mainly represented by ENE trending thrust faults (TB1) and bylow-angle contractional shear zones. Thrust faults are characterizedby the occurrence of slickenlines showing a general SE to SSE trans-port direction and are accompanied by flexural folding (FB1). Thisfolding event produced a NE–SW trending, overturned to recumbentramp anticlines and footwall synclines (Figs. 4 and 10a) which de-form the structures of the event DA (Fig. 8a). Shear zones are mainlydefined by duplex geometry, which are well developed within se-quences, with lithologies characterized by high competence contrast(e.g. ophiolite-rocks and their sedimentary covers) duplicating theprimary contacts (Figs. 5d and 8d). Duplexes are characterized by

n-metamorphosed lower unit refolded by the FB1 fold exposed near Kali Limenes alongowing a counter-clockwise and a left-hand sense of shear within the lower ophiolite-l lithon of gneissic rocks (g) associated with metabasites (β) of the intermediate unit,2 for location). d) Duplex structures in lower unit metapelites exposed S of Mourne

N

2%46

L s-c intersectionlineationsn. data: 36

A2

N

+++

+ + + + +

+

+++

+

X

XX

X

X

X

XX

XX

X

XX

X

X XX

X

XX

X

X

X X

XX

L stretchinglineations

A1

a b

Fig. 9. Stereoplots (lower hemisphere equal-area stereographic projections) of the linear structures of the DA event affecting (a) the un-metamorphosed lower unit and (b) theintermediate (+) and upper (x) units.

329L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

floor/link thrust intersection lines (LB1d) orientated along a mean NEdirection, thus suggesting a top to SE direction of shear (Figs. 4a and10b). Thrust faults, shear zones and duplexes affecting both matrixand blocks, probably developed during the imbrications of the differ-ent tectonic slices that presently characterize this unit. Kinematic

N

2%61014

FB1

FB1

old axesn. data: 34

a

N

2%610

old axesn. data: 87

c

low

er u

nit

inte

rmed

iate

/upp

er u

nit

: crenulation lineations in the intermediate u

: roof/floor link thrust lineations;

: poles to thrust planes

: crenulation lineations in the upper unit;

Fig. 10. Stereoplots (lower hemisphere equal-area stereographic projections

data derived from the analysis of minor duplex structures, fold geom-etry and slickenside surfaces with striae indicate a general top to SEsense of shear.

In the intermediate and upper units, structures related to the DB

event include centimeter to meter-sized symmetric south-verging

N

2%61014

LB1d oof/floor linkthrust intersectionlineationsn. data: 24

b

N

d

nit;

) of the structures of the DB event affecting the ophiolite bearing units.

330 L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

folds (FB1) with axes trending from NNE to NE (Figs. 4 and 10c) whichdeform the earlier SA1 foliation and the associated FA1 folds (Fig. 11a).FB1 also deforms the previous LAI stretching lineation,which consequentlyshows a great dispersion from WNW to NNE directions (Fig. 9b). Thehinge zones of the major folds exhibit well-developed SB1 crenulationcleavages (Fig. 11b) that produce NE-striking LB1c foliation–crenulationintersection lineations (Figs. 4 and 10c). FB1 is frequently associatedwith low-angle shear zones (TB1) that, characterized by cataclastic belts,are superimposed on the older SA1 foliation developing in the brittle–duc-tile transition. The TB1 often exhibits duplex geometry with NE trendingLB1d floor/link thrust intersection lines (Figs. 4 and 10d). The TB1 also in-cludes the shear zones that bring the upper unit over the intermediateone. These major shear zones are characterized by large-scale boudinagethat involves meter- to kilometer-sized lithons of oceanic (serpentinitesand rare metabasites) and continental (Asteroussia rock-units) blocks.NE trending thrust faults (TB2) splay out from the major low-angleshear zones forming the imbrications of the three superimposedmélangeunits. The major TB2 show cataclastic bands of variable thicknesses char-acterized by the occurrence of slickenlines indicating a present-day SEtectonic transport (Fig. 10d), are accompanied by NE–SW trending asym-metrical large folds (FB2) represented by overturned to recumbent rampanticlines and footwall synclines.

4.3. DC deformation event

This event includes the structures related to the large-scale over-thrusting process which led to the tectonic superposition of theophiolite-bearing allochthonous nappes on top of the platform andpelagic domains (Tripolitza and Pindos units) belonging to the Adria(Cretan) block. Overthrusting developed throughout a 100 m thickflat-lying shear zone of regional extent. This shear zone consists of a

a

b

FA1

FB1

Fig. 11. a) Rootless intrafolial FA1 fold deformed by the DB folding event (FB1) affect-ing micaceous schists and metarenites of the intermediate unit (see Fig. 2 for location).b) Well developed crenulation cleavage affecting schists and quartzites of the interme-diate unit exposed S of the Xiro ridge (see Fig. 2 for location).

silty–marly-clay matrix, mainly deriving from the Paleogene turbiditesof the Tripolitza and Pindos units, containing sheared blocks of metricto kilometric size sampled from both the allochthonous terranes ofthe hanging wall and the pelagic and platform carbonate units ofthe footwall. This tectonic horizon corresponds to the “Thrust breccia”described by Krahl (1982) and it seems to represent a common fea-ture that characterizes the basal thrust of the ophiolite-bearingnappes on the continental margin units (Papanikolaou, 2009). Themain structures affecting this basal shear zone are mainly representedby ENE trending low-angle contractional shear zones (TC1) character-ized by duplex geometry and by thrust faults (Fig. 12a). Thrust planesare characterized by the occurrence of slickenlines indicating a gener-al SE transport direction (Fig. 12b), and are accompanied by NE–SWtrending overturned to recumbent folds (FC1). Blocks of competentrocks, in which the DA and DB events-related structures are in placespreserved, are usually highly fractured and are affected by boudinageand by synthetic shear planes, defining lithons elongated along a SEdirection.

4.4. DD deformation event

This event includes semi-brittle to brittle contractional structures,which superimposed on the pre-existing structures, affect both thematrix and blocks of all the ophiolite-bearing units. They are repre-sented by WNW–ESE to NW–SE trending, mainly south-vergingthrust faults (TD1) with planes characterized by roughly subverticalslickenlines (Fig. 13a and c). Shear-zones also develop duplex geom-etry with floor/link thrust intersection lines (LD1d) trending along ameanWNW–ESE direction thus suggesting a top to the SSW directionof shear (Fig. 13a and c). Thrusting is associated with open to tight,asymmetrical SSW-verging folds (FD1) with axes orientated along anaverage NW–SE direction (Fig. 13b and d). In places, folding is accom-panied by axial plane cleavage mostly developed in more competentlayers and by rare crenulation cleavages on the hinge zones.

Furthermore, the entire pile of nappes is affected by roughlyWNW–ESE trending large-scale folds and thrusts, which can be relat-ed to the Late Miocene–Early Pleistocene contractional event(s) alsoaffecting the Neogene sediments (Tortorici et al., 2010).

5. Timing of deformation

The DA event includes all those structures related to the building ofthe Cretan mélange by a progressive shear deformation that occurredduring oceanic subduction. Stratigraphic constraints from the sedimen-tary sequences involved in the lower unit suggest that this event main-ly developed during the Paleogene. The lower unit is in fact composedof a matrix deriving from the deformation of thin-bedded Cretaceous–Eocene turbiditic sequences containing blocks of Middle-Late Jurassicophiolites with remnants of their sedimentary covers, Cretaceous toPaleocene oceanic sediments and Cretaceous to Middle Eocene pelagiclimestones. A Late Cretaceous–Paleocene to Late Eocene age could betherefore considered reasonable for the development of this portionof the Cretan accretionary wedge. This event also includes the struc-tures characterizing the intermediate and upper units that producedthe typical paragenesis of the greenschist and blueschist facies, respec-tively. The intermediate unit includes blocks of continental basementrocks intruded by Upper Cretaceous granitoids, thus implying thatthis portion of the Cretan mélange underwent the greenschists meta-morphism during the Paleogene times (probably Eocene), just beforeits exhumation and emplacement above the un-metamorphosed por-tion of the wedge. The upper unit rock-assemblage experienced ablueschist facies metamorphism dated at a Late Jurassic age (Seidelet al., 1981). Considering that this unit has been correlated with the Cy-cladic blueschist units (Fassoulas, 1999; Fassoulas et al., 1994; Katzir etal., 2007) and taking into account that the rocks of the upper unit ex-hibit a common structural pattern with the lower and intermediate

230/30

N

2%61014

Poles tothrust planesn. data: 26

DC

Mean slip vectorvalue: 328/45

N

2%61014

a b

Fig. 12. Contour plots (lower hemisphere equal area stereographic projections) of poles to DC thrust planes (a) and associated slickensides (b). The mean attitude of thrust planes,weighted by frequency and spacing, is reported in diagram (a); the mean value of slip vectors associated to thrust planes is also reported in diagram (b).

331L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

units of the Cretan mélange, a probable Eocene age is thus suggestedfor this HP/LT tectono-metamorphic event. The upper unit of the Cre-tan mélange could indeed be correlated with the Cycladic blueschistunit because of their similar structural position in the nappe pile. TheCycladic blueschist unit that also includes the ophiolitic Selçukmélange(Ring and Layer, 2003), lies in fact above the Basal unit which has beencorrelatedwith the Tripolitza unit of the external Hellenides (Shaked etal., 2000; Ring and Layer, 2003). Considering that geochronological

N

2%6101418

L roof/floor linkthrust intersectionlineationsn. data: 30

D1d

N

a

c

low

er u

nit

inte

rmed

iate

/upp

er u

nit

: roof/floor link thrust lineations;

Fig. 13. Stereoplots (lower hemisphere equal-area stereographic projections

data from the Cycladic blueschist unit constrained the HP/LT metamor-phic peak at ages between 55 and 45 Ma (Ring et al., 2007) we there-fore assume an Early-Middle Eocene age for the HP/LTmetamorphism affecting the upper unit of Cretan mélange.

The DB related structures that developed in the early collisionduring the uplift and exhumation of the metamorphic units andtheir emplacement above the un-metamorphosed lower unit. Thisevent predates the overthrust of the whole Cretan mélange above

N

2%61014

F fold axesn. data: 30

D1

N

F fold axesn. data: 67

D1

2%61014

b

d

: poles to thrust planes

) of the structures of the DD event affecting the ophiolite bearing units.

332 L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

the platform and pelagic domains (Tripolitza and Pindos units) ofthe Adria (Cretan) continental paleomargin (event DC). The turbidi-tic sequences involved in the basal shear zone (TC) which brings theophiolite-bearing nappes above the Tripolitza and Pindos units,contain nannofossil associations characterized by the occurrenceof Discoaster deflandrei, Dictyococcites bisectus, Ericsonia Formosa,E. subdistica, Helicosphaera euphratis and Sphenolithus moriformisindicating ages ranging between the Late Eocene and the Early Oli-gocene. Consequently, the DB event could be confinedwithin a shortperiod between the Late Eocene and the Early Oligocene. This age isconsistent with that provided by Papanikolaou (2009) being alsoquite comparable with dating estimation obtained by fission-trackthermochronologic data (Thomson et al., 1998).

The DD event was generated during the later stage of continentalcollision producing the WNW–ESE trending large-scale thrust andfolds whose development testifies a change in the orogenic transportfrom a southeastward (events DA–DC) to a southwestward direction.Similar change in the collision-kinematics has been also recognized inthe Plattenkalk and Phyllite–quartzite nappes (Chatzaras et al., 2006).In particular, contractional structures related to a NNE compressioncharacterized the Early-MiddleMiocene brittle stage of the exhumationof these units (D2 deformation phase of Chatzaras et al., 2006). Also con-sidering that the UpperMiocene–Lower Pleistocene sediments of west-ern Crete are affected by roughly south-verging thrust and folds(Tortorici et al., 2010), we suggest that the DD event can be reasonablyconfined between the end of the Early Miocene to the Early-MiddlePleistocene.

The regional emplacement of the Cretan mélange above the Tripo-litza and Pindos domains (DC event) can thus be constrained in theLate Oligocene–Early Miocene time-span.

6. Concluding remarks

Geological, structural and petrographic analyses carried out onthe ophiolite-bearing nappes of central Crete yielded new data tocharacterize the tectono-stratigraphic architecture and the struc-tural features of the so called “Cretan mélange” (Langosch et al.,2000; Seidel et al., 1977, 1981) and for a better understanding itsrole and tectonic significance in the construction of this segmentof the external Hellenides. Our data emphasize that the Cretanmélange can be subdivided into three main tectonic units charac-terized by different metamorphic facies. They are represented byan un-metamorphosed to weakly metamorphosed lower unit, agreenschist to HP greenschist intermediate unit and a HP/LTupper unit. These units show, as a whole, peculiar features compa-rable with the Type IV mélange of Cowan (1985), thus suggestingthat they may be interpreted as distinct portions of an accretion-ary wedge. In this context, the lower unit is thus interpreted as atectonic pile built up at the toe of the wedge where frontal accre-tion was dominant whereas, the intermediate and upper unitscould represent the innermost and deeper subducted portions ofthe wedge exhumed and superimposed on top of each other dur-ing the early stages of continent–continent collision.

The units of the Cretan mélange experienced a tectonic evolutioncontrolled by four major deformation events which produced severalgroups of structures that developed in response to a continuous com-pression firstly acting along a NNW–SSE direction (events DA–DC) andafterwards close to a NNE–SSW orientation (event DD). The first DA

event produced distinct sets of structures that developed at differentcrustal levels along major shear zones during the oceanic subduction.In the un-metamorphosed lower unit the deformation of this eventwas mostly related to frontal accretion processes developed at the toeof the accretionary wedge while in the intermediate and upper unitsproduced the main transposed foliation. The structures and metamor-phic features of the intermediate and upper units suggest that these tec-tono-metamorphic units underwent a greenschist (P-t values of 7–9 kb

and 350 °C) and HP/LT (P-t values of 12–14 kb and 350°–450 °C) sub-duction-related events, respectively. These primary features were sub-sequently greatly modified by DB deformation event that caused theextrusion and uplift of these units along the subduction channel duringthe onset of continental collision. The latest stage of the DB event pro-duced in brittle conditions the thrusting of these units onto the un-me-tamorphosed portions of thewedge causing the tectonic imbrications ofthe distinct ophiolite-bearing units. The DC eventwas dominated by theemplacement of the whole Cretan mélange on the continental paleo-margin of the Adria (Cretan) Block. Finally, the DD event was character-ized by thrusting with associated folding that developed during thecontinental collisionwith a southwestward tectonic transport involvingthe entire pile of Cretan nappes.

A similar sequence of structures that developed in response to anearlier NW–SE and a later NE–SW compression directions, grouped intwo principal deformation phases (D1 and D2), has been also recog-nized in the external units of the Plattenkalk and Phyllite-quartzitenappes (Chatzaras et al., 2006). It is worth noting that the Upper Cre-taceous–Lower Miocene DA–DC related structures could be comparedwith the Upper Oligocene–Lower Miocene structures of the D1 phase.As well, the Lower Miocene–Lower Pleistocene structures of the DD

event could be indeed compared with that belonging to the Lower-Middle Miocene of the D2 phase. This strongly supports the hypothe-sis that distinct and adjacent paleotectonic domains were involved ina continuous large-scale tectonic process migrating in both time andspace. We therefore suggest that the DA–DC events recorded in theophiolite bearing units and the D1 phase of the Plattenkalk and Phyl-lite–quartzite nappes, developed along a lithospheric convergentzone. This subduction zone firstly incorporated the inner portions ofthe accretionary wedge and subsequently the continental paleomar-gin of the Cretan (Adria) Block creating in the later stage a crustalstacking involving the buoyant Cretan continental crust (i.e. Platten-kalk and Phyllite–quartzite units). The DD event and the D2 phaseproduced the structural features that affected the entire pile of Cretannappes. However, Paleogene westward shearing events have been in-ferred from the analyses of the E–W trending stretching lineationsand the roughly NNE–SSW oriented fold axes recognized on the Pre-veli and Vatos ophiolite-bearing units (Fassoulas, 1999; Fassoulaset al., 1994; Hall et al., 1984). These structures, as shown by the struc-tural analysis presented in this paper, can be conversely interpretedas part of widely dispersed LA1 and FB1 groups, respectively.

Our results strongly suggest that the Cretan allochthonous tectonicwedge was accreted during the Paleogene subduction of a Late Juras-sic–Cretaceous oceanic realm beneath the continental margin of thePelagonian domain then involved in the continental collision with theCretan Block with a uniform SSE direction of tectonic transport(Fig. 14). The Early-Middle Eocene greenschist to blueschist faciesmetamorphism can be related to the underthrusting of the inner por-tions of the accretionary wedge beneath the Pelagonian continentalbasement at depth of about 35–40 km recording the total consumptionof the oceanic lithosphere and the onset of the continental collision(Fig. 14). Subsequently, during the Late Eocene–Early Oligocene the ex-humation and emplacement of the intermediate and upper units abovethe frontal portion of the accretionary wedge mainly due to deepduplexing (Cello and Mazzoli, 1996; Silver et al., 1985) occurred(Fig. 14). During this stage slices of basement-continental rocks draggedfrom the backstopwere incorporatedwithin the deepest portions of themélange (e.g. upper unit) whereas, larger blocks (e.g. Asteroussia conti-nental basement rocks) were sliced in the shallower portions of the ex-truded wedge (e.g. intermediate unit) by thrusting of the overridingplate (Ring and Glodny, 2010). The entire accretionary wedge wasthus involved in the continental collision and emplaced (Fig. 14) inthe Late Oligocene–Early Miocene above the Cretan continental margindomains (Tripolitza and Pindos domains). Portions of continentalpaleodomains (i.e. Plattenkalk and Tripolitza basement) were draggedwithin the subduction zone and successively stacked and exhumed at

EARLY OLIGOCENELATE EOCENE

LATE OLIGOCENE

LATE CRETACEOUSMIDDLE EOCENE

Cretan wedge

PelagonianBlock

Cretan Block Pindos Ocean

Plattenkalkdomain

Tripolitza domain Pindos domain

L i t h o s p h e r i c m a n t l e

S N

TripolitzaPindos

Tripolitza domainPlattenkalk domain PelagonianBlock

PelagonianBlock

Pindos domain

SN

Plattenkalk domain

NS

Eastern Mediterraneanoceanic domain

Cretan wedge

Cretan wedge

L i t h o s p h e r i c m a n t l e

L i t h o s p h e r i a n t l ec m

(D event)A

(D event)B

(D event)C

Fig. 14. Cartoon showing palinspastic profiles (not in scale) across the Pelagonian (Internal Hellenides Platform continental domains) and the Adria (Cretan) blocks showing thetectonic evolution of the Pindos-Cycladic Ocean (cf. Papanikolaou, 2009) and the Cretan accretionary wedge from the Late Cretaceous to the Late Oligocene.

333L. Tortorici et al. / Tectonophysics 568–569 (2012) 320–334

the leading edge of the upper plate. Finally, from the end of the EarlyMiocene the full continent–continent collision produced the large-scalecontractional structure that driven by a SSW shortening direction orig-inated the Cretan segment of the External Hellenides.

The results of this study strongly suggest that the ophiolite-bearing units of central Crete may represent a suture zone relatedto the closure of a single oceanic domain located between thesoutheastern edge of the Adria (Cretan) Block to the south, andthe Pelagonian continental terranes, to the north (Fig. 14). Froma geodynamic perspective, in the frame of the paleotectonic evolu-tion and of the paleogeography of the eastern Mediterranean, thisoceanic realm may represent the Pindos-Cycladic Ocean subductedbeneath the Internal Hellenides Platform continental domains(Papanikolaou, 2009) thus assuming the significance of a southernoceanic seaway of the largest eastern Neotethys that developedsince the Triassic between the Eurasia and Africa continentalmasses (Bortolotti and Principi, 2005; Dercourt et al., 1986; Gar-funkel, 2006; Papanikolaou, 2009; Ring and Layer, 2003). The Cre-tan accretionary wedge thus represents the more external suturezone of the Hellenides that developed during the northward sub-duction of the African plate beneath the southern margin of Eur-asia (Papanikolaou, 2009). The continuous southward retreat ofthe subducting slab therefore controlled both the consumption ofthe distinct branches of the oceanic realms and the introductionwithin the subduction channel of continental blocks generatingthickened crustal wedges associated with the exhumation of theHP metamorphic units (Brun and Faccenna, 2008; Jolivet andBrun, 2010). The continuous retreat of the subduction zone also causeda progressive increasing of the arc-curvature that consequently couldhave generated possible rotations along the edges of the arc. Despitecounter-clockwise rotations (10°–20° up to 40°) are reported in Creteonly since the Late Miocene (Duermeijer et al., 1998), we hypothesize

that the change in transport directions from south-southeast (DA–DC

events and D1 phase of Chatzaras et al., 2006) to south-southwest (DD

event and D2 phase of Chatzaras et al., 2006) recognized in the nappepile of Crete, could be related to a counter-clockwise rotation of the Cre-tan Block that accompanied the final subduction of the easternMediter-ranean oceanic domain beneath the island of Crete.

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