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The Variscan orogeny in Chios (Greece): Carboniferous accretion along a Palaeotethyan active margin A. Zanchi, 1 E. Garzanti, 2 C. Larghi, 3 L. Angiolini 3 and M. Gaetani 3 1 Dipartimento di Scienze dell’Ambiente e del Territorio, 2 Dipartimento di Scienze Geologiche e Geotecnologie, Universita ` degli studi di Milano–Bicocca, P.za della Scienza 1, 20126 Milan, Italy; 3 Dipartimento di Scienze della Terra ÔA. DesioÕ, Universita ` di Milano, Via Mangiagalli 34, 20133 Milan, Italy Introduction The Variscan Orogen can be traced eastward to the Pelagonian and exter- nal domains of the Hellenides (Neu- bauer and Raumer, 1993; Kotopouli et al., 2000; Vavassis et al., 2000; Dornsiepen et al., 2001), the Cycladic Attica Massif (Ring et al., 1999a; Engel and Reischmann, 2001; Reisch- mann et al., 2001), and the Sakarya Zone of the Pontides (Okay et al., 1996; Okay and Tuysuz, 1999). Car- boniferous deformation, metamor- phism and magmatism is generally ascribed to northward subduction of Palaeotethys and subsequent Gondw- ana–Laurasia collision. Subduction continued until the Late Triassic Cim- merian orogeny, as documented in the Karakaya Unit, an accretionary com- plex located in the southern part of the Sakarya Zone. This event was related to very different scenarios, from back-arc spreading within Sak- arya and subsequent closure (Stamp- fli, 2000; Stampfli and Borel, 2002), to accretion of Cimmerian microblocks (Sengor and Sungurlu, 1984) or ocea- nic plateaux to the southern margin of Laurasia (Okay, 2000; Okay et al., 2002) or to Gondwana (Pickett and Robertson, 1996). Although still debated (Eren, 2001), the Gondwanan Anatolide–Tauride block escaped the Late Palaeozoic Variscan deformation and was definitively accreted to Laur- asia during the Late Cretaceous Palaeogene (Okay and Tuysuz, 1999; Ring et al., 1999b). A strongly deformed Palaeozoic turbiditic succession including olisto- liths occurs on Chios Island (Fig. 1), and on the Karaburun peninsula gen- erally held to be part of the Izmir– Ankara Suture, a Cretaceous accre- tionary complex recording the closure of Neotethys between the Anatolide– Tauride Block and the Pontides. Lar- gely based on detailed data collected on Chios by Besenecker et al. (1968, 1971), the ÔChios me´langeÕ has been controversially interpreted as related to either northward (Papanikolau and Sideris, 1983; Stampfli et al., 1991) or southward (Robertson and Pickett, 2000) subduction of Palaeotethys. As Chios occupies a key position between the Variscan and Gondwana units, the aim of this paper is to present new stratigraphic and struc- tural data on the Chios Palaeozoic turbidites in order to unravel their depositional and deformational his- tory in the geodynamic evolution of western Palaeotethys. Geological setting Chios was studied by PhD students from Marburg (Besenecker et al., 1968, 1971), providing excellent strat- igraphic and structural data (Fig. 2). Two main thrust sheets occur in the island. The Lower Unit (Ôauthochtho- nousÕ of Besenecker et al., 1968) includes siliciclastic turbidites and embedded olistoliths of Silurian to Carboniferous rocks, named here as Volissos turbidites, and a Mesozoic carbonate succession. The Upper Unit (ÔallochthonousÕ Besenecker et al., 1968) occurs in isolated klippen, dis- placed by faults related to the Neo- gene Aegean extension. It includes Upper Carboniferous turbidites, Low- er Permian sandy to marly carbonates, Middle Permian shallow-water lime- stones, overlain by red siltstones and Jurassic platform carbonates. The Volissos turbidites The Volissos turbidites include microconglomerates, sandstones and mudrocks, commonly organized in Bouma-type sequences and mainly embedding calcareous, chert and vol- canic olistoliths. Tectonic repetitions and intense deformation prevent assessment of original stratigraphic thickness (possibly 3–4 km) and rela- tionships. Thin-bedded, fine-grained sand- stones, silty marls and fossiliferous lenticular grainstones near Papalia and Nagos include resedimented shal- low-water fossils (Besenecker et al., 1968; Herget, 1968; Roth, 1968). For- aminifers, calcareous algae, con- odonts, corals, and brachiopods (Gigantoproductinae, Phrycodothyris) ABSTRACT New stratigraphic and structural data on the turbiditic succes- sion of Chios (Volissos turbidites) suggest that this clastic wedge formed during the Early Carboniferous. These turbidites, fed long-distance by erosion of the Variscan orogen, were most likely deposited in a Palaeotethyan remnant-ocean basin. They were severely deformed and structurally thickened at anchi- metamorphic conditions before the close of the Palaeozoic. Both contractional and layer-parallel extensional structures, high strain rates, and broken-in-matrix fabrics along thick shear zones may suggest deformation at the toe of an accretionary wedge. Stratigraphic, petrographic and structural data indicate that Chios represents the westernmost part of Palaeotethys which escaped the Carboniferous collision between Gondwana and Laurasia, but received great volumes of terrigenous sediments from the Variscan belt, favouring the growth of a large accretionary prism. Terra Nova, 15, 213–223, 2003 Correspondence: Dr Andrea Zanchi, Dipartimento di Scienze dell’Ambiente e del Territorio, Universita` degli studi di Milano–Bicocca, P.za della Scienza 1, 20126 Milano, Italy. E-mail: andrea.zanchi @unimib.it Ó 2003 Blackwell Publishing Ltd 213 doi: 10.1046/j.1365-3121.2003.00483.x

The Variscan orogeny in Chios (Greece): Carboniferous accretion along a Palaeotethyan active margin

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Page 1: The Variscan orogeny in Chios (Greece): Carboniferous accretion along a Palaeotethyan active margin

The Variscan orogeny in Chios (Greece): Carboniferous accretionalong a Palaeotethyan active margin

A. Zanchi,1 E. Garzanti,2 C. Larghi,3 L. Angiolini3 and M. Gaetani31Dipartimento di Scienze dell’Ambiente e del Territorio, 2Dipartimento di Scienze Geologiche e Geotecnologie, Universita degli studi di

Milano–Bicocca, P.za della Scienza 1, 20126 Milan, Italy; 3Dipartimento di Scienze della Terra �A. Desio�, Universita di Milano, Via

Mangiagalli 34, 20133 Milan, Italy

Introduction

The Variscan Orogen can be tracedeastward to the Pelagonian and exter-nal domains of the Hellenides (Neu-bauer and Raumer, 1993; Kotopouliet al., 2000; Vavassis et al., 2000;Dornsiepen et al., 2001), the CycladicAttica Massif (Ring et al., 1999a;Engel and Reischmann, 2001; Reisch-mann et al., 2001), and the SakaryaZone of the Pontides (Okay et al.,1996; Okay and Tuysuz, 1999). Car-boniferous deformation, metamor-phism and magmatism is generallyascribed to northward subduction ofPalaeotethys and subsequent Gondw-ana–Laurasia collision. Subductioncontinued until the Late Triassic Cim-merian orogeny, as documented in theKarakaya Unit, an accretionary com-plex located in the southern part ofthe Sakarya Zone. This event wasrelated to very different scenarios,from back-arc spreading within Sak-arya and subsequent closure (Stamp-fli, 2000; Stampfli and Borel, 2002), toaccretion of Cimmerian microblocks(Sengor and Sungurlu, 1984) or ocea-nic plateaux to the southern margin ofLaurasia (Okay, 2000; Okay et al.,2002) or to Gondwana (Pickett

and Robertson, 1996). Although stilldebated (Eren, 2001), the GondwananAnatolide–Tauride block escaped theLate Palaeozoic Variscan deformationand was definitively accreted to Laur-asia during the Late Cretaceous –Palaeogene (Okay and Tuysuz, 1999;Ring et al., 1999b).A strongly deformed Palaeozoic

turbiditic succession including olisto-liths occurs on Chios Island (Fig. 1),and on the Karaburun peninsula gen-erally held to be part of the Izmir–Ankara Suture, a Cretaceous accre-tionary complex recording the closureof Neotethys between the Anatolide–Tauride Block and the Pontides. Lar-gely based on detailed data collectedon Chios by Besenecker et al. (1968,1971), the �Chios melange� has beencontroversially interpreted as relatedto either northward (Papanikolau andSideris, 1983; Stampfli et al., 1991) orsouthward (Robertson and Pickett,2000) subduction of Palaeotethys.As Chios occupies a key position

between the Variscan and Gondwanaunits, the aim of this paper is topresent new stratigraphic and struc-tural data on the Chios Palaeozoicturbidites in order to unravel theirdepositional and deformational his-tory in the geodynamic evolution ofwestern Palaeotethys.

Geological setting

Chios was studied by PhD studentsfrom Marburg (Besenecker et al.,1968, 1971), providing excellent strat-

igraphic and structural data (Fig. 2).Two main thrust sheets occur in theisland. The Lower Unit (�authochtho-nous� of Besenecker et al., 1968)includes siliciclastic turbidites andembedded olistoliths of Silurian toCarboniferous rocks, named here asVolissos turbidites, and a Mesozoiccarbonate succession. The Upper Unit(�allochthonous� Besenecker et al.,1968) occurs in isolated klippen, dis-placed by faults related to the Neo-gene Aegean extension. It includesUpper Carboniferous turbidites, Low-er Permian sandy to marly carbonates,Middle Permian shallow-water lime-stones, overlain by red siltstones andJurassic platform carbonates.

The Volissos turbidites

The Volissos turbidites includemicroconglomerates, sandstones andmudrocks, commonly organized inBouma-type sequences and mainlyembedding calcareous, chert and vol-canic olistoliths. Tectonic repetitionsand intense deformation preventassessment of original stratigraphicthickness (possibly 3–4 km) and rela-tionships.Thin-bedded, fine-grained sand-

stones, silty marls and fossiliferouslenticular grainstones near Papaliaand Nagos include resedimented shal-low-water fossils (Besenecker et al.,1968; Herget, 1968; Roth, 1968). For-aminifers, calcareous algae, con-odonts, corals, and brachiopods(Gigantoproductinae, Phrycodothyris)

ABSTRACT

New stratigraphic and structural data on the turbiditic succes-sion of Chios (Volissos turbidites) suggest that this clasticwedge formed during the Early Carboniferous. These turbidites,fed long-distance by erosion of the Variscan orogen, were mostlikely deposited in a Palaeotethyan remnant-ocean basin. Theywere severely deformed and structurally thickened at anchi-metamorphic conditions before the close of the Palaeozoic.Both contractional and layer-parallel extensional structures,high strain rates, and broken-in-matrix fabrics along thick shear

zones may suggest deformation at the toe of an accretionarywedge. Stratigraphic, petrographic and structural data indicatethat Chios represents the westernmost part of Palaeotethyswhich escaped the Carboniferous collision between Gondwanaand Laurasia, but received great volumes of terrigenoussediments from the Variscan belt, favouring the growth of alarge accretionary prism.

Terra Nova, 15, 213–223, 2003

Correspondence: Dr Andrea Zanchi,

Dipartimento di Scienze dell’Ambiente

e del Territorio, Universita degli studi

di Milano–Bicocca, P.za della Scienza 1,

20126 Milano, Italy. E-mail: andrea.zanchi

@unimib.it

� 2003 Blackwell Publishing Ltd 213

doi: 10.1046/j.1365-3121.2003.00483.x

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indicate a middle–late Visean age(Groves et al., 2003).

Sandstone petrography

The Volissos turbidites are quartzo-lithic (Q50 ± 6, F16 ± 6, L34 ± 7;parameters from Dickinson, 1985),relatively rich in feldspars, and includeabundant low- to high-rank metamor-phic rock fragments (19 ± 5 of QFLgrains). Composition indicates prov-enance chiefly from a thick-skinned,alpine-type collision orogen (Fig. 3),where low-grade metamorphic rockswere largely exposed in its axial part(Garzanti et al., 2003). Felsitic tomicrolitic volcanic rock fragmentsare common (7 ± 5 of QFL grains),and volcanic arenites with abundantvolcanic quartz and felsitic clastsoccur locally (Agio Gala, Metoxi),indicating subordinate but consistentsupply from a volcanic arc. Sedimen-tary rock fragments are subordinate,but chert is common, particularly inthe lower part of the section (4 ± 3 ofQFL grains). Carbonate grains areabsent to sporadic. Serpentine-schistgrains are rare. Dense-mineral assem-blages, strongly depleted because ofdiagenetic dissolution in the anchi-

metamorphic Volissos turbidites,chiefly include zircon, tourmaline,rutile and red to brown Cr spinel.Less depleted assemblages of theUpper Unit include more abundantgarnet and chloritoid, confirmingprovenance from low-grade metamor-phic rocks.

The olistoliths

The blocks (10 m to kilometric size)include massive and well-bedded lime-stones, cherty limestones, radiolaritesand volcanic rocks (mainly low-Kcalc-alkaline dacites and basalticandesites; Pe-Piper and Kotopouli,1994) with acidic pyroclastic rocksand tuffites (Kampia, Melanios,Aghio Gala). Blocks of conglomeratesand shales are subordinate. Smallbodies of serpentinized mantle perido-tites (E. Rampone, pers. comm. 2002)occur in southern Chios as tectonizedolistoliths embedded within the turbi-dites.The age of limestone blocks ranges

from Early Silurian (Llandovery:Besenecker et al., 1968) to Early Car-boniferous. Silurian limestone blocksoccur around Agrelopo, whereas Car-boniferous blocks prevail to the west.

Radiolarians (Entactinidae, Pseu-dospongoprunum sagittatum) and con-odonts (e.g. Palmatolepis gracilis)found in cherty olistoliths (Marmaro,Amani) indicate Late Silurian, andLate Devonian – ?Early Carbonifer-ous ages. We found conodonts (Loch-riea commutata, Gnathodus bilineatus,Lochriea mononodosa) in calcareousbreccias (Selino, Amani), indicating alate Visean – early Serpukovian age.Fossils within the Volissos turbiditesand olistoliths are thus Visean to earlySerpukovian, somewhat older thanpreviously suggested (Herget, 1968).

Provenance

Field observations indicate at least twosources of sediments, a distal one sup-plying the bulk of sand-sized detritus,and a proximal one shedding volcanicdetritus and sedimentary olistoliths.The main source was most likely

represented by basement and covernappes within a segment of the Var-iscan belt, which as with other high-relief collision orogens supplied hugeamounts of detritus to associatedbasins (Doglioni et al., 1999). Weenvisage long-distance transport oforogenic detritus via a river-deltasystem subparallel to tectonic strike,prior to final deposition by turbiditycurrents in a deep-water basin (Gra-ham et al., 1975).Significant and locally dominant

detritus from calc-alkaline volcanicrocks, volcanic olistoliths and Cr-spinel (Neubauer and Stattegger,1995) suggest deposition at a conver-gent plate margin close to an oceanicsubduction zone. Analogues of such atransport system can be found at bothsides of the Himalayan range, wherecontinent–continent convergence isreplaced laterally by oceanic subduc-tion, and orogenic detritus has longbeen funnelled in forearc to remnant-ocean basins (Critelli et al., 1990;Garzanti et al., 1996). Provenanceof the Volissos turbidites thus com-pares closely with that of bothNias Island (Indonesia) and Barbados(Lesser Antilles) accretionary prisms(Velbel, 1985). Although the natureof the substratum is unknown, theywere most likely deposited in a rem-nant-ocean basin (Ingersoll et al.,1993).Sedimentary olistoliths, docu-

menting unroofing of a Silurian to

Fig. 1 Generalized tectonic map of the Aegean and surrounding regions (SMZ:Serbo-Macedonian Zone; SVZ: Sava–Vardar Zone; PL: Pelagonian; PN-SPL: Pindosand Sub-Pelagonian; EX-HE: External Hellenides; ACM: Attica–Cycladic Massif;BFZ: Bornova Flysch Zone; Iz-An: Izmir–Ankara suture zone; PM: Pamphyliansuture).

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Lower Carboniferous continental-margin succession, were derivedfrom structural highs confining the

turbidite basin, possibly the outerslope of a Peri-Gondwanan blockinvolved in extensional deformation

while approaching the subductionzone or during accretion in theprism.

Fig. 2 Structural map of Chios (from Besenecker et al., 1971). The arrow with r indicates the position of serpentinitic olistoliths.

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Tectonic deformation in Chios

Structural observations have been car-ried out mostly in the Lower Unit ofnorth-western Chios. Variscan andAlpine events were separated by usingsuperposition criteria and relativechronology, and by comparing thestructures of the Palaeozoic successionwith those of its unconformableMesozoic stratigraphic cover. Exten-sion related to the Aegean Sea open-ing will not be discussed.

The Lower Unit

Strong deformation of the Volissosturbidites is the result of severalsuperposed tectonic events, includingrecent extension during the finalexhumation of the unit. Althoughmost authors represent the unit as asheared matrix containing olistolithswith generally preserved stratigraphiccontacts, pervasive folding and thickshear zones affect the whole unit,especially along lithological boundar-ies with strong competence contrasts.Both layer-contractional and exten-sional structures occur, often form-ing a tectonic melange related to

high strain rates and non-coaxialdeformation. Fold axes trend N–Sand NNW–SSE, axial planes are ver-tical or dip eastward (Fig. 4). Foldsare generally close to isoclinal with awell-developed slaty cleavage.Layer-parallel extension leading to

complete bedding disruption occurs inseveral places, where N–S- to NNW–SSE-trending thick shear zones, par-allel to the described fold axes, showpervasive scaly foliation, C–S shears,and brittle boudinage of competentsandy bodies forming block-in-matrixfabrics. At Kampia beach, the upperboundary of a rigid volcanic olistolithis a thick shear zone with scaly foli-ation and web structures forming apebbly tectonite (Kusky and Bradley,1999). Rigid sandstone bodies formasymmetric sandy blocks (Needham,1995), often crossed by R1 secondaryfractures (Fig. 5).Similar fabrics, complicated by

recent extensional shear zones, occuralong the western coast (Fig. 5). Here,N–S-trending folds with a well-devel-oped slaty cleavage give way to cata-clastic shear zones with a pervasivescaly foliation and shear planesarranged with a C–S geometry, asso-

ciated with P and R1 fractures. Closeto Kefala (site K78a), the slaty matrixis folded, sheared and thrusted uponthe rigid volcanic olistolith of Kampia.Similar shear zones occur in southernChios (Merikounta Bay) below theunconformable Mesozoic cover.Metamorphism associated with

deformation does not exceed verylow-grade conditions (sparse chloriteand sericite beards along cleavage),even in the lowermost part of the unit.Scaly fabrics are dominated by cata-clastic flow. An eastward decrease inmetamorphic conditions is also sug-gested by CAI (Conodont AlterationIndex, from 6 to 3) of Palaeozoicconodonts within the olistoliths.NNW–SSE-trending isoclinal folds

occur in phyllites exposed at thenorth-east tip of Chios and on Inous-ses Island, where the turbiditic succes-sion displays a low greenschist-faciesmetamorphic overprint.Superposed E–W andNE–SW chev-

ron folds and kink bands are wide-spread. E–W folds generally occurbelow the contact with theUpper Unit.Open NE–SW folds, commonly asso-ciated with thrust faults, cross previousfabrics along major shear zones.

Fig. 3 Sandstone composition. The Volissos turbidites of the Lower Unit (western, central and eastern areas) plot in the �recycledorogen� field (RO), with several samples close to the �magmatic arc� field (MA; Dickinson, 1985; CB ¼ �continental block� field).The Agio Gala sample is an arc-derived volcanic arenite. The Upper Unit turbidites are somewhat poorer in feldspars and richer inchiefly terrigenous sedimentary grains. Provenance of Chios turbidites compares with analogous remnant-ocean turbidites fedfrom erosion of distant orogenic belts and tectonically incorporated within accretionary prisms soon after deposition (Nias,Barbados, Makran; data after Moore, 1979; Velbel, 1980; Critelli et al., 1990). QFL and Lm ⁄Lv ⁄Ls plots after Ingersoll et al.(1993). The Lm pole includes a few serpentine-schist lithic grains. Ninety per cent confidence regions about the mean werecalculated after Weltje (2002).

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The structural setting of the overly-ing Mesozoic cover is very different.According to Herget (1968), it ischaracterized by NE–SW folds that

can be related to thrust propagation atshallow levels. Examples of thesestructures are the Lonaki anticlinenorth of Mt. Oros (Fig. 6) and the

Placoto anticline south of Amades,where overturned Lower Triassic stra-ta form an open NE–SW-trendingantiform. Folds with similar trend

Fig. 4 Mesoscopic structural data measured in the Volissos turbidites and in the phyllites of Inousses; Schmidt’s projection, lowerhemisphere. Black dots are fold axes, triangles are poles to slaty cleavage, large empty dots are poles to bedding planes. Thin linesare cyclographic projections of shear zones and reverse faults; black dots represent striations with relative sense of motion. Most ofthe observed structures trend NNW–SSE. In some plots polyphase fold assemblages are also represented (K54). SuperposedNE–SW and E–W structures (K21, K78b, K79b) are related to the Alpine deformation which is evident in the Mesozoic cover ofthe Volissos turbidites and in the upper tectonic units.

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are evident in north-eastern (Oura andJannia folds: Herget, 1968) and cen-tral Chios (Tietze, 1969).Our structural analyses reveal a

major deformation event documentedonly in the Volissos turbidites, and notin the Mesozoic cover. Pervasive fold-ing, slaty-cleavage, thick shear zoneswith scaly foliations occur only in theVolissos turbidites, and may haveformed at the toe of an accretionarywedge, where layer-parallel extensionin a matrix flowing along rigid blocksled to formation of a tectonic mel-ange. Similar features are observed inthe external part of forearc regions,where tectonic accretion of trench-derived sediments occurs (Lundbergand Moore, 1986).

The Upper unit

This unit (�allochthonous�) forms iso-lated klippen displaced by majorfaults related to the opening of theAegean Sea. Around Marmaro, par-

allel chevron folds along the mainthrust fronts, related to south-vergentthrust imbrication, trend from E–W toESE–WNW. Imbrication of thisnappe caused the formation of aduplex within the Lower Unit, theSkukla thrust sheet of Kauffman(1969), which forms an open rampantiform at Mesoraki, indicatingsouthward motion. Secondary foldsin Triassic strata close to the thrustfront also trend E–W. NE–SW folds,which formed before southwardmotion, occur in the overturnedLower Triassic succession at Skuklaand south of Marmaro.

The Palaeozoic/Mesozoicunconformity

Besenecker et al. (1968) hypothesizedthe occurrence of an angular uncon-formity at the base of the Mesozoicsuccession, but they were unable toobserve it directly. Along a recentroad cut, on the western slope of Mt.

Pelineon, we finally observed theunconformity (Fig. 7). The Volissosturbidites are intensely deformed andoverlain with erosional contact by a2–3-m-thick conglomeratic bed inclu-ding rounded clasts from the underly-ing succession, followed by quartzoseconglomerates and cross-laminatedsandstones. Closed folds affecting theturbidites a few metres below the un-conformity trend N–S, whereas basalTriassic strata are subhorizontal.The overlying transgressive succes-

sion includes arenites and carbonates,followed by the Marmoratrapeza For-mation yielding late Early Triassicfaunas (Gaetani et al., 1992).

Discussion and conclusions

• Fossils within the Volissos tur-bidites and embedded olistolithsindicate deposition during theVisean-Serpukhovian (late Early Car-boniferous). The common occurrenceof carbonate, chert and volcanic

Fig. 5 Tectonic fabrics of the Volissos turbidites. A: Closed folds with slaty cleavage at Cape Melanios. B: Cataclastic shear zone atEzoussa; C–S fabrics are evident in the left side of the broken folds; shear sense is top to the left (west). C: Scaly foliations formingweb structures at Kampia beach: R1 fractures and brittle boudinage suggest top to the right (west). D: Previous melange fabricsfolded by NE–SW-trending folds related to the Alpine orogenesis.

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olistoliths points to an intense synsed-imentary tectonic activity.• The petrographic composition of

the turbidites suggests long-distancetransport of detritus derived from theVariscan belt. Common to locallydominant volcanic detritus indicatesdeposition along a convergent platemargin, near a volcanic arc.• NNW–SSE folds and thick shear

zones occur only in the Volissos turbi-dites and in the phyllites of Inousses.These structures are absent in theMesozoic cover and in the uppertectonic units, where structures dis-play different trends (Fig. 8) and fea-tures.• Fabrics related to bedding-paral-

lel extension forming tectonic mel-anges, pervasive folding, and rockassociations (Gray and Foster, 1998,their table 1; Kusky and Bradley,

1999) may suggest deformation inthe superficial part of an accretionarywedge (Fig. 9).• The newly discovered angular

unconformity separating the Volissosturbidites from its Mesozoic coverproves that tectonic accretion of theturbiditic wedge was shortly followedby intense deformation and uplift, butthe region was not involved in contin-ent–continent collision, and sedimen-tation resumed with quartzose beachconglomerates at the beginning of theMesozoic.All observations point to deposition

of the Volissos turbidites in a rem-nant-ocean basin, a gulf of Palaeotet-hys connected along strike with, andfed by, the Variscan belt (Fig. 10). Weenvisage sedimentation as taking placewhile Palaeotethyan oceanic crust wasactively subducting beneath the south-

ern margin of Laurasia, and wasshortly followed by tectonic accre-tion within the frontal part of anarc–trench system. This is consistentwith the 18�N ± 7� palaeolatitudeobtained for the late Early Triassicof Chios (Muttoni et al., 1995), andalso the strong affinity of Viseanmicrofossils and brachiopods foundwithin the Volissos turbidites withthose from the South Urals, Europeand Algeria (i.e. Legrand-Blain, 1980;Groves et al., 2003).Carboniferous metamorphic com-

plexes and subduction-relatedintrusives in the Pelagonian andAttico-Cycladic Massif have beenrelated to continental collisionbetween Laurasia and Gondwana(Kotopouli et al., 2000), taking placeto the west of Chios. Preservation ofthe Chios accretionary wedge suggests

Fig. 6 Typical structures of the Mesozoic cover of the Lower unit: the Lonaki anticline (modified from Herget, 1968). The majorstructure, parasitic folds and minor thrust faults trend NE–SW, suggesting SE-vergent thrust motion (Lonaki 1 and 2). Folds withsimilar trends but with opposite dip directions on axial planes occur in the valley between Pithios and Mt. Oros (Oros 1, 2 and 3;Fig. 4). Triangles are poles to fracture cleavage; other symbols as in Fig. 4.

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that Palaeotethys was still open to theeast of these domains. Chios canthus be considered as a key palaeo-geographical element, documenting

the westernmost preserved part ofthe arc–trench system formed alongthe Palaeotethyan subduction zone,where great volumes of terrigenous

sediments derived from the Variscanbelt in the west reached the trench,favouring the growth of a large accre-tionary prism.

Fig. 7 The Late Palaeozoic unconformity between the Volissos turbidites and the basal Triassic succession. Unit A mainly consistsof turbidite-derived clasts, unit B of quartzose conglomerates and sandstones.

Fig. 8 Comparison among axes of meso-megascopic folds measured in the three major units of Chios. The NNW–SSE clusterpresent in the Volissos turbidites corresponds to the Variscan deformational event, which is completely absent in its Mesozoiccover and in the upper thrust sheets. Numbers refer to observed structures; maximum density is 8.15 in A, 7.21 in B and 14.47 in C.Contour interval at 1%.

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Acknowledgments

This research was supported with MIUR40% grants (1999–2001). Prof. PandelisTsoflias, Athens, is thanked for obtainingfield permits. F. Cordey (Lyon) and C.Corradini (Modena) are thanked for helpwith radiolarian and conodont determina-tions. The paper benefited from the reviewsby P. Matte, F. Neubauer and W. Franke.

Sergio Ando is thanked for the densemineral analyses.

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Received 14 November 2002; revised versionaccepted 26 March 2003

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