successive structural events in the hatay ophiolite of southeast turkey: distinguishing oceanic,...

Tectonophysics 473 (2009) 208–222

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Successive structural events in the Hatay ophiolite of southeast Turkey:Distinguishing oceanic, emplacement and post-emplacementphases of faulting

Jennifer Inwood a,⁎, Mark W. Anderson a, Antony Morris a, Alastair H.F. Robertson b

a School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UKb School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK

⁎ Corresponding author. Now at Borehole Research GUniversity of Leicester, University Road, Leicester LE1 7R

E-mail address: ji18@le.ac.uk (J. Inwood).

0040-1951/$ – see front matter © 2008 Elsevier B.V. Adoi:10.1016/j.tecto.2008.10.037

a b s t r a c t

Article history:

Keywords:OphioliteStructuralPalaeostressTectonicTurkeyReactivation

sented and interpreted for the Cretaceous Hatay ophiolite, which was emplacedonto the Arabian continental margin during latest Cretaceous (Maastrichtian) time. Although lacking apreserved metamorphic sole, a thick serpentinitic basal shear zone provides evidence of emplacementkinematics, whilst structures developed in an extensive Cenozoic sedimentary cover help to constrain thenature of post-emplacement deformation. Combining field structural measurements with palaeostressanalyses enables several discrete structural events to be recognised, of which three appear to pre-date theCenozoic sedimentary cover. The earliest event involved extension parallel to the ophiolitic sheeted dykecomplex and relates to oceanic spreading whereas the second and the third events relate to compression andstrike-slip during intra-oceanic displacement, or emplacement of the ophiolite onto the Arabian continentalmargin. Some structures at the base of or within the ophiolite that were previously attributed to sea-floorspreading processes (e.g. “oceanic detachment faults”) are more likely to have formed during subsequentophiolite displacement/emplacement and post-emplacement formation of the regional Hatay Graben.

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1. Introduction and geological setting

Ophiolites typically experience a complex tectonic history, includingdeformation during some or all of the following phases: intraoceanicdeformation related to seafloor spreading; initial, intra-oceanic detach-ment; emplacement onto a continental margin, and post-emplacementtectonic events. Some ophiolites reached their final positions only afterseveral phases of post-emplacement deformation. Additionally, tectonicinteractions may occur between newly forming structures and pre-existing structures. Relating specific structures to specific phases ofdeformation can be difficult, and as a result there are often differinginterpretations of both the mode of formation and the emplacement ofindividual ophiolites (see Robertson, 2006). The present study of theHatay ophiolite exemplifies such problems and indicates ways inwhichdifferent tectonic processes and settings can be distinguished, whichshould also be applicable to other ophiolites.

The Hatay ophiolite of southeastern Turkey is a relatively intactophiolite with an almost complete ophiolitic stratigraphy up to 7 kmthick, missing only a metamorphic sole and a deep-sea radiolaritecover (Dubertret, 1955; Vuagnat and Çoğulu, 1967; Aslaner, 1973;

roup, Department of Geology,H, UK.

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Parrot, 1973; Çoğulu et al., 1975; Tinkler et al., 1981; Delaloye andWagner, 1984; Pişkin et al., 1986; Robertson, 1986). This ophiolite isbelieved to have formed by supra-subduction zone spreading in asoutherly Neotethyan oceanic basin (e.g. Robertson, 1998; Bağci et al.,2005, 2008) followed by emplacement onto the Arabian platformduring the Maastrichtian (Dubertret, 1955; Aslaner, 1973; Tinkler etal., 1981). The ophiolite consists of two structurally distinct massifsseparated by the steeply dipping, NW-SE striking, Tahtaköprü Fault(Fig. 1). The relatively undeformed southwesterly massif forms abroad NE-SW trending antiformal structure with the deepeststructural levels of the ophiolite cropping out in the centre. Thismassif exposes plutonic rocks up to the level of a sheeted dykecomplex (e.g. Dubertret, 1955; Delaloye andWagner, 1984; Dilek et al.,1991; Dilek and Delaloye, 1992). By contrast, extrusive sequences andminor volumes of ferromanganiferous sediments (umbers) crop outin structurally complex small areas to the northeast of the TahtaköprüFault (Fig. 1) (e.g. Erendil, 1984; Robertson, 1986). Although theTahtaköprü Fault has a major effect on outcrop patterns, its timing andnature are not constrained mainly owing to limited exposure.

The main ophiolitic massif in the southwest forms a thick thrustsheet over Lower Cretaceous (Aptian–Albian) carbonate rocks of theArabianplatform, separated bya thinunit ofmelange (e.g. Aslaner,1973;Robertson, 1986). The contact between the ophiolite and an underlyingMesozoic carbonate platform, interpreted as the highest level ofcontinental crust, is only exposed in two small areas (Aslaner, 1973),

Fig. 1. Geological map, also showing structural sampling localities. Structural measurements within the Hatay ophiolite and its sedimentary cover focus on 13 key areas, mainlylocated within the basal shear zone, the ophiolite and its sedimentary cover in order determine the structural history of the ophiolite.

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one of which is an erosional window near Kömürçukuru (Fig. 1) wheresheared serpentinites contain large allochthonous limestone blocks. Thelowest level of the ophiolitic tectono-stratigraphy is exposed in a streamgully incised into thick-bedded, to massive, limestone a few kilometressouthwest of Kömürçukuru that is interpreted as part of the regionalArabian carbonate platform (e.g. Aslaner, 1973).

The ophiolite is covered transgressively by Upper Cretaceous toMiocene sedimentary sequences with a total thickness of ~3 km(Pişkin et al., 1986; Boulton et al., 2006). The lowest part of the

Maastrichtian succession is a widespread conglomerate horizoncontaining 70–80% ophiolitic detritus (Tinkler et al., 1981; Boultonet al., 2006). In the northeast the ophiolitic sheeted dykes areunconformably overlain by Maastrichtian non-marine to shallow-marine sediments that were deposited presumably after erosion ofophiolitic extrusive rocks (Erendil, 1984; Pişkin et al., 1986; Boultonand Robertson, 2007). The Upper Maastrichtian sediments areoverlain, concordantly, by Palaeocene to Upper Eocene clays, sand-stones, limestones and marls. A Miocene succession is transgressive

Fig. 2. Tectonic map of Turkey showing major structural features and the locations of the Troodos, Hatay and Baёr–Bassit ophiolites (adapted from various authors cited in the text).Inset map: a more detailed view centred on southeastern Turkey (adapted from Gürsoy et al., 2003).

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on the older sedimentary sequences and the ophiolite with a totalthickness of around 1.6 km (Boulton and Robertson, 2007) TheMiocene succession includes extensive conglomerates with abundantophiolitic detritus. Above this a Pliocene succession consists ofsandstones, marly limestones and clays whilst Quaternary sedimentsinclude poorly cemented conglomerates, travertines, alluvium andbeach sands (Pişkin et al., 1986; Boulton and Robertson, 2007).

Published structural work on the Hatay area has focused on aspectsof the ophiolite (e.g. Dilek and Thy, 1998) and on the sedimentary cover(e.g. Pişkin et al., 1986; Boulton et al., 2006; Boulton and Robertson,2008). The main objectives of the present work are to provide:

1. An overview of the structural development of the ophiolite bycombining field observations and structural analyses (e.g. palaeos-tress analyses) of the ophiolite basement and the sedimentary cover;

2. To use new structural evidence to test previous tectonic inter-pretations, notably whether oceanic and emplacement-related aswell as post-ophiolite emplacement events are present;

3. To assess the interactions between faults during successivestructural events and the influence of the pre-existing basementarchitecture on younger deformation systems;

4. To develop a new structural model for the Hatay ophiolite includingpre-, syn- and post-emplacement phases, with implications forophiolites elsewhere.

1.1. Regional tectonic setting

The geological history of the Mediterranean regionwas dominatedby the opening of the Neotethys Ocean mainly during Early Mesozoictime and its progressive closure during later Mesozoic–Cenozoic time(Robertson et al., 1991; Robertson and Comas, 1998). Present-daydeformation in the eastern Mediterranean region is primarilyinfluenced by interaction of the African and Eurasian plates (Fig. 2),notably involving an extensional regime inwestern Turkey (McKenzie,1972; Le Pichon and Angelier, 1979; Jackson, 1994). The region to theeast of Cyprus is characterised by the intersections of several majorregional structural lineaments including the East Anatolian Fault

(EAF) and the Dead Sea Fault (DSF). These are commonly believed tomeet in a triple junction between the African/Arabian, Eurasian andAnatolian plates in the region of Kahramanmaraş (e.g. McKenzie,1972; Arpat and Şaroğlu, 1972; Şengör et al., 1985; Lyberis et al. 1992;Westaway 1994). Triple junctions are inherently unstable (McKenzieand Morgan, 1969) and so are difficult to locate in the past. Anothersuggestion is that the EAF is unconnected to the DSF zone andcontinues southwest through the Gulf of Iskenderen to Cyprus (e.g.Hempton, 1987; Taymaz et al., 1991; Westaway, 1994; Yurtmen et al.,2000). In addition, dominantly sinistral strike-slip faults trendingENE-WSW in the Baër–Bassit region of Syria are interpreted to runeastwards from Cyprus as a zone of distributed deformation (Kemplerand Garfunkel, 1994; Ben-Avraham et al., 1995) linking with the DSF(Robertson, 1998; Al-Riyami et al., 2000; Morris et al., 2002;Hardenberg and Robertson, 2007).

The Hatay region lies at the northeastern corner of the Mediterra-nean and is characterised by a complex network of faults (Fig. 2). Thisregion has been interpreted to contain the intersections of severalmajorstructures. A triple junction between the EAF, DSF and eastwardsextension of the Cyprus Arc has been postulated within the Amik basin(Fig. 2, inset) (Över et al., 2004a). The mountainous Kızıldağ massif(Fig.1) has been interpreted to comprise thenorthern blockof a Cyprus–Antakya transform(CAT)and to indicate anactive tectonic regimedue toits height (1750 m) in relation to its proximity to the sea (Över et al.,2004a). The northern endof theDSFappears to splay into separate faults(Nur and Ben-Avraham,1978;Walley, 1988). The cumulative slip acrossthese faults is estimated as ~70–80 km fromoffset of theHatay ophiolite(Freund et al., 1970; Dewey et al., 1986; Lyberis et al., 1992).

The Hatay Graben extends from the Mediterranean coast north-eastwards to Antakya (Fig. 1) and developed after the emplacement ofthe Hatay and Baёr–Bassit ophiolites onto the Arabian platform(Delaloye et al., 1980; Tinkler et al., 1981; Parlak et al., 1998) with thepresent topographic basin developing during the Pliocene–Quatern-ary (Boulton et al., 2006; Boulton and Robertson, 2008). The grabencontinues northwards through the Amik plain, an area variouslynamed as the Hatay Graben (Perinçek and Çemen, 1990), the Amanosfault zone (Lyberis et al., 1992), or the Karasu rift (Westaway, 1994;

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Rojay et al., 2001; Över et al., 2004b). There are different interpreta-tions of the linkage between this more northerly tectonic basin andthe major EAF and DSF zones, which are either considered to be thenorthward continuation of the DSF zone (Tinkler et al., 1981; Parlaket al., 1998; Tatar et al., 2004), the southward continuation of the EAFzone (Şengör et al., 1985; Lyberis et al., 1992), or separate from both(Yürür and Çhorowicz, 1998).

1.2. The Hatay ophiolite and its tectonic evolution

There are also contrasting views regarding the structural evolutionof the Hatay ophiolite, as outlined below.

Most of the faults and folds observed within the ophiolite havegenerally been interpreted to be of post-emplacement origin (Tinkleret al., 1981; Pişkin et al., 1986), even if part of the outcrop pattern canbe interpreted as emplacement, or pre-emplacement-related. Analternative view is that certain structures preserve original seafloorrelationships (Dilek and Thy, 1998). The structural work presentedhere helps resolve some of the existing differences in interpretation.

The approach thatweuse here is to identify younger eventsfirst, thosethat are theoretically the least complicated and the easiest to recognise inthe field; these are then removed from the structural data base (i.e.backstripped), aiding the recognition of earlier structures and events.

1.2.1. Post-emplacement structuresInformation on post-emplacement structures can be gained from

analysis of the sedimentary cover, particularly where this is widelyexposed. Earlier tectonic events cannot be clearly identified in anophiolite without knowledge of any post-emplacement deformation.Tinkler et al. (1981) suggest that the post-emplacement history of theHatay ophiolite was characterised by several episodes of normalfaulting and folding, with structures trending approximately NE-SWand running parallel to the Hatay Graben. Seven events were reportedbeginning with ophiolite emplacement and ending with recent raisedbeaches, although due to age uncertainties, several of the faulting andfolding events could represent local expressions of the same regionalevent (Tinkler et al., 1981). The one- to two-kilometre uplift of thecentral part of the ophiolite was attributed by Pişkin et al. (1986) topre-Miocene NNW-SSE normal faulting. The contact between thegabbros and sheeted dyke complex along the coast (Fig. 1) is tectonic,possibly marked by a post-emplacement normal fault (e.g. Delaloyeet al., 1980). Recently, the structural history and setting of theMaastrichtian to Quaternary sedimentary cover of the ophiolite havebeen reassessed using a combination of sedimentary and structuraldata (Boulton and Robertson, 2008).

1.2.2. Structures formed during emplacementInformation on the mode of emplacement can be provided by

structural analysis of the metamorphic sole of an ophiolite, wherepresent. For example, the metamorphic sole of the Baër–Bassitophiolite in northern Syria allows a southeastward direction ofemplacement to be determined, which is consistent with the vergenceof structures in unmetamorphosed units beneath (Al-Riyami et al.,2002). The primary emplacement direction can still be determined,although these structures were transected by a Neotectonic strike-slipsystem.Where ametamorphic sole is lacking or not exposed, as for theHatay ophiolite, useful information on emplacement can still begained from structures close to the zone of emplacement. The basalshear zone of the Hatay ophiolite is exposed in small tectonicwindows and the structures preserved within these units provideinformation on the emplacement of the ophiolite. Previous authorshave suggested that some of the structures and the outcrop pattern ofthe Hatay ophiolite formed during emplacement. In particular, thecontact between the ultramafic rocks and the gabbros has beeninterpreted as a reverse fault (e.g. Tinkler et al., 1981; Pişkin et al.,1986; Delaloye et al., 1980).

1.2.3. Primary seafloor spreading structuresEarly (i.e. intra-oceanic) events may be so overprinted by

subsequent events that any related structures can be difficult torecognise in the field. However, the style of deformation may providea key to interpretation, because intra-oceanic magmatic processes canresult in ductile deformation, together with brittle processes whichcommonly predominate at higher levels in the oceanic lithosphere. Inaddition, determining the structural chronology of events may shedlight on pre-emplacement processes. One interpretation is that theinternal structure of the ophiolite, the areal distribution betweenophiolite subunits and the temporal and spatial relations betweenmagmatic and tectonic features can be attributed to intra-oceanicextensional tectonic processes (Erendil, 1984; Tekeli and Erendil,1985; Dilek and Delaloye, 1992; Dilek and Thy, 1998). Key structureswithin the Hatay ophiolite, including an inferred intraoceanicstructural graben along the coast, are believed to be indicative of aspreading-related origin for the faults and are thus inconsistent withcontractional deformation during convergence and ophiolite empla-cement (Dilek and Thy, 1998).

Some structural characteristics of the Hatay ophiolite can becompared with those observed in the Troodos ophiolite, whichpreserves many original seafloor relationships (e.g. Simonian andGass, 1978; Varga and Moores, l985; Allerton and Vine, l987; Vargaet al., l987; Dilek et al. 1990; Robertson, 1990; Robinson and Malpas,1990; Macleod and Murton, l993; Robertson and Xenophontos, 1993).For example, in Hatay, Dilek and Thy (1998) reported the presence ofan intra-oceanic structural graben characterised by two major faultsets along the coast, with a dyke-parallel set displaying listricgeometry and forming horst and graben structures. Spreading inducedfaulting and fracturing of sheeted dykes has been described from theTroodos ophiolite (Dietrich and Spencer, l993). These Hatay fault setswere envisaged as being similar to those documented in the Troodosophiolite (e.g. Varga and Moores, l985; Varga et al., 1987) and so torepresent a rifted spreading axis. Dilek and Thy (1998) specificallyinterpreted the Tahtaköprü fault as an accommodation zone thatfacilitated differential movements between adjacent ridge segmentsduring the generation of Neotethyan oceanic lithosphere. Theseauthors also compared smaller oblique-slip faults that are perpendi-cular to the contacts between major ophiolitic lithologies to similarstructures documented from the Mid-Atlantic Ridge (Karson andRona, 1990). Other structures including mineralisation of fault zonesand the cross-cutting of basaltic dykes within the ophiolite werecompared to seafloor examples (Dilek and Thy, 1998).

The exposed boundary between the serpentinised mantle and thecrustal units of the Hatay ophiolite is mostly tectonic and juxtaposes theuppermost levels of the ophiolite with mantle units along low-angletectonic contacts (Dilek and Thy,1998). These relationships are suggestedby Dilek and Thy (1998) to indicate high amounts of tectonic extension,driven by asymmetrical extension along a low-angle detachment surface.Low-angleextensionextensional faultinghasbeen inferred forcontinentaldetachment faults (core complexes; e.g. Wernicke, 1985), intra-oceanicdetachments (such as the mega-mullions of the Mid-Atlantic Ridge; e.g.Tucholke et al., l998) and detachment faults developed near the ocean–continent boundary (such as in the North Atlantic; e.g. Manatschal et al.,2001, and in the Alps; e.g. Manatschal et al., 2003).

The boundary between the dykes and gabbros is also interpreted byDilek and Thy (1998) as a low-angle detachment surface. In thisinterpretation the uplift and doming of the ultramafic corewas believedto have resulted from isostatic rebound of an unloaded footwall,facilitated by serpentinisation and diapiric activity during and afterdisplacement of the oceanic lithosphere from its original spreadingenvironment (Dilek and Thy, 1998). A locally important low-angledetachment fault has been identified between the massive gabbros andthe sheeted dykes within the inferred Solea graben of the Troodosophiolite, Cyprus (Varga et al., 1987), and might also exist in the Hatayophiolite if the two ophiolites formed in a similar tectonic setting.

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These are all hypotheses that can be tested using the newstructural data collected during this study.

2. Methodology

2.1. Structural sampling

Structural analysis concentrated on data collection from threemain settings:

1. The basal shear zone of the ophiolite and the limestones of theunderlying Arabian platform are important for interpreting thestructures relating to emplacement of the ophiolite, particularly inthe absence of a metamorphic sole.

2. Faults within themain body of the ophiolite record all of the phasesof deformation; thus an analysis of the structural development ofthe ophiolite as a whole is essential.

3. Investigation of faults affecting the sedimentary cover helpsconstrain post-emplacement deformation, is important for thedetermination of sequential structural events, and assists withback-stripping of post-emplacement structural events.

Structural measurements were made of 617 faults: 452 of these arefrom the ophiolitic basement and its associated shear zone; 165 fromthe overlying sedimentary cover and three specifically from theophiolite-sedimentary cover contact (Fig. 1). Just over a third of the617 faults (148 basement faults and 71 cover faults) within thecomplete dataset exhibit slickenfibres or other well constrained senseof slip indicators and are thus suitable for palaeostress analysis (i.e.the ‘palaeostress subset’). Where there is a good correlation betweenthe dominant trends in the fault strikes of the complete dataset andthe palaeostress subset (Fig. 3) this indicates that the subset isrepresentative of the overall structure in the region.

2.2. Procedure for identification of structural trends

The general patterns observed from the 617 faults measuredwithin the ophiolitic basement and cover provide a good indication ofthe structural patterns (Fig. 3). Although there is a large dispersion infault strikes within the study area as a whole, it is possible to identifyfour main trends (Fig. 3). However, only by determining the move-ment direction of faults and cross-cutting relationships can the timingor nature of structural events be established. Palaeostress determina-tions can aid the recognition of such key events, although these rely oncertain assumptions (e.g. a homogenous stress field) and have severallimitations (see Angelier, 1994). Fault slip data input into a basicpalaeostress analysis package (for analysis of the Hatay data thepackage used was TectonicsFP version 1.6 by Franz Reiter and PeterAcs, based on TectonicsVB, by Hugo Ortner for Apple Mackintosh)allows the directions of the principal stress axes (σ1 (P), σ2 (B) and σ3

(T)), the stress ratio: (Φ=(σ2−σ3)/(σ1−σ3)) and confidence limitson the solutions to be obtained. Previously, palaeostress determina-tions were provided for faults within the sedimentary cover butwithout reference to structures within the ophiolitic basement(Boulton et al., 2006; Boulton and Robertson, 2008).

In order to facilitate palaeostress analysis, faults were separatedinto ophiolitic basement and sedimentary cover, and into normal,reverse and strike-slip faults prior to further analysis and subdivisionaccording to a variety of parameters e.g. locality and orientation (seealso Inwood, 2005). Faults that are confined to the cover units wereonly affected by post-emplacement events allowing a relativelystraightforward interpretation. By contrast, fault patterns within theophiolite are potentially complicated by reactivation, rotation, orinteraction during successive events (Inwood, 2005). An importantstep in the recognition of such earlier events is the backstripping ofthese younger fault trends, as noted above.

3. Results

3.1. Inherited structure of the ophiolitic basement and the Hatay Graben

The boundaries between the tectonites, gabbros and the sheeted dykecomplex of the Hatay ophiolite run NE-SWand are oftenmarked by largegullies. The ophiolite has awell-developed, generally sub-vertical, sheeteddyke complex orientated on average E–W in present-day coordinates(Fig. 4a). As such, it is oblique to the general NE-SW trend of the outcroppattern. Dykes around Işikli in the NW are shallower and have morevariable strikes. Along the coast dykes generally dip northwards in thenorth and southwards in the south. Most previous workers (e.g. Tinkleret al., 1981; Pişkin et al., 1986) documented similar orientations of thesheeteddykecomplex.However,Dilek andThy (1998) reported that alongthecoast afirst setofdiabasedykes strikesNE-SW,whereas a secondsetofgreybasaltic dykes strikesNNW-SSE. Thesegenerationsofdykeswerealsoobserved during this study, although no difference in orientation betweengenerations was established.

The layering in cumulate gabbroswasmeasured at various localities,all of which are located on the southeast limb of the main ophioliticantiform, reflecting the quality of exposures and ease of access. Onaverage, the cumulate layering dips towards the NW at 57° (Fig. 4b),although there is marked variation even within a single area. Theorientation of the assumed palaeovertical (i.e. sheeted dykes) andpalaeohorizontal (pillowed lava flows; consistent planar cumulatelayering) within the ophiolite can be used to gauge the degree ofrotation about a horizontal axis. In addition, pillowed lava flows andsheet flows exposed in the NE massif of the ophiolite (Fig. 1), wherepresent, generally dip shallowly towards the SE (Fig. 4c).

The Hatay Graben has resulted in significant vertical displace-ments, thought to be in the order of several kilometres (Tinkler et al.,1981; Lyberis et al., 1992) and the major graben-bounding faults areknown to have produced horizontal axis rotations within the blocksadjacent to the faults (Boulton et al., 2006; Boulton and Robertson,2008). The dip of the sedimentary cover sequences within the Hatayregion can be used to indicate the amount by which post-emplacement faulting has tilted the successions. The dip of thesedimentary sequences is generally low with over a third of beds (of121measured) dipping between 20° and 30° (Fig. 4d). The variabilityof dip of the sedimentary bedding observed during this study showsthat a simple coherent tilt towards the main graben-bounding faultin the SE cannot be assumed (see also Boulton et al., 2006; Boultonand Robertson, 2008). This lack of consistency in orientationprevents simple backstripping of younger tilts from earlier structuraldata and suggests that local smaller-scale faults influence horizontalaxis rotations at least as much as the major faults in the region. Forexample, Boulton et al. (2006) show that many of the small faults,especially near the axis of the Hatay Graben, relate to mainlyPliocene oblique slip, which post-dates Miocene extension withinthe region.

3.2. Nature of faults and shear zones

During this work it was observed that the structures within theophiolite are dominated by brittle fracturing. Major faults arecharacterised by considerable erosion and landslipping, and streamsand rivers often follow these major structures, thus limiting the usefuloutcrop in some areas. Where exposed, the majority of faults havesimple planar to gently undulose surfaces, and narrow, or absentdamage zones. However, some faults, particularly within the gabbrosand ultramafic rocks in the Işikli area, and within areas of thesediments south of Belen (Fig. 1), are characterised by wider areas ofdeformation and local brecciation. Slickenlines observed on faultplanes within the ophiolite are occasionally mineralised and markedby steps indicating the local sense and direction of movement. Inaddition, slickenlines are commonly preserved in the sedimentary

Fig. 3. Dominant trends and comparisons of fault trends. The rose diagrams show the strike of all faults measured, as well as separated into basement and cover units. Although thereis a large dispersion in the datasets it is possible to recognise key trends. Measurements from traces on the published (Pişkin et al., 1986)map are further broken down into length andnumber. Faults measuredwithin the study area, where themovement direction could be identified, are suitable for palaeostress analyses. The smaller stereonets on the right separatefaults measured in the basement into separate ophiolite lithologies.

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cover. Locally, more than one orientation of slickenlines is present inthe sedimentary rocks (Över et al., 2002), but no chronology of faultmovement direction could be confirmed from this evidence (Boultonand Robertson, 2008). Movement direction could be distinguished for42% of the faults measured during this work. From this it is clear thatthe majority of faults, both in the ophiolitic basement (55%) andwithin the sedimentary cover (88%), are normal faults; also, strike-slipfaults are slightly more numerous than reverse faults. The differentfault types are ubiquitous throughout the area.

Limited access and exposure make it difficult to constrain thecontact geometries between the deeper levels of the ophiolite(tectonites, gabbros and the sheeted dyke complex) and for thisreason three alternative schematic cross-sections are shown in Fig. 5.Dilek and Thy (1998) suggested that many of the contacts betweenthese ophiolitic lithologies preserve primary seafloor spreadingrelations; e.g. detachment faults (Fig. 5a). Alternatively, the lowertwo sections illustrate how the outcrop pattern could be explained byreverse faulting (i.e. during emplacement of the ophiolite) (Fig. 5b) orby normal faulting (i.e. during neotectonic extension) (Fig. 5c). Eachof the major lithological boundaries dips steeply relative to thecumulate layering contrary to what would be expected if they wereextensional detachment faults. The observed orientation is insteadmore consistent with an origin as post-emplacement normal faults. Inaddition, the sheeted dykes are steeply inclined even close to thecontact with the gabbros wherever observed. This contrasts, forexample, with the inferred Solea Graben in the Troodos massif,

Cyprus, where the sheeted dykes are rotated sub-parallel to a clearlydefined extensional detachment between the gabbros and sheeteddykes (Varga et al., 1987).

The sheared serpentinites and entrained limestone blocks of thebasal shear zone of the ophiolite are characterised by a penetrativefabric and the development of relatively brittle low-angle shears withan S–C arrangement. SE- to SW-trending lineations (Fig. 6) are definedby serpentinite mineralisation within the ultramafic rocks and post-depositional carbonate mineralisation within the limestones. Theshear zone is dominated by brittle-style SE- and NW-dipping faults(Fig. 6). The basal shear zone is directly overlain by ophioliticextrusive rocks along its tectonic contacts. Where observed, thesecontacts dip shallowly to the NW.

3.3. Recognition of key structural trends

Although fault orientations are widely dispersed, as expected dueto the complex tectonic history of the region, four main trends areidentified: E–W, N–S, NW-SE and NE-SW striking. Within theophiolitic basement faults the NE-SW and E–W striking trends aredominant. All four trends can be recognised within the sedimentarycover, although relatively fewer E–W striking faults were measuredcompared to within the ophiolite. The results for the sedimentarycover are similar to those reported by Boulton et al. (2006) andBoulton and Robertson (2008). These trends are generally observablewhether the lengths or the numbers of faults are considered (Fig. 3),

Fig. 4. Inherited structures of the Hatay ophiolite. (a) The average orientation of the sheeted dyke complex is E–W in present-day coordinates. The smaller stereonets beneathillustrate trends within the sheeted dyke complex at selected localities. The E–Worientation is especially consistent along the coastal road and within the Karaçay valley, whereasNW-SE striking dykes are dominant at Işikli. At this locality the dip of the dykes is generally shallower with more variability in orientation. (b) Cumulate layering striking NE-SWdominates with layering striking E–Walso being a significant trend. The smaller stereonets beneath illustrate the trends from selected localities. The NE-SW striking trend is moresignificant along the coast and in the Karaçay valley, whereas the E–Wtrend is more significant in the Kisecik valley. (c)Within the extrusive sequences, measurements of pillow lavasand sheet lava flow indicate dominance of an ENE-WSW striking trend, which is consistent at all localities except Antakya. (d) The sedimentary cover sequences display a lack ofconsistency in bedding orientations, although almost all are shallowly dipping. No coherent pattern emerges even following further separation into localities.

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although some local differences exist (see below). The variation infault strike trends between key localities is illustrated on Fig. 6.

3.3.1. E–W striking faultsE–W trending faults represent a clear trend that appears to be

predominant when fault length is considered. E–W striking faults aremore dominantwithin the basement than the cover (Fig. 3), especiallywithin the sheeted dyke complex (Fig. 6; Coast South and Işikli).Lineament analysis across the wider Hatay region (Över et al., 2004a;Boulton et al., 2006) identifies similar trends. The present datasetallows the identification of a major ~75 km ENE-WSW lineamentbranching into three main segments trending 60°, 90° and 70°. Theassociation between sub-parallel dykes and faults within the base-

ment suggests that faulting either reflects primary spreading-relatedtectonic processes or subsequent reactivation of such fabrics. Shear-ing/slip along dyke margins is commonly observed and indicatesreactivation. Within gabbros and ultramafic rocks at deeper structurallevels in the ophiolite (i.e. to the north of the sheeted dyke complex onthe coast (Fig. 1)) the E–W fault trend is observed to become lesssignificant.

The E–W striking faults measured are predominantly normal inmovement direction in both the ophiolitic basement and thesedimentary cover. Within the basement, faults of several otherorientations transect the E–W striking faults. For example, along thecoastal road, faults oriented NE-SW consistently cut E–W strikingfaults. In several instances, the existence of two slickenside lineations

Fig. 5. Three possible cross-sections of the ophiolite that may explain the outcrop patterns observed within the Hatay ophiolite. The upper section is after Dilek and Thy (1998),whereas the two lower sketch sections illustrate two contrasting interpretations compiled from previous work and the authors' observations during the present fieldwork. See textfor discussion and the geology map of Fig. 1 for the approximate location of the cross-sections.

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on fault planes, particularly within the sheeted dyke complex exposednear the coast suggests that these faults were reactivated by youngerevents. Thus, these faults appear to be the oldest of those observed.

Within the cover sequences, E–W striking faults represent asignificant trend within the sandstones and limestones along the roadto the SE of Belen (Fig. 6). Palaeostress analysis of E–W striking faultswithin the sedimentary cover indicates that they have disparatedirections of slip vectors with no coherent pattern and lowconfidences in principal palaeostress stress axes; they are thereforeunlikely to have formed during one single event. A similar conclusionwas reached by Boulton et al. (2006) and Boulton and Robertson(2008). It is possible that this group of faults formed related to anolder event and were later rotated or reactivated, accounting for thedispersion in the slickenlines measured, or resulted from basementstructures propagating upwards into the cover sequences duringsuccessive younger faulting events (see Section 4).

3.3.2. NE-SW striking faultsAnalysis of the published map (Pişkin et al., 1986) indicates that

NE-SW striking structures are ubiquitous across the area, a featureconfirmed by the lineament analysis of Över et al. (2004a). Many ofthese structures are identified here as faults, particularly those withinthe basal shear zone of the ophiolite (Kömürçukuru area) (Fig. 6).Others mark major contacts between units within the ophiolite,although these are commonly at least partly tectonic in nature; forexample, faults oriented NE-SW are observed north of a gullyseparating the sheeted dyke complex from gabbros (GPS 0759022;4007029). NE-SW striking faults are significant in both the basementand the cover.

Within the ophiolitic basement the majority of the NE-SW strikingfaults are normal, although they are augmented by NE-SW strikingreverse faults and a small number of strike-slip faults. Cross-cuttingrelationships allow a sequential timing of these faults to be developed,beginning with: (i) an early reverse faulting event; (ii) developmentof NE-SW strike-slip faults, and finally (iii) NE-SWnormal faulting. Forexample, gabbros exposed along the coast road (GPS 0758985;4007065) are cut by numerous low-angle shear zones which show awell developed serpentinite fabric. Serpentine slickenlines, coupledwith fabric overprints, suggest both reverse and normal movementalong these shear zones. These are interpreted as low angle, NE-SWstriking, thrust faults which were later reactivated as normal faults.Further, also along the coast road (GPS 0757347; 4009664), a steepSE-dipping strike-slip fault is observed to cross-cut low angle, SE-dipping reverse faults. This steep fault is continuous throughout a cliff(N8 m) on which very clear strike-slip lineations in the centre of the

fault plane are overprinted by normal slickensides suggestingsubsequent reactivation.

Faults of NE-SW orientation are dominant within the cumulategabbros and ultramafic rocks and parallel to the average layeringobserved in the cumulate rocks. Assuming that at least some of thesefaults were formed after tilting, the cumulate layering could haveinfluenced the development of these faults in a similar way to thatobserved within the sheeted dyke complex.

Within the Kömürçukuru basal shear zone (Fig. 6) NE-SW strikingfaults dominate; these are generally reverse faults where the move-ment direction could be determined. Southeast-orientated lineationswithin the basal shear zone are associated with NE-SW striking brittlefaults but a lack of lineation data precluded their inclusion in thepalaeostress analysis. Where a full set of kinematic data could beobtained, palaeostress analysis of the reverse faults suggests thatthese formed under a single structural event. The reverse faultsobserved elsewhere within the ophiolite could also have formedduring this event.

Within the sedimentary cover, NE-SW striking faults are almostinvariably normal. This trend is clear within the Uçedik valley (Fig. 6),and dominates faults within muddy siltstones that were measured onthe turn-off from Belen (Fig. 6). Palaeostress analysis suggests that theNE-SW striking normal faults within both the cover and the basementrecord the same event which is, therefore, relatively young; this iscompatible with the timing of faulting events that is inferred for thebasement, as indicated above.

3.3.3. NW-SE striking faultsNW-SE trending structures are clearest in the sedimentary cover

(see also Boulton et al., 2006; Boulton and Robertson, 2008) but lesssignificant when considering the complete dataset of measured faults(Fig. 3). This trend is very significant at certain localities, mostlywithin the cover, particularly in the Uçedik valley and in sandstonesand limestones exposed along a road to the SE of Belen (Fig. 6). NW-SEstriking faults are often characterised by the development of breccia,e.g. along the stream sections measured in Işikli and near Gulderen.

Movement directions obtained from NW-SE striking faults suggestthat these almost invariably show a normal sense of movement in thesedimentary sequences and are also predominantly normal within theunderlying ophiolite. Palaeostress analysis suggests that the NW-SEstriking normal faults within both the cover and basement comprisepart of the same structural event.

Within the basement, a few of the NW-SE to more NNW-SSEstriking faults are of strike-slip type. Palaeostress analysis indicatesthat these strike-slip faults could relate to the same deformation as

Fig. 6. Fault strikes illustrated by locality. The rose diagrams illustrate fault strikes from selected locations throughout the Hatay ophiolite and its sedimentary cover. Analysis bylocalities allows spatial variations in orientation to be recognised. The rose diagrams are presented in the three key sampling locations with faults from ophiolite localities on the left,sedimentary cover on the right and the basal shear zone below. Within the ophiolite localities the lighter grey shading in the plots indicates measurements of sheeted dykes werepredominant within the locality whereas the darker grey indicates moremeasurements from the cumulate sequence. Although these rose diagrams indicate significant differences inorientation between localities, most identified trends are recognised across the ophiolite and cover indicating that the faults are not spatially discrete. Within the basement differenttrends dominate in different localities and the inherited structure appears to have an influence on fault strikes. For example, E–Wstriking faults are a significant trend in the southernsection of the coastal road where the E–Wstriking sheeted dyke complex is likely to have an influence. Within the cover, faults along the Belen road display two dominant directions,N–S striking and E–W striking. Faults elsewhere often pick out either the NW-SE striking trend or NE-SW striking trend. A good road section between Antakya and Altinözu allows alarge number of fault orientations to be observed and both NE-SWand NW-SE trends are recognised, whereas both trends may not be observed in localities where a smaller numberof faults could be measured. Within the basal shear zone brittle fault planes display a dominant NE-SW trend. Lineations measured within this zone are dispersed with a set orientedSE-NW and a subsidiary set oriented NE-SW most significant.

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the small number of NE-SW striking strike-slip faults observed withinthe basement (see Section 3.3.2). Cross-cutting relationships suggestthat these strike-slip faults formed subsequently to both the E–Wstriking and the reverse (NE-SW striking) faults in the basement. Forexample, within the sheeted dyke complex at Işikli (GPS 0752817;4024390) a steep dextral NNW-SSE trending strike-slip fault cuts anE–W trending fault. Since these faults are not seen in the coversequence they are assumed to have formed prior to deposition of theoverlying sediments.

Some NW-SE striking faults record an older lineation on the faultplane that is overprinted. For example, in Işikli, the fault plane of a NE-dipping fault displays normal lineations (with a rake of 82° NW) thatoverprint shallower lineations (with a rake of 18° NE). This reinforcesthe idea that the NW-SE striking faults that formed under the normalfaulting event, as recognised by palaeostress analysis, are youngerthan those formed under the suggested strike-slip faulting event.

3.3.4. N–S striking faultsN–S faults form a subordinate component of the total measured

fault population (Fig. 3) and are less apparent in the faults measuredwithin the study area than on the published map of Pişkin et al.(1986). Separation of faults into cover and basement, combined withspatial analysis, highlights the faults of N–S orientation: at certainlocalities (e.g. near Belen) N–S striking faults represent a clear trendwithin the sedimentary cover (Fig. 6). The Pişkin et al. (1986) mapsuggests that N–S striking faults become more abundant towards thenorth (around Belen) and also eastwards, which might suggest a linkwith movements along the Dead Sea Fault Zone to the east. Some ofthe faults within the N–S category are not dissimilar in strike to themore NNW-SSE and NNE-SSW striking faults of the NW-SE and NE-SW trends observed in adjacent areas of the cover. From initialpalaeostress analyses based on strike it difficult to determine whetherthe N–S striking faults comprise a separate trend within the studyarea; the analysis is compatible with some of the normal faults withinthe N–S grouping forming in conjunctionwith the NE-SW striking andNW-SE striking faults during a post-emplacement event.

3.4. Structural synthesis

A comprehensive structural analysis of the ophiolite and sedimen-tary cover, coupled with that of Boulton et al. (2006) and Boulton andRobertson (2008), allows several outstanding issues regarding thetectonic evolution of the Hatay ophiolite to be resolved. Severalpatterns become apparent from the analysis of regional structures.There is a clear NE-SW orientation of outcrop boundaries, and this isalso a dominant fault trend. The strikes of the different terrains withinthe Amanos range, of which the Hatay ophiolite forms part, similarlytrend NE-SW (Pişkin et al., 1986). The present-day average E–W strikeof the sheeted dyke complex in Hatay is thus oblique to this trend. As ageneral rule, sedimentary sequences have shallow-moderate (b30°)dips, although the marked variability does not allow a simplebackstripping of the sedimentary dip to be applied to restore the dipof structures within the ophiolitic basement.

Analysis of the spatial pattern of fault orientation shows that thefour dominant strike trends exist throughout the area studied,although there is some spatial variation. N–S striking faults aremore prevalent in the east and, as such, may be linked to the generallyN–S trending Dead Sea Fault. The NE-SW and NW-SE striking faulttrends identified in both basement and cover units are orientedslightly more NNE-SSW and NNW-SSE within the cover, with eitherone, or both of these trends (e.g. in the Uçedik valley), dominatingeach locality. This slight variation in trend is highlighted by thepalaeostress analysis (Fig. 7).

As a result of the fault analysis presented within this paper it ispossible to identify five clear structural events/trends that haveaffected the Hatay ophiolite (Fig. 7). The first three of these events are

confined to the ophiolitic basement with their relative timingdetermined from cross-cutting relationships. The earliest event canbe linked with deformation during the genesis of the oceanic crust,whereas the two later events that affected the basement only can beattributed to emplacement of the ophiolite. Two younger trends post-dated the ophiolite emplacement and are well-constrained within thesedimentary cover. However, these two latest events also affected theophiolitic basement. It was not possible to determine the relative ageof the two youngest trends because two consistent fault planes relatedto each event were not observed in proximity.

Based on all the available information the following tectonicscenarios are envisaged (Fig. 7).

3.4.1. Intraoceanic deformation

3.4.1.1. Event 1: N–S extension characterised by E–W striking normalfaults. The parallelism of the early (present-day) E–W strikingfaults with the (present-day) E–W striking sheeted dyke complex,along with the cross-cutting relationships and multiple slickensidelineation development, indicates that these faults comprise theearliest structural event within the ophiolite. This N–S extensionevent (present-day orientation) is likely to be linked with thedevelopment of the sheeted dyke complex early in the seafloorhistory of the ophiolite, including initial intrusion and later exten-sional re-activation.

3.4.2. Emplacement-related deformation

3.4.2.1. Event 2: NW-SE contraction characterised by NE-SW strikingthrust faults. This event is interpreted to follow the N–S extensionevent. The kinematic compatibility and similarity in orientationsbetween the structures observed within the basal shear zone and thereverse faults observed elsewhere suggest that all of these structuresformed during the emplacement of the ophiolite onto the Arabianplatform. If this is the case, the observed spread of lineationorientations, dispersed from the SW to SE in the basal shear zone,can be explained by local variations in the direction of thrusting andsurging during emplacement over the Arabian platform. The brittlefaults associated with these lineations within the basement strikepredominantly NE-SW. Thus, there is general consistency with theoverall SE direction of emplacement inferred for the related Baër–Bassit ophiolite of Syria although, there again, considerable localvariation in emplacement direction exists (Al-Riyami et al., 2002).

3.4.2.2. Event 3: N–S contraction characterised by conjugate strike-slipfaults. Large dextral NNW-SSE and sinistral NNE-SSW strikingstrike-slip faults are observed to cut E–W striking faults and NE-SWstriking reverse faults in several localities, but are not observed in thesedimentary cover, indicating that these faults represent the youngestpre-sedimentary cover event. These faults could be linked to the finalstages of ophiolite emplacement, which could have involved asignificant amount of strike-slip displacement. Stress ratios for bothcompression events are near zero. Assuming these are real values (i.e.unaffected by the complexity of fault interaction within the base-ment), a compressional regime characterised by thrust faulting couldhave switched to a compressional regime characterised by strike-slipfaulting in the later stages of ophiolite emplacement implying a flip inσ2 and σ3 principal stress axes.

3.4.3. Post-emplacement Neotectonic deformation affecting both theophiolite and the cover sequence (event order unknown):

3.4.3.1. Trend 4: NW-SE extension characterised by NNE-SSW strikingnormal faults. This well-constrained event is characterised bynormal faults in conjugate arrangement and is recognised within thebasement and the cover. No other faults are observed to cross-cut

Fig. 7. The recognition and timing of successive faulting events recognised to have affected the Hatay ophiolite allows a structural synthesis to be produced. Representative fieldphotographs are shown alongside a stereonet illustrating the faults that were used for the palaeostress analysis. Stereonets showing faults that were potentially reactivated duringeach event are shown to the right. For all stereonets, the fault traces in black represent faults within the ophiolitic basement and fault traces in grey represent those within thesedimentary cover.

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these NE-SW striking faults which themselves are observed to cross-cut faults in other orientations, particularly along the Mediterraneancoast. Some of the faults interpreted to be activated under this eventrecord an older lineation on the fault plane that is overprinted. Thefaults forming under this event are parallel to the present-day

orientation of the boundaries between ophiolitic units and may beresponsible for the outcrop pattern and the tilting of the cumulatesequences. In a complementary study the fault patterns and the stressregimes have been linked to the timing of sedimentation within theHatay Graben (Boulton et al., 2006, 2007; Boulton and Robertson,

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2007). The work by these authors indicates that NW-SE extensiondominated during the Early–Middle Miocene when the neotectonicHatay Graben was forming (Boulton and Robertson, 2008).

3.4.3.2. Trend 5: NE-SW extension characterised by NNW-SSE strikingnormal faults. As for the NW-SE extension, this event ischaracterised by normal faults in conjugate arrangement as recog-nised within both the basement and cover. No other faults areobserved to cut faults in this orientation.

The NNE-SSW trend and the NNW-SSE trend occur throughout theregion, with no preferred chronology (Boulton et al., 2006; Boultonand Robertson, 2008). There is a strong incidence of strike-slipfaulting affecting the Pliocene sediments, as documented by numer-ous faults within the axial zones of the Hatay Graben (Boulton et al.,2006; Boulton and Robertson, 2008). These faults are interpreted toreflect a change from pure extension during the Early–MiddleMiocene to one of transtension during the Pliocene, coupled to theregional westward escape of Anatolia from the Arabia/Eurasiacollision zone to the east (Boulton and Robertson, 2008). An analysisof instantaneous deformation as documented by regional GPSmeasurements suggests that today the Hatay Graben is experiencingoblique extension (Boulton and Robertson, 2008).

4. Reactivation and influence of the inherited structure of theophiolite

In an area that has experienced amulti-event tectonic history, suchas Hatay, the orientation and style of faults forming under youngersystems may be influenced by the pre-existing architecture of thebasement (Fig. 8). Faults from older stress systems can be reactivatedunder subsequent systems (Fig. 7).

Multiple directions of slickenside lineations were not commonlyobserved on individual faults in either the ophiolite or cover (see alsoRojay et al., 2001; Över et al., 2002; Boulton et al., 2006; Boulton andRobertson, 2008). However, a small number of faults measured inboth the ophiolite and the cover do display evidence of two lineations(Fig. 8) suggesting reactivation. Based on this study, the oldestidentified, E–W trending faults appear to be most prone to reactiva-tion, particularly in the form of either dextral or sinistral strike-slipfaults in the younger post-emplacement extensional regimes (Fig. 7).An example of the susceptibility of E–W trending faults to reactivationwas observed in Altinözu, where one fault with a NE-plunginglineation is interpreted as relating to trend 4, whereas a sinistralstrike-slip lineation could be related to trend 5. Many of the faults thatdo not fall simply into one of the constrained palaeostress directionscan be explained by reactivation of earlier structures under latersystems (Fig. 7). This could produce faults with different orientationsto the predicted theoretical orientation (where the assumption ismade that no interaction occurs with pre-existing structures). Thepost-cover NE-SW extension event appears likely to have incorpo-rated a large number of reactivated faults, especially E–W strikingfaults within the ophiolitic basement. The contact between theophiolite and the overlying sedimentary cover in places appears tohave been utilised by this tectonic event as a fault plane. The inheritedstructure of the basement appears to have a localised influence inareas where there is a clear pre-existing fabric. For example, theconsistent E–W strike of the sheeted dyke complex is influential infault development along the coast and the cumulate layering appearsto locally cause an increase in the dominance of layering-parallelfaults, such as within the Karaçay valley.

A further complication could be the reactivation and propagationof earlier basement structures into the overlying sedimentary coverduring subsequent deformation, producing faults that are in differentorientations to those predicted (Fig. 8). Analogue models by Duboiset al. (2002) submitted brittle and viscous layers to extension,followed by oblique or parallel extension or contraction, bothwith and

without a ‘sedimentary cover’. These authors found that where thesecondary deformation was oblique, newly formed faults could beparallel to the older grabens and oblique to the directions of theprincipal stress. In cases without sedimentation, all older faults werereactivated, whereas in cases with sedimentation in which thethickness and competency of the overlying material are significant(similar to the Hatay area), only certain faults from the older regimewere reactivated (Dubois et al., 2002). In the sedimentary cover of theHatay ophiolite, E–W striking normal faults display a lack ofconsistency in slickenside lineations and comprise the dominantstrike of faults that display two lineations. This group of faults ispotentially influenced by inherited basement structures.

5. Testing of previous tectonic interpretations of the Hatayophiolite

The main tectonic hypothesis that our new structural data can testis the importance of oceanic events in the emplaced ophiolite. Dilekand Thy (1998) hypothesised that the formation of almost all of themajor structural featureswithin theHatay ophiolite occurredwhilst onthe seafloorwithin a dominantlyextensional tectonic regime related toseafloor spreading. In general, similar fault trends are recognisedduring this study but these are interpreted differently. Dilek and Thy(1998) suggested that the sheeted dyke complex represents anintraoceanic extensional NE-SW oriented graben, with boundary-parallel NE-SW trending dykes dipping NW in the west (coastalsheeted dykes) and SE in the east (Karaçay valley). However, theobserved strike of the sheeted dyke complex is E–W; i.e. oblique to thegraben boundaries. These authors suggested that NE-SWdyke-parallelfaults and NW-SE trending tear faults within the coastal sheeted dykesformed related to extensional tectonics on the seafloor, and then diedout in within deeper oceanic lithologies with the tear faults beingoverlain by undeformed Maastrichtian sediments. Both of these faultstrendswere also recognised during this study and the orientation of σ3

calculated from the NE-SW trending faults is similar to that inferred byDilek and Thy (1998). While some faults of this orientation might beearly-formed, the majority are likely to be of post-ophiolite emplace-ment age based on cross-cutting relationships and the similarity inorientationwith faults in the sedimentary cover (see also Boulton et al.,2006 and Boulton and Robertson, 2008). The tear faults observed byDilek and Thy (1998) have oblique to strike-slip lineations and maycorrelate to the NNW-SSE trending strike-slip faults of Event 3. Thebasal shear zone of the ophiolite was interpreted by Dilek and Thy(1998) as a ductile zone of seafloor origin but is actually observed to bedominated by relatively brittle structures that are more likely to haveformed during emplacement. The location of this zone directly abovethe Arabian platform limestones and the inferred overall SE directionof emplacement from analysis of shear zone structures supports thisinterpretation. Generally, a prevalence of ductile, intrusive and cross-cutting magmatic relationships as described by Dilek and Thy (1998)could not be confirmed during this study; most observations areinstead related either to emplacement or post-emplacement processesrather than representing a structural graben of seafloor origin orprimary seafloor relationships (e.g. extensional detachments) pre-served along contacts between units.

Previous work on post-emplacement structureswithin the sedimen-tary cover is largely superceded by recently published detailed structuralanalysis of the Hatay Graben sediments (Boulton and Robertson, 2008)but earlier papers also contain interpretations of structures within theophiolite that require evaluation. The suggestion that the boundariesbetween ophiolitic units are either controlled by emplacement (e.g.between the mantle rocks and gabbros) or post-emplacement (e.g.between the gabbros and sheeted dykes) structures (Tinkler et al.,1981;Pişkin et al., 1986; Delaloye et al., 1980) are compatible with theinterpretations of this paper. Tinkler et al. (1981) reported severalepisodes of post-emplacement normal faulting from field and

Fig. 8. Fault reactivation: three basic scenarios that may occur subsequent to deposition of the sedimentary cover sequences onto the ophiolitic basement and following the initiationof post-cover phases of faulting. The top block illustrates the pre-existing architecture of the Hatay ophiolite and shows the faults that formed during the intraoceanic andemplacement-related events. The style of later deformation events may be influenced by the consistent layering of the sheeted dykes and cumulate sequence as well as the complexnetwork of earlier faults. In both case one and case two newly developing faults are not influenced by the inherited structure of the basement and form in their theoreticalorientations. In case one the network of old faults is widely reactivated to accommodate strain in the basement. In case two, newly developing faults transect all units. Case threeillustrates a scenario with increasingly complex fault interaction: most new faults cut all units but certain basement structures propagate into the cover framework. Analogue modelssupport the hypothesis that the orientation of pre-existing faults is influential andmay propagate through into the cover sequences during younger events. In the study region, newlyforming faults cut through all units (as in case two), although a localised influence of the pre-existing basement architecture is recognised (as in case three).

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sedimentaryevidence, althougheventswerenot constrained sufficientlyin timing to ascertain whether each represents a discrete event.

6. Discussion

The structural analysis presented here exemplifies the multiplestages of deformation that can affect a regional ophiolitic terrane. Veryfew comparable structural studies have been carried out in otherophiolites and we recommend that structural studies of ophiolitesshould in future include similar study of sedimentary cover units,where present. The analysis has also highlighted the influence of thepre-existing architecture of the ophiolitic basement on the deforma-tion of its sedimentary cover, which in turn indicates that basementunits should be included in structural studies of sedimentary rocks,where practicable. The orientations of most of the faults within thesedimentary cover seem to have been unaffected by the inheritedstructure of the basement, although some basement structures maypropagate into the cover framework. Spatially, faults from all eventsoccur over the whole extent of the study area. However, where a

strong preferred orientation is inherited, such as an E–W strike fromthe coastal sheeted dyke complex, reactivation of earlier structures inthese orientations is significant and leads to a localised increase in thenumber of faults in these orientations.

The two post-emplacement trends are least well constrained intiming. Due to the lack of unequivocal cross-cutting relationships thepossibility that these are coeval cannot be ruled out and it is possiblefor four sets of conjugate faults to develop under a single stress regime(Reches, 1978, 1983). In this case, formation can occur under non-plane (triaxial) strain conditions, or in a transtensive system asconcluded by Boulton et al. (2006) and Boulton and Robertson (2008).

Published palaeostress analyses within the Hatay region haveconcentrated on the sedimentary cover sequences rather than theophiolite (Över et al., 2002; Boulton et al., 2006; Boulton andRobertson, 2008), with a few studies focussed on SE Anatolia andalong the Dead Sea Fault (e.g. Hatzor and Reches, 1990; Zanchi et al.,2002; Diabat et al., 2004) and further north (Över et al., 2004b,c),providing some indication that changes occur spatially, either awayfrom the vicinity of the major faults or due to along-strike variations

221J. Inwood et al. / Tectonophysics 473 (2009) 208–222

(e.g. Kempler and Garfunkel, 1994; Över et al., 2004c). Post-emplacement deformation affecting the Hatay region has beenclarified by recent work by Boulton et al. (2006) and Boulton andRobertson (2007), and enabled the validity of previous work to beevaluated. Changes in regime from pre-Miocene compression toextension in the Early–Mid-Miocene and finally to transtension in theLate Miocene/Pliocene are identified (Boulton and Robertson, 2007).The analyses of post-emplacement faults within the ophiolitic base-ment and sedimentary cover presented here are comparable withthose of Boulton et al. (2006) and Boulton and Robertson (2008) withthe recognised NE-SW and NW-SE striking normal fault trendscompatible with the identified periods of extension/transtension inthe region, although large numbers of Pliocene strike-slip faults arealso recognised within the Hatay Graben (Boulton and Robertson,2008). The sinistral, generally N–S trending Dead Sea Fault Zone hasbeen suggested as being influential in the post-emplacement historyof the Hatay ophiolite (Tinkler et al., 1981, Pişkin et al., 1986) but thedecrease in N–S faults westwards suggests that this fault may havelimited direct influence within the study area.

Rotations during the combination of structural events identifiedduring this study can account for most of the observed structuralframework of the ophiolite. For example, the orientation of cumulatelayering can be explained by strike-parallel tilting associated withpost-emplacement trend 4, or possibly during the reverse faulting ofevent 3. The combination of rotations possible under the identifiedstructural events can also account for observations of dispersion inmagnetic declinations within the Hatay ophiolite and its sedimentarycover (Inwood, 2005; Morris et al., 2006; Inwood et al., 2009). Thegreater spread of magnetic declinations observed in the ophioliticlithologies compared to those in the sedimentary cover (Kissel et al.,2003; Inwood, 2005) implies a pre-cover origin for the dispersion(Inwood, 2005). This ties in with the structural analysis because thestructural events most likely to account for the spread of declinationsare vertical axis rotations during emplacement-related thrusting(Allerton, 1998), or subsequent strike-slip faulting. The observeddifferential rotations but general lack of consistency betweenlocalities highlighted by this study by analyses of bedding orientationsand fault tilts are also supported by palaeomagnetic data suggestingthat differential rotations have occurred between areas (Inwood,2005). However, further consideration of palaeomagnetic aspects areoutside the scope of this paper.

7. Conclusions

• It is possible to identify successive structural events even in anophiolitic terrane affected by multiple stages of deformation such asthe Cretaceous Hatay ophiolite.

• Structural analysis that focussed on key units; i.e. the basal shearzone of the ophiolite, the main body of the ophiolite and itstransgressive sedimentary cover has allowed successive structuralevents to be identified in the evolution of the Hatay ophiolite,namely oceanic spreading; intra-oceanic displacement/continentalmargin emplacement and post-emplacement deformation.

• Five structural events/trends can be identified from a combinationof field observations, structural measurements and palaeostressanalysis.Event 1: Dyke-parallel normal faulting during seafloor spreading.Event 2: Compressional-related faulting associated with intra-oceanic displacement or emplacement onto the Arabian continen-tal margin.Event 3: Strike-slip faulting related to the latest stages ofemplacement onto a continental margin.Trends 4 and 5: Post-emplacement extensional faulting, possiblyacting coevally in an extensional or transtensional stress regime.

• The orientation of ophiolite lithologies, boundaries and bedding areeasily explained by a combination of rotations during several events,

which can also account for other observations such as dispersion ofmagnetic declinations.

• The inherited structure of the ophiolitic basement influenced thestyle of subsequent deformation phases with both reactivation ofolder structures and complex interaction and propagation into thecover framework of localised significance.

Acknowledgements

The research in this paper was funded by a University of PlymouthPhDstudentship (J. Inwood).Wewould like to acknowledge the supportof Ulvican Ünlügenç throughout the duration of the work presentedhere.Wewould also like to acknowledge the assistance provided duringfieldwork in Turkey of all of our field assistants, but particularly that ofSelahattin Üyüdücü in the Autumn 2002 field season during which thestructural measurements for this paper were collected. The authorswould also like to thank the reviewers J. D. A. Piper, K. K. Al-Riyami andC.Xenophontos for their constructive comments.

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