Earth and Planetary Science Letters 280 (2009) 105–117

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Earth and Planetary Science Letters

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Neotethyan intraoceanic microplate rotation and variations in spreading axisorientation: Palaeomagnetic evidence from the Hatay ophiolite (southern Turkey)

Jennifer Inwood a,⁎, Antony Morris a, Mark W. Anderson 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

Turkey

⁎ Corresponding author. Present address: Borehole RGeology, University of Leicester, University Road, Leices2523327; fax: +44 116 2523918.

E-mail addresses: ji18@le.ac.uk (J. Inwood), amorris@manderson@plymouth.ac.uk (M.W. Anderson), Alastair.(A.H.F. Robertson).

0012-821X/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.epsl.2009.01.021

a b s t r a c t

a r t i c l e i n f o

Article history:

Insights into tectonic process Received 22 September 2008Accepted 14 January 2009Available online 23 February 2009

Editor: L. Stixrude

Keywords:ophiolitepalaeomagnetismrotationtectonicNeotethys

es operating in ancient ocean basins are provided by analyses of fragments of oceaniclithospherepreserved asophiolitesduring collisional orogenesis.Herewepresent a palaeomagnetic analysis of theUpperCretaceousHatay (Kizil Dağ) ophiolite of Turkey thatprovides evidence for intraoceanicmicroplate rotationandvariations in ridge axis orientation inaNeotethyanoceanbasin.Magnetizations at46 sitesare shown tobepre-deformational in origin and rotated from the relevant reference direction. A net tectonic rotation approach to theanalysis of the data provides information on permissible net rotation poles and angles and allows uncertainties ininput vectors to be considered. Results demonstrate that all levels of the ophiolite have been rotated anticlockwiseby angles in excess of 90° around steeply inclined axes. The Hatay ophiolite formed in the same supra-subductionzone spreading system as the Troodos ophiolite (Cyprus), which is known to have rotated 90° anticlockwise in anintraoceanic setting in the Late Cretaceous to Early Eocene. By considering our results in the context of the knowntimingof the Troodos rotation,we infer that50–60° of rotationof theHatayophiolite tookplaceaspartof anareallyextensive “Troodos microplate”. This phase of rotation was triggered by initial impingement of the Arabiancontinental margin with the Neotethyan subduction trench, consistent with models for modern day oceanicmicroplate rotation in complex convergent plate boundaries. The Hatay ophiolite then became detached from theactively rotatingmicroplate andwas emplacedonto theArabianmargin in theMaastrichtian, undergoing a further30–40° of anticlockwise rotation during thrusting. Back-stripping of rotations allows correction of the Hataysheeted dykes to their initial orientations. The restored dyke trend of 020° differs from that inferred previously forthe Troodos sheeted dyke complex, demonstrating a primary variation in orientation of Neotethyan spreadingaxes. Such variability is commonly observed in modern spreading systems in marginal basins; these may act asanalogues for the supra-subduction zone spreading inferred for many ophiolites.

© 2009 Elsevier B.V. All rights reserved.

1. Introduction

It is now accepted that ophiolites represent fragments of oceaniclithosphere preserved during collisional orogenesis. Ophiolites pro-vide fundamental insights into oceanic tectonic processes associatedwith their formation at spreading centres and subsequent deforma-tion during plate convergence, and are also important for regionalpalaeogeographic reconstructions. Numerous ophiolitic units areexposed throughout the eastern Mediterranean region and areinterpreted to have mainly formed by supra-subduction zonespreading within Neotethyan oceanic basins during Late Cretaceoustime. The most extensively studied unit is the Troodos ophiolite of

esearch Group, Department ofter LE1 7RH, UK. Tel.: +44 116

plymouth.ac.uk (A. Morris),Robertson@ed.ac.uk

ll rights reserved.

Cyprus, which has been uplifted without complex internal tectonicdisruption, leaving its spreading fabric largely intact. Palaeomagneticresearch on the Troodos ophiolite has shown that tectonic rotationsare a fundamental crustal response to oceanic extensional andtransform faulting (Allerton and Vine, 1987; Bonhommet et al.,1988; Morris et al., 1990; Allerton and Vine, 1991; Hurst et al., 1992;Morris et al., 1998). The ophiolite and its sedimentary cover alsopreserve a unique palaeomagnetic record of oceanic microplaterotation that may be linked to plate-scale geodynamic interactions(Clube et al., 1985; Clube and Robertson, 1986; Abrahamsen andSchonharting, 1987; Robertson 1990). More recently, palaeomagneticresults have been reported from the Upper Cretaceous Baër-Bassitophiolite of Syria (Morris et al., 2002; Morris and Anderson, 2002).This formed in the same southern Neotethyan oceanic basin as theTroodos ophiolite but was subsequently emplaced onto the Arabiancontinental margin during the Maastrichtian, undergoing extensivetectonic dismemberment (Al-Riyami et al., 2000, 2002). Extreme andlocally variable anticlockwise rotations are observed in the Baër-Bassitunits (Morris et al., 2002) that may be related in part to neotectonic

106 J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

activity, but which more likely reflect Late Cretaceous emplacement-related tectonic processes and/or intraoceanic rotation as documen-ted for the Troodos ophiolite.

The large Upper Cretaceous Hatay (or Kizil Dag) ophiolite ofsouthernTurkey is crucial to understanding the pattern and significanceof tectonic rotations in oceanic crust of the southern Neotethyan basin.This aerially extensive ophiolite is exposed 250 km to the NE of Troodosand 40 km to the north of Baër-Bassit (Fig.1a). It was emplaced onto theArabian continental margin together with the Baër-Bassit ophiolite aspart of the same, large unit (Robertson, 2002). Internal tectonicdisruption of the Hatay ophiolite is very much less than that of theBaër-Bassit unit, and it retains a clearly defined Penrose-type pseudos-tratigraphy like the Troodos ophiolite. Here we present the firstpalaeomagnetic data from this major terrane. Pre-deformationalmagnetic remanences are analysed using a net tectonic rotationapproach that allows quantification of rotation axes and angles andtheir associated uncertainties. The results provide evidence for oceanicmicroplate- and emplacement-related rotation events and for primaryvariations in the orientation of spreading axes within the southernNeotethyan ocean basin, allowing comparison to processes operating inmodern marginal basin systems.

2. Geological setting

TheHatay ophiolite of Turkey and the related Baër-Bassit ophiolite ofSyria comprise the westernmost part of the ‘Ophiolitic Crescent’ of thenorthern margin of Arabia (Ricou, 1971) (Fig. 1a). The Hatay massifcovers 950 km2 (25×45 km) and is composed of an ophiolite sequenceup to 7 km thick. It is split into a large southwesternmassif and a smallernortheasternmassif byahigh-angle fault, knownas theTahtaköprü Fault(Fig.1b). The succession in themainmassif (Delaloye andWagner,1984)begins with serpentinized tectonised harzburgite with local intercala-tions of dunite, wehrlite, lherzolite and feldspathic peridotites. Theultramafic rocks are separated from the overlying layered sequence by a50–100m thick shear zone (Dilek and Thy,1998). The layered ultramaficand gabbroic rocks display cumulate textures and locally showaweakly-to moderately-developed foliation parallel to layering defined by thealignment of pyroxene and plagioclase crystals (Dilek and Thy, 1998).Isotropic gabbros become dominant higher in the plutonic section, andare intruded by small bodies of plagiogranites, leucocratic gabbro anddolerite. Dolerite dykes become abundant towards the top of thegabbros, passing upwards into a sheeted dyke complex. Locally, thegabbro-dyke contact is a low-angle shear zonemarked by hydrothermalalteration. The best exposures of sheeted dykes occur along the coast in a4.5 km long continuous section (Delaloye et al., 1980). Dykes there aregenerally subvertical and E–W striking, although some differences inorientation are observed along the section. Extrusive igneous rocks arenot preserved in the main massif.

The smaller ophioliticmassif to theNEof the Tahtaköprü Fault (Fig.1b)lacks the coherent internal structure and pseudostratigraphy observed inthe main massif (Dilek and Thy, 1998). Here a highly attenuated uppercrustal sequence is in tectonic contact with underlying upper mantle orlower crustal rocks. These relationships are best exposed in two localitiesnear the villages of Kömürçukuru and Tahtaköprü. Extrusive sequencesaround Kömürçukuru are nearly 600 m thick and comprise massive andpillow lava flows with intercalated metalliferous sedimentary rocks(Erendil, 1984; Robertson, 1986) and are in faulted contact with isotropicgabbros beneath (Dilek and Thy,1998). At Tahtaköprü, the approximately400m thick extrusive sequence overlies serpentinized peridotites along agently SE-dipping normal fault (Dilek and Thy, 1998).

The Hatay ophiolite forms a 7 km thick thrust sheet emplaced overlimestones of the Arabian platform, fromwhich it is separated by only a

Fig. 1. Location maps. (a) The eastern Mediterranean ‘peri-Arabian ophiolite crescent’ of Rophiolite of Oman; (b) Simplified geological map of the Hatay ophiolite, showing the locationletter of each site designating the sampling area: K = Karaçay valley; J = Kisecik valley; C

thin (10s of metres) melange with no metamorphic sole present(Robertson, 1986, 2002). The contact is only exposed in two smallareas making emplacement relations difficult to determine (Aslaner,1973). However, kinematic indicators suggest emplacement towards theSE in the well-developed metamorphic sole of the smaller Baër-Bassitophiolite to the south, which is interpreted as the thinned andstructurally dismembered leading edge of the emplaced ophiolitesheet (Al-Riyami et al., 2002). The combined Hatay/Baër-Bassit thrustsheet was emplaced in themiddle Maastrichtian, with the timing of thisevent precisely bracketed by the ages of the youngest carbonates in theunderlying authochthon (early Maastrichtian) and the oldest post-emplacement sedimentary cover sequences (late Maastrichtian).

The post-emplacement sedimentary cover of the Hatay ophiolite(Fig. 1b) reaches a total thickness of around 3 km (Piskin et al., 1986). AMaastrichtian basal conglomerate horizon (Erendil, 1984; Piskin et al.,1986) overlies the ophiolite (Tinkler et al., 1981), and is succeededconcordantly bya series of claystones, sandstones, limestones andmarls ofMaastrichtian to Late Eocene age (Piskin et al., 1986). The Miocenesequence unconformably overlies either the older sedimentary sequencesor the ophiolite (Boulton and Robertson, 2007) and is succeeded byPliocene sandstones, marly limestones and claystones and then byQuaternary conglomerates, travertines, alluviumandbeach sand (Boultonet al., 2006).

3. Sampling and methods

We have sampled the Hatay layered sequence (ultramafic andgabbroic cumulates), the sheeted dyke complex and the extrusivesequence at 43 sites along key, representative sections (Fig. 1b) forpalaeomagnetic analyses in order to quantify any tectonic rotationsthat have affected the ophiolite. Three additional sites were sampledwithin gabbros that are exposed as host-rock screens between dykes.An average of eight samples per sitewere drilled in situ using standardpalaeomagnetic procedures. At one pillow lava site (ML01) sampleswere collected as small hand-samples from cooling-related jointblocks by attaching a flat disc which provided a suitable surface fororientation. Sampling was restricted to exposures that showed eitherconsistent palaeovertical indicators (exposures of multiple, sub-parallel sheeted dykes) or palaeohorizontal indicators (laterallycontinuous, planar layering in gabbroic rocks; coherent sequences ofpillowed and sheet lava flows). The orientations of these indicatorswere measured in the field to an accuracy of ±5°. A standardpalaeomagnetic analysis based on simple tilt corrections wouldassume that these measured surfaces represent initially vertical/horizontal planes. However, the net tectonic rotation approachadopted here allows uncertainties in initial orientations (e.g. potentialpalaeoslopes in lava sequences) to be incorporated into the analyses.

Natural remanences of the ophiolitic samples were measured in theUniversity of Plymouth palaeomagnetic laboratory using a Molspinfluxgate spinner magnetometer (noise level=0.05×10−3 A/m).Samples were subjected to stepwise alternating field (AF) and thermaldemagnetization. Characteristic remanent magnetizations (ChRMs)were found using orthogonal vector plots and principal componentanalysis (Kirschvink, 1980) and site mean remanence directions werecomputed using Fisherian statistics (Fisher,1953). A range of supportingrockmagnetic analyseswere performedon selected samples, both at theUniversity of Plymouth palaeomagnetic laboratory, and more exten-sively at the Institute for Rock Magnetism, Minneapolis. These includedhysteresis measurements (to determine magnetic domain states), lowtemperature susceptibility experiments (to identifymagnetic inversionsrelated to ferromagnetic mineralogy), and the determination of Curietemperatures.

icou (1971) extending eastwards from the Troodos ophiolite of Cyprus to the Semailof palaeomagnetic sampling sites. Sites were located in six main localities, with the first= Coastal section; I = Isikli; M = Kömürçukuru region; T = Tahtaköprü region.

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4. Results and analysis

4.1. Magnetic mineralogy and palaeomagnetic results from the ophiolite

The magnetic mineralogy experiments demonstrate the presenceof fine magnetic grain sizes with pseudo-single domain propertiescapable of retaining a stable magnetization throughout the protracted

Fig. 2.Magnetic characteristics of rocks from the Hatay ophiolite. (a) A Day plot (Day et al., 197and the extrusive sequence of the Hatay ophiolite. The majority of samples contain pseutimescales; (b) Typical examples of orthogonal demagnetization diagrams, showingwell-defifield and thermal treatment. Solid circles = horizontal plane; open symbols = vertical N–S

history of the ophiolite (Fig. 2). Magnetic mineralogy, however,displays variation dependent on crustal level. Clear Verwey transitionsand high Curie temperatures (TCs) in the deeper crustal levels(ultramafic cumulates and cumulate gabbros) indicate that Ti-poortitanomagnetite/magnetite is themajor carrier of themagnetic signal,whilst the absence of the Verwey transition and lower TCs of thehigher crustal levels (extrusive rocks) indicate the presence of a more

7) of hysteresis parameters for samples from the cumulate rocks, sheeted dyke complexdo-single domain grains capable of retaining a stable magnetization over geologicalned stable end-point remanence directions in all lithologies isolated by both alternatingplane Note that the vertical projections are on the horizontal axes.

109J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

Ti-rich titanomagnetite. These mineralogies are compatible withacquisition of stable remanences during or soon after genesis of theophiolitic crust at an oceanic spreading centre.

Stable components of magnetization were isolated at all sites,following removal of minor secondary components during initialdemagnetization. Typical examples of demagnetization behaviour areshown in Fig. 2. Most samples are dominated by univectorial, singlecomponent decay to the origin. Both AF and thermal demagnetizationexperiments yielded identical remanence directions (Fig. 2), althoughthermal demagnetization data are occasionally noisier than the AFdata. Stable components of magnetization were identified fromindividual samples and subsequently combined to give a meanChRM for each site. In situ magnetic remanences from all sites areshown in the stereographic equal area projections of Fig. 3 and arelisted in Table 1. Magnetizations are predominantly of normal polarity,consistent with remanence acquisition during the Cretaceous longnormal polarity interval (chron C34N; Cande and Kent, 1992).Directions are unrelated to the present-day geocentric axial dipolarfield in the Hatay region and are generally directed towards the westor southwest (Fig. 3), indicating substantial anticlockwise tectonicrotation since magnetization acquisition. Magnetization directions ofsites within host gabbro screens in the sheeted dyke complex areindistinguishable from those of the associated dykes. Reversedpolarity remanences were observed at only one isolated locality inthe northwestern corner of the ophiolite (Isikli; sites ID01–04; Fig.1b), where a moderately dipping series of sheeted dykes is in faultedcontact with the underlying plutonic section. These localised reverseddirections suggest that magnetization acquisition in this single sectionoccurred later than in the main ophiolite (and potentially may post-date crustal accretion).

4.2. Timing of magnetization acquisition

This is determined by using field tests of palaeomagnetic stability,themost common of which is the palaeomagnetic tilt test (McElhinny,1964; McFadden and Jones, 1981). However, in regions wheredifferential vertical axis rotations may have occurred, use of thestandard area-wide tilt test based on full remanence vectors(declination and inclination) is invalid. In addition, palaeomagneticdata from sheeted dykes may be affected by components of rotationaround dyke-normal axes which are impossible to identify fromstructural observations alone, again making standard tilt testsunreliable. In order to take account of these complications we adoptan alternative approach that uses the distribution of inclinations fromsites where a palaeohorizontal can be determined. This inclination-

Fig. 3. Lower hemisphere stereographic projections of site mean remanence directions (in sitconfidence around site mean remanences.

only tilt test formulation (Enkin and Watson, 1996) is independent ofthe structural history and assumes that the angle between theinclination and the identified palaeohorizontal at a site remainsconstant during rigid body rotation. A statistically significantimprovement of clustering of inclinations upon tilt correction fromsites with different structural orientations implies that a pre-tiltmagnetization has been identified (Enkin and Watson, 1996). Datafrom the 19 palaeohorizontal sites from the Hatay layered gabbro andextrusive sections yield the following statistics:

In situ I = 48:6- + 36:3-=−18:2- k = 4:2Tilt − corrected I = 32:5- + 5:2-=−4:9- k = 28:4

where I and k are the maximum likelihood estimates of the true meaninclination in degrees and the Fisher precision parameter respectively.Stepwise untilting gives a maximum k value of 29.0 at 90% untilting(Fig. 4), suggesting that remanences were acquired before significanttectonic disruption of the ophiolitic crust.

Where a sample collection consists of several groups of sites, eachfrom a separate coherent block or section, the declination informationwithin each block is usable and need not be discarded. In thesecircumstances the “block-rotation Fisher” analysis of Enkin andWatson (1996) is applicable. This maximises the use of the remanencedata and yields improved estimates of mean inclination for subse-quent use in a parametric resampling tilt test formulation (Enkin andWatson, 1996). This approach yields the following statistics for the sixblocks containing palaeohorizontal sites:

In situ I = 42:6- + 9:8- =−9:5- k = 7:9Tilt − corrected I = 32:4- + 4:6-=−4:5- k = 32:3

Stepwise untilting gives a maximum k value of 33.1 at 90%untilting (Fig. 4), again supporting acquisition of remanence prior todeformation (Enkin and Watson, 1996).

In both cases a parametric re-sampling implementation of the tilttest (Enkin and Watson, 1996), using 1000 re-sampling trials andincorporating a circular standard deviation of 5° on the poles topalaeohorizontal surfaces, indicates an optimum untilting with 95%confidence limits close to 100% of untilting. This constitutes a positiveresult indicating acquisition of remanence prior to deformation of thesampled sequences (Enkin and Watson, 1996), and suggests that theobserved magnetizations were acquired during or shortly afteroceanic crustal genesis.

u/geographic coordinates, without tilt correction). Ellipses = projection of α95 cones of

Table 1Palaeomagnetic data from the Hatay ophiolite.

Site Lithology n In situ k α95 Structure Lat. Long.

Dec Inc

Dyke sampling sitesCoastal sectionGroup 1 (southern section)CD01 Dolerite sheeted dykes 11 196.1 46.2 35.1 7.8 130/83 36° 07.89′N 35° 54.77′ECD02 Dolerite sheeted dykes 11 201.0 61.3 125.9 4.1 317/80 36° 07.89′N 35° 54.77′ECD03 Dolerite sheeted dykes 9 208.3 64.6 72.9 6.1 116/80 36° 07.89′N 35° 54.77′ECG01 Gabbro screen between dykes 6 194.6 59.6 166.9 5.2 – 36° 07.89′N 35° 54.77′E

Group 2 (central section)CD04 Dolerite sheeted dykes 6 243.6 66.7 36.1 11.3 160/66 36° 08.39′N 35° 54.63′ECD05 Dolerite sheeted dykes 8 262.1 51.4 26.8 11.0 190/74 36° 09.02′N 35° 54.16′ECD12 Dolerite sheeted dykes 10 231.9 46.9 23.7 10.1 162/56 36° 08.43′N 35° 54.60′E

Group 3 (northern section)CD06 Dolerite sheeted dykes 7 342.1 69.8 224.2 4.0 010/72 36° 09.47′N 35° 53.83′ECD07 Dolerite sheeted dykes 7 298.4 81.2 50.3 8.6 010/72 36° 09.47′N 35° 53.83′ECD08 Dolerite sheeted dykes 10 341.3 72.7 132.2 4.2 016/68 36° 09.51′N 35° 53.79′ECD09 Dolerite sheeted dykes 9 328.4 76.3 53.8 7.1 360/78 36° 10.11′N 35° 53.25′ECD10 Dolerite sheeted dykes 7 336.9 62.6 55.1 8.2 003/69 36° 09.91′N 35° 53.42′ECD11 Dolerite sheeted dykes 14 322.9 73.4 105.2 3.9 006/74 36° 09.79′N 35° 53.51′E

Karaçay ValleyKD01 Dolerite dykes cutting layered gabbros 9 211.1 64.4 57.0 7.4 153/63 36° 11.40′N 35° 59.35′EKD02 Dolerite dykes cutting layered gabbros 8 192.8 63.0 173.1 4.6 163/77 36° 11.40′N 35° 59.35′EKD03 Dolerite sheeted dykes 6 237.8 41.7 42.8 10.4 195/72 36° 11.60′N 35° 58.84′EKD08 Dolerite sheeted dykes 7 243.9 51.1 139.7 5.1 350/88 36° 14.77′N 35° 58.45′EKD09 Dolerite sheeted dykes 10 269.6 58.8 109.6 4.6 001/82 36° 13.67′N 35° 57.65′EKD10 Dolerite sheeted dykes 10 228.6 32.4 130.8 4.2 174/72 36° 12.37′N 35° 57.60′EKD11 Dolerite sheeted dykes 7 237.5 45.5 64.4 7.6 173/79 36° 12.45′N 35° 57.51′EKD12 Dolerite sheeted dykes 5 201.6 30.1 44.9 11.5 168/70 36° 12.37′N 35° 57.54′EKG02 Gabbro screen between dykes 7 238.0 38.3 43.1 9.3 – 36° 11.60′N 35° 58.84′EKG03 Gabbro screen between dykes 6 272.5 58.5 129.9 5.9 – 36° 13.67′N 35° 57.65′E

IsikliID01 Dolerite sheeted dykes 6 131.8 −11.7 76.2 7.7 040/45 36° 19.70′N 35° 48.91′EID02 Dolerite sheeted dykes 8 153.9 −35.9 225.2 3.7 026/48 36° 19.83′N 35° 48.90′EID03 Dolerite sheeted dykes 7 139.8 −18.8 209.4 4.2 040/43 36° 20.02′N 35° 49.19′EID04 Dolerite sheeted dykes 9 142.6 −11.9 175.8 3.9 030/38 36° 20.02′N 35° 49.19′E

Layered gabbbro sampling sites

Coastal sectionCC01 Layered gabbros 7 191.2 80.5 207.4 4.2 290/44 36° 11.20′N 35° 52.22′ECC02 Layered gabbros 9 287.5 67.7 601.5 2.1 304/40 36° 10.11′N 35° 53.25′E

Kisecik ValleyJC01 Layered gabbros 4 305.7 46.3 55.2 12.5 342/45 36° 17.03′N 36° 02.96′EJC02 Layered gabbros 9 271.6 56.2 56.6 6.9 355/45 36° 17.07′N 36° 03.20″EJC03 Layered gabbros 6 274.0 47.3 50.7 9.5 342/45 36° 17.01′N 36° 03.23′EJC04 Layered gabbros 8 268.2 38.9 57.0 7.4 351/41 36° 17.37′N 36° 03.38′E

Karaçay ValleyKC01 Layered gabbros 7 185.7 65.5 82.1 6.7 308/72 36° 11.40′N 35° 59.35′EKC02 Layered gabbros 10 198.8 66.3 146.7 4.0 300/58 36° 11.40′N 35° 59.35′EKC03 Layered gabbros 10 199.3 67.0 260.1 3.0 297/58 36° 11.40′N 35° 59.35′EKC04 Layered gabbros 10 217.9 79.1 320.9 2.7 280/47 36° 11.44′N 35° 59.11′E

Lava sampling sites

Kömürçukuru regionML01 Basaltic pillow lavas 7 226.1 27.0 109.9 5.8 118/33 36° 25.86′N 36° 08.70′EML02 Basaltic sheet flow 8 292.7 17.6 75.8 6.4 171/36 36° 25.78′N 36° 08.38′EML03 Basaltic pillow lavas 6 278.9 13.9 37.4 11.1 171/36 36° 25.58′N 36° 08.44′EML04 Basaltic pillow lavas 4 262.3 22.0 63.7 11.6 171/36 36° 25.64′N 36° 08.46′E

Tahtaköprü regionTL01 Basaltic pillow lavas 6 278.4 15.0 12.2 20.0 151/62 36° 23.42′N 36° 12.03′ETL02 Basaltic pillow lavas 6 281.1 21.7 40.9 10.6 151/62 36° 23.42′N 36° 12.03′ETL03 Basaltic pillow lavas 6 268.3 5.1 26.7 13.2 151/62 36° 22.68′N 36° 10.61′ETL04 Basaltic pillow lavas 6 280.9 23.0 33.7 11.7 151/62 36° 22.68′N 36° 10.60′ETL05 Basaltic pillow lavas 5 289.6 21.5 117.1 7.1 151/62 36° 22.68′N 36° 10.60′E

n=number of specimens; Dec=declination; Inc=Inclination; k=Fisher precision parameter; α95=semi-angle of 95% cone of confidence; Structure=dip direction and dip ofinferred palaeovertical/horizontal.

110 J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

4.3. Selection of reference direction

Tectonic interpretation of palaeomagnetic data is achieved bycomparing observed magnetization vectors with a reference(expected) magnetization vector, commonly calculated from anappropriate apparent polar wander path (APWP). The Hatay, Baër-Bassit and Troodos ophiolites are all interpreted to have formed in a

southern Neotethyan ocean basin that formed by the rifting ofmicrocontinental fragments from the northern Gondwanan (African)margin. African APWPs for the Late Cretaceous (Westphal et al., 1986;Besse and Courtillot, 1991, 2002) yield expected directions ofmagnetization for the Hatay region with northerly declinations(within the limits of uncertainty of the mean poles) and inclinationsof approximately 30°. However, reference directions calculated in this

Fig. 4. Variation in the Fisher precision parameter with progressive untilting of sampledsites and localities where the palaeohorizontal can be inferred, indicating a positiveinclination-only tilt test (Enkin and Watson, 1996). Thin line = results using site-leveldata; Thick line= results using the block-rotation formulation of the Enkin andWatson(1996) method.

111J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

way do not take into account the shortening (palaeolatitudinal shift)associated with plate convergence in the period between crustalformation at a Neotethyan spreading axis and southwards emplace-ment of the Hatay ophiolite onto the continental margin. This suggeststhat an appropriate reference inclination should be slightly steeperthan that defined from African APWPs. A more appropriate referenceinclination is provided, therefore, by the extensive tilt correctedpalaeomagnetic data from the coeval Troodos ophiolite. A recentsynthesis of all available data (Morris et al., 2006) indicates a meanTroodos inclination of 38°. However, the mean Troodos declination(273°; Morris et al., 2006) reflects the well-known Late Cretaceous toEocene palaeorotation of the “Troodos microplate”. In this study,therefore, we adopt an unrotated reference magnetization vector ofDec=000° (based on African APWPs), Inc=38° (based on Troodosdata).

Fig. 5. An example of the net tectonic rotation analysis using data from site CD10 as an illustrsitu remanence); RMV= reference magnetization vector; PDN= present dyke normal; IDNcircle of radius ß (=angle between SMV and PDN) centred on RMV; subscripts 1 and 2 referfive estimates of SMV, RMV and PDN, distributed around their respective α95 cones of confidesolution (only solution R1 is shown). These define an envelope that represents a first-orderhistogram illustrates the associated distribution of net tectonic rotation angles.

4.4. Determination of net tectonic rotations

Standard palaeomagnetic corrections for the effect of tectonictilting upon magnetization directions involve rotating inferredpalaeohorizontal/vertical surfaces back to horizontal/verticalaround strike-parallel axes. The total deformation at a site is,therefore, arbitrarily decomposed into components of tilting andvertical axis rotation. In complexly deformed terrains, where foldaxes are seldom horizontal and where multiple phases of deforma-tion may occur, this procedure can introduce serious declinationerrors (MacDonald, 1980; Kirker and McClelland, 1996). It is moreappropriate, therefore, to describe the deformation at a site in termsof a single rotation about an inclined axis, which restores both thepalaeohorizontal/vertical to its initial orientation and the site meanmagnetization vector to the appropriate palaeomagnetic referencedirection. This single rotation may then be decomposed into anynumber of component rotations on the basis of additional structuraldata (Kirker and McClelland, 1996).

The net tectonic rotation algorithm employed here is that devisedby Allerton and Vine (1987) for use within the sheeted dyke terrane ofthe Troodos ophiolite of Cyprus, and which was later modified byMorris et al. (1998) to yield estimates of uncertainties in rotation axisorientations and angles. This technique can be applied to bothpalaeovertical and palaeohorizontal cases, with the key assumptionbeing that no internal deformation of a sampled unit has occurred.Under this circumstance, the angle ß between the magnetizationvector and the normal to the dyke/flow is constant during deforma-tion (Allerton and Vine, 1987).

The analysis involves finding an initial normal to the palaeover-tical/horizontal plane which conserves the angle ß and is ashorizontal/vertical as possible. The mean site magnetization vector(SMV) is then restored to the reference magnetization vector (RMV)and the present palaeosurface normal to its initial orientation. Therotation axis which allows this restoration is located at the intersec-tion of the great circle bisectrix of the SMV and RMV and that of thepresent and initial palaeosurface normals (Fig. 5a). The net tectonicrotation is described by the azimuth and plunge of the axis of rotation,and the angle of rotation; a positive angle represents an anticlockwiserotation (Allerton and Vine, 1987). Two solutions are generated inthose cases where dykes can be restored to the vertical, and additionalcriteria (e.g. compatibility with observed structures) may be used to

ation. (a) The Allerton and Vine (1987) algorithm. SMV= site magnetization vector (in= initial calculated dyke normal; R = axis of net tectonic rotation; dashed line indicatesto alternative solutions; (b) multiple application of this method to all combinations ofnce (Morris et al., 1998); (c) gives 125 estimates of the net tectonic rotation axis for eachapproximation of the 95% region of confidence around the true rotation axis. The inset

Table 2Net tectonic rotation parameters.

Site Preferred solution

Axis Angle Initial strike/dip

Dyke sitesCoastal sectionGroup 1 (southern section)CD01 056/82 157 016/90CD02 015/78 160 028/90CD03 027/75 147 170/90

Group 2 (central section)CD04 066/66 99 158/90CD05 092/72 85 180/90CD12 100/67 103 167/90

Group 3 (northern section)CD06 030/54 87 182/90CD07 039/59 102 021/90CD08 033/54 88 011/90CD09 033/57 97 002/90CD10 019/55 87 177/90CD11 031/58 94 007/90

Karaçay ValleyKD01 066/66 117 167/90KD02 061/67 131 169/90KD03 108/73 105 025/90KD08 041/81 117 016/90KD09 032/75 101 011/90KD10 126/79 122 024/90KD11 087/80 113 013/90KD12 116/78 146 041/90

Isikli: Sheeted dyke complexID01 311/51 86 191/90ID02 348/52 75 184/90ID03 322/51 82 191/90ID04 317/46 80 357/90

Site Preferred solution

Axis Angle Initial dip

Layered gabbro sitesCoastal sectionCC01 060/54 97 9CC02 068/62 69 10

Kisecik ValleyJC01 129/61 42 31JC02 113/45 60 6JC03 122/57 64 18JC04 133/59 71 14

Karaçay ValleyKC01 079/44 94 9KC02 076/54 100 5KC03 075/55 100 6KC04 056/59 101 1

Extrusive sitesKömürçukuru regionML01 275/73 156 6ML02 295/63 92 5ML03 285/64 104 16ML04 19

Tahtaköprü regionTL01 300/55 128 12TL02 287/54 128 12TL03 287/54 128 12TL04 309/55 130 7TL05 312/53 122 14

Axis=azimuth and plunge of rotation pole; Angle=angle of rotation (positive angle=anticlockwise rotation); Initial strike/dip=restored dyke orientation; Initial dip=restored dip of inferred palaeohorizontal.

112 J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

select a preferred solution. Importantly, this method can resolverotations of dykes around margin-normal axes that are impossible toobserve in the field and which may result in misinterpretation of datawhen standard tilt corrections are employed (Borradaile, 2001;Morrisand Anderson, 2002).

In the modification of this method (Morris et al., 1998), theAllerton and Vine (1987) algorithm is applied to all combinations of

each of five orientations for the three vectors input into the analysis(i.e. RMV, SMV, normal to palaeosurface; Fig. 5b). These orientationsare distributed around the α95 circles for each vector (an α95 of 5° isassigned to the structural data). This yields 125 combinations ofinput vectors, and an output consisting of a minimum of 125 andmaximum of 250 estimates of the net tectonic rotation axis and angleat each site. The envelope on a stereonet which completely enclosesthe set of estimated rotation axes (Fig. 5c) provides a first-orderapproximation of the associated 95% confidence region. Thisenvelope is the only practicable means of describing the confidenceregion, since the net tectonic rotation technique does not yieldrotation axis estimates which are symmetric around the meanestimate. The associated rotation angles can be plotted as histograms(Fig. 5c). This method indicates the range of rotation axes and angleswhich are possible at a site given the uncertainties in orientation ofthe various input vectors.

4.5. Net tectonic rotation solutions

The analyses demonstrate that, without exception, sites haveexperienced major rotation around moderately to steeply inclinedaxes. The net tectonic rotationparameters found by single application ofthe Allerton and Vine (1987) technique to our data are given in Table 2,whereas the stereonets of Figs. 6 and 7 show the site-level envelopes ofpotential rotation axes within each locality together with histograms ofestimated rotation angles compiled at the locality level. In the case of thesheeted dyke sites, we have accepted the net tectonic rotation solutioninvolving anticlockwise rotation since this is consistentwith the senseofdisplacement of in situ directions away from the reference direction(Fig. 3) and generally yields smaller rotation angles.

The most extensive data come from the sheeted dyke sectionsexposed along the coastal road and in the Karaçay river valley. Withthe exception of sites in the southern section of the coastal exposures,net tectonic rotation solutions from these localities are very similar,with subvertical to steeply plunging E to NE-directed rotation axesand rotation angles of 85–100° (Fig. 6). Nearly identical rotationangles are also observed in sheeted dykes exposed in the Isikli area,but here rotation poles are less steeply plunging and NW-directed(Fig. 6). The Isikli dykes are less steeply dipping than in the mainsheeted dyke complex (Table 1) and have been tilted in the hangingwall of a normal fault zone (Dilek and Thy, 1998). Hence the moremoderately inclined net tectonic rotation poles reflect a combinationof this component of tilting and a substantial rotation around asteeply plunging axis. Analysis of data from the southernmostsampled section of sheeted dykes along the coast (sites CD01–03)again demonstrates steeply plunging (to sub-vertical) rotation axes,but here rotation angles are significantly larger than in the sections tothe north with a modal value of 150–160°. The net tectonic rotationanalysis also provides information on admissible initial dyke strikes(see Table 2), but discussion of this aspect of the analysis is deferredto Section 5 below.

Sites in lower crustal layered sequences along the coastal, Karaçayand Kisecik sections have also been rotated around broadly E-directed, moderately plunging rotation axes (Fig. 7a). Rotation anglesvary within and between sections from 65–75° to 95–105°. TheAllerton and Vine (1987) technique does not require that measuredlayering represents a true palaeohorizontal surface, but insteadplaces the initial pole to layering as close to vertical as possible (andhence layering as close to horizontal as possible) during calculationof a single net tectonic rotation solution. However, a geometricconsequence of the analysis in these cases is that the azimuth of theinitial pole to layering is forced to lie along the declination of thereferencemagnetization vector. An alternative approach is to assumethat the net tectonic rotation parameters from the sheeted dyke sitesin each locality also describe the deformation in the layeredsequences, and use these solutions to restore the orientation of

Fig. 6. Results of net tectonic rotation analyses of palaeomagnetic data from sites in the sheeted dyke complex of the main massif of the Hatay ophiolite.

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layering to its pre-deformational position. This is particularlyapplicable in the case of the Karaçay valley section where dykeswarms (sites KD01–02) cross-cut the layered sequence (sites KC01–04). Back-stripping themean net tectonic rotation calculated for sitesKD01–02 from the SMVs and present day poles to layering at sitesKC01–04 restores the SMVs to a direction indistinguishable from thereference magnetization vector (Fig. 8a) and the layering to anapproximately shallow easterly dipping orientation (note: thisanalysis provides additional justification for preferring anticlockwisesolutions for the dyke sites since the alternative clockwise solutionsresult in layering dipping at unrealistic initial angles in excess of 70°).In addition, the orientation of dyke screens cutting the layeredsequence in the Karaçay valley is in close agreement with theorientation of dykes in the main Karaçay sheeted dyke section,suggesting that the lower crustal layered sequences and sheeteddyke sequences have experienced little or no relative rotation. Hence,although no dykes cross-cutting the layered sequencewere observedin the coastal section, it is appropriate to use the net tectonic rotationsolutions from the northern section of the coastal sheeted dykecomplex to restore the orientation of the layered sequence (to theimmediate north) to its initial, pre-deformational position. Again,this results in an inferred initial orientation that dips shallowlytowards the east (Fig. 8a) and SMVs close to the reference direction.The significance of these restored orientations is discussed below.

Finally, net tectonic rotation solutions from localities in theextrusive sequences of the ophiolite within the NE massif (to the NE

of the Tahtaköprü Fault; Fig. 1b) indicate large anticlockwise rotationsaround moderate to steeply plunging W to WNW-directed axes(Fig. 7b). The analysis yields broad distributions of rotation angleswith modal values of approximately 90–120°, apart from at site ML01which yields higher rotation angles of 150–160°. This latter site isisolated from the other sites at the Kömürçukuru locality, whichconsist of semi-continuous exposures of pillowed and sheet flowswith consistent orientations, and the result from this site is consideredto be anomalous. Rotation angles at remaining sites are significantlylarger than those seen in the main southwestern massif of theophiolite. The structural style of the NE ophiolitic massif ischaracterised by tectonic juxtaposition by low angle normal faultingof upper crustal extrusive rocks with underlying serpentinizedmantleperidotites (Dilek and Thy, 1998). The pillow and sheet flows arelocally steeply dipping, e.g. in the Tahtaköprü locality, suggesting asignificant component of tilting during normal fault displacement.Hence the larger net rotation angles may reflect a combination oftilting around subhorizontal axes and the major component ofrotation around more steeply inclined axes seen elsewhere. Higherrotation angles in the NE massif could also potentially result from asmall component of relative rotation of the ophiolitic massifs acrossthe Tahtaköprü Fault. This structure has been interpreted as anaccommodation zone related to ridge segmentation by Dilek and Thy(1998), on the basis of the different internal structures of the massifson either side of the inferred fault. However, no kinematic informationis currently available for this structure, which is not clearly exposed in

Fig. 7. Results of net tectonic rotation analyses of palaeomagnetic data. (a) Results from sites in the lower crustal layered sequence (ultramafic and gabbroic cumulates) of the mainmassif of the Hatay ophiolite; (b) Results from sites in the extrusive sequences of the northeastern massif of the Hatay ophiolite (to the NE of the Tahtaköprü Fault).

114 J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

the field. In either case it is clear that the NE massif has experienced asimilar history of large, bulk anticlockwise rotation to that documen-ted for the main SE massif.

5. Discussion

5.1. Potential settings for rotation

The analysis above demonstrates that large anticlockwise rotationsare ubiquitous throughout the Hatay ophiolite, both geographicallyand pseudostratigraphically. Such rotations are also evident if asimpler analysis based on standard tilt corrections is performed(although this approach does not facilitate assessment of the effects ofuncertainties in magnetization vectors and structural orientations).Differences in rotation angle between localities areminor compared tothe magnitude of calculated net rotations. Overall the data areconsistent with bulk rotation of the entire ophiolite thrust sheet ofthe order of 90°, but this could be of composite origin reflectingdeformation under one or more of the following rotation scenarios:

(i) deformation during crustal accretion by sea-floor spreading,e.g. at a ridge-transform intersection, as inferred for parts of theTroodos ophiolite (see review by Morris et al., 2006);

(ii) post-spreading oceanic rotation, e.g. as part of a rotatingmicroplate;

(iii) thrust emplacement onto the Arabian continental marginduring the Maastrichtian;

(iv) post-emplacement neotectonic deformation associated withthe development of the modern plate tectonic configuration ofthe eastern Mediterranean.

Regarding scenario (i), transform-related tectonism has been wellcharacterised within the coeval Troodos ophiolite, and is restricted toareas adjacent to the fossil Southern Troodos Transform Fault Zone(STTFZ;MacLeod et al.,1990). The key evidence for transform tectonism-related rotations is the presence of cross-cutting igneous units withsignificantly different directions of magnetization, indicating synchro-nous magmatic activity and fault block rotation. These relationships arenot observed in the Hatay ophiolite, nor are the very large and localiseddifferences inmagnetization directions seen in the STTFZ. Scenario (iv) isinconsistent with palaeomagnetic data from the Tertiary sedimentarycover sequences of theHatay ophiolite (Kissel et al., 2003; Inwood, 2005)that indicate magnetization directions close to present day north(combined mean direction: Dec=347°, Inc=36°, α95=16°). These datasuggest only minor post emplacement anticlockwise rotation has occur-red, compatible with a small anticlockwise rotation of the Arabian Plate(e.g. Kissel et al., 2003; Gürsoy et al., 2009). These considerations there-fore lead to the conclusion that the large bulk rotation of the underlyingophiolite most likely reflects oceanic microplate rotation (scenario (ii)),emplacement-related rotations (scenario (iii)), or a combination of both.

Fig. 8. Restoration of cumulate layering and dyke strikes to their pre-deformational orientations. (a) Back-stripping the mean net tectonic rotations observed in sheeted dykecomplex sites KD01–02 and CD06–11 from the SMVs and orientation of layering in the associated layered sequences. This yields initial orientations of SMVs (circles) close to thereference magnetization vector (star) and cumulate layering dipping initially to the east (great circles and associated poles (crosses)). Small circles (shaded: KC01–04; unshaded:CC01–02) around SMVs indicate the associated α95 envelopes; (b) The distribution of initial dyke strikes at 24 sheeted dyke sites (3000 solutions) resulting from the preferredanticlockwise solutions of the net tectonic analysis approach.

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5.2. Oceanic microplate rotation

The Troodos and Hatay ophiolites are interpreted as remnants ofoceanic lithosphere formed in the same southern Neotethyan oceanbasin (Robertson, 2002), and are petrogenetically-related (Lytwynand Casey, 1993). Although independent rotation of these ophiolitescannot be excluded, the sense and similar magnitude of rotation ineach suggests a linked rotation history. Palaeomagnetic studies of theTroodos ophiolite and its in situ sedimentary cover show that the 90°anticlockwise palaeorotation of the Troodos microplate occurred overan extended period from the Late Cretaceous to the Early Eocene(Clube et al., 1985; Clube and Robertson, 1986; Morris et al., 1990),with 50–60° of rotation complete by the Maastrichtian, i.e. the time oftectonic emplacement of the Neotethyan crust now preserved in theHatay and Baër-Bassit ophiolites. Hence, a major component of thebulk rotation of the Hatay unit documented heremay have taken placeas part of a “Troodos microplate”.

In this scenario, impingement of the passive margin of Arabia withan intraoceanic subduction zone in the Late Cretaceous initiatedanticlockwise rotation of the overriding supra-subduction zone crust,following previous models suggested by Clube and Robertson (1986)and Robertson (1990). As Africa–Eurasia convergence continued, afragment of the rotated oceanic crust above the subduction zonebecame detached and emplaced upon the Arabian continental marginin the Maastrichtian (to form the Hatay/ Baër-Bassit ophiolites), butrotation of crust to the west (now represented by the Troodosophiolite) continued until the Early Eocene.

Clube and Robertson (1986) inferred that the Troodos microplatewas essentially confined to the present day area of Cyprus. Thenorthern boundary of the rotated unit was believed to lie between theTroodos Massif and the Kyrenia Range (northern Cyprus; Robertsonand Woodcock, 1986), but would restore further north when Eoceneand Late Miocene regional shortening is accounted for. The easternboundary was placed between the Troodos and Hatay ophiolites(Clube and Robertson, 1986) on the basis of the difference in presentday orientation between dykes in the sheeted complexes of theseophiolites. However, we demonstrate that this difference is a primaryone (see below) and not the result of large relative rotations betweenthe terranes. Geological constraints therefore do not delimit thepresent day eastwards extent of the Troodos microplate. Furtherpalaeomagnetic investigations are now required in the more easterlyemplaced ophiolites in southern Turkey (e.g. the Göksun, Ispendere,

Kömürhan and Guleman ophiolites; Rizaoglu et al., 2006; Robertsonet al., 2007) in order to identify the areal extent of units that haveexperienced substantial anticlockwise rotation. However, we note thatlarge clockwise rotations have been documented in the Oman(Semail) ophiolite (e.g. Weiler, 2000) at the eastern end of the‘Ophiolitic Crescent’ (Fig. 1a). This suggests that the plate-scalegeometry of the Arabian continental ‘indentor’ and its interactionwithNeotethyan subduction trenches prior to final collision provided thekey control on the distribution of anticlockwise- and clockwise-rotated Neotethyan oceanic crust.

Modern oceanic microplate rotation is observed in two tectonicsettings: (a) between overlapping spreading centres in fast spreadingmid ocean ridge systems, where propagation of offset ridge tipsresults in edge-driven rotation of the intervening oceanic lithosphere(e.g. the Juan Fernandez, Easter and Galapagos microplates, EastPacific Rise; Searle et al., 1993; Klein et al., 2005); and (b) on a range ofscales in the forearc regions of convergent plate margins (e.g. offshorePapua New Guinea; Wallace et al., 2004; Martinez and Taylor, 1996),where collision of continental crust with subduction trenches resultsin the fastest GPS-determined tectonic block rotations (Wallace et al.,2005). This latter setting provides the closest modern analogue forNeotethyan oceanic microplate rotation. For example, collision ofcontinental crust of the New Guinea Highlands with the Finisterre arcis regarded as the trigger for rapid rotation of the over-riding SouthBismarck Sea plate (Wallace et al., 2004). Analysis of GPS data fromsuch regions ledWallace et al. (2005) to propose a general mechanismfor rotation in which a change from collision of a buoyant indentor tonormal subduction along the strike of a convergent margin exerts atorque on the upper plate, leading to microplate rotation. This isdirectly comparable to the inferred plate configuration of southernNeotethys in the Late Cretaceous, with a transition from collision ofthe Arabian continental marginwith a subduction trench in the east toocean–ocean subduction further to the west (Clube and Robertson,1986; Robertson, 1990).

5.3. Rotation during ophiolite emplacement

Tectonic rotations during thrust sheet emplacement have com-monly been inferred from palaeomagnetic data in convergent zones(e.g. McClelland and McCaig, 1989; Allerton, 1998; Muttoni et al.,2000; Platt et al., 2003). However, extreme rotations in such systemsare localised phenomena within thrust zones that have experienced

116 J. Inwood et al. / Earth and Planetary Science Letters 280 (2009) 105–117

lower rotations overall (e.g. Platt et al., 2003). More commonly, thrust-related rotations are of the order of a few 10s of degrees. It is unlikely,therefore that all of the Hatay bulk rotation could be attributed tothrust sheet rotation during tectonic emplacement. However, such amechanism may reasonably be invoked to account for a residualrotation of 30–40° if it is assumed that the Hatay crust formed part ofthe Troodosmicroplate and rotated by 50–60° as part of this unit priorto emplacement in the Maastrichtian, as outlined above. Emplace-ment-related processes may also potentially account for observedsmaller variations in rotation between sampling localities. Smallvariations in rotation history may also result from post-emplacementfaulting (see Inwood et al., in press). Our preferredmodel of sequentialintraoceanic microplate- and emplacement-related tectonic rotationsis also consistent with the highly-rotated palaeomagnetic datareported previously from the structurally dismembered and lessextensive Baër-Bassit ophiolite exposed to the south of Hatay innorthern Syria (Morris et al., 2002; Morris and Anderson, 2002). Thisunit is interpreted as the highly deformed leading edge of theemplaced ophiolite sheet (Al-Riyami et al., 2002). However, in contrastto the Hatay ophiolite, intraoceanic and emplacement-related rota-tions in the Baër-Bassit unit are extensively modified by variable post-emplacement rotations (Morris and Anderson, 2002) relating to thedevelopment of a major neotectonic strike-slip fault system thatrepresents the expression of the plate boundary zone between theAfrican (Arabian) and Eurasian (Anatolian) plates (Al-Riyami et al.,2000, 2002).

5.4. Initial dyke orientations

The net tectonic rotation algorithm employed in our analysis(Allerton and Vine, 1987) provides constraints on initial dykeorientations in the case of data from sheeted dyke sections. Thepreferred anticlockwise solutions (Table 2) yield a restored dyke trendof ~020° (Fig. 8b). This direction represents the best estimate of theorientation of the Neotethyan spreading axis responsible for thegeneration of the Hatay ophiolitic crust. Similar analyses in thesheeted dyke complex of the Troodos ophiolite (Allerton, 1989)indicate an original average restored trend of 325°, when remanencedata are compared to the westerly directed Troodos magnetizationvector as a reference direction. Correcting for the palaeorotation of theTroodos ophiolite these data indicate an average orientation of 053°for the Troodos spreading axis. Hence, our data identify for the firsttime substantial differences (c. 33°) in the primary orientation ofspreading axes within the southern Neotethyan ocean, between theTroodos and Hatay ridge segments. Differences of this magnitude havebeen observed in the complex spreading geometries developed inpresent-day marginal basins (e.g. Lau Basin, Taylor et al., 1996;Philippine Sea, Sdrolias et al., 2004; Manus Basin, Martinez and Taylor,1996), further supporting the analogy between these modern systemsand ancient supra-subduction zone spreading systems like thesouthern Neotethys.

Finally, the geometric relationships revealed by our analyses(Fig. 8) suggest that by the time of remanence acquisition at sitesKC01–04 the cumulate layering in the Karaçay sequences had beentilted by an average of 25°, and were subsequently intruded by thedyke screens sampled at sites KD01–02. We note the coincidencebetween the restored N–NNE strikes of the dykes and cumulatelayering (Fig. 8). This is compatible with some models for thedevelopment of cumulate sequences involving downwards ductileflow of hot crystal mushes, resulting in layering that dips towards thespreading centre (e.g. Quick and Denlinger, 1993).

6. Conclusions

The Hatay ophiolite of southern Turkey retains stable magnetiza-tions which are unequivocally shown to be of pre-deformational

origin by a positive inclination-only tilt test. Net tectonic rotationanalysis of magnetization directions reveals ubiquitously large antic-lockwise rotations at all sampling localities. The data are bestexplained by a model involving 50–60° rotation of the Hatay crustas part of an intraoceanic “Troodos” microplate within the southernNeotethyan basin, followed by a subsequent 30–40° anticlockwiserotation during thrust emplacement of the Hatay ophiolite onto theArabian continental margin in the Maastrichtian. Minor variability inrotation solutions between localities may be due to a combination ofemplacement- and post-emplacement-related faulting. The plate-scale geometry of the Arabian ‘indentor’ and its interaction with asegment of subduction trench, while normal subduction continued tothe immediate west, is likely to have provided the key control onintraoceanic rotation of Neotethyan crust. A similar rotation mechan-ism has been proposed to explain rapid microplate rotation in presentday complex convergent plate boundaries (Wallace et al., 2005). Thegeometric analysis of net tectonic rotations indicates an initialorientation of 020° for the Hatay sheeted dykes and hence theassociated spreading axis. This trend differs from that inferred for thecoeval Troodos spreading axis, revealing primary differences in ridgeorientations within the southern Neotethys, comparable to those seenin some modern marginal basin spreading systems.

Acknowledgements

We acknowledge the support of Ulvican Ünlügenç (ÇukurovaUniversity, Adana) throughout this project. We would also like tothank our field assistants, particularly Ali Kop. Inclination-only tilttests were performed using software developed by Randy Enkin. AVisiting Fellowship (2004) from the Institute for Rock Magnetism inMinneapolis, University of Minnesota, USA, enabled the laboratoryfacilities at the Institute to be used to perform rock magneticanalyses. This research was financed by a University of Plymouth PhDstudentship (Inwood)with additional financial support for fieldworkfrom the Geological Society of London (Fund for Fieldwork, 2002–3and 2003–4) and the British Federation for Women Graduates(Johnstone and Florence Stoney Studentship, 2003–4). The authorswould like to thank reviewers Rob Van der Voo and an anonymousreviewer for their constructive comments.

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