eEarth, 3, 27–35, 2008 www.electronic-earth.net/3/27/2008/ eEarth © Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Geometry of the Turkey-Arabia and Africa-Arabia plate boundaries in the latest Miocene to Mid-Pliocene: the role of the Malatya-Ovacık Fault Zone in eastern Turkey R. Westaway1,*, T. Demir2, and A. Seyrek3 1Faculty of Mathematics and Computing, The Open University, Eldon House, Gosforth, Newcastle-upon-Tyne NE3 3PW, UK 2Department of Geography, Harran University, 63300 S¸anlıurfa, Turkey 3Department of Soil Science, Harran University, 63300 S¸anlıurfa, Turkey *also at: IRES, Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK Received: 27 August 2007 – Published in eEarth Discuss.: 22 November 2007 Revised: 18 March 2008 – Accepted: 15 July 2008 – Published: 5 August 2008 Abstract. We suggest a working hypothesis for the geometry MOFZ terminated southward, in a zone of localised crustal of the strike-slip faults that formed the boundaries between shortening adjoining the suture of the former Neotethys the Turkish, African and Arabian plates in the latest Miocene Ocean in the Kahramanmaras¸-Pazarcık region of SE Turkey. to Mid-Pliocene (LMMP), between ∼7–6 Ma and ∼3.5 Ma. The different motion of the Turkish plate relative to Arabia, This geometry differed significantly from the modern and, thus, relative to Eurasia, means that senses and rates of geometry; the northern Dead Sea Fault Zone (DSFZ) was crustal deformation can be expected to have been different located east of its present line and the TR-AR boundary was during the LMMP phase from at present, throughout the formed by the Malatya-Ovacık Fault Zone (MOFZ), located eastern Mediterranean region. well north of the modern East Anatolian Fault Zone (EAFZ). The MOFZ is potentially the most problematic aspect of such a scheme, given the dramatically different interpretations of 1 Introduction it that have been proposed. However, the presently-available evidence, albeit limited, is consistent with our proposed Eastern Turkey forms the modern boundary zone between interpretation. Significant differences between the proposed the African (AF), Arabian (AR), Eurasian (EU) and Turkish LMMP fault geometry and the modern geometry include, (TR) plates (Fig. 1). The right-lateral North Anatolian Fault first, the transtensional geometry of the MOFZ, the modern Zone (NAFZ) takes up westward motion of the Turkish EAFZ being typically a left-lateral transform fault zone plate relative to Eurasia; the left-lateral East Anatolian Fault but with localized transpression. Second, the MOFZ slip Zone (EAFZ) accommodates WSW motion of the Turkish rate was much lower than the ∼9–10 mm a−1 EAFZ slip plate relative to Arabia. The overall effect of both fault rate; it is estimated as ∼2–3 mm a−1, having produced systems is to accommodate NNW motion of Arabia relative no more than ∼8 km of slip during its approximately to Eurasia by westward motion of the Turkish plate. This three million year long activity. The Euler vector is modern geometry of the NAFZ and EAFZ, which converge tentatively inferred to have involved relative rotation between at Karlıova (Fig. 1), is thought to have developed in the the Turkish and Arabian Plates at ∼0.85±0.15◦ Ma−1 Mid-Pliocene (e.g., Westaway, 2003, 2004, 2006; Westaway about a pole at ∼37.75±0.15◦ N, ∼38.8±0.3◦ E. Third, et al., 2006). unlike at present, there was no throughgoing linkage of Most of the NAFZ is thought to have come into being left-lateral faulting between the LMMP DSFZ and the in the late Late Miocene, around 7 Ma or thereabouts (e.g., MOFZ; instead, the DSFZ terminated northward, and the Tuys¨ uz¨ et al., 1998; Armijo et al., 1999; Yaltırak et al., 2000; Westaway, 2003, 2004, 2006; Westaway et al., 2005). However, during the latest Miocene – Mid-Pliocene (LMMP) Correspondence to: R. Westaway the regional kinematics were different from at present; it has ([email protected]) been proposed (e.g., Westaway and Arger, 2001) that the Published by Copernicus Publications on behalf of the European Geosciences Union. 28 R. Westaway et al.: Turkey-Arabia and Africa-Arabia plate boundaries Fig. 1. Regional map showing the location of the study area in relation to the rivers Tigris and Euphrates and the active strike-slip faults (simplified from Westaway, 2004, which lists original sources of information) bounding the Arabian (AR), African (AF), Turkish (TR), and Eurasian (EU) plates. DSFZ, EAFZ and NAFZ denote the Dead Sea Fault Zone (left-lateral), East Anatolian Fault Zone (left-lateral), and North Anatolian Fault Zone (right-lateral), respectively. Lake Hazar occupies a pull-apart basin on the EAFZ. Note right-lateral offsets of the rivers Euphrates and Peri across the NAFZ and left-lateral offsets of the rivers Euphrates and Murat across the EAFZ. Mountain ranges forming as a result of distributed shortening along the DSFZ are labelled thus: L. M., the Lebanon Mountains; C. R., the Syrian Coastal Range (Jebel Nusayriyah); A. M., the Amanos Mountains. K. V. denotes the Karasu Valley. G. Antep is an abbreviation for Gaziantep. The suture of the Neotethys Ocean follows the change from yellow to colourless ornament at the boundary between Anatolia and the Arabian Platform. The meaning and significance of letters to denote individual faults and other structures are discussed in the text. eastern end of the NAFZ was at Erzincan, not at Karlıova, working hypothesis for the geometry of plate motion during and this structure was conjugate to a different left-lateral fault the LMMP and to investigate the extent to which the MOFZ system, the Malatya-Ovacık Fault Zone (MOFZ) (Figs. 1, (which, admittedly, is potentially the most problematic 2), although this idea has since been criticised (Kaymakc¸ı aspect of the scheme) is consistent with the proposal. et al., 2006). The aims of this study are to suggest a eEarth, 3, 27–35, 2008 www.electronic-earth.net/3/27/2008/ R. Westaway et al.: Turkey-Arabia and Africa-Arabia plate boundaries 29 Fig. 2. Map of the study region, showing sites of (?) Late Miocene – Pliocene basaltic volcanism (triangles; omitted outside the Elazıg˘ region) in relation to the Euphrates river system and to major strike-slip fault zones: the NAFZ, MOFZ and EAFZ. Light grey shading illustrates schematically the Malatya Basin. Large light grey dots indicate the estimated extent of such deposits in the swath of territory west of the Malatya Fault that we have investigated (see supplement for details: http://www.electronic-earth.net/3/27/2008/ee-3-27-2008-supplement. pdf). Mammal sites illustrated include Karababa in the Malatya Basin (see supplement for details) and (from Unay¨ and de Bruijn, 1998) Surs¨ ur¨ u¨ near Elazıg˘ and Hacısam farther east. Dashed dark grey line with yellow ornament marks the Neotethys suture, as delimited by the northern margin of outcrop of rocks of the Cenozoic carbonate sequence of the Arabian Platform (after Altınlı, 1961; Baykal, 1961; and Tolun, 1962). Between points marked, this suture roughly coincides with strands of the EAFZ. Triangles indicate young basaltic necks, with arrows indicating schematic directions of basalt flow from them; Gb, K and S denote the Gum¨ us¸ba¨ glar,˘ Karatas¸, and Sarıbuc¸uk necks near Elazıg.˘ Ke, Ad, Gs, Ay, Ka and Gt indicate the Kepezdagı,˘ Adamkıran, Gunes¸li,¨ Aygormez¨ Dagı,˘ Karaca Dag˘ and Goktepe¨ flow units of the Kepezdagı˘ basalt. For geological maps of this area see Westaway and Arger (2001). Thick black line indicates the location of the cross-section in Fig. S2 in the online supplement. Arrow symbols denote piercing points from river offsets; * symbols denote possible piercing points from structural evidence. Those on the NAFZ and EAFZ are not discussed here; see, instead, Westaway and Arger (2001) and Westaway (2003, 2004). 2 Geometry of the Turkey-Arabia and Africa-Arabia Westaway et al. (2006), which discuss alternative possible plate boundaries scenarios, discussion that is not repeated here. Westaway and Arger (2001) summarised the earlier literature on the 2.1 Present geometry of deformation age of this fault system, and concluded that it was ∼3 Ma. Westaway (2003) revised this estimate to ∼4 Ma; subsequent The fault zones coloured blue in Fig. 1 indicate the modern more detailed analysis by Westaway et al. (2006) adjusted it plate-boundary geometry. The summary here follows recent to 3.73±0.05 Ma. interpretations, such as by Westaway (2003, 2004) and www.electronic-earth.net/3/27/2008/ eEarth, 3, 27–35, 2008 30 R. Westaway et al.: Turkey-Arabia and Africa-Arabia plate boundaries The NAFZ enters the study region with an ESE trend (A 2.2 Relationship to the earlier phase of deformation in Fig. 1). It continues ESE past Erzincan, offsetting the Euphrates and Peri rivers right-laterally (B), before ending As already noted, the NAFZ is thought to have become active at its intersection with the EAFZ at Karlıova. during the Messinian stage of the Late Miocene, although opinions have differed (cf. Tuys¨ uz¨ et al., 1998; Armijo The modern left-lateral boundary between the Turkish et al., 1999; Yaltırak et al., 2000; Westaway, 2003) as to and African plates trends NE across the NE Mediterranean whether its initiation was around the start of the Messinian, at Sea, where it is known as the Misis-Kyrenia fault zone (C). ∼7 Ma, or in the “latest Miocene” (i.e., during the Messinian, It then passes onshore, end-on, into the similarly-oriented therefore probably closer to a numerical age of ∼6 Ma). Yakapınar-Goksun¨ fault zone (D). Near its NNE end the The NAFZ is thus older than the modern configuration of latter bends to a west-east orientation and, now known as the northern DSFZ and the EAFZ.