Neotectonic deformation linking the east Anatolian and Karataş‐Osmaniye intracontinental transform fault zones in the Gulf of İskenderun, southern Turkey, deduced from paleomagnetic study of the Ceyhan‐Osmaniye volcanics

Abstract

Left‐lateral strike slip along the Dead Sea Fault Zone (DSFZ) between the African and Arabian plates is partitioned into a complex set of motions at its northern extension where Arabia impinges into the Anatolian collage. As a result, the nature of the contemporary link between the east Anatolian and Dead Sea transforms is unclear. To quantify strike slip motion expressed as tectonic rotations along the inferred southwest continuation of the East Anatolian Fault Zone (EAFZ), we have investigated the paleomagnetism of young (<1 Ma) volcanics in the Adana Basin‐Gulf of İskenderun region comprising the Ceyhan‐Osmaniye volcanic suite. This volcanism is sited close to the intersection between the sinistral Karataş‐Osmaniye Fault Zone (KOFZ) and the Neotethyian Suture. Nine sites from a basaltic lava field in the vicinity of Osmaniye are entirely of normal polarity and, in the context of their very young morphologies, are assigned to the Brunhes Chron; declinations are mostly clockwise from the present field. This age assignment identifies rapid Recent (<780 ka) uplift at the head of the Gulf of İskenderun and is linked to a diversion of the Ceyhan river drainage and ongoing regional tilting. Eight sites yield a mean declination of 11.3 ± 10°, implying clockwise block rotation on Riedel‐type fractures on the northwest side of the KOFZ. Seven lavas sites from a volcanic succession near Botaş at the southwestern extension of the volcanic lineament are of reversed polarity and rotated counterclockwise by 43 ± 7° with respect to the present field. Polarity, K‐Ar, and morphological evidence indicate an assignment toward the latter part of the Matuyama Chron and identify rapid Neogene block rotation of a flake within the KOFZ. An inferred maximum slip rate of 0.6 cm/year on this fault zone is comparable with lower estimates of slip on the EAFZ and suggests that most strike slip on the DSFZ is now being partitioned to the west of the Gulf of İskenderun on a developing strike slip zone linking with the Cyprus Arc.

The kinematics of central-southern Turkey and northwest Syria revisited

“…Arger et al (2000) and was shown by Gürsoy et al (2003) to be reverse-magnetised, so its probable age is ~800 ka, late in the Matuyama chron. Seyrek et al (2008) and offsetting the NE margin of the outcrop by ~400 m along a bluff indicative of downthrow to the SE by ~50 m. In-situ basalt is evident on the NW side of this fault (c. YF 64169 89705) and on its SE side (c. YF 64576 89986), at points that are ~500 m apart, but the area in between has been obliterated to build a motorway to serve the port, so it is hard to say whether this is a true leftlateral offset.…”

Late Cenozoic uplift of the Amanos Mountains and incision of the Middle Ceyhan river gorge, southern Turkey; Ar–Ar dating of the Düziçi basalt

“…Farther SW, the Botaş basalt (11 in Fig. 3) was K-Ar dated by Arger et al (2000) to 630 ± 180 ka (± 2σ) and was shown by Gürsoy et al (2003) to be reversemagnetised. An age for it late in the Matuyama chron (∼800 ka) can thus be deduced.…”

“…The subsequent realisation by Westaway (2003Westaway ( , 2004 that the northern DSFZ is strongly transpressive eliminates any geometrical requirement for active leftlateral slip along the line of the KOFZ or Düziçi Fault, contrary to what had been deduced previously, based on the assumption that the active left-lateral faults in this region are all transform faults. The argument by Gürsoy et al (2003) that the KOFZ must be active to account for vertical-axis rotations measured palaeomagnetically in the Ceyhan-Osmaniye basalts is not compelling, as these measurements can readily be explained differently (see the online supplement). In other recent interpretations, such as that by Robertson et al (2004), and in some older schemes (e.g., Kelling et al, 1987), the KOFZ is regarded as a reverse-fault zone associated with the development of the mid-Cenozoic subductionaccretion complex; its along-strike continuation north and east of Osmaniye thus trends SSW-NNE along the Neotethys suture, not SW-NE across the Amanos Mountains (Fig.…”

“…This analysis will be based on our own fieldwork, supplemented by unpublished documents prepared by the Devlet Su İşleri (DSİ) Genel Müdürlüğü (General Directorate of State Water Works), which show the basalt and fluvial sediments in the vicinity of the Aslantaş Dam before this dam was built. Recent investigations of other parts of this volcanic field, farther west (and thus excluded from the present study), include those by Parlak et al (1997), Polat et al (1997), Yurtmen et al (2000) and Gürsoy et al (2003).…”

Palaeomagnetic study of the Kepezdağ and Yamadağ volcanic complexes, central Turkey: Neogene tectonic escape and block definition in the central-east Anatolides

“…The differential character of this deformation is now well established by regional palaeomagnetic studies (Gürsoy et al, 1997(Gürsoy et al, , 1998(Gürsoy et al, , 2003Tatar et al, 2002;Piper et al, 2006Piper et al, , 2010. These show that block rotations produced by high strains north of the indenter are strongly counter clockwise (CCW) but become relatively less CCW as the strain diminishes to the west of the indenter, so that rotations diminish to near-zero in central Anatolia; still further to the west they become progressively more clockwise (CW) near the western extremity of the extruded terranes.…”