Neotectonic intersection of the Aegean and Cyprus tectonic arcs: extensional and strike-slip faulting in the Isparta Angle, SW Turkey
Introduction
The main purpose of this paper is to present new field data from neotectonic faults in the Isparta Angle area of SW Turkey (Fig. 1), and to interpret them in the light of knowledge of the neotectonic evolution of the eastern Mediterranean region. We also discuss supporting evidence from shallow seismic data, to the south, within Antalya Bay. We report new structural data that show that the Isparta Angle is characterised by major extensional fault lineaments that were active in Late Pliocene–Recent time. These faults overprint dominantly right-lateral strike-slip faults of latest Miocene–Early Pliocene age. A short-lived phase of Late Miocene thrusting occurred prior to this, related to compression and/or right-lateral transpression, concentrated along parts of the basin margins. A regional tectonic model is discussed which suggests that deformation was controlled by a combination of right-lateral shear at the eastern edge of the Aegean extensional province (Fig. 1), a change in regional stress regime, and inherited zones of basement rheological weakness.
Section snippets
Tectonic–sedimentary development of the Isparta Angle
The Isparta Angle (Blumenthal, 1963) is a triangular-shaped region, about 120 km long N–S and ca. 50 km wide in the south (Fig. 1). It is a major re-entrant that separates the western and central Tauride Mountains, and extends offshore into Antalya Bay. The structural and tectonic history of the Isparta Angle can be traced back to the early Mesozoic when rifting of the North African continent occurred (e.g. Dumont et al., 1979a; Poisson et al., 1984; Robertson and Dixon, 1984; Şengör et al.,
Previous work
Field studies in western Turkey during the late 1970s and early 1980s (Table 1) indicated that the area as a whole (including the Isparta Angle) had undergone NNE–SSW extension in Middle–Late Miocene time, followed by N–S extension in the Pliocene. This then changed to NE–SW extension sometime in the Quaternary (Dumont et al., 1979b; Angelier et al., 1981; Zanchi et al., 1983; Mercier et al., 1989).
The Isparta Angle, as defined by Blumenthal (1963)encompasses a large region (here termed the
Study methods
In total, nearly 1000 measurements of faults were taken from both the flanks and from the core of the inner Isparta Angle angle, including the mountainous coastal area southwest of Antalya city (here termed Kemer lineaments, Fig. 2; Glover, 1995). Measurements were made on outcrops of fault scarps ranging from a few centimetres to several metres in size, often related to much larger fault scarps that were inaccessible. The quality of fault scarps measured varied from rare, smooth, polished
Structural data from the Isparta Angle
We present fault data, beginning with the apex of the Isparta Angle, followed by its eastern flanks, then from the Miocene and Pliocene sediments of the Aksu basin in the core of the Isparta Angle and finally from the western flank, mainly from the spectacular fault-bounded coastline to the south of Antalya, bordering Antalya Bay (Kemer lineaments). Areas of data collection are indicated in Fig. 2 (marked as boxes).
Numerous fault planes were measured at each locality. The fault data are mainly
Outer isparta angle areas
Additional clues concerning the neotectonic setting come from the outer Isparta Angle area, including the prominent Kırkkavak Fault in the east and fault lineaments in the west (Bey Daǧları margin). There is also shallow reflection seismic evidence from Antalya Bay to the south.
Discussion of fault data
The results obtained are summarised in Table 3. Normal fault directions trend NW–SE, ranging to NNE–SSW, whereas right-lateral faults are NE–SW, with an additional dominant NW–SE direction in the Kemer area. In addition, the offshore extensional graben in Antalya Bay is oriented broadly NW–SE. It is not possible to determine the orientations of the faults bounding the offshore graben because of the constraints of the limited two-dimensional data. Slickenfibre data of fault superimposition from
Regional neotectonic setting
Anatolia is known to be rotating anticlockwise as it is translated westwards, accompanied by subduction and southward retreat (`roll-back') of the Aegean subduction zone. The driving force of westward tectonic escape towards the Aegean is the collision of Eurasia and Arabia in the Zagros region (McKenzie, 1972, McKenzie, 1978; Dewey and Şengör, 1979; Jackson and McKenzie, 1984; Şengör et al., 1985), under the influence of a rigid boundary to the north, comprising oceanic crust in the Black Sea,
Conclusions
Onshore fault and offshore shallow seismic data shed light on the neotectonic (Late Miocene–Recent) tectonic evolution of the Isparta Angle, located at the junction of the Aegean and Cyprus tectonic arcs and between the actively deforming western Aegean and the distributed deformation region of central Anatolia. During the Quaternary–Recent the inner areas of the Isparta Angle experienced crustal extension and strike-slip and cannot be considered to be related to a compressional plate boundary,
Acknowledgements
The first author acknowledges a Ph.D. studentship from Shell Expro (U.K.), held at the Department of Geology and Geophysics, University of Edinburgh. We particularly benefited from discussions with R. Flecker, A. Poisson, J. Dixon, and J. Woodside. M. Ergün kindly made available the shallow seismic data. The manuscript was improved following comments by Rachel Flecker, James Jackson and Simon Price, and we thank them for their constructive reviews. We are indebted to Steve Grant at Esso UK for
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