The Çubukludağ graben, south of İzmir: its tectonic significance in the Neogene geological evolution of the western Anatolia
Introduction
The western Anatolia is situated in the eastern part of the Aegean extensional province, which covers the Aegean Sea and the surrounding regions (figure 1). The landscape of the western Anatolia is dominated by large E–W grabens and a number of approximately N–S-trending grabens (figure 1). The E–W grabens are by far the dominant set and control the drainage pattern.
In western Anatolia the N–S extension has been known since Philipson 〚1〛 and confirmed by rather frequent earthquakes along the grabens. The structural pattern and their age relationship are complex 〚2〛. According to a group of views all grabens of the region are partly coeval, have been formed under the on-going N–S extensional regime, which began during the Late Oligocene–Early Miocene period 〚3〛, 〚4〛, 〚5〛, 〚6〛, 〚7〛. According to another view the N–S and E–W grabens are produced by successive events, and they have formed under different tectonic regimes. They suggest also that the E–W grabens began to form during the Late Miocene, but the N–S extensional regime was interrupted during the Late Miocene–Early Pliocene period either by a brief phase of cessation and erosion 〚8〛, 〚9〛 or by a short phase of N–S compression 〚10〛, 〚11〛, 〚12〛, 〚13〛, 〚14〛.
Some of the previous studies based primarily on structural analyses of the space and aerial photographs together with the available seismic data. They established orders of the tectonic events, but on the timing of the development of these structural elements they have to content mostly with the data previously available on the literature. According to these works 〚13〛, 〚14〛 the Aegean region has undergone the following subsequent tectonic phases;
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1. NW–SE extensional phase (Middle–Late Miocene);
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2. N–S extensional phase (Early Pliocene–Quaternary);
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3. NE–SW extensional phase (Quaternary period).
The views and models proposed have been based commonly on inadequate base. They have not been satisfactorily confirmed by the field data and therefore they are widely debated 〚8〛, 〚15〛. In order to test the models we have selected the Çubukludağ region, located between İzmir and Karaburun, where there is a large N–S elongated Neogene outcrop (figure 2), delimited in the north and south by the two E–W-trending fault zones, formed in association with the E–W-trending Gediz graben and the fault-bounded Kuşadası basin respectively (figure 1). We mapped and studied the region in detail, and compared the models proposed on the timing and the generation of the graben system. In the paper firstly we introduce the new data and then discuss geological evolution of the region, in the light of the new and the previously available data.
Section snippets
Stratigraphy
In the region there are two major rock groups; a foundation and a cover. The foundation corresponds to the pre-Neogene rocks, above which the Neogene units were formed as the cover (figures 1and 3).
The foundation is formed by two different rock groups cropping out in the east and the west (figure 2); a metamorphic association and a flysch sequence respectively 〚16〛, 〚17〛. The metamorphic association represents the northwestern tip of the Menderes Massif (figure 1), which is lately regarded as a
Structural geology
The Çatalca formation is only locally exposed in the study area. However from the present outcrops this unit is seen tilted eastward and displays small-scale open folds, folded around the approximately E–W-trending fold axes. The shortening deformation did not effect the younger rocks.
The morphological depression bounded by the Orhanlı fault zone and the Göllükaya fault zone is known as the Yeniköy corridor (figure 2). It is located between the Seferihisar horst in the west and the chain of
Discussion
The Çatalca formation crops out extensively in western Anatolia and the Aegean islands 〚3〛, 〚8〛. Its lithostratigraphic and facial characteristics remain relatively uniform throughout the region (figure 3) as noted previously by Benda 〚26〛, Becker-Platen et al. 〚29〛. Two major features of this unit may be readily distinguished; 1) lacustrine shales are the dominant rocks in the sequence, 2) the unit contains frequent lignite beds having the common Eskihisar sporomorph association 〚26〛.
In the
Conclusion
The following concluding summary may be deduced from the data and the discussion given above. During the Early–Middle Miocene period shale-dominated, lignite bearing lacustrine sediments were deposited in the area studied. The present outcrops represent only a small fraction of the lake basin(s). The Lower–Middle Miocene succession was folded and rose above the lake level before the Late Miocene, and this occurred prior to the initiation of the N–S extensional tectonic regime. During the Late
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