Magnetostratigraphy of early–middle Miocene deposits from east–west trending Alaşehir and Büyük Menderes grabens in western Turkey, and its tectonic implications
Published:January 01, 2009
Sevket Sen, Gürol Seyitoğlu, 2009. "Magnetostratigraphy of early–middle Miocene deposits from east–west trending Alaşehir and Büyük Menderes grabens in western Turkey, and its tectonic implications", Collision and Collapse at the Africa–Arabia–Eurasia Subduction Zone, D. J. J. Van Hinsbergen, M. A. Edwards, R. Govers
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In western Turkey, the Alaşehir and Büyük Menderes grabens form east–west trending major tectonic structures. Their sedimentary fill is important for regional tectonic models for the late Cenozoic evolution of the Aegean region. These deposits are divided into four units dated between the early Miocene and Quaternary. We studied the magnetostratigraphy of two sections in the Alaşehir graben and one in the Büyük Menderes, partly covering the first and second sedimentary units. Detailed palaeomagnetic analysis allowed us to determine ChRM component for these rocks. The Zeytinçayı river and road sections (Alaşehir graben) record several polarity reversals, which are tentatively correlated to the interval C5Cn.3n–C5ADr (approximately between 14.6–16.6 Ma) of the ATNTS2004. This correlation is also supported by palaeontology and radiometric dating of syn-extensional intrusions. In the Eycelli section (Büyük Menderes graben) only three polarity zones are recorded, and their tentative correlation with the interval of C5Bn.1r–C5Br (14.88–15.97 Ma) is in overall in agreement with the record of Eskihisar sporomorph association in this formation. These results place the initiation of the Alaşehir and Büyük Menderes grabens in the early Miocene. The palaeomagnetic declinations from the Alaşehir graben indicate about 25° anticlockwise rotation, whereas that of the Büyük Menderes graben indicate a clockwise rotation of about 30–40°. These contradictory vertical-axis rotations might be explained by detachment faults in the region. In Tertiary formations of western Turkey, contradictory block rotations are common and likely reflect thin-skinned deformation in the area rather than rigid crustal movements. Therefore, average anticlockwise rotations in western Turkey cannot be used as evidence for the model of back-arc spreading in the Aegean region.
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Collision and Collapse at the Africa–Arabia–Eurasia Subduction Zone
The Mediterranean and northern Arabian regions provide a unique natural laboratory to constrain geodynamics associated with arc–continent and continent–continent collision and subsequent orogenic collapse by analysing regional and temporal distributions of the various elements in the geological archive. This book combines thirteen new contributions that highlight timing and distribution of the Cretaceous to Recent evolution of the Calabrian, Carpathian, Aegean and Anatolian segments of the Africa–Arabia–Eurasia subduction zone. These are subdivided into five papers documenting the timing and kinematics of Cretaceous arc–continent collision, and Eocene and Miocene continent–continent collision in Anatolia, with westward extrusion of Anatolia as a result. Eight papers provide an overview and new data from stratigraphy, structure, metamorphism and magmatism, covering the geological consequences of the largely Neogene collapse that characterizes the segments of interest, in response to late stage reorganization of the subduction zone, and the roll-back and break-off of (segments of) the subducting slab.