Evidence of Late Cretaceous oroclinal bending in north-central Anatolia: palaeomagnetic results from Mesozoic and Cenozoic rocks along the İzmir–Ankara–Erzincan Suture Zone
Mualla Cengiz Cinku, Mumtaz Hisarli, Ann M. Hirt, Friedrich Heller, Timur Ustaömer, Nurcan Kaya, Erdinç Öksüm, Naci Orbay, 2016. "Evidence of Late Cretaceous oroclinal bending in north-central Anatolia: palaeomagnetic results from Mesozoic and Cenozoic rocks along the İzmir–Ankara–Erzincan Suture Zone", Palaeomagnetism in Fold and Thrust Belts: New Perspectives, E. L. Pueyo, F. Cifelli, A. J. Sussman, B. Oliva-Urcia
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The Sakarya Zone and the Kırşehir Block of northern Turkey are separated by the İzmir–Ankara–Erzincan Suture (IAES) Zone which is the remnant of the northern branch of the Neotethys Ocean. During the closure of the IAES in the Late Cretaceous, northwards drift of the Kırşehir Block and its eventual indentation into the Sakarya Zone produced crustal deformation defined by thrusts and reverse faults, mainly between the indenting Kırşehir Block and the Sakarya Zone. Previous palaeomagnetic studies in the eastern part of the Pontides and the Sakarya Zone showed that palaeomagnetic declinations could record the deformation that resulted in the curvature of the IAES. In order to define the tectonic deformation of the northern part of the Kırşehir Block, we present new palaeomagnetic data from 57 different sites that include Mesozoic–Cenozoic sedimentary and volcanic rocks. The results from Late Cretaceous rocks (40 sites) indicate that large clockwise rotations of c. 140–165° occurred in the eastern limb of the bend, while anticlockwise rotations progressively decreased from c. 80° to 55° from SW to NW in the western limb of the bend. In contrast, small clockwise and anticlockwise rotations are observed in the flat-lying segment of the suture zone. These rotation patterns are consistent with the geometrical trends of the IAES in northern Turkey. Declinations of seven different Middle Eocene sites within the Kırşehir Block are rotated anticlockwise by c. 30–10°. This indicates that the deformation in the Sakarya Zone and the Kırşehir Block continued in the Middle Eocene.
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Palaeomagnetism is a technique used to understand complex deformation patterns in fold-and-thrust belts; it can be used to characterize the distribution, magnitude and timing of vertical axis rotations, an elusive variable using other methods. A combination of palaeomagnetic and structural geology analyses has helped to unravel the geometry and kinematics of fold-and-thrust belts around the world and of different geological ages for more than 50 years. This volume comprises three sections: the first shows thorough overviews of western Mediterranean arcs and the western Carpathians; the second depicts several examples from the Andes, the Alps, Anatolia, Pyrenees, Iberian Ranges and the Atlas; and the third shows the latest research on the use of palaeomagnetism to understand fold-and-thrust belts in 3D and 4D in a more quantitative way and it also includes some methodological proposals to avoid common errors. In the papers of the first two sections, the combination of palaeomagnetic analyses with structural data, AMS or magnetostratigraphic analyses demonstrate the usefulness of palaeomagnetism in deciphering complex deformation patterns in fold-and-thrust belts.