Mualla Cengiz Çinku

The Tectonic History of the Niğde-Kırşehir Massif and the Taurides since the Late Mesozoic: Paleomagnetic Evidence for Two-Phase Orogenic Curvature in Central Anatolia†

The Nigde-Kirsehir Massif, known also as the Central Anatolian Block, is bordered by the sutures of the NeoTethys Ocean. The Massif suffered several deformation phases during and after the consumption of the surrounding oceans and the post-collisional events of the continental pieces of Anatolia in latest Cretaceous to Miocene. Previous paleomagnetic studies on the Nigde-Kirsehir Massif and its surroundings displayed either insufficient data or have claimed large rotations and/or remagnetization. In order to understand the tectonic history of the Nigde-Kirsehir Massif and its adjacent blocks we have sampled 147 different sites in the age range of Upper Jurassic to Miocene from the Nigde-Kirsehir Massif throughout its W/SW and E/SE boundaries and the Central- Southeastern Taurides. The results display that except the limestones in Central Taurides, all rocks examined carry a primary magnetization. Among these an important finding is that rotations between the Massif and the Central-Eastern Taurides indicate an oroclinal bending with counterclockwise rotation of R=41.1°±7.6° in the SE and clockwise rotation of R=45.9°±9.3° in the Central Taurides from Upper Cretaceous rocks with respect to the African reference direction. Paleomagnetic rotations in the SE Taurides are compatible with the vergent direction of the thrusts generated from consumption of the Intra-Tauride ocean prior to post collisional convergence between Taurides and the Massif. In the Central Taurides it has been shown that the clockwise rotation of 45.9±9.3 started in Middle Eocene, because of a remagnetization in Upper Creataceous limestones. The deformation was linked to the final closure of the southern Neotethys and the collision between the African and Eurasian plates. In the Nigde-Kirsehir Massif counterclockwise rotation up to 25.5°±7.3° is recognised during Middle Eocene and interpreted in terms of block rotation together with the Taurides. After the Miocene a counterclockwise rotation of 16.8°±3.9° along the Eastern Taurides shows that this area was mostly affected by the westward movement of Anatolia despite the Nigde-Kirsehir Massif and its SW/W area-the Central Taurides, which is recognised as stable with counterclockwise rotation less than 10°.

Evidence of Late Cretaceous oroclinal bending in north-central Anatolia: palaeomagnetic results from Mesozoic and Cenozoic rocks along the İzmir–Ankara–Erzincan Suture Zone

Abstract 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.