Murat Özkaptan

Age and paleoenvironmental reconstruction of partially remagnetized lacustrine sedimentary rocks (Oligocene Aktoprak basin, central Anatolia, Turkey)

The age and paleoenvironmental record of lacustrine deposits in the Aktoprak basin of south-central Turkey provides information about the evolution of topography, including the timing of development of an orographic rain shadow caused by uplift of the mountain ranges fringing the Central Anatolian Plateau. New magnetostratigraphy-based age estimates, in combination with existing biostratigraphic ages, suggest that the partially remagnetized Kurtulmus Tepe section of the basin is Chattian (Upper Oligocene). The mean carbon and oxygen stable isotope ratios (δ18O= 24.6 ± 2.0 ‰, δ13C= −4.9 ± 1.1‰) are largely constant through the section and indicative of a subtropical, open freshwater lake. These isotopic values are also similar to those of the Chattian Mut basin to the south, on the Mediterranean side of the modern orographic barrier (Tauride Mountains), and indicate absence of an orographic barrier during Late Oligocene basin deposition. Post-depositional partial remagnetization occurred after tilting of the basin sequence and was mineralogically controlled, affecting grey, carbonate-rich rocks (average %CaCO3= 82), whereas interlayered pink carbonate-poor rocks (average %CaCO3= 38) carry a primary, pretilt magnetization. The pink rocks are rich in clay minerals that may have reduced the permeability of these rocks that carry a primary magnetization, concentrating basinal fluid flow in the carbonate-rich grey layers and leading to the removal and reprecipitation of magnetic minerals. The normal and reverse polarities recorded by the remagnetized rocks suggest that remagnetization occurred over a protracted period of time.

Vertical-axis rotations accommodated along the Mid-Cycladic lineament on Paros Island in the extensional heart of the Aegean orocline (Greece)

The Aegean–west Anatolian orocline formed due to Neogene opposite rotations of its western and eastern limbs during opening of the Aegean back-arc basin. Stretching lineations in exhumed metamorphic complexes in this basin mimic the regional vertical-axis rotation patterns and suggest that the oppositely rotating domains are sharply bounded along a Mid-Cycladic lineament, the tectonic nature of which is enigmatic. Some have proposed this lineament to be an extensional fault accommodating orogen-parallel extension, while others have considered it to be a transform fault. The island of Paros hosts the only exposure of the E- to NE-trending lineations characterizing the NW Cyclades and the N-trending lineations of the SE Cyclades. Here, we show new paleomagnetic results from isotropic, ca. 16 Ma granitoids that intruded both domains and demonstrate that the trend difference resulted from post–16 Ma ∼90° clockwise and 10° counterclockwise rotation of the NW and SE blocks, respectively. We interpret the semiductile to brittle, low-angle, SE-dipping Elitas shear zone that accommodated this rotation difference to reflect the Mid-Cycladic lineament. We conclude a two-stage exhumation history for Paros that is consistent with regional Aegean reconstructions. Between ca. 23 and 16 Ma, the metamorphic rocks of Paros were exhumed from amphibolite-facies to greenschist-facies conditions along a top-to-the-N detachment. The Elitas shear zone then started to exhume the northwestern, clockwise-rotating domain from below the southeastern, counterclockwise rotating domain since 16 Ma. From this, we infer that the Mid-Cycladic lineament is an extensional shear zone, consistent with geometric predictions that Aegean oroclinal bending was accommodated by orogen-normal and orogen-parallel extension.

Palaeomagnetic and geochronological evidence for a major middle Miocene unconformity in Söke Basin (western Anatolia) and its tectonic implications for the Aegean region

Cenozoic convergence between the Eurasian and African plates and concurrent slab roll-back processes have produced a progressive extension in back-arc areas, such as the Aegean region and western Anatolia. There is still a long-standing controversy as to whether this was a continuous or stepwise process. To shed light on this controversy and on the driving mechanism of regional extension, we present palaeomagnetic and geochronological results from the Söke Basin located at the southeastern rim of the İzmir–Balıkesir Transfer Zone. Our improved geochronology shows that volcanic activity in the region occurred between 11.66 and 12.85 Ma. Middle to late Miocene palaeomagnetic data for the Söke Basin show a c. 23° clockwise rotation, whereas early Miocene data show a c. 28° counterclockwise rotation. The primary nature of the magnetization is indicated by a positive tilt test. The resulting c. 51° counterclockwise rotations during the middle Miocene signify a major tectonic reorganization, during a period when an interruption of exhumation of metamorphic massifs has been reported. We suggest that the İzmir–Balıkesir Transfer Zone is the main driver of the reorganization in the region. The regional fingerprint of this tectonic reorganization coincides with the acceleration of trench retreat and illustrates the surface impact of tearing of the Hellenic slab. Supplementary material: Details of 40Ar/39Ar analysis including heating steps and the output (.pmag) file including details of paleomagnetic analysis performed in this study are available at https://doi.org/10.6084/m9.figshare.c.3690871