Exhumation with a twist: Paleomagnetic constraints on the evolution of the Menderes metamorphic core complex, western Turkey

Abstract

Much remains to be understood about the links between regional vertical axis rotations, continental extension, and shortening. In western Turkey, Miocene vertical axis rotations have been reported that occur simultaneously with the extensional exhumation of the Menderes metamorphic core complex, which has been related to back‐arc extension in the eastern part of the Aegean back arc. In this paper we explore the spatial and temporal relationships between vertical axis rotations in southwestern Turkey and extensional unroofing of the Menderes Massif. To this end, we provide a large set of new paleomagnetic data from western Turkey, and integrate these with the regional structural evolution to test the causes and consequences of oroclinal bending in the Aegean region. The Lycian Nappes and Bey Dağları are shown to rotate ∼20° between 16 and 5 Ma, defining the eastern limb of the Aegean orocline. This occurred contemporaneously with the exhumation of the central Menderes Massif (along extensional detachments) and after the latest Oligocene to early Miocene exhumation of the northern and southern Menderes massifs. Exhumation of the latter two was not associated with vertical axis rotations. The lower Miocene volcanics in the region from Lesbos to Uşak, to the north of the central Menderes Massif underwent a small clockwise rotation, insignificant with respect to Eurasia. This shows that exhumation of the central Menderes Massif was associated with a vertical axis rotation difference between the northern and southern Menderes massifs of ∼25°–30°. This result is in excellent agreement with the angle defined by the trends of Büyük Menderes and Alaşehir detachments, as well as the angle defined by the regionally curving stretching lineation pattern across the central Menderes Massif. These structures define a pivot point (rotation pole) for the west Anatolian rotations. The rotation of the southern domain, including the southern Menderes Massif, the Lycian Nappes, and Bey Dağları, must have led to N–S contraction east of this pole. The eastern limit of the rotating domain is formed by the transpressional couple of the Aksu thrust and Kırkkavak Fault in the center of the Isparta angle. Previously reported clockwise rotations in the volcanic fields near Afyon may be the result of distributed N–S shortening east of the pivot point. The precise accommodation of this shortening history remains open for investigation. Late Oligocene to early Miocene extension in the eastern part of the Aegean back arc was NE–SW oriented and likely bounded by a discrete transform. This transform may be associated with an early evolution of the eastern Aegean subduction transform edge propagator fault. Oroclinal bending in the west Anatolian region is likely related to a reconnection of the eastern part of the Aegean orocline with the African northward moving plate in tandem with roll back in the Aegean back arc, comparable to a recently postulated scenario for western Greece.

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

“…In the southern Menderes massif, coeval top-to-the S extensional shear has also been recognized and volcanoclastic rocks were unconformably deposited in the early Miocene (figure 4) [Bozkurt and Satır, 2000;Gessner et al, 2001aGessner et al, , 2001b. From the middle Miocene to the late Miocene-Pliocene, exhumation was localized in the central Menderes massif along the top-to-the NE Alaşehir and the top-to-the S Büyük ductile-brittle detachments (figure 7) [Hetzel et al, 1995b;Gessner et al, 2001b;Lips et al, 2001;Thomson & Ring, 2006;van Hinsbergen et al, 2010b]. Additional syn-tectonic sedimentary basins were emplaced in the hanging walls of these structures [Sen and Seyitoglu, 2009].…”

“…While no significant rotation was recorded north of the Menderes massif, the central Menderes massif underwent 25-30° counterclockwise rotation during its exhumation (i.e. 15-5 Ma ago), concomitantly with the ~20° counterclockwise rotation recorded in the Lycian nappes and the Bey Dağları platform (figure 3) [Kissel et al, 1993;van Hinsbergen et al, 2010avan Hinsbergen et al, , 2010b. Further east, the central Taurides experienced an ~40° clockwise rotation between the middle EoceneOligocene (figure 3) [Kissel et al, 1993] that also affects the Tavşanlı and Afyon units further north to a lesser degree [Pourteau et al, 2010].…”

“…In addition, in order to fit the NE-SW to E-W stretching lineation of the Phyllite-Quartzite unit in the Peloponnese (figure 3) with the regional N-S to NNE-SSW extension, a similar clockwise rotation has to be applied to this HP-LT unit during its final exhumation in the Peloponnese. In opposition, 20-30° counterclockwise rotations have been recorded further east in the eastern Cyclades, the central Menderes, the Lycian nappes and the Bey Dağları platform (figure 3) [Kissel et al, 1993;van Hinsbergen et al, 2010avan Hinsbergen et al, , 2010b. These opposite rotations are related to the increasing curvature of the trench during the middle and late Miocene (figure 11) with no rotation recorded at the hinge, such as in Crete where the strike of the stretching lineation of the exhumed PhylliteQuartzite and the Plattenkalk units fits with the regional N-S to NNE-SSW extension (figure 3).…”

“…Following this accretionary event, this massif has been exhumed in a back-arc extensional context, forming a dome-like structure [e.g. Gessner et al, 2001b;Lips et al, 2001;van Hinsbergen et al, 2010b]. This succession of tectonic events resulted in a complex metamorphic succession that is still largely debated today, notably due to the existence of a pre-Alpine tectono-metamorphic history [Şengör et al, 1984;Candan et al, 2001].…”

The Gediz River fluvial archive: A benchmark for Quaternary research in Western Anatolia

“…This result suggests a small but significant counterclockwise rotation, which is surprising, given the young age of the lavas, the absence of evidence for significant local deformation of the volcanic fields around Kula, and the recent notion that on a regional scale in the Selendi basin, and surrounding basins, no significant vertical axis rotations occurred since the middle Miocene (van Hinsbergen et al, 2010). It is possible that our lava sites come from a very limited time span, overrepresenting secular variation of the Earth's magnetic field (although the scatter of data is not very tight and may represent secular variation).…”