Paleomagnetic evidence for an inverse rotation history of Western Anatolia during the exhumation of Menderes core complex

Abstract

Within the Aegean extensional system, the Izmir-Balikesir Transfer Zone (IBTZ) is a crucial element in the late Cenozoic evolution of western Anatolia since it accommodates the differential deformation between the Cycladic and the Menderes metamorphic core complexes. Here, we determine the rotational history of western Anatolia using new paleomagnetic data from 87 sites in Miocene volcano-sedimentary rocks to better understand the role of the IBTZ. Our results reveal two discrete and opposite major rotational phases during the Miocene. The first phase is derived from early Miocene volcanic, sedimentary and granitic rocks and is controlled by detachment and strike-slip faults. It is characterized by an average (net) 23 ± 6° clockwise (CW) rotation within the IBTZ since the early Miocene. Our new data from the Menderes part on the other hand show an average -23 ± 10° counter-clockwise (CCW) rotation. The data from the Cycladic part show no significant (net) rotation since the early Miocene. The second phase is derived from middle-late Miocene volcanic and sedimentary rocks and is controlled by high-angle normal and strike-slip faults. The rotations from this phase show a very consistent pattern of -22 ± 11° CCW within the IBTZ, while now the Menderes part shows an average CW rotation of 25 ± 14°.Our paleomagnetic results hence document a major change and inversion of rotation. Between the early and late Miocene the IBTZ region experienced a large 45° CW rotation, while during the same time interval the Menderes part outside the zone experienced a similar (48°) CCW rotation. After that, the IBTZ became narrower and the sense of rotation inverted to CCW (-23 ± 10° since the late Miocene), while in the Menderes part it inverted to CW (25 ± 14° since the late Miocene). Our new results do therefore fit the hypotheses of two-stage-extension scenario, rather than a one-single-phase of extension. We also conclude that the observed rotations are not directly related to major detachment faulting, but to the change in extensional regime of western Anatolia. The focal mechanism solutions of recent seismic events corroborate that the IBTZ is still active and transfers west Anatolian extensional strain into the south Aegean Sea.