Sequential rotation of stretching axes, and block rotations: a structural and paleomagnetic study along the North Anatolian Fault

Abstract

Fault kinematics of the western part of the North Anatolian Fault, an active transcurrent fault, were investigated. Consistent, successive counterclockwise rotation of incremental stretching directions was derived from the seven areas investigated. We assumed that the changes in stretching directions correlate to the consistent rotation of one or several blocks, caused by interaction of major fault segments. In order to test this hypothesis, we compared magnetic remanence directions measured within Tertiary calc-alkaline volcanic rocks with the changes in stretching direction. In spite of the successive changes in stretching, systematic changes in remanence directions were not observed. Most of the latter show no or low angular distances to the reference direction of D ≈ 335°, I ≈ 50°. Both positive and negative signs are inferred for movements about subhorizontal and subvertical axes where magnetic remanence directions suggest rotation. We conclude that changes in the overall deformation explain the systematic changes in incremental directions better than consistent external rotation. A deformation path is proposed that includes NE-SW and N-S shortening during the Paleogene and, possibly, Lower Miocene, NW-SE shortening and penecontemporaneous local N-S extension for the Miocene and NW-SE to E-W shortening and SW-NE to N-S extension for the Pliocene until the Present.