Late Miocene transcurrent tectonics in NW Turkey: evidence from palaeomagnetism and 40Ar-39Ar dating of alkaline volcanic rocks

A number of intra-continental alkaline volcanic sequences in NW Turkey were emplaced along localized extensional gaps within dextral strike-slip fault zones prior to the initiation of the North Anatolian Fault Zone. This study presents new palaeomagnetic and 40Ar-39Ar geochronological results from the lava flows of NW Turkey as a contribution towards understanding the Neogene-Quaternary tectonic evolution of the region and possible roles of block rotations in the kinematic history of the region. 40Ar-39Ar analyses of basalt groundmass indicate that the major volume of alkaline lavas of NW Turkey spans about 4 million years of episodic volcanic activity. Palaeomagnetic results reveal clockwise rotations as high as 73 degrees in Thrace and 33 degrees anticlockwise rotations in the Biga Peninsula. Movement of some of the faults delimiting the areas of lava flows and the timing of volcanic eruptions are both older than the initiation age of the North Anatolian Fault Zone, implying that the region experienced transcurrent tectonics during Late Miocene to Pliocene times and that some of the presently active faults in the region are reactivated pre-existing structures.