Late Cenozoic tectonics and volcanism along the North Anatolian Fault:: new structural and geochemical data

Different types of volcanic activity have developed along the North Anatolian Fault zone (NAF) in Turkey. Detailed analysis of satellite images and Digital Elevation Models (DEMs), and field observations have been made in order to understand the tectonics and the distribution of volcanic vents. In the Anatolian block, some faults are oblique to the NAF, and delimit extensional escape wedges. Vents rooted on open tension fractures show that emplacement of the volcanism is related to tensional fracturing of the Anatolian continental block, which we attribute to the onset of free borders in the south and west. Along the NAF, earliest extension (v1) is directed S to SSW and the latest (v2) towards W to WSW, parallel to the sinistral slip along the NAF. Major and trace element geochemical data indicate that the dominant calc-alkaline rocks are associated with various alkaline lavas. K-Ar ages of the volcanics range from 22 to 8.5 Ma in Galatia Massif, 900 to 100 ka in Niksar and 3 to 12 ka in Erzincan. Isotopic and trace element data are interpreted as reflecting a dominantly lithospheric mantle source, slightly mixed with asthenospheric liquids. Most magmas were fractionated and contaminated by continental crust during their ascent. v1 and v2 tectono-volcanic events have propagated through time and space from west to east. The v1 extension is late Oligocene in the Galatia Massif, late Miocene in Niksar and late Pliocene in Erzincan. The v2 extension and strike-slip event along the NAF began in the late Miocene in the Galatia Massif, early Pliocene in Niksar and Quaternary in Erzincan. Signature from an asthenospheric source in the second event in the three regions suggests that an ancient suture zone (Galatia Massif) and/or the lithospheric NAF transform (Niksar and Erzincan) have served to channel small quantities of asthenospheric melts existing at the base of the Lithosphere. (C) 2001 Elsevier Science B.V. All rights reserved.