Extension in NW Iran driven by the motion of the South Caspian Basin

Abstract

Contrasted tectonic styles occur in northern Iran. West of Kopet Dagh, the south Caspian basin is an aseismic and possibly rigid block involved in the collision zone between Eurasia and Arabia. To the NW, large scale velocity field of Iran given by recent repeated GPS surveys suggests ∼8 mm/yr of right-lateral displacement for the WNW–ESE faults in the Tabriz region. More surprisingly, geodetic motion also suggests a prominent N 30° extension north to the Tabriz fault where compression would be expected.In order to quantify more precisely the right-lateral movement of the Tabriz region, the extension of NW Iran and the motion of the south Caspian basin, we deployed a dense GPS network in NW Iran, from Central Iran to the Turkish, Armenian and Azerbaijan borders. Three repeated surveys from 2002 to 2004 assess that the Tabriz fault concentrates entirely the ∼8 mm/yr of right-lateral movement observed in NW Iran. This rate is in good agreement with a recurrence interval time of 250–300 yr proposed from historical seismicity studies. We found also two zones of extension, one just north of the Tabriz fault in the south of the Talesh plateau and another close from the Azerbaijan border north of the Talesh plateau. We suggest that the existence of a northward subduction of the south Caspian Basin could explain such an extension in the core of the Arabia–Eurasia collision. Increasing evidences of quaternary extensional tectonics in the region from Armenia to Alborz may lead to significantly alter our understanding of the northern Iran tectonics and challenge the traditional Arabian indenter plate tectonics.