Pliocene-Quaternary reorganisation of the Arabia-Eurasia collision

Mark Allen1, James Jackson2, Eric Blanc1, Mohammad Ghassemi3, Richard Walker2

1 CASP, Department of Earth Sciences, University of Cambridge, 181A Huntingdon Road, Cambridge, CB3 0DH

2 Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ

3 Geological Survey of Iran, Azadi Square, Meraj Avenue, 13185-1495, Tehran, Iran

mark.allen@casp.cam.ac.uk

Initial collision between the Arabian and Eurasian plates may have begun as early as the late Eocene. There was a major reorganisation in the collision zone at ~5 Ma, shown by the initiation of deformation or acceleration of strain rates in many regions. Major fold growth in the Zagros Simple Folded Zone and in the South Caspian Basin began at ~3-5 Ma. This is the same time as the start of westward extrusion of Anatolia, between the North and East Anatolian faults, and roughly coincident with an increase in exhumation rates in the Greater Caucasus. Slip rates on the Dead Sea Fault System doubled in the early Pliocene-Quaternary interval, to ~10 mm/yr. There are several possible explanations for this reorganisation. (1) Arabia accelerated its separation from Africa at ~5 Ma, as oceanic spreading began in the Red Sea. (2) Prior to 5 Ma, strain may have been taken up in northern parts of the Arabian margin, now imbricated within the High Zagros. (3) Construction of the Turkish-Iranian Plateau took place in the late Miocene, but ceased at about 5 Ma, possibly because it became easier to shorten and thicken the crust in peripheral areas of the collision zone than to continue uplifting the plateau.

It is now possible to compare the active velocity field for the collision zone, derived mainly from GPS studies, with the finite shortening or strike-slip offset on individual fault systems and the timing of initial deformation in each area. Present shortening or slip rates extrapolated for 3-5 million years account for the finite strain observed in each of the above areas which began deforming at 3-5 Ma, confirming that short term (10 yr) and long term (million yr) deformation rates are consistent across the broad collision zone.