LATE PERMIAN TO LATE TRIASSIC PALEOMAGNETIC DATA FROM IRAN - CONSTRAINTS ON THE MIGRATION OF THE IRANIAN BLOCK THROUGH THE TETHYAN OCEAN AND INITIAL DESTRUCTION OF PANGAEA

A palaeomagnetic study of Late Permian to early Jurassic rocks from th e Alborz and Sanandaj-Sirjan zones in Iran and a compilation of select ed palaeopoles from the Carboniferous to the present provide an update d history of the motion of the Iranian block within the Tethys Ocean. The Iran assemblage, part of Gondwana during the Palaeozoic, rifted aw ay by the end of the Permian. We ascertain the southern-hemisphere pal aeoposition of Iran at that time using magnetostratigraphy and show th at it was situated close to Arabia, near to its relative position toda y. A northward transit of this block during the Triassic is shown, wit h an estimated expansion rate of the Neotethyan ridge of 100-140 km My r(-1). The northward convergence with respect to Eurasia ended during the Ladinian (Middle Triassic), and is marked by a collision in the no rthern hemisphere with the Turan platform, which was the southern marg in of the Eurasian continent at that time. No north-south component of shortening is evidenced north of Iran afterwards. An analysis of the declinations from the Late Permian to the present shows different, lar ge rotations, emphasizing the important tectonic phases suffered since the Triassic. Finally, we propose palaeomagnetic reconstructions of t he Tethys area during the Late Permian and the Late Triassic, showing that the Palaeotethys Ocean was narrower than previously thought, and did not widen its gate to the Panthalassa before the Triassic period.