Possible Ancient Continental Margins in Iran

Abstract

The ophiolites of the Alpine folded region of Iran are examined as an indication of the extent of ancient oceanic realms bordered by ancient continental margins. They are grouped into four geographically and geologically distinct zones, differing from each other in composition, structure, and age. The possibility of these four zones marking former continental margins is then checked against the background of the general structural evolution of Iran. It is concluded that during Paleozoic time Iran was an extension of the Arabian platform, and thus a part of Gondwanaland, possibly bordered by a “Paleo-Tethys” in the north, along the present northern foot of the Alborz Range. Closing of the “Paleo-Tethys,” short of a possible modern relict in the South Caspian depression, may have been related to Hercynian orogenic processes in the ScythoTuranian plate to the north and was completed by Liassic time. A rift in the Arabian-Iranian platform along the “Main Zagros Thrust line” in the early Mesozoic or late Paleozoic was followed by the formation of a “Neo-Tethys” in the south, possibly interrelated and simultaneous with the closing of the “Paleo-Tethys” in the north. Further breakup of Iran led to the formation of several branch troughs of the “Neo-Tethys” and temporary isolation of a “Central-and-East Iranian Microcontinent” in the late Mesozoic. Closing of the “Neo-Tethys” in the early Maestrichtian was followed by reintegration of the “microcontinent” and folding of central and north Iran during the Paleocene paroxysm of the Alpine orogeny.