The Breaking of the Iranian Block during the Cretaceous and the Opening of New Oceanic Basins within the Tethys Ocean: The Case of the Sabzevar-Nain Basin and Its Geodynamic History

Abstract

The Jurassic subduction of the Neo-Tethys oceanic crust under the western continental margin of the Iranian Block has led to the fragmentation of the Iranian Block in the back-arc basin, leading to the opening of three oceanic basins around it. The ophiolitic belts surrounding central Iran are the indicators of the closure of these basins. The Sabzevar-Nain Basin is one of these basins, which has been created between the micro-block of central Iran in the south and the Alborz Mountain Ranges in the north. This basin opened in the late Jurassic as a rift and then became a trough in the early Cretaceous. Finally, this basin developed into an oceanic basin in the early late Cretaceous. The sedimentation in this basin can be divided into pre-rift, syn-rift and oceanic environments. All of these sediments are strongly folded and faulted. The closure of this basin started during the Paleocene with a subduction under the southern margin of the Alborz Mountain Ranges. The collision event between the northern margin of the micro-block of central Iran and the southern margin of the Alborz Mountain Ranges occurred in the early Eocene. The result of this event was the creation of a wide collision zone, forming a volcanic arc and a back arc basin on the active of the Alborz Mountain Ranges, an ophiolitic belt, and post- collision intrusion masses that appear everywhere in the collision zone. In the point of lithology, these intrusion masses are composed of granite, diorite, and granodiorite. The magmatic activities that started in the Paleocene-early Eocene continued until early Quaternary.