The geotectonic history of the Makran and adjacent areas of southern Iran

Abstract

The Makran mountain range in Southern Iran has been entirely covered by regional mapping on a scale of 1:250,000, but, in contrast to the mapping of Oman on the other side of the Gulf, the recent mapping is little known. The Cenozoic accretionary prism in the south fronts onto a Mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver, which is followed by a zone of largely intact Mesozoic ophiolite complexes. To the north of this lies the Jaz Murian depression, a desert expanse with no bedrock outcrop. The Sanandaj-Sirjan/Bajgan–Dur-Kan microcontinental sliver, which extends from Turkey through the Zagros to the Makran, is one of a number of microcontinents which detached from Gondwana no later than the early Triassic (NW Iran, Yazd, Tabas, Lut, Birk, Helmand, Farah). During the Mesozoic, these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times, ranging from early Cretaceous to end-Palaeogene. An analogy is drawn with the present-day Mediterranean. The “Sistan Ocean”, in the east, was infilled with an immense thickness of abyssal turbidites during the Eocene before it closed. The field evidence indicates that there was a second Cenozoic accretionary prism here, but sedimentation ceased after the Eocene, on its collision with the back of the main Makran prism. This eastern Sistan trough, now completely occluded, is compared with the still open tract separating the Makran from Oman at the present time and its northern extension which has been similarly occluded by collision beneath the Zagros. Some residual, very shallow inland seas persisted inland from the Makran through the Neogene. The occurrence of blueschists in the inner ophiolite belt of the Makran is discussed. Abyssal turbidite sedimentation continued in the main southern zone of the Makran into the early Miocene, to be succeeded by thick shallow water sequences including reefal limestones. Intense tectonic dislocation at the end of the Miocene was accompanied by a shift of the subduction front to its present position out in the Indian Ocean and uplift, leading to the deposition of spectacular Pliocene–Pleistocene fanglomerates.