Origin of the Hafit structure: Implications for timing the Tertiary deformation in the Northern Oman Mountains

The Hafit structure belongs to a group of large-scale, post-obduction periclines that deform the Late Cretaceous-Tertiary sediments of the Oman Mountains Foredeep. Due to one-sided compression from the ENE, the Hafit structure grew as a detachment fold above a basal decollement which is probably located in the Upper Cretaceous Lower Fiqa shale. Its reversed vergence, back thrust and the folds superposed on its limbs, are explained as being caused by simple shear modification of the original structure. The interpretation that the Hafit structure and other foreland folds in the Northern Oman Mountains have resulted from a Zagros-related late Eocene-Miocene compressional event, is at variance with the stratigraphical and sedimentological evidence from the Hafit area. This evidence shows that the Hafit structure grew synchronously with sedimentation from just before the Middle Eocene, until the end of the Miocene, whilst the related structures to the east of it were initiated at the beginning of the Palaeocene. With further evidence of a similar early start to the Tertiary deformation emerging from other parts of the Northern Oman Mountains, it becomes necessary to push back the date of initiation of the Tertiary compressional event to the Palaeocene and to set it apart from the Plio-Pleistocene Zagros deformation.