Cenozoic tectonic inversion, buttressing, and emergent faulting along the Wadi Kabir Fault, northern Oman

The geology of northern Oman is distinctive because of the emplacement of the massive Semail Ophiolite onto the stable Arabia platform in the late Cretaceous followed by the later development of the Jebal Akhdar and Saih Haitat domes.  East of Muscat, the Wadi Kabir Fault forms an important and long-lived structure at the northern edge of the Saih Hatat dome.  In the Bandar Jissah area, Triassic carbonates occur in the footwall of the NNE-dipping Wadi Kabir Fault while rocks of the Semail Ophiolite, newly discovered rocks of the metamorphic sole, and a sequence of Paleogene-Eocene sedimentary rocks crop out in the footwall.  Previous workers posit that regional extension commenced via early low-angle detachment faulting (‘Banurama detachment’) that was followed by higher-angle normal faulting along the Wadi Kabir and associated faults which developed as basin-bounding structures for the Paleocene Bandar Jissah rift basin.  Folds in the hanging wall cover sequence are interpreted as the product of rollover during extension and basin formation.

Our detailed mapping as well as structural and kinematic analysis illustrates that folds in the hanging wall are contractional structures that formed due to tectonic inversion along the Wadi Kabir and other faults.  The overall shortening is modest (~10%) and primarily confined to the hanging wall rocks, consistent with buttressing against mechanically rigid rocks in the footwall of the Wadi Kabir Fault.  The low-angle ‘Banurama detachment’, which places Paleogene-Eocene sedimentary rocks over Triassic carbonates, records south-directed thrust movement (not north-directed extensional slip) and with contractional slip past the null point.  This structure appears to be an emergent fault in which the reactivated cover strata above the Wadi Kabir fault were thrust southward over the ground surface and shed sediment from the growing hanging wall anticline.

These structures require an interval of shortening/transpression in northern Oman that post-dates rift basin formation and deposition of mid-Eocene marine sediments in the Seeb Formation. The Wadi Kabir Fault also has localized zones of listwaenite preserved in its damage zone that is derived from ophiolitic rocks in the hanging wall. Collectively, the Wadi Kabir Fault is a long-lived structure that’s experienced multiple episodes of both extensional and contractional slip since the Cretaceous.