Fold-and-thrust belt and foreland basin of the United Arab Emirates: Sedimentary structures, basement morphology, and tectono-stratigraphic evolution

Abstract

The subsurface structural geometries of the United Arab Emirates (UAE) fold-and-thrust belt (FTB) and foreland basins are interpreted from seismic, well data, and gravity and magnetic data, integrated with surface geology. We also determined the basement depths, as well as the relation between shallow sedimentary structures and deep basement features. Miocene to Lower Jurassic sequences were interpreted and mapped. Additionally, we outlined subsurface extent of Sumeini and Hawasina allochthonous nappes. The tectonic subsidence curves suggest that the final major passive margin rifting event occurred in the early Aalenian and lasted till Oxfordian. Loading of the Semail ophiolite thrust sheet and accompanying allochthonous thrust sheets resulted in uplift at ca. 95 Ma and rapid subsidence at ca. 83 Ma, indicating the transition of the Arabian margin from a rifted passive margin to a foreland basin. The region witnessed an accelerated subsidence during the late Oligocene-Miocene, attributed to the initial collision of the Central Iran and Arabian plates. The Permian-Jurassic NW-SE oriented rift faults were reactivated as thrust faults during the Late Cretaceous ophiolite obduction and late Oligocene-Miocene continental collision. Two different tectonic regimes are identified in the FTB. Based on the seismic reflection profiles and derivative maps of gravity and magnetic data, the northern regime has NNW–SSE striking thrusts, backthrusts and folds. It is characterized by major inversion of the rift faults with up to 3,700 m thrusting throw. Four major west-verging and east-dipping thrusts, which cross the northern area, form fault-propagation folds and dissect the entire stratigraphy. Whereas the southern regime around Jabal Hafit is dominated by the Tarabat backthrust, which cuts across the Upper Cretaceous and Cenozoic successions. Moreover, the Mesozoic platform carbonates are dissected by inverted faults (pop-up structure) in this regime. The Hawasina décollement, together with the inverted basement structures formed the Jabal Hafit anticline as a backthrust structure. On the other hand, results of the 3D gravity inversion indicate that the basement depths range from 11.5 km along uplifted areas of the FTB to 18.8 km within the deeper parts of the foreland basin. Significant northward increases in both basement depth and the thickness of the late Oligocene-early Miocene successions indicate a northward increase in the severity of thrusting and crustal loading along the main Khusub thrust. The basement uplifts are found to be correlated with shallower anticlinal features, indicating a direct relationship between basement uplifts and shallow sedimentary structures and hence indicating reactivation of basement structures during the Zagros collision.