The structure and evolution of the UAE-Oman mountains and associated foreland basins

The structure and evolution of the UAE-Oman mountains and associated foreland basins
M.Y. Ali, A.B. Watts and M. Searle (Oxford University)

Summary

The UAE-Oman mountain belt is 750 km long, up to 3 km high, and exposes the largest and best-preserved ophiolite thrust sheet complex in the world. The belt was developed since ca 96 million years ago during Late Cretaceous obduction of the Oman Ophiolite onto the passive continental margin of Arabia. While the surface geology of the mountains is reasonably well known, the deep structure is not. We propose here to carry out the first integrated study that combines the results of geological field mapping with geophysical studies of the deep structure of the UAE-Oman mountains and foreland basins of the UAE. The objective of our work is to better understand the structure of the leading edge of the Arabian plate and the mechanisms by which oceanic plates are emplaced onto continents and continental plates collide and mountains form. The UAE-Oman mountains are an ideal ‘focus site’ for our study. The UAE forms the northern part of the Late Cretaceous Ophiolite belt of Oman that has not yet undergone continent-continent collision, whereas the Musandam Peninsula in the far north (UAE and Oman) shows the initial contact between the Arabian plate with the Central Iran plate. Musandam is, in fact, a transition between the Late Cretaceous tectonics of Oman and the Tertiary plate collision tectonics of the Iranian Zagros Mountains. By studying the deep structure of the Musandam transition zone, together with geological age constraints, we will be able to constrain the evolution of the continental collision process from pre-collision ophiolite obduction tectonics (Oman) to early continental collision (Musandam).

Fig. 1. Summary geological map of the UAE foreland basin and northern Oman mountains. The thick black lines, open circles and colour coded profile shows the location of the seismic reflection profiles, exploratory wells, and Bouguer gravity anomaly data used in this paper. The thick green line shows Profile AA’, along which the data has been projected. The thick blue lines show the locations of deep seismic reflection profiles in the northern UAE.

Fig. 2. Interpreted seismic reflection profile showing the UAE foreland basin and the underlying rifted margin sequences. Note the progressive onlap of the Fiqa on the Mesozoic shelf carbonates which delineates the transition from an extensional rifted margin setting to a compressional foreland basin setting. The exploratory wells, W1, W2 and W3 are shown along the profile.

Fig. 3. True scale geological cross-section (vertical = horizontal scale) across Jabal Hafit with measured dips and bed thicknesses.

Fig.4. (a) Uninterpreted seismic profile across Jabal Hafit (for location see Figure 1). (b) Interpreted seismic profile showing series of thrust fault and high amplitude fold.

Fig.5. (a) Seismic reflection profile in the immediate vicinity of the well W2 showing well-to-seismic tie. (b) Backstripping of biostratigraphic data from well W2 showing the total sediment accumulation at the well together with the backstripped tectonic subsidence and uplift. Note that the early part of the backstrip is concave-up and resembles the tectonic subsidence curves of rifted margins. We interpret the inflection points at ~80 Ma and ~25 Ma as due to orogenic loading.