The crust and upper mantle structure of the UAE-Oman mountains: insights from new gravity and seismological data

Thesis

The UAE-Oman mountains are a ~700 km long mountain belt located on the north-eastern margin of the Arabian plate, extending from the Musandam peninsula in the north, through the United Arab Emirates (UAE) and Oman to terminate at the eastern tip of Arabia. These mountains contain a series of stacked thrust sheets that incorporate a full “half ocean” sequence, including: deep ocean sediments and volcanoclastic exotics; shelf and slope sediments; and an obducted slab of oceanic crust and upper mantle known as the Semail ophiolite. The obduction of these thrust sheets emplaced a significant load on the Arabian margin, and the resulting flexure and subsidence led to the formation of a foreland basin inland from this load. Significant sedimentation has also occurred on the seaward side of the ophiolite since its obduction, with up to 10 km of deposition since the end of the Cretaceous, concealing the eastern termination of the ophiolite, and the present day transition from continental to oceanic crust.

This thesis utilises passive seismic and gravity data acquired across two east-west profiles. We aim to constrain the thickness and subsurface geometry of this ophiolite, investigate its offshore extent, constrain the crustal thickness of the underlying Arabian margin, and investigate the transition from continental to oceanic crust offshore in the Gulf of Oman.

Receiver functions and gravity modelling across these profiles revealed: a ~15 km sedimentary sequence and a ~36 km Moho in the foreland basin to the west, suggesting a stretching factor for the rifted Arabian margin of 1.49; a ~10 km flexural root beneath the UAE-Oman mountains, offset ~20 km landwards from the primary ophiolite load; that the Semail ophiolite dips eastwards at ~30◦, increasing from 5 − 10 km depth near Masafi to ~25 km depth near the Gulf of Oman coastline; that high ophiolite densities (~3120 kg m−3) are required to reproduce the ~160 mGal Bouguer anomalies observed across the ophiolite, implying minimal bulk serpentinisation (< 30%); that the ophiolite extends offshore below the hinterland sediments in the Gulf of Oman in a steep normal fault; and that the Moho thins rapidly east of Masafi to transition from thinned continental crust of the Arabian margin to in situ oceanic crust of the Gulf of Oman ~30 km offshore.

Authors: Keats, B

• DOI: 10.5287/ora-rykzexdpd
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English