The tectonics of the Musandam Peninsula in northern Oman shows a transition between the Late Cretaceous ophiolite emplacement related tectonics recorded along the Oman Mountains and Dibba Zone to the SE and the Late Cenozoic continent-continent collision tectonics along the Zagros Mountains in Iran to the northwest. Three stages in the continental collision process have been recognized. Stage one involves the emplacement of the Semail Ophiolite from NE to SW onto the Mid-Permian–Mesozoic passive continental margin of Arabia. The Semail Ophiolite shows a lower ocean ridge axis suite of gabbros, tonalites, trondhjemites and lavas (Geotimes V1 unit) dated by U-Pb zircon between 96.4–95.4 Ma overlain by a post-ridge suite including island-arc related volcanics including boninites formed between 95.4–94.7 Ma (Lasail, V2 unit). The ophiolite obduction process began at 96 Ma with subduction of Triassic–Jurassic oceanic crust to depths of > 40 km to form the amphibolite/granulite facies metamorphic sole along an ENE-dipping subduction zone. U-Pb ages of partial melts in the sole amphibolites (95.6– 94.5 Ma) overlap precisely in age with the ophiolite crustal sequence, implying that subduction was occurring at the same time as the ophiolite was forming. The ophiolite, together with the underlying Haybi and Hawasina thrust sheets, were thrust southwest on top of the Permian–Mesozoic shelf carbonate sequence during the Late Cenomanian–Campanian. Subduction ended as unsubductable cherts and limestones (Oman Exotics) jammed at depths of 25–30 km. The Bani Hamid quartzites and calc-silicates associated with amphibolites derived from alkali basalt show high-temperature granulite facies mineral assemblages and represent lower crust material exhumed by late-stage out-of-sequence thrusting. Ophiolite obduction ended at ca. 70 Ma (Maastrichtian) with deposition of shallow-marine limestones transgressing all underlying thrust sheets. Stable shallow-marine conditions followed for at least 30 million years (from 65–35 Ma) along the WSW and ENE flanks of the mountain belt. Stage two occurred during the Late Oligocene–Early Miocene when a second phase of compression occurred in Musandam as the Arabian Plate began to collide with the Iran-western Makran continental margin. The Middle Permian to Cenomanian shelf carbonates, up to 4 km thick, together with pre-Permian basement rocks were thrust westwards along the Hagab Thrust for a minimum of 15 km. Early Miocene out-of-sequence thrusts cut through the shelf carbonates and overlying Pabdeh foreland basin in the subsurface offshore Ras al Khaimah and Musandam. This phase of crustal compression followed deposition of the Eocene Dammam and Oligocene Asmari formations in the United Arab Emirates (UAE), but ended by the mid-Miocene as thrust tip lines are all truncated along a regional unconformity at the base of the Upper Miocene Mishan Formation. The Oligocene–Early Miocene culmination of Musandam and late Cenozoic folding along the UAE foreland marks the initiation of the collision of Arabia with Central Iran in the Strait of Hormuz region. Stage three involved collision of Arabia and the Central Iran Plate during the Pliocene, with ca. 50 km of NE-SW shortening across the Zagros Fold Belt. Related deformation in the Musandam Peninsula is largely limited to north and eastward tilting of the peninsula to create a deeply indented coastline of drowned valleys (rias).

Seismic reflection profile, gravity anomaly, and exploratory well data have been used to determine the structure and evolution of the United Arab Emirates (UAE) foreland basin. The basin is of tectonic significance because it formed by ophiolite obduction in the northern Oman Mountains and flexural loading of an underlying Tethyan rifted margin. Existing stratigraphic data shows that this margin is characterised by an early syn-rift sequence of mainly Triassic age that is overlain by a post-rift sequence of Lower Jurassic to Upper Cretaceous age. Backstripping of the well data provides new constraints on the age of rifting, the amount of crustal and mantle extension, and the flexural effects of ophiolite load emplacement. The tectonic subsidence and uplift history at the wells can be generally explained by either a uniform extension model with an initial age of rifting of 210 Ma and a stretching factor, β, of 2.5 or a depth-dependant extension model with crustal extension factor of, γ, 1.3 and a mantle extension factor, β, of 2.5. While both models account for the general exponential decrease that is observed in the tectonic subsidence and uplift between 210 Ma and 95 Ma, we prefer the depth-dependant model because the depth-to-Moho that is implied better accounts for the increase that is observed in the regional Bouguer gravity anomaly between the UAE foreland and the Oman coastline. However, there are discrepancies, which we attribute to uncertainties in palaeobathymetry, sea level, and stratigraphic ages. Irrespective, the backstrip curves suggest that there was a significant thinning of the continental crust prior to ophiolite emplacement. The timing of emplacement cannot be constrained precisely, but the backstrip curves suggest that ophiolite loading and foreland basin flexure was initiated during the Late Cretaceous. The basin shape can be explained by a simple model in which both surface (i.e. topographic) and subsurface (i.e. ophiolitic) loads were emplaced on a lithosphere with an effective elastic thickness, T_e´ of c. 20–25 km. This T_e is similar to what we would expect for loading of extended continental lithosphere 80 My after a rifting event. It predicts a c. 4 km flexural depression and a few hundred metres flanking bulge that is presently located beneath the Abu Dhabi region. The bulge is obscured, however, by at least 2 km of sediment, possibly because of an increase in accommodation space due to dynamic effects associated with the subduction of the Arabian Plate beneath the Eurasian Plate.

Four main Late Cretaceous and Tertiary phases of crustal shortening and thrust-related deformation are recognised in the northern Oman Mountains, each phase ending with a regional unconformity throughout the Oman Mountains and the UAE foreland. The earliest is the major thrust emplacement of the Semail Ophiolite, and underlying Haybi, Hawasina and Sumeini duplexes from NE to SW onto the depressed northeastern continental margin of the Arabian Plate during the Cenomanian to Campanian-early Maastrichtian (D1). A prominent widespread unconformity that places Maastrichtian Qahlah Formation laterite, sandstones and conglomerates and Simsima Formation rudist - Acteonellid gastropod limestones over all underlying allochthonous units is recognised throughout the Oman Mountains. SW-verging folds and thrusts in Triassic to Cretaceous carbonate slope facies rocks exposed in Jabal Sumeini (Sumeini Group and Hamrat Duru Group) have been emplaced over uppermost Cretaceous Juweiza Formation conglomerates at the highest level of the Aruma foreland basin. These Sumeini D1 structures are abruptly truncated by an unconformity, above which are Middle Maastrichtian beds showing up to 95% ‘death assemblage’ rudists and gastropods just below the Cretaceous – Tertiary boundary (top of Simsima Formation). A second deformation event (D2) affected the Simsima Formation and underlying Sumeini Group, Hamrat Duru complex and Semail Ophiolite rocks. This phase shows gentle folding about NW-SE fold axes (e.g. Jabal Rawdah), along a similar trend to the Late Cretaceous D1 event. This trend is also parallel to a regional set of NW-SE aligned fractures in the UAE foreland. A major angular unconformity occurs beneath the Upper Palaeocene – Eocene shallow-marine limestones (Umm Er Radhuma, Rus and Dammam formations). Many foreland jabals in eastern Abu Dhabi (Jabals Qatar, Malaqet, Mundasa) show gentle post-Eocene folding formed during the third stage of crustal shortening (D3). The large pericline of Jabal Hafit is a double-plunging, east-verging box fold that formed after deposition of the Oligocene Asmari Formation limestones and Miocene Fars Formation gypsum and clays, the youngest beds affected by the fold. This Late Miocene – Pliocene phase of crustal shortening (D4) is the youngest phase of deformation in the eastern Al Ain-Buraimi region.

The area to the southeast of the city of Al Ain, Abu Dhabi, United Arab Emirates, is part of an arcuate sedimentary basin whose trend gradually changes from NNW near Al Ain to NNE at Ras Al Khaimah. The basin is bounded to the east by the generally N-trending Oman Mountains and on the west by an arcuate, overall west-verging fold-thrust front that involves Mesozoic carbonates. The fold-thrust front is part of the overall compressional system of Late Cretaceous age (with Late Tertiary reactivation) associated with obduction and emplacement of the Semail Ophiolite, Haybi, Hawasina and Sumeini sheets onto the continental margin of the Arabian Plate. Near Al Ain, the fold-thrust front is expressed as the remarkable, NNW-trending Jabal Hafit that rises one kilometer above the gravel-filled Al Jaww Plain. Gravity and magnetic investigations were carried-out in the Al Jaww Plain, an area of approximately 550 square km. The interpretation of these new data, including measurements of physical properties of rock samples from the area, were integrated with a new interpretation of an industry seismic reflection profile to provide constraints on the modelling of the subsurface structure and evolution of the sedimentary basin beneath Al Jaww Plain. We recognised four major tectono-stratigraphic units in the seismic profiles: autochthonous shelf carbonates, the Hawasina allochthon, Upper Cretaceous foreland basin sediments (primarily Fiqa Formation), and Tertiary neo-authochthonous units. Along-strike variations in the residual Bouguer gravity field were interpreted as being due to either variations in the thickness, or even total absence, of the Hawasina sheet. Comparison of two E-W gravity profiles, one in the southern part of our study area and the other to the north, suggest that the Hawasina sheet underlies little of the southern area but almost all of the northern area. Magnetic anomalies are weak (< 50 nT) over most of the area but peak (> 300 nT) in the easternmost part of the southern profile, where the high-susceptibility rocks of the Semail Ophiolite are exposed. Thus, we interpret that no continuation of the ophiolite extends westward from this outcrop into the subsurface of the study area. The structural geometries described here have resulted from two major tectonic events. The first, a Late Cretaceous phase, emplaced the obduction-related allochthonous thrust sheets of the Oman Mountains westward onto the Mesozoic carbonate platform. This phase primarily affected the eastern part of the study area and contributed to both the high magnetic (> 300 nT) and residual Bouguer gravity (> 14.0 mGal) anomalies. The second event, a Tertiary deformation phase, affected most parts of the area and produced a series of asymmetrical anticlines and synclines trending in a NNW-SSE direction. This phase contributed to the low residual gravity anomaly (< -9.0 mGal) in the center of the study area. We modelled that area as containing a sequence of post-Eocene carbonate sediments with a minimum thickness of 2.0 km. The Tertiary folding and thrusting formed as a result of a regional compressive deformation, whose principal compressive stress axes were sub-parallel to those of the Late Cretaceous compressional stress regime. The younger event reactivated high-angle reverse faults within the Mesozoic platform succession. Precise timing of the Tertiary deformation is debatable; it is most likely that the rejuvenation of the E-W to ENE-WSW Cretaceous stress regime took place in the Late Eocene-Miocene but gradually shifted to become N-S to NE-SW. This shift could be due to the collision of the Arabian and Eurasian plates and the opening of the Red Sea which started during Late Eocene and continues until the present-day.

Gravity measurements onshore and offshore of the United Arab Emirates (UAE) have been used to construct a new Bouguer gravity anomaly map of the region. The gravity data, which has been gridded at 2,700 m × 2,700 m interval, has been used to constrain the tectonic elements, major lineation trends and structures of the Neoproterozoic basement of the Arabian Plate and the distribution of infra-Cambrian salt basins. Advanced transformation techniques (including first vertical derivative, total horizontal derivative, tilt derivative and Euler deconvolution) were applied to identify gravity source edges as an aid to structural interpretation and geological modelling of the study area. Three major structural provinces (fold-and-thrust belt, foreland and salt tectonic provinces) were identified based on the residual Bouguer gravity anomaly field. The eastern fold-and-thrust belt province is associated with short-wavelength positive gravity anomalies, which are attributed to the allochthonous series of the Semail Ophiolite and its related thrust sheets. The central foreland basin province is characterised by NNW-oriented negative gravity anomalies associated with deepening of the basement and thickening of Aruma and Pabdeh sediments in the foredeep basins and flexure of the top and base of the crust by the load of the Semail Ophiolite. The western salt tectonic province displays well-defined local gravity lows superimposed on a regional gravity high, which probably reflects the swelling of infra-Cambrian salt above a shallowing of the basement and thinning of the foredeep sediments. In addition, gravity modelling constrained by seismic and well data indicates the presence of substantial infra-Cambrian salt bodies in all basins of the UAE both onshore and offshore including the southern area of the Rub’ Al-Khali Basin. An extensive array of previously unmapped N-S, NW- and SW-trending lineaments affecting the basement and possibly overlying sediments are mapped in the UAE. The N-S Arabian trending lineament represents the effect of a major structure, along which many important oilfields are located (e.g. Bu Hasa). The SW trend has regular spacing and is dominant in the southern and central part of Abu Dhabi, east of the Falaha syncline. The NW-SE lineament is the most striking and includes two well-defined trends that cross Abu Dhabi Emirate, which in this paper are named as the Abu Dhabi Lineaments. These lineaments are associated with a linear gravity high extending from the southwestern border with Oman to the offshore close to Zakum oilfield. They are probably related to the Najd Fault System.