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The Oman-United Arab Emirates ophiolite has been used extensively to document the geological processes that form oceanic crust. The geometry of the ophiolite, its extension into the Gulf of Oman, and the nature of the crust that underlies it are, however, unknown. Here, we show the ophiolite forms a high velocity, high density, >15 km thick east-dipping body that during emplacement flexed down a previously rifted continental margin thereby contributing to subsidence of flanking sedimentary basins. The western limit of the ophiolite is defined onshore by the Semail thrust while the eastern limit extends several km offshore, where it is defined seismically by a~40-45°, east-dipping, normal fault. The fault is interpreted as the southwestern margin of an incipient suture zone that separates the Arabian plate from in situ Gulf of Oman oceanic crust and mantle presently subducting northwards beneath the Eurasian plate along the Makran trench.

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Seismic reflection profiles, exploratory well, and outcrop data are used to determine the stratigraphy and tectonic subsidence and uplift history of the western Musandam peninsula. Five major regional megasequences have been recognized: (1) Permian to Late Cretaceous rifted margin sequence, (2) Late Cretaceous Aruma foreland basin sequence that evolved in response to the obduction of the Semail Ophiolite, (3) early–mid‐Cenozoic Pabdeh foreland basin sequence that formed due to orogenic loading associated with the early continent–continent collision of the Arabian and Eurasian plates in the Zagros mountains of central Iran, (4) a sequence above the mid‐Miocene unconformity that marks the final stage of continent–continent collision, and (5) a sequence above the late Pliocene unconformity interpreted as tilting due to the latest stage of continent–continent collision. In addition, seismic and outcrop data captured multiple west‐verging and east‐dipping thrust faults associated with the deformation of the Hagab thrust, which causes repetition of the Permian–Mesozoic shelf sequence and the early–mid Cenozoic foreland basin sequence. The tectonic subsidence and uplift derived from backstripping can be explained by a model in which the margin developed by uniform depth extension with an initial age of rifting of 260 Ma and a final age of rifting of 185 Ma. Moreover, the tectonic subsidence indicates two compressional events that commenced at ~94 Ma and ~25 Ma, respectively. These events are attributed to the obduction of the Semail Ophiolite and the culmination of the Musandam peninsula, respectively.

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, Te´ of c. 20–25 km. This Te 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.

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).

Highly efficient and very stable iron and/or cobalt-based catalysts for the ammonia synthesis reaction were synthesized by one-step pyrolysis of metal phthalocyanine precursors.

Direct seismic waves (P- or S-waves) are used to locate and further characterize microseismic events. The resolution of information obtained from direct waves depends on the peak frequencies of the waveforms. The peak frequency results from combination of the source, propagation, and the receiver effects. For frequencies below the corner frequency, propagation effects control the peak frequency in observed seismograms of microseismic events. The frequency dependence of direct body waves can be modeled by attenuation, specifically the global attenuation factor. This model is consistent with observed data along surface profiles explaining the difference between the peak frequencies of P- and S-waves. In addition, the model is consistent with the peak frequencies observed on downhole monitoring arrays. This can be used to invert effective attenuation providing additional unique measurement from microseismic events. The corner frequency can be estimated from the average stress drop and analytical source models such as a circular crack model. Typical stress drops for various magnitude ranges are discussed. The peak frequencies are usually below the corner frequencies of microseismic events smaller than moment magnitude 0.7 for surface monitoring and moment magnitude −0.5 for downhole monitoring. Understanding of the frequency dependence of the direct waves allows us to optimally design monitoring networks and mainly invert effective attenuation providing unique measurement from microseismic monitoring.