Geophysical imaging of ophiolite structure in the United Arab Emirates

Abstract

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.

Crustal Structure of the UAE‐Oman Mountain Range and Arabian Rifted Passive Margin: New Constraints From Active and Passive Seismic Methods

“…In agreement with Ali et al. (2020), we associate the surface between the ophiolite and sediment infill as a major east‐dipping normal fault that probably marks the eastern extension of the Arabian continental crust. Pilia, Hu, et al.…”

“…A proxy for crustal thickness can be calculated from the arrival time of the SsPmp phase relative to the incident S wave, as in the following equation: Records from STN15 and STN19 have been modified from Ali et al (2020). Receiver gathers display the identified seismic phases (colored lines) and predicted travel times based on the final model shown in Figure 6 (red dots).…”

“…Expected traveltimes and waveforms were computed with the aid of synthetic seismograms constructed using the reflectivity method of Fuchs and Müller (1971). For this endeavor, we assume a mantle half-space and a single crustal layer with thickness below each station based on the seismically and gravimetrically constrained cross-sections in Ali et al (2020). The effective number of retained VDSS traces was on average higher than 10 per station, with typically around 70% of seismograms removed from our data set to ensure that only high-quality VDSS traces are included in our computations.…”

“…They present a structural interpretation with the Semail ophiolite as thick as ∼5 km near the shoreline, although even in this case picking the bottom reflector of the ophiolite proved to be extremely challenging. More recently, Ali et al (2020) showed that onshore the western part of the Semail ophiolite is relatively thin, thickening to the east (with a dip of 40°-45°) where it is ∼15 km along the coastline, and that it terminates along a NE-dipping normal fault immediately offshore the UAE. They describe the ophiolite as a body with high density, high magnetic susceptibility and high P-wave velocity.…”

“…In this study, we combine active and passive seismic data to reconstruct the crustal structure across two transects orthogonal to the UAE-Oman mountain range. While a number of active seismic profiles have been shown in Ali et al (2020), namely reflection transect 1012 and refraction transects D1 and D4 (Figure 1), here we present a series of new depth-migrated reflection images from the Gulf of Oman and the PILIA ET AL. Stations are progressively counted from west to east along Line D1 (STN01-STN17) and from east to west along Line D4 (STN18-STN25).…”