Lithospheric evolution of eastern Arabia

The geology of eastern Arabia is dominated by a vast cover of mostly Phanerozoic sedimentary rocks and little was known about the architecture of the middle and lower crust. On the easternmost margin, obduction of the Semail Ophiolite during late Cretaceous times is the youngest first-order tectonic process that shapes the present-day geology across the Oman Mountains in northern Oman and the eastern United Arab Emirates. Within the obducted units, Neoproterozoic to Cretaceous autochthonous rocks of the Arabian shelf are exposed in two tectonic windows and provide a detailed view of the geodynamic evolution of the shallow Arabian continental crust during and after obduction. A new, unprecedented 3-D anisotropic shear-wave velocity (V_s) model reveals that - prior to obduction - the assembly of the eastern Arabian lithosphere in Neoproterozoic times and its modification during the Permian breakup of Pangea strongly control the present-day lithospheric architecture. Building upon previous geodynamic models that were restricted to the upper crust, reconstruction of the entire lithospheric evolution resolves some key unknowns in eastern Arabia’s geodynamics:

• The NNE-striking Semail Gap Fault (SGF) is primarily an upper crustal feature but another NE-striking deep crustal boundary zone west of the Jabal Akhdar Dome segments the Arabian continental crust in two structurally different units.

• While Permian Pangea rifting occurred on both eastern and northern margins of eastern Arabia, large-scale mafic intrusions occurred mostly east of the SGF. Eastward crustal thinning localizes at the eastern limit of obducted units, east of which the lower crust is strongly intruded and likely underplated.

• Late Cretaceous exhumation and overthrusting at the end of ophiolite obduction is the likely cause for crustal thickening below today‘s topography of the Oman Mountains.

• Lithospheric thickness is ~200-250 km in central Arabia but only ~100 km below the Oman Mountains. Thinning of the continental lithosphere is attributed to late Eocene times, which explains contemporaneous basanite intrusions into the continental crust and provides a plausible mechanism for observed crustal-scale extension and the broad, margin-wide emergence of the Oman Mountains. Thus, uplift of the mountain range might be unrelated to Arabia-Eurasia convergence.