Abstract
AbstractMountain building in the Al-Hajar Mountains (NE Oman) occurred during two major shortening stages, related to the convergence between Africa–Arabia and Eurasia, separated by nearly 30 Ma of tectonic quiescence. Most of the shortening was accommodated during the Late Cretaceous, when northward subduction of the Neo-Tethys Ocean was followed by the ophiolites obduction on top of the former Mesozoic margin. This shortening event lasted until the latest Santonian – early Campanian. Maastrichtian to Eocene carbonates unconformably overlie the eroded nappes and seal the Cretaceous foredeep. These neo-autochthonous post-nappe sedimentary rocks were deformed, along with the underlying Cretaceous tectonic pile, during the second shortening event, itself including two main exhumation stages. In this study we combine remotely sensed structural data, seismic interpretation, field-based structural investigations and apatite (U–Th)/He (AHe) cooling ages to obtain new insights into the Cenozoic deformation stage. Seismic interpretation indicates the occurrence of a late Eocene flexural basin, later deformed by an Oligocene thrusting event, during which the post-nappe succession and the underlying Cretaceous nappes of the internal foredeep were uplifted. This stage was followed by folding of the post-nappe succession during the Miocene. AHe data from detrital siliciclastic deposits in the frontal area of the mountain chain provide cooling ages spanning from 17.3 to 42 Ma, consistent with available data for the structural culminations of Oman. Our work points out how renewal of flexural subsidence in the foredeep and uplift of the mountain belt were coeval processes, followed by layer-parallel shortening preceding final fold amplification.
Highlights
The processes of progressive thrust propagation into the foreland basin and associated depocentre migration have been well known for decades (e.g. Lyon-Caen & Molnar 1985; Homewood et al 1986; Ricci Lucchi, 1986; DeCelles & Giles, 1996; Lacombe et al 2007)
Our results indicate a coherent late Eocene – Miocene stage of mountain building, whose understanding provides additional constraints on the structural evolution of the Oman Mountains and has implications for the petroleum system
Integrated field structural analysis, remote sensing and seismic interpretation were used in this study to unravel the architecture and tectonic evolution of the foreland basin postdating the Cretaceous nappe emplacement in the Oman Mountains
Summary
The processes of progressive thrust propagation into the foreland basin and associated depocentre migration have been well known for decades (e.g. Lyon-Caen & Molnar 1985; Homewood et al 1986; Ricci Lucchi, 1986; DeCelles & Giles, 1996; Lacombe et al 2007). The first is very well constrained by the remarkable obduction of one of the most studied ophiolite complexes in the world, the Semail ophiolite (Searle, 2014 and references therein) This ophiolite complex overthrusted southwestward the deformed Arabian passive margin during the Late Cretaceous, including the imbricated pelagic sediments of the Hawasina Basin (Fig. 1b; Glennie et al 1973; Béchennec et al 1988). This shortening event was associated with uplift and erosion of the forebulge and deposition of syn-tectonic sediments of the Aruma Group (Nolan et al 1990; Béchennec et al 1992) ahead of the advancing wedge. Our results indicate a coherent late Eocene – Miocene stage of mountain building, whose understanding provides additional constraints on the structural evolution of the Oman Mountains and has implications for the petroleum system
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