Seismic Tomography of the Oman Ophiolite
Final Report Abstract
The Semail Ophiolite in northern Oman is the world‘s largest, best preserved and exposed oceanic lithosphere on land. Since its first description in the late 1960‘s it has become the global reference site for a wide range of geoscientific studies, most prominently on the creation of oceanic lithosphere, initiation of subduction, the geodynamics of obduction and continental subduction and continental exhumation from subduction zones, to name a few. Five decades of geological fieldwork provide a detailed picture of the tectonic evolution of the shallow crust in northern Oman, while geophysical images of the continental crust below the obducted ophiolite have been sparse. From 2013 – 2016 we operated a temporary seismic network across the Oman Mountains, the first of its kind in eastern Arabia, that provided the basis for a detailed study on the crustal architecture below the ophiolite. We evaluated and implemented a novel method to measure surface wave dispersion curves from crosscorrelation functions of ambient seismic noise. The method evaluates the phase of the cross-correlation spectrum against the phase of the Hankel function which makes it more robust to cycle-skipping than previously described evaluation against zero-crossings of the Bessel function. We also extended a previously available probabilistic inversion scheme to invert surface wave dispersion curves for isotropic shear wave velocity (Vs) models, to simultaneously invert Rayleigh and Love waves for radial anisotropic Vs. Applying these novel routines in ambient noise seismic tomography, accompanied by Receiver Function analysis, we provide a high resolution, radially anisotropic model of the eastern Arabian continental crust. This model allows us to resolve some key unknowns in eastern Arabia’s geodynamics: 1. Several NE-striking structural boundaries in the middle and lower crust are attributed to Pan-African tectonics and align with first-order lateral changes in surface geology and topography. 2. The well-known Semail Gap Fault (SGF) is mostly an upper crustal feature whereas two other deep crustal faults parallel to the SGF are segmenting the crust from NW to SE. 3. Permian Pangea rifting occurred on both eastern and northern margins of eastern Arabia, but largescale mafic intrusions and underplating occurred mostly east of the SGF. 4. While obduction is inherently lithospheric by nature, involving lithospheric-scale processes on both the obducting and subducting plate, its effects are mostly observed at shallow crustal depths. Lateral variations in obduction geometry and dynamics are explained by inherited Pan-African and Permian structures. 5. Exhumation and overthrusting of continental rocks at the late stage of late Cretaceous obduction is the likely cause for crustal thickening below today‘s topography of the Oman Mountains. 6. Thinning of continental lithosphere below eastern Arabia in late Eocene times – possibly related to thermal effects of the incipient Afar mantle plume - provides a plausible mechanism for the broad emergence of the Oman Mountains and in particular the Jabal Akhdar Dome. Thus, uplift might be unrelated to Arabia-Eurasia convergence as previously believed.
Publications
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Ambient noise characteristics and Green’s Functions across the Oman ophiolite. DGG Tagung 2017, Potsdam, SO.A-027
L. Wiesenberg, C. Weidle, P. Agard, C. Ducassou, I. El-Hussain, C. Prigent, T. Meier
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Ambient Noise Tomography Across the Oman Ophiolite. DGG Tagung 2018, Leoben, SO-P-12
L. Wiesenberg, C. Weidle, A. El-Sharkawy, T. Meier
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COOL project – an unprecedented high quality dataset across the Oman Ophiolite. 10th Gulf Seismic Forum, Muscat, Oman, 19-22 March 2018
C. Weidle, L. Wiesenberg, T. Meier, P. Schwarz, H. Heinisch, P. Agard, C. Ducassou, I. El- Hussain
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Postobductional Kinematic Evolution and Geomorphology of a Major Regional Structure — The Semail Gap Fault Zone (Oman Mountains). Tectonics, American Geophysical Union (AGU), 2019, 38, 2756-2778
Scharf, A., Mattern, F., Moraetis, D., Callegari, I. & Weidle, C.
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Structural Analysis of northern Oman using Receiver functions. AGU Fall Meeting, San Francisco, USA, 9-12 December 2019, T21G-0421
L. Wiesenberg, F. Krueger, C. Weidle and T. Meier
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3D Structural Analysis of the Oman Ophiolite and the Lithosphere of the Eastern Arabian Continental Margin. PhD Thesis, Christian-Albrechts-Universität zu Kiel, 2020
Wiesenberg, L.
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Towards a 3-D structural model of the Oman Ophiolite and its underlying continental lithosphere. International Conference on Ophiolites and the Oceanic Lithosphere: Results of the Oman Drilling Project and Related Research, Muscat, Oman, 12-14 Jan 2020
L. Wiesenberg, C. Weidle, A. El-Sharkawy, T. Meier, F. Krüger, S. Lebedev, I. El-Hussain
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Structure of the offshore obducted Oman margin: emplacement of Semail ophiolite and role of tectonic inheritance. Journal of Geophysical Research: Solid Earth, 2021, 126, e2020JB020187
Ninkabou, D., Agard, P., Nielsen, C., Smit, J., Gorini, C., Rodriguez, M., Haq, B., Chamot‐Rooke, N., Weidle, C. & Ducassou, C.
