Multiphase Structural Evolution of a Continental Margin During Obduction Orogeny: Insights From the Jebel Akhdar Dome, Oman Mountains

The structural evolution of the carbonate platform in the footwall of the Semail ophiolite emplaced onto the passive continental margin of Arabia helps to better understand the early stages of obduction‐related orogens. These early stages are rarely observable in other orogens as they are mostly ove...

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Bibliographic Details
Published in:Tectonics (Washington, D.C.) D.C.), 2018-03, Vol.37 (3), p.888-913
Main Authors: Grobe, A., Virgo, S., Hagke, C., Urai, J. L., Littke, R.
Format: Article
Language:English
Subjects:
Anticlines
Basins
boudinage
Carbonates
Clay
Continental margins
Convergence
Cretaceous
Deformation
Evolution
Fault lines
Faults
Fractures
Frameworks
Graben
Hydrocarbons
Mountains
Nappes
Obduction
Oceanic crust
Oman
ophiolite
Ophiolites
Orogeny
Outcrops
Passive margins
Plate convergence
Plate tectonics
Platforms (geology)
Radiometric dating
Seismology
shear
Shear zone
Structural analysis
Thinning
Veins (geology)
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Summary:The structural evolution of the carbonate platform in the footwall of the Semail ophiolite emplaced onto the passive continental margin of Arabia helps to better understand the early stages of obduction‐related orogens. These early stages are rarely observable in other orogens as they are mostly overprinted by later mountain building phases. We present an extensive structural analysis of the Jebel Akhdar anticline, the largest tectonic window of the Oman Mountains, and integrate it on different scales. Outcrop observations can be linked to plate motion data, providing an absolute timeframe for structural generations consistent with radiometric dating of veins. Top‐to‐S overthrusting of the Semail ophiolite and Hawasina nappes onto the carbonate platform during high plate convergence rates between Arabia and Eurasia caused rapid burial and overpressure, generation and migration of hydrocarbons, and bedding‐confined veins, but no major deformation in the carbonate platform. At reduced convergence rates, subsequent tectonic thinning of the ophiolite took place above a top‐to‐NNE, crustal‐scale ductile shear zone, deforming existing veins and forming a cleavage in clay‐rich layers in early Campanian times. Ongoing extension occurred along normal‐ to oblique‐slip faults, forming horst‐graben structures and a precursor of the Jebel Akhdar dome (Campanian to Maastrichtian). This was followed by NE‐SW oriented ductile shortening and the formation of the Jebel Akhdar dome, deforming the earlier structures. Thereafter, exhumation was associated with low‐angle normal faults on the northern flank of the anticline. We correlate the top‐to‐NNE crustal‐scale shear zone with a similar structure in the Saih Hatat window to develop a unified model of the tectonic evolution of the Oman Mountains. Plain Language Summary The Oman Mountains are a prime location to study the influences of thrusting of oceanic crust (ophiolites) over passive margin sediments. Exceptional outcrops enabled us to measure over 1,500 crosscutting relationships of veins, faults, and fractures that represent the base of the presented comprehensive tectonic model of the Oman Mountains. Obduction caused very little deformation in the buried continental margin, while afterward exhumation by top‐to‐NNE ductile shearing and subsequent normal faulting caused tectonic thinning of the ophiolite, and resulted in the formation of a precursor of the Jebel Akhdar Dome. Thermochronology and radiometric dating of vei
ISSN:0278-7407
1944-9194
DOI:10.1002/2016TC004442