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Discussion papers
https://doi.org/10.5194/se-2018-78
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2018-78
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Aug 2018

Research article | 14 Aug 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study Jebel Akhdar, Oman

Arne Grobe1,2, Christoph von Hagke1, Ralf Littke2, István Dunkl3, Franziska Wübbeler1, Philippe Muchez4, and Janos L. Urai1 Arne Grobe et al.
  • 1Structural Geology, Tectonics, and Geomechanics, EMR Group, RWTH Aachen University, Germany
  • 2Geology and Geochemistry of Petroleum and Coal, EMR Group, RWTH Aachen University, Germany
  • 3Sedimentology & Environmental Geology, Geoscience Center Georg-August-Universität Göttingen, Germany
  • 4Geodynamics and Geofluids Research Group, Department of Earth and Environmental Sciences, KU Leuven, Belgium

Abstract. The Mesozoic sequences of the Oman Mountains experienced only weak post-obduction overprint and deformation, thus they offer a unique natural laboratory to study obduction. We present a study of the pressure and temperature evolution in the passive continental margin under the Oman Ophiolite, using numerical basin models calibrated with thermal maturity data, fluid inclusion thermometry and low-temperature thermochronology. Thermal maturity data from the Adam Foothills constrain burial in the foredeep moving in front of the advancing nappes to be at least 4km. Peak temperature evolution in the carbonate platform under the ophiolite is only weakly dependent on the temperature of the overriding nappes which have cooled during transport from the oceanic subduction zone to emplacement. Fluid-inclusion thermometry yields pressure-corrected homogenization temperatures of 225 to 266°C for veins formed during progressing burial, 296–364°C for veins related to peak burial and 184 to 213°C for veins associated with late-stage strike-slip faulting. In contrast, the overlying Hawasina nappes have not been heated above c. 170ºC, as witnessed by only partial resetting of the zircon (U-Th)/He thermochronometer.

In combination with independently determined temperatures from solid bitumen reflectance, we infer that the fluid inclusions of peak-burial-related veins formed at minimum pressures of 225–285MPa. This implies that the rocks of the future Jebel Akhdar Dome were buried under 8–10km of ophiolite on top of 2km of sedimentary nappes, which is in agreement with thermal maturity data of solid bitumen reflectance and Raman spectroscopy. Burial of the passive margin under the ophiolite results in sub-lithostatic pore pressures, in agreement with observations on veins formed in dilatant fractures in the carbonates. We infer that overpressure is induced by rapid burial under the ophiolite nappes. Obduction-related tilt of the passive margin in combination with overpressure in the passive margin caused fluid migration towards the south in front of the nappes. Exhumation of the Jebel Akhdar as indicated by our zircon (U-Th)/He data, integrated with existing data, started as early as the late Cretaceous to early Cenozoic, linked with extension along a major listric shear zone with top-to-NNE shear sense, together with an early phase of extensional dome formation. The carbonate platform and obducted nappes of the whole Jebel Akhdar cooled together below c. 170°C between 50 and 40Ma, before the final stage of anticline formation.

Arne Grobe et al.
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The Mesozoic sequences of the Oman Mountains experienced only weak post-obduction overprint and deformation, thus they offer a unique natural laboratory to study obduction. We present a study of the pressure and temperature evolution in the passive continental margin under the Oman Ophiolite, using numerical basin models calibrated with thermal maturity data, fluid inclusion thermometry and low-temperature thermochronology.
The Mesozoic sequences of the Oman Mountains experienced only weak post-obduction overprint and...
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