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International Journal of Earth Sciences

, Volume 99, Issue 5, pp 1007–1025 | Cite as

Deformation mechanisms of deeply buried and surface-piercing Late Pre-Cambrian to Early Cambrian Ara Salt from interior Oman

  • Johannes Schoenherr
  • Zsolt Schléder
  • Janos L. Urai
  • Ralf Littke
  • Peter A. Kukla
Original Paper

Abstract

We compared microstructures of Late Pre-Cambrian to Early Cambrian Ara Salt diapirs from the deep subsurface (3.5–5 km) of the South Oman Salt Basin and from surface-piercing salt domes of the Ghaba Salt Basin. Laterally, these basins are approximately 500 km apart but belong to the same tectono-sedimentary system. The excellent data situation from both wells and outcrops allows a unique quantification of formation and deformation mechanisms, spanning from sedimentation to deep burial, and via re-activated diapir rise to surface piercement. Microstructures of gamma-irradiated and etched thin sections indicate dislocation creep and fluid-assisted grain boundary migration as the main deformation mechanisms operating in the deep subsurface. Microstructures from the surface are characterised by large ‘old’ subgrain-rich crystals. These ‘old’ grains are partly replaced by ‘new’ subgrain-free and subgrain-poor crystals, which show gamma irradiation-decorated growth bands and fibrous microstructures, indicative of pressure solution creep and static recrystallisation, most likely due to surface piercement and exposure. Using subgrain size piezometry, the maximum differential stresses for the subsurface salt is 1.7 MPa and those for the surface-piercing salt is 3.4 MPa, the latter value displaying the high stress conditions in the diapir ‘stem’ as the salt rises on its way to the surface.

Keywords

Salt diapirism Oman Recrystallisation Deformation mechanism Rock salt 

Notes

Acknowledgments

The authors are grateful to Petroleum Development Oman LLC (PDO) and to the Ministry of Oil and Gas Oman for granting permission to publish this study. We thank PDO for sponsoring and providing the subsurface samples. Manfred Thomé from the Research Centre Jülich, Germany is acknowledged for gamma-irradiation of the rock salt samples and Michael Siemann from the Technical University of Clausthal-Zellerfeld (Germany) for the bromine measurements. The manuscript benefited from thorough reviews of Anne-Marie Boullier and Oliver Schenk.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Johannes Schoenherr
    • 1
    • 5
  • Zsolt Schléder
    • 1
    • 2
  • Janos L. Urai
    • 1
  • Ralf Littke
    • 3
  • Peter A. Kukla
    • 4
  1. 1.Lehr- und Forschungsgebiet Geologie, Endogene Dynamik RWTH AachenGermany
  2. 2.Midland Valley Exploration Ltd.GlasgowUK
  3. 3.Lehrstuhl für GeologieGeochemie und Lagerstätten des Erdöls und der KohleRWTH AachenGermany
  4. 4.Geologisches Institut RWTH AachenGermany
  5. 5.ExxonMobil Exploration CompanyHoustonUSA

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