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Evolution of the Oman Tethyan Continental Margin |
1 Department of Geology and Geophysics, West Mains Road, Edinburgh EH9 3JW, UK
2 Department of Oceanography, University of Southampton, UK
3 Department of Earth Sciences, University of Leeds, Leeds, UK
4 United States Geological Survey, Denver Federal Center, Denver, CO, USA
The Hatta Zone, Northern Oman Mountains, is interpreted as a c. 50 km long left-lateral offset of the North Oman passive continental margin that was generated by right-lateral transform faulting during spreading of the Neo-Tethys ocean. During Early-Late Triassic time, slumps, debris flows and calciturbidites composed of redeposited upper slope and shelf carbonates accumulated at the base of a steep carbonate platform slope (Maqam Fm., Mayhah Fm.; Sumeini Group). Clasts in channelized conglomerates include basement-derived quartzose sandstone, schist and basic extrusives. Basaltic pillow lavas were erupted at the foot of the Late Triassic continental rise of the Hatta Zone transform lineament (Zulla Fm.). During Early to mid Jurassic time, oolitic and lithoclastic calciturbidites and debris flows accumulated on tectonically unstable base of slope (Mayhah Fm.) and continental rise (Guweyza Limestone Fm.) settings. During mid-Cretaceous time (Albian-Cenomanian), alkaline magmatism constructed seamounts along the inferred oceanward extension of the Hatta transform lineament. K/Ar ages of diabase sills range from 109 Ma ± 4 Ma, to 105 Ma ± 3 Ma on sills, while basalts gave ages of 104 Ma ± 4, to 93 Ma ± 4. During the Late Cretaceous ophiolite emplacement, abyssal plain and base of slope units were deformed into a major transverse culmination (Jebel Quimah), mainly controlled by collision with the Hatta Zone continental margin transform lineament. Hanging wall imbrication and overturning of structurally high thrust sheets occurred above an inferred footwall ramp. As the Semail ophiolite overrode a northfacing transform escarpment margin, footwall slope sediments were sheared and deformed into a major lateral ramp, now represented by the Jebel Raudha-Masfut ridge. Normal faulting and deep erosion ensued, followed by Maastrichtian-early Tertiary shallow marine carbonate deposition on an unstable shelf. During renewed, mid-Tertiary deformation the Hatta Zone was reactivated, giving rise to NW-SE trending open-folding at right angles to the regional W-directed compression, followed by differential erosion to form the present lineament.
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