Wadi Mayh

March 2007
(English)

Back to Oman page,
terug naar Oman page

A slice through strongly folded Permo-Triassic carbonates along the east flank of the Saih Hatat dome


Map to Google Earth

The Saih Hatat is a large, 70km x 50km, deeply eroded anticlinal structure in the southern limb of the Oman Mountain range, directly south of Muscat. The core of the anticline provides a window into the deepest structural levels of the Oman Mountains through the overlying Samail ophiolite. Wadi Mayh drains the Saih Hatat window to the east, cutting a deep spectacular gorge through the old limestones flanking the Saih Hatat and running in the sea at Yiti.

For the non-geologist

The Wadi Mayh gorge shows some magnificent cuts through intensely folded limestones, some 300 million years old.

Large scale (km's) isoclinal fold visible in the Jabals along Wadi Mayh

For the Geologist

Geological mapping has revealed a major structural discontinuity separating two units with very different structural and burial histories. The lower unit, with a strong metamorphic zoning, indicating rapidly increasing pressures and temperatures, is well developed towards the north eastern flank of the dome. The increasing degree of metamorphism is mapable as systematic mineralogical changes. The increasing degree of metamorphism is associated with an increasing intensity of deformation. The easternmost rocks, near As Sifah at the coast, reveal evidence of strong deformation under very high pressures which resulted in eclogites and blueschists.

The structurally lowest units in the northeast have been severely deformed with intense transposition foliation and regional recumbent closures in the quartz mica schists, mafic schists and calc-schists.

The pressures and temperatures recorded by the mineral assemblages in these rocks indicate depths of some 40-60 km. Increasing intensity of metamorphism and the orientation of the metamorphic zones reflects an increasing burial and deformation towards the northeast.

The eclogites at 500–580 °C, 18–22 kbar, the blueschists at 380–420 °C, 7–8 kbar 

The rocks of the upper unit are lower metamorphic grade, weakly deformed homoclinally dipping shelf carbonates.

Mineral assemblages in the upper unit indicate metamorphic conditions of 325–440 °C, 6–9.5 kbar for the upper plate lawsonite rocks, and 280–315 8C, 3–6 kbar for the upper plate high-T greenschists.

The two different slabs of rocks, with different metamorphic and structural histories, indicate significant displacement across the sub-horizontal structural discontinuity between them.

The lower unit has been interpreted as a slab of the distal continental margin of Arabia that has been under - thrusted to at least 40 km depth and subsequently exhumed in the Late Cretaceous (90-70Ma) in a convergent plate boundary setting. During exhumation the two different rock units, with different structural style, stratigraphy and metamorphic histories have been juxtaposed along the ductile narrow shear zone that is now exposed almost horizontally in the Saih Hatat dome.

U-Pb dating pf zircons in minerals associated with the eclogite conditions gave an age of 79.1 ± 0.3 Ma. High pressure metamorphism associated with subduction of the edge of the Arabian plate took place after the formation of the ophiolite crustal sequence at 95 Ma, and after the formation of the amphibolite-grade metamorphic sole at 95–93 Ma beneath a hanging wall of probably always oceanic crust and upper mantle.

Isoclinal folds and shear zones, Wadi Mayh, E 656357.7– N 2591151.5
(UTM WGS 84)

References:

  • Breton, J.P., 2005, From subduction to exhumation. Two days tectonic and metamorphic transect from tanuf to Sifa. Fieldtrip through Jabal Akhdar and Saih hatat. GSO Field Guide 13.
  • Breton, J.P., F. Béchennec, J. Le Métour, L. Moen-Maurel and P. Razin, 2004, Eoalpine (Cretaceous) evolution of the Oman Tethyan continental margin : insights from a structural field study in Jabal Akhdar (Oman Mountains). GeoArabia, Vol. 9, No. 2, pp. 41-58.
  • El Shazly, A.K., M. Bröcker, B. Hacker, and A. Calvert, 2001, Formation and exhumation of blueschists and eclogites from NE Oman.: new perspectives from Rb-Sr and 40Ar/39Ar datin. Journal Metamorphic Geology, 19, pp. 233-248.
  • Gray, D.R., J.McL. Miller, and R.T. Gregory, 2005, Strain state and kinematic evolution of a fold-nappe beneath the Samail Ophiolite, Oman. Journal of Structural Geology, 27- pp. 1986-2007.
  • Le Metour J., , F. Bechennec, J. Roger & R. Wyns. BRGM, 1992. Geological Map of Muscat.

@ J. Schreurs March 2007