Samail Ophiolite Obduction and New Structural Constraints from Saih Hatat and Hawasina Windows

By

David R. Gray¹, Robert T. Gregory²

(1) University of Melbourne, Melbourne, Australia (2) Southern Methodist University, Dallas, TX

 The popular view of Samail Ophiolite emplacement involves Late Cretaceous closure of the former Tethys Ocean by "piggy-back" thrusting with northeast to southwest emplacement of successively lower "thrust slices" from an external oceanic domain over and towards a "passive" Arabian continental margin. The recognition of major NE-facing isoclinal fold closures in carbonates of both the Saih Hatat and Hawasina windows however, provides a major contradiction for the Oman Mountains.Isoclinal folds that verge away from the Arabian craton have been previously recognised, but have been simply related to back-thrusting. These folds are extensively developed however, have regional scale and extent, and are the major structures of the Saih Hatat dome. Their presence 1) indicates that for at least part of the history the platform to slope carbonates sequences were "thrust" to the northeast, and 2) requires non-passive margin behaviour for part of the ophiolite obduction. Ar-Ar geochronology from the Saih Hatat window requires Late Cretaceous (~76 to 70Ma) movement of the para-autochthonous Arabian margin rocks to the NE due to underthrusting of the margin. This is an important part of the tectonic evolution (and ophiolite obduction) that has not been previously recognised.

Therefore, models involving craton-directed thrusting with domal culminations related to deep-seated, footwall and lateral ramps are too simplistic for the overall tectonic evolution of this part of the Arabian Peninsular. Such models may however, be more applicable to the Tertiary structure and Tertiary evolution of the Mountains.