Igneous Rocks in the Hawasina Nappes and the Hajar Supergroup, Oman Mountains: Their Significance in the Birth and Evolution of the Composite Extensional Margin of Eastern Tethys

Abstract

The main phases in the structural evolution of the Arabian continental margin were accompanied by significant magmatism the geochemistry of which gives data on its geodynamic setting.The history of the margin began in the Late Permian with a phase of extension and rifting within Gondwana that gave rise to the Hamrat Duru basin, separating the Arabian platform to the south from the Baid platform to the north.This phase was characterized by considerable magmatic activity, represented in the basin by the Al Jil Formation and along the edges of the two bordering platforms by the Saiq and Baid formations. The volcanic rocks, mainly basaltic pillow lavas, are dominantly alkaline with minor transitional components and are characteristic of an intracontinental basin. However, MORB tholeiites are encountered locally.Renewed extension and rifting in the Middle to Late Triassic, affecting mainly the Baid platform, led to the formation of the Al Aridh trough, the Misfah horst and the Umar basin, on the internal side of the Hamrat Duru basin. Important magmatic activity in the new structures marked this phase. Volcanic rocks, mainly basalts and andesites, are in general of within-plate alkaline type, characteristic of continental rift zones. However, in the most distal part,the Umar basin, the volcanic sequences evolve towards transitional and locally to MORB tholeiitic types. This suggests strong crustal thinning in this area, which was probably continuous with the Neo-Tethyan sea floor.During the Jurassic and Cretaceous, magmatic activity was less important on the Arabian continental margin, and was characterized mainly by alkaline to peralkaline sills and dykes intruding a variety of rock types. However a small amount of extrusive rocks were poured out in the Hamrat Duru basin in the Jurassic and along the border of the Arabian Platform in the Late Cretaceous (Muti Formation) concomitantly with the onset of the Eo-Alpine tectogenesis.KeywordsVolcanic RockLate CretaceousIgneous RockPassive Continental MarginPillow BasaltThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.