Pangea rifting in eastern Arabia—new insights from mafic dikes of the Saih Hatat Dome (Oman Mountains)

Abstract

Dolerite dikes in the Cambro-Ordovician Amdeh Formation of Oman were never studied in detail and their affiliation to a particular magmatic interval was debatable. We studied the composition, structure, tectonic setting, and age of five dolerite dikes and compared their composition and orientation to those of rocks of other magmatic episodes to assign the dikes to one of them. We provide novel information on these dikes, derived from transmitted and reflective light microscopy, X-ray diffraction, and fluorescence and structural analyses. The dolerites are low-alkali tholeiitic basalts, displaying a monotonous, fine, uniform texture. They mainly contain diopside and albitized anorthite, as well as some clinochlore, epidote, actinolite, quartz, muscovite, goethite, rutile, and pyrite. The dolerites are rich in silicon (Si), aluminum (Al), and iron (Fe) and low in titanium (Ti) and potassium (K). The sodium (Na) content is considerably higher than that of potassium. The five dikes strike either ∼NNW or ∼SW, paralleling the north-northwestern and southwestern rift arms of the regional Permian rift-rift-rift triple junction related to the breakup of Pangea. Geochemical plots of our rock samples and literature information demonstrate compositional similarities with Permian, rift-related mafic rocks of the region. Field relations of an unmapped sixth dolerite dike indicate an intra-Permian intrusion age as well. We conclude that the dikes represent Permian dikes of the Pangean rift system. Our samples plot in fields of oceanic volcanic arcs and continental back-arcs, attributed to melts generated from a subducted pre-Permian slab of corresponding composition. The source material remelted through decompression during Pangean rifting.