Cretaceous high pressure metamorphism in NE Oman and its relationship to subduction and ophiolite nappe emplacement

Abstract

An occurrence of glaucophane-bearing schists is reported from near Muscat in NE Oman in rocks which underlie the Upper Cretaceous Semail ophiolite nappe. These blueschists formed by the metamorphism of quartz sandstones, shales and basic igneous rocks belong to a pre-Permian basement in the area. Metamorphic micas (phengites) from these rocks have been dated at between 101 and 80 Ma (K-Ar ages) indicating a mid- to late-Cretaceous age for the high pressure event. A syn- to late-F 1 assemblage of almandine + glaucophane + phengite in the pelites shows that the peak of metamorphism reached about 400–450°C and 4–8 kbars pressure. This was followed by a greenschist facies overprint with the formation of epidote and albite porphyroblasts in the meta-igneous rocks and a widespread retrogression to chlorite. The high pressure metamorphism is ascribed to the effects of partial subduction of the NE Oman continental margin during the initial stages of ophiolite obduction and the subsequent greenschist facies event to uplift of the area during the later stages of emplacement of the nappes.