The Ophiolite Mélange of Masirah, Oman

Abstract

The Masirah Ophiolite consists of serpentinites, gabbroic intrusions, an extensive sheeted dyke complex, pillow lavas, and sediments. It is truncated to the W by a NNE-trending, 5 km wide vertical mélange zone: a megabreccia with blocks up to 2 km long of all the above lithologies. The mélange trend is perpendicular to that of the sheeted dyke complex, a common relationship between a transform fault and spreading centre. Many of the features of the mélange can be explained by serpentinite diapirism along a major ocean crust fracture. However, the distribution of other reported ophiolites along the SE coast of Arabia and the intrusion of the Masirah Ophiolite by granite, whose geochemistry indicates melting of continental crust, both suggest upthrust of ocean crust onto the Arabian continent. The Masirah Mélange and the dyke trends within the ophiolite are parallel, respectively, to the Owen Fracture (and other transforms) and to magnetic anomalies in the Indian Ocean. It is suggested that both mélange and ophiolite are related to a late Cretaceous stage in the evolution of the Indian Ocean, and may not correlate with the Semail Ophiolite of the Oman Mountains, as has been previously supposed.