Tectonics, geochronology and geochemistry of the Precambrian rocks of Oman

Abstract

Abstract precambrian rocks crop out in NE Oman (Qalhat and Jebel Ja’alan), in SE Oman (near Mirbat) and offshore on the Kuria Muria Islands. Similar rocks occur on Socotra and Abd el Kuri. In all these localities the Precambrian rocks include metasediments of greenschist or amphibolite facies, intruded by dolerites, granodiorites and granites and cut by doleritic and felsitic dykes which in the Mirbat area, form a dense swarm. Foliation trends vary but are predominantly ENE-WSW. Geochronological data show that the rocks are late Proterozoic (800-600 Ma) in age and are therefore chronologically and compositionally similar to the Pan-African rocks of the Afro-Arabian Shield. Unmetamorphosed, weakly deformed Infracambrian sediments in the Huqf-Haushi Uplift and in the Saih Hatat and Jebel Akhdar windows are not cut by the dyke swarms, which are therefore probably late Proterozoic in age although radiometric dating suggests a lower Palaeozoic age. These widely distributed late Proterozoic metamorphic rocks indicate that the middle Proterozoic ( c. 1700 Ma) gneisses in the Afif Terrain in eastern Saudi Arabia do not mark the eastern limit of the Pan-African belt. Before the breakup of Gondwanaland that limit must have lain between the Oman-Somalia region and the Archaean and middle Proterozoic terranes of the Bundelkhand and Aravalli areas of India.