Magma systems related to the Red Sea opening

Abstract

Four distinct magma environments can be recognized in association with the Red Sea basin: 1. (1) mid-ocean ridge basalts within the present actively spreading axial trough 2. (2) basaltic dikes and layered gabbros within the extended Precambrian crust on the Arabian margin 3. (3) granites and rhyolites developed in the extended Precambrian crust; and 4. (4) plateau basalts asymmetrically distributed on the Arabian flanks of the Red Sea. These magmas developed as the result of the initial break-up of Africa and the establishment of an oceanic spreading center within the Red Sea. Original asymmetric continental extension occurred on east-dipping detachment faults in the Oligocene and caused MORB-like magmas to invade an extending Precambrian crust. Contemporaneous small-scale mantle convection initiated limited partial melting under the Arabian plate to form the undersaturated alkali-olivine plateau basalts. Slow extension through the Miocene allowed an evaporite basin to develop in the Red Sea, while small volumes of rift and plateau basalts formed on the Arabian plate. A small change in plate motion in the Pliocene initiated the seafloor spreading in the axial trough, where MORB magmas formed oceanic crust. Rise of the asthenosphere produced small-scale thermal perturbations under the Arabian plate controlled by an east-dipping master detachment fault. Small-scale mantle convection extended partial melting (2–5%) eastward under the Arabian plate producing more undersaturated diverse alkali-olivine plateau basalts. Distinct chemical and isotopic signatures of these four magma types lead to obvious actualistic correlations with the geodynamic setting.