Problems concerning the evolution of oceanic lithosphere in the northern Red Sea

Abstract

The pole of rotation for the opening of the Red Sea at 36.5°N, 18.0°E (Arabia from Africa) implies the fastest spreading rates are in the south and are about 50% less in the north. Various studies show the spreading rate in the south to be about 1 cm/yr over the last 4–5 Ma. Problems arise as to the nature of the lithosphere beneath the northernmost Red Sea. The problem is further complicated by the fact that the Red Sea may have evolved in three phases. The first is the Gulf of Suez phase (mainly Oligocene), the second corresponds to the first (62 km) movement along the Aqaba-Dead Sea shear (?latest Oligocene-early Miocene) and the third to the second (45 km) movement along the Aqaba-Dead Sea shear (Plio-Pleistocene). These motions and their implications for the northernmost Red Sea are assessed. The northern Red Sea differs from the central and southern Red Sea in having no clear magnetic lineations. Only a few isolated circular anomalies are observed. There are two possible explanations: 1. (1) there is extremely thinned continental lithosphere occasionally pierced by strongly magnetised volcanic centres, or, 2. (2) the oceanic lithosphere is present but without magnetic anomalies. It is suggested that the first explanation applies to the first (Gulf of Suez) phase and the second explanation to the two later (Aqaba-Dead Sea) phases. It is further suggested that the lack of magnetic anomalies may be due to a combination of large thicknesses of unstable sediments (salt), high temperatures and low sea floor spreading rates. These lead to the evolution of oceanic lithosphere with slow cooling, inhibiting the acquisition of strong magnetisation and giving subdued magnetic anomalies.