KINEMATIC ANALYSIS OF RED SEA MARGIN FAULTS IN ERITREA

The Red Sea margin in Eritrea is characterized by a prominent NNW-SSE striking linear tectonic feature that marks the topographic break between the Red Sea basin/Danakil Depression in the E from the escarpment/plateau to the W. It represents the main boundary fault along which a total of 2200m displacement had occurred in the Cenozoic. W of the main boundary fault in the escarpment and on the plateau occur prominent E- to ENE-dipping faults displacing early sub-horizontal faults. In the Pleistocene sediments at Buia (Danakil depression), located on the immediate hanging wall of the major boundary fault, normal faults occur as antithetic and synthetic pairs.

For this study, fault plane-striation pair data from the hanging wall of the major boundary fault and from prominent fault systems on the escarpment/plateau are analyzed. The pairs of measurements were then used to construct Angelier plots from which the extension/shortening axes were calculated using the Right Dihedra Method. The axes were then checked for coherency with results obtained by the P-T axes method. The results indicate that major faults on the outer escarpment/plateau represent dominantly sinistral strike-slip faults, the axis of maximum extension direction being SSW (190/12); the axis of maximum extension for the main boundary fault at Buia is ESE (118/80). Further N on the same boundary fault, the axis of maximum extension is 086/77 suggesting the prevalence of normal to oblique sense movement on the fault. There are also NNE to NE plunging striations, whose relationship with the E or ESE directed movement is not obvious. On the escarpment too, the fault systems mainly represent a normal sense and give comparable maximum extension direction as the main boundary fault.

It is concluded that the evolution of the Red Sea margin fault system in Eritrea conforms to a two-stage scenario comprising of an early N-S sinistral transtension, and a later, down-to-the-E normal to oblique-slip faulting on the main boundary fault.