Abstract

Eritrea's war of independence precluded checking a 12 yr old prediction that a low-angle detachment along which the Red Sea opened might be exposed on the western shore. Following Eritrea's success, we have found a suite of regional-scale detachments along which northeast-southwest extension began in rocks that were ductile at depth but became increasingly brittle as they cooled adiabatically on the way to exhumation. The only signs of Red Sea detachment in the rift shoulder are steep and low-angle faults offsetting Oligocene dikes and lavas. By contrast, low-angle, ductile mylonites with a consistent top-to-the-basin sense of shear were superimposed on steep Pan-African fabrics in the coastal lowlands. These mylonites define core complexes beneath hanging walls of embrittled mylonites and synextensional dikes in which panels of domino fault blocks face both toward and away from the basin over low-angle semi-brittle detachments. Both the early ductile and later semi-brittle low-angle detachments were extended by a later set of grabens that probably sole out to an even younger detachment beneath the coastal lowlands.

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