A NEOPROTEROZOIC SUPRA-SUBDUCTION TERRANE IN NORTHERN ERITREA, NE AFRICA

The western part of a tectonic block in the complex Pan-African archit ecture of northern Eritrea contains partly re-equilibrated low-T high- P assemblages (550 degrees C, 14.5 kbar), basalts with oceanic geochem istry and a major olistostrome containing lenses of serpentinite. Thes e features demonstrate subduction zone products. East of this accretio nary wedge the block is dominated by island-are volcanic and volcanicl astic rocks, and various calc-alkaline plutons. A bimodal Volcanic sui te of primitive andesitic basalts and evolved dacites and ignimbrites represents early submarine are development and emergent volcanism, res pectively. Intense, polyphase deformation culminated in sinistral tran spression with crustal-scale imbrication between several east-verging thrusts. A tectonically bounded unit in the internal part of this are association also contains relict high-P assemblages (650 degrees C, 10 -13 kbar) in oceanic basalts, which are possibly products of tectonic underplating as the are developed. Oceanwards collapse of the tectonic ally inflating are may explain formation of evolved, subaerial volcani c rocks within small extensional basins. Down-to-west extensional stru ctures may have been inverted during terrane accretion to act as east- verging shear zones during late thickening. The area remains to be cor related with those areas in Arabia that were juxtaposed with it before Red Sea opening.