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Journal of the Geological Society; 1998; v. 155; issue.3; p. 551-566;
DOI: 10.1144/gsjgs.155.3.0551
© 1998 Geological Society of London

Article

A Neoproterozoic supra-subduction terrane in northern Eritrea, NE Africa

C. R. DE SOUZA FILHO1,2 & S. A. DRURY1

1 Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, UK
2 University of Campinas, IG, PO BOX 6152, CEP 13081-970, Campinas, São Paulo, Brazil

The western part of a tectonic block in the complex Pan-African architecture of northern Eritrea contains partly re-equilibrated low-T, high-P assemblages (550°C, 14.5 kbar), basalts with oceanic geochemistry and a major olistostrome containing lenses of serpentinite. These features demonstrate subduction zone products. East of this accretionary wedge the block is dominated by island-arc volcanic and volcaniclastic rocks, and various calc-alkaline plutons. A bimodal volcanic suite of primitive andesitic basalts and evolved dacites and ignimbrites represents early submarine arc development and emergent volcanism, respectively. Intense, polyphase deformation culminated in sinistral transpression with crustal-scale imbrication between several east-verging thrusts. A tectonically bounded unit in the internal part of this arc association also contains relict high-P assemblages (650°C, 10–13 kbar) in oceanic basalts, which are possibly products of tectonic underplating as the arc developed. Oceanwards collapse of the tectonically inflating arc may explain formation of evolved, subaerial volcanic rocks within small extensional basins. Down-to-west extensional structures may have been inverted during terrane accretion to act as east-verging shear zones during late thickening. The area remains to be correlated with those areas in Arabia that were juxtaposed with it before Red Sea opening.

Key Words: Ethiopia • Proterozoic • terranes • structural geology • geochemistry




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