Late Proterozoic Evolution of the Northern Part of the Hamisana Zone, Northeast Sudan: Constraints on Pan-African Accretionary Tectonics

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New structural data from the Red Sea Hills, northeast Sudan, add constraints to accretionary tectonic processes that acted in the Arabian-Nubian shield during the late Proterozoic. Geometric constraints provided by field data are used together with Landsat Thematic Mapper imagery to interpret the regional distribution and structural relations of spectrally and lithologically distinctive rock assemblages. In contrast to interpretations reported elsewhere, these studies indicate that the Hamisana zone, a prominent structural feature in the northern Red Sea Hills, post-dated terrane accretion. It is characterized by east-west crustal shortening and by steep folds and thrust faults. Calc-alkaline magmatism was contemporaneous with and outlasted main phase deformation, thus deformation occurred in an intra-arc setting. Thrust faults were reactivated after east-west contraction, compromising their usefulness in delineating 'sutures' or as piercing points across older faults.

Pan-African accretionary processes may have been analogous to Phanerozoic ophiolite and island arc accretion in the western North American Cordillera, where penetrative deformation occurred in response to periodic intra-plate shortening events rather than an ultimate collision of unrelated crustal fragments. Such an analogy implies a mechanism for crustal thickening by structural as well as igneous processes during evolution of an accretionary belt in a long-lived convergent margin setting, consistent with the long-standing observation that Pan-African magmatism became more evolved with time. This view emphasizes that an interplay of deformation and magmatism resulted in protracted accretion and crustal thickening, in contrast to models where crustal shortening results directly from collision of a volcanic arc, microcontinent, or other buoyant features.

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Journal of the Geological Society, v. 149, issue 5, p. 743-750