Mapping Precambrian structures in the Sahara desert with SIR-C/X-SAR radar: The Neoproterozoic Keraf suture, NE Sudan

A major N-trending Neoproterozoic suture between composite are terranes of the Arabian-Nubian Shield in the east and older crust of the Nile Craton to the west is inferred to trend N-S close to the Nile in northern Sudan. We used shuttle imaging radar (SIR) C/X synthetic aperture radar (SAR) imagery to find and map these structures in the poorly known Keraf Suture which are not apparent on visible or near IR imagery due to extensive sand cover. L band (23 cm wavelength) radar images best resolve geologic structure; the other frequencies of the SIR-C/X-SAR system (X and C bands) permit qualitative evaluation of the effects of surface versus subsurface backscattering. Interpretation of L band images supported by field work indicates that the Keraf Suture is similar to 50 km wide and >550 km long, making it the longest basement structure recognized to date in NE Africa. The northern part of the Suture comprises ophiolitic rocks which were thrust westward over tightly folded sediments of the Nile Craton. The southern Keraf Suture is dominated by N- and NNW-trending, left-lateral strike-slip faults that affect previously deformed passive margin sediments. Associated with these faults are NE-trending transpressional folds and a possible transtensional basin. These structures are interpreted to be due to NW-SE oblique collision between the Arabian-Nubian Shield and the Nile Craton, as east and west Gondwana collided in the last 150 m.y. of Neoproterozoic time.