Proterozoic fold and thrust belt imaged on reflection seismic in Arabian plate basement

Abstract

Major structures are imaged on 2D reflection seismic data within the Precambrian basement of the western Rub’ Al-Khali of Saudi Arabia for the first time. In this area the base-Cambrian Angudan Unconformity that defines top basement is at a depth of 1–2 km with a gentle easterly dip. Large antiformal structures are clear on 2D reflection seismic within the basement. The antiforms are separated by zones that are interpreted as low-angle faults. No basal detachment is seen and the faults pass below the base of reflection seismic at a depth of approximately 12 km. Individual folds have dimensions in the order of 20 km wavelength and 2 km amplitude and occur between 3 and 10 km depth. The structural style is interpreted as compressional by comparison with thrust systems and accretionary prisms elsewhere. Regional studies indicate that basement is comprised of a series of north-south trending oceanic Proterozoic terranes that were brought together in the Ediacaran East African Orogeny. Based on current regional tectonic maps the newly-imaged fold belt is on the east margin of the Khida-Abas terrane. Depth conversion shows the thrusts dip at approximately 10° north in the line of section. A novel combination of cross-section to structural trend obliquity estimates combined with matched filtering of potential field data indicate the fold and thrust belt trends 015°-195° with ESE vergence. This compressional belt may be some internal structure of the Khida-Abas terrane, or may be a non-outcropping accretionary prism on the margin of that terrane, or may even represent a set of amalgamated microterranes that do not outcrop along trend. Either way, these observations represent a major, previously undescribed element of this sector of the East African Orogen.