The Rovuma Delta deep-water fold-and-thrust belt, offshore Mozambique

Abstract

We interpret two-dimensional seismic reflection data from the Rovuma Delta basin deep-water fold-and-thrust belts. Two major arcuate complexes with different architecture and extent are identified. While in the northern Palma arcuate complex a multitude of steep, east-dipping thrust-related fold anticlines formed above a single main detachment, in the southern Mocimboa arcuate complex multiple detachments resulted in the formation of thrust duplexes. In between the two arcuate domains, only few thrust-related fold anticlines developed. Our interpretation of the Rovuma basin is a linked system of up-dip extension and down-dip compression that is mainly driven by gravity tectonics. Sediment loading and a hinterland uplift due to the development of the East African Rift System since the Oligocene is proposed as origin of the delta. It is shown that the main, seaward-dipping detachment in Early Cenozoic strata is likely under-compacted and overpressured shale. Conversely, shale diapirism is questionable since the shape and location of such structures in the fold-and-thrust-belts appear simply indicating steeply dipping imbricated folds, rooted by a near vertical thrust. We suggest that mainly a different rheology and thickness and thus efficiency of the shale detachment across the delta resulted in different morphologies and geometries of the deep-water fold-and-thrust-belts. • The Rovuma Delta is a linked system of up-dip extension and down-dip compression • Two arcuate complexes with different architecture and extend: Palma and Mocimboa • The southern Mocimboa complex shows multiple detachments with thrust duplexes • DWFTBs are formed by gravity-driven under thick seaward-dipping shale detachment