Constraints on deformation mechanisms of the Barberton Greenstone Belt from regional stratigraphic and structural data of the synorogenic Moodies Group

Abstract

Abstract Understanding the deformation styles and mechanisms which affect the Barberton Greenstone Belt (BGB) contributes to our ability to interprete the dynamic evolution of Paleoarchean greenstone belts and of the continental lithosphere. A variety of actualistic and non-actualistic, in part contradictory tectonic settings and processes (including gravitational collapse, terrane accretion, foreland basin shortening, continental rifting, doubly-vergent subduction and partial convective overturn) have been proposed to explain BGB deformation at a variety of scales. We compare these models and their regional 3-D predictions with emphasis on the BGB’s youngest deformed stratigraphic unit, the Moodies Group (ca. 3.21\xa0Ga), also adding new structural data. We find that none of the tectonic models accounts for all major structural features of the BGB nor can any model adequately explain the regionally and temporally heterogeneous distribution of deformation styles within the greenstone belt. However, the partial convective overturn model, despite some weaknesses and oversimplifications, appears to be suited best to explain the geometry, orientation and formation of the dominating structural element of the BGB, the vertically-plunging Onverwacht Anticline (OA) with its 10-km-thick fold limbs. The formation and deformation of the adjacent smaller, commonly steeply doubly-plunging synclines filled with synorogenic siliciclastic sediment of the Fig Tree and Moodies groups could be partially explained as spatial adjustments to the rise and tilting of the OA although disparate processes acting at different scales need to be considered. In comparison to this large-scale vertical redistribution of mass by several tens of km, (sub-)horizontal displacements may have played a subordinate role at greenstone-belt scale, except along the regionally highly strained southern BGB margin in Eswatini.