The geology of the Pan-African Saldania Belt, South Africa, and regional correlations

Abstract The arcuate Saldania Belt marks the intersection of two high-angle orogenic systems that record the final-stage amalgamation of southwest Gondwana and subsequent tectonics along Gondwana’s southern margin in the Late Ediacaran to Mid Cambrian. The northerly trending western Saldania Belt represents the southernmost extension of interior belts of the West Gondwana Orogen. The belt records the oblique, low-angle convergence and closure of oceanic realms between the Kalahari Craton and South American cratonic blocks between 550 and 520 Ma. The lithological and structural inventory is that of a fore-arc realm situated along the southwestern leading edge of the Kalahari Craton in which folded, low-grade metamorphic metaturbidites of the fore-arc basin (Malmesbury group) overlie imbricated, mélange-like rocks of a structurally lower accretionary complex (Swartland complex). Oblique subduction below the Kalahari Craton resulted in sinistral, strike-slip partitioned transpression (folding and strike-slip shearing) of the fore arc. Uniformly low grades of metamorphism and the preservation of ca. 540 Ma subaerial volcanics indicate only very limited burial of rocks. The soft collisional event and late-stage, short-lived (540 to 530 Ma) peak of plutonism and volcanism of the Cape Granite Suite relate to the opening of a slab window during ridge subduction or detachment of the subducting slab. The southern Saldania Belt, in contrast, was located along the southern edge of the Kalahari Craton and Gondwana. Its evolution was closely linked to the paleo-Pacific convergent margin of the Terra Australis. Earlier passive-margin sedimentation of the Kaaimans and Kango groups and the Gamtoos complex in the late Ediacaran was reversed during the onset of northward subduction below the Kalahari Craton at ca. 530 Ma, leading to the formation of a north-verging, retro-arc, foreland fold and thrust belt. The timing of deformation along the southern Saldania Belt broadly coincides with the final amalgamation of Gondwana along the western belt. The two high-angle belts converge and are deflected against each other in the region that later accommodated the location of the Permo-Triassic Cape Syntaxis. Unconformably overlying rift-type sedimentary rocks of the Klipheuwel and Kansa groups across the Saldania Belt indicate regional extensional processes along the southern margin of Gondwana in the Mid- to Late-Cambrian (515 Ma) and prior to the deposition of the extensive, Mid-Ordovician (ca. 470 Ma) to Early-Carboniferous Cape Supergroup.