Structural diversity within a thrust complex reflecting progressive overprinting during a protracted orogenic process of terrane accretion, Natal belt, South Africa

Abstract The Tugela Terrane, forming the northern segment of the Mesoproterozoic Natal belt, South Africa, represents an example of accretionary tectonics that were initiated by closure of the Tugela Ocean basin, and culminated in accretion of magmatic arcs against the southern margin of the Archean Kaapvaal Craton during the assembly of Rodinia. A detailed structural analysis of the Madidima thrust sheet, part of the Tugela Terrane, reveals five distinct deformation events, D1 to D5. Deformation varied between dominantly non-coaxial during D2, D3 and D5, and dominantly coaxial during D4, the latter being interpreted as a phase of gravitational collapse. While D2 ductile shearing characterizes the most pervasive event that defines the tectonic grain of the sheet, most, if not all, of the structural imprints can be understood as representing consecutive stages of deformation overprinting during a protracted orogenic process of arc-continent convergence. The observed structural complexity is partly due to this multiple overprinting in the course of orogeny, but also due to the broadly synchronous formation of different types of folds within the thrust sheet, and the corresponding variation of foliation orientations. The persistently north-east-directed tectonic transport during at least three of the deformation events is accompanied by intense transposition of early-formed structures, multiple foliation reactivation and formation of transpression-related structures.