Chapter 5.5 Orogenic Tectono-Thermal Evolution

Abstract

The metamorphic zonation of the Damara and Kaoko belts is very similar. Both have paired medium-pressure, Barrovian-type and low-pressure–high-temperature, Buchan-type belts with abundant to scattered granites in the latter and large-scale nappe structures in the former. In each, minerals of the early, highest pressure assemblages are enclosed in decompression coronas that record as much a 3 kbar of decompression within 20–30 myr. Unique to the western Kaoko Belt is a granulite-facies metamorphic event with associated calc-alkine magmatism at approximately 650 Ma, thus predating the peak of metamorphism and deformation in the Damara and Gariep belts at about 542 Ma. During both the M1 and M2 phases of metamorphism in the Damara Belt, the southern Central Zone was the leading edge of the high-temperature–low pressure active continental margin, whereas the Southern Zone and Southern Marginal Zone of that belt formed the low-temperature–medium pressure regions of the accretionary wedge riding atop the subducting Kalahari plate. In contrast to the above, only low-grade metamorphism is recorded further south in the Gariep and Saldania belts. There the main structural imprint was caused by sinistral transpression with top-to-northeast transport, similar as in the Kaoko Belt.