High-Temperature Polymetamorphism in the Central Zone of the Limpopo Granulite Complex (South Africa): Structural and Petrological Evidence

摘要

The problem of confirmation of HT (high-temperature) metamorphism in Precambrian granulite complexes appeared rather recently. The central zone of the Limpopo complex (Fig. 1) is the best polygon for its solution. The results of our investigations demonstrate that gneiss, which underwent deformations (D) and granulite metamorphism (M) in the Neoarchean (D2/M2), was subjected to one more stage of HT metamorphism, but in the Paleoproterozoic (D3/M3). Started from isobaric heating (IH) of rocks in the middle crust, the event D3/M3 was finished with their decompression cooling (DC), i.e., exhumation of rocks from the middle part of the continental crust towards the surface [2, 4-6, 10]. This evidence was based on studies of circular structures, namely sheath folds. This report contains the first data on analogous phenomena within the shear zones (shift deformations) on a regional scale. The absence of signs of earlier events was suggested in them, but it turned out to be completely wrong.