Generation of early Archaean grey gneisses through melting of older crust in the eastern Kaapvaal craton, southern Africa

摘要: Abstract We report zircon ages, Hf-in-zircon isotopes as well whole-rock geochemistry and Hf–Nd isotopic systematics for Palaeoarchaean grey gneisses of the Ancient Gneiss Complex Swaziland, oldest components Kaapvaal craton, southern Africa. The compositions in these compositionally heterogeneous, multicomponent, migmatitic are highly variable, even zircons dating back to 3.66 Ga, suggesting growth from melts representing a mix juvenile anatectic material derived differentiated continental crust Eoarchean late Hadean age. In contrast, initial Nd Hf frequently not agreement with data that mostly show approximately chondritic values strongly radiogenic Hf. consider it likely both Lu–Hf Sm–Nd systems were disturbed partly reset during later episodes partial melting crustal reworking, most pervasive 3.2 Ga tectono-metamorphic event. Primitive mantle-normalized trace element patterns variable influence residual plagioclase garnet sources high contents incompatible elements. conjunction best explained by incorporation older into gneisses. Our support evidence other Palaeoarchean terranes recycling, seen components, played an important role early evolution. Rocks previously classified subduction-related tonalite–trondhjemite–granodiorite suite complex, their chemistry alone cannot be used reconstruct tectonic settings.