The geochemical nature of the Archean Ancient Gneiss Complex and Granodiorite Suite, Swaziland: a preliminary study

摘要: Abstract The Ancient Gneiss Complex (AGC) of Swaziland, an Archean gray gneiss complex, lies southeast and south the Barberton greenstone belt includes most structurally complex highly metamorphosed portions eastern Kaapvaal craton. AGC is not precisely dated but apparently older than 3.4 Ga. consists three major units: (a) a bimodal suite closely interlayered siliceous, low-K gneisses metabasalt; (b) homogeneous tonalite gneiss; (c) siliceous microcline gneiss, metabasalt, minor metasedimentary rocks — termed metamorphite suite. A geologically younger gabbro-diorite-tonalite-trondhjemite suite, Granodiorite Suite, spatially associated with intrusive into it. largely two types gneiss: one has SiO2 14%, low Rb/Sr ratios, depleted heavy rare earth elements (REE's); other > 75%, Al2O3 metamorphic show Al2O, K2O/Na2O ratios about 1, high moderate REE abundances negative Eu anomalies. K/Rb are very (∼130); tonalitic (∼225); (∼300); (∼400). Rocks differ geochemically in several ways from volcanic hypabyssal Upper Onverwacht Group diapirs trondhjemite that intrude Swaziland Group.