6533b827fe1ef96bd1286519

RESEARCH PRODUCT

Archaean Crystalline Rocks of the Eastern Kaapvaal Craton

subject

description

The eastern part of the Kaapvaal Craton represents a classical granitoid-greenstone terrain and contains the oldest rocks of the African continent, exhibiting about 1000 Ma of crustal evolution from 3.66 to 2.67 Ga. The granitoid rocks predominantly consist of the tonalite–trondhjemite–granodiorite (TTG) association with true granites becoming abundant at about 3 Ga. Greenstones are represented by the well-preserved and well-studied 3.54–3.2 Ga Barberton Greenstone Belt and smaller ca. 3.45 Ga greenstone belt remnants infolded in TTG gneisses around the BGB as well as in the Ancient Gneiss Complex in Swaziland. The origin of both the TTGs and greenstone units is still debated as strong deformation and medium- to high-grade metamorphism have obliterated most of the original rock relationships. This is largely due to an extensive tectono-magmato-metamorphic event at ca. 3.2 Ga that affected virtually the entire eastern part of the craton. Heat provided by mantle-derived melts during this event led to extensive intracrustal melting, with melt migration resulting in depletion of the lower crust in radioactive and other mobile elements. Long-lived extraction of granitoid magmas up to about 2.67 Ga increased the rigidity of the lower crust, causing tectonic stabilization of the Kaapvaal Craton.