Horizontal accretion and stabilization of the Archean Zimbabwe Craton

Abstract

Structural-metamorphic data and mineral ages from the northern parts of the Zimbabwe craton indicate that Archean crustal formation and stabilization evolved in two stages. In the Shamva-Bindura greenstone belt, early layer-parallel shear zones began to form at 2670 Ma and accommodated imbricate stacking of oceanic and volcanic arc material between large nappe structures with felsic gneiss cores. The resultant crustal pile of anomalously hot felsic and mafic crustal slices reached isostatic and mechanical equilibrium at a thickness of 35 km. Further shortening of this pile caused strain partitioning into vertical strike-slip zones. The subsequent establishment of an equilibrium geotherm resulted in large-scale crustal melting and diapirism between 2620 and 2600 Ma. The rise of the melt and diapirs caused a second transient metamorphic imprint and much of the strain pattern regarded as typical for the Zimbabwe craton. This diapiric stage led to cooling and stabilization of the craton.