Gravitational and diapiric structural history of the eastern portion of the Archean Murchison greenstone belt, South Africa

Abstract

The structural history of the eastern portion of the Murchison greenstone belt can be explained in terms of three deformational events. Early high-angle faults, formed during gravity slumping of unstable ensimatic crust, provided a regional synformal framework for the preservation of linear homoclinal and synclinal greenstone belt assemblages. A second stage of deformation was initiated by the emplacement of discrete diapric gneiss plutons into and around the greenstone belt margins, leading to the development of the “granite/greenstone pattern”. Cleavage, lineation, flattening of early open folds, and reactivation of early faults developed concomitantly, and with increasing intensity, throughout the second stage of deformation. Syntectonic granitoids were emplaced into the greenstone belt assemblages along subvertical upthrusts and high-angled reverse faults. These faults are somewhat conformable with the regional lithological trends and developed between the first and second stages of deformation. A third and final deformation event is registered in the sinistral ductile shear zones of the Letaba shear zone along the northern flank of the Letaba schist belt. Kinkband, crenulation, and chevron folds are related to this final event of deformation.