The early Proterozoic sedimentary record in the Blouberg area, Limpopo Province, South Africa; implications for the timing of the Limpopo orogenic event

At present, the timing and geometry of a presumed collision of the Limpopo Belt (southern Africa) remain controversial. Data from tectonic and metamorphic studies, and a number of radiometric dates, have been interpreted to produce widely varying models. In this work. we aim to help constrain these models using data from the sedimentary rocks in the Blouberg area, which lie above and adjacent to the Palala Shear Zone in the southwestern part of the belt. Here, a thick sedimentary package consisting of the syn-tectonic Blouberg Formation, medial parts of the Waterberg Group and the Soutpansberg Group is developed nonconformably above the granulite-grade gneiss of the Limpopo Belt. These three sedimentary units are separated from each other by angular unconformities. The youngest rocks of this succession (the Soutpansberg Group) have an imprecise age of ca. 1.8-1.97Ga. The inferred long tectono-sedimentary history necessary to produce these three unconformity-bounded sequences is interpreted to support an older, Archaean-age (ca. 2.6-2.7Ga) for the timing of the Limpopo collision, rather than reflecting a younger Proterozoic (ca. 2.0Ga) event. It is proposed that syn-sedimentary tectonism recorded in the Blouberg Formation may reflect a southward-vergent 2.0Ga tectonic event, though this is interpreted as reactivation within the Limpopo Belt, rather than the primary collision itself. (C) 2004 Elsevier Ltd. All rights reserved.