Proterozoic geochronology and tectonic evolution of southern Africa

Abstract

The Precambrian foundation of southern Africa consists of Archaean cratonic nuclei surrounded by belts formed during three separate Proterozoic orogenic episodes. Crust that formed or was reworked at 2.05-1.8Ga is represented by orogenic belts (e.g. Kheis-Magondi, Ubendian-Usagaran) that partly wrap the ancient craton margins or form extensive basement in younger belts. Orogenic belts formed at 1.35-1.0Ga record arc magmatism and collisional events during assembly of the Rodinia supercontinent. The Namaqua-Natal Belt defines a major convergent plate boundary active at this time along the southern margin of the Archaean Kaapvaal Craton, and the western part of this belt is inferred to link with a largely buried, NE-trending orogen present in the Kalahari region. Orogenesis in the same time frame farther north is recorded by the Kibaran and Irumide Belts, which are separated by the Palaeoproterozoic Bangweulu Block but are inferred to have undergone a linked tectonic evolution. East of the Irumide Belt, extensive Mesoproterozoic arc crust occurs in Malawi and Mozambique, although strong Neoproterozoic overprinting of the arc rocks makes their original relations unclear. Breakup of Rodinia is signalled by widespread Neoproterozoic alkaline and bimodal magmatism associated with rift zones which, in some cases, evolved into major ocean basins. Subsequent amalgamation of Gondwana led to collisional orogenesis culminating at 575-505 Ma in the Mozambique and West Congo-Kaoko-Gariep-Saldania Belts along the present eastem and western margins of southern Africa. Coeval deformation in the interconnecting, transcontinental Damara-Lufilian-Zambezi Orogen may reflect destruction of linked rifts and narrow ocean basins driven by farfield stresses from the collisional plate margins.

Syn-orogenic high-temperature crustal melting: Geochronological and Nd–Sr–Pb isotope constraints from basement-derived granites (Central Damara Orogen, Namibia)

“…The basal deposits that unconformably overlie the basement complexes are rift-related siliciclastic rocks of the Nosib Group (Gray et al, 2008;Miller, 1983Miller, , 2008. Quartz syenites, alkaline ignimbrites and alkali rhyolites in the upper Nosib Group constrain the minimum age to c. 750 Ma (Hanson, 2003;Hoffman et al, 1996;. The overlying Otavi Group is dominated by carbonates that rimmed the basins between the cratons (Gray et al, 2008).…”

Geophysical Modelling of the Molopo Farms Complex in Southern Botswana; Implications for Its Emplacement Within the 2 Ga Large Igneous Provinces of Southern and Central Africa

“…Carney et al, 1994;Key and Ayres, 2000;Singletary et al, 2003). The associated thermal anomaly is recorded in widespread rock and mineral ages of about 2000 Ma in Palaeoproterozoic and Archaean rocks of southern Africa, including the Limpopo Belt (van Breemen and Dodson, 1972;Hanson, 2003). The MFC has been dated at 2044 ± 24 Ma (Coetzee and Kruger, 1989), which is a similar age to other Palaeoproterozoic intrusions and lavas of southern Botswana such as the Moshaneng Complex ( Figure 1; Key and Ayres, 2000;Hanson, 2003).…”

“…On the larger sub-continental scale it has already been noted that the MFC is part of major Palaeoproterozoic igneous event (Hanson, 2003;Hanson et al, 2004). This Large Igneous Province, defined by the ~2.0 Ga magmatic rocks (and associated thermal anomalies identified by K-Ar mineral and rock ages) is not confined to a single craton, although the major ultramafic/mafic intrusions are best seen in the Kaapvaal Craton (Figure 1).…”

“…The Molopo Farms Complex (MFC) is a layered ultramafic-mafic intrusion, straddling the southern border of Botswana with South Africa, that is part of a major magmatic and thermal event dated between about 2.0 and 2.1 Ga, referred to as a Large Igneous Province by Hanson (2003) and Hanson et al (2004). This province comprises large granitic and ultramafic/mafic intrusions (including the Bushveld Complex) and less common extrusive volcanic complexes into/onto the Kalahari and Congo Cratons (e.g.…”

“…The associated thermal anomaly is recorded in widespread rock and mineral ages of about 2000 Ma in Palaeoproterozoic and Archaean rocks of southern Africa, including the Limpopo Belt (van Breemen and Dodson, 1972;Hanson, 2003). The MFC has been dated at 2044 ± 24 Ma (Coetzee and Kruger, 1989), which is a similar age to other Palaeoproterozoic intrusions and lavas of southern Botswana such as the Moshaneng Complex ( Figure 1; Key and Ayres, 2000;Hanson, 2003). The MFC underlies an area of about 13,000 km 2 of southernmost Botswana and adjacent parts of South Africa across the Molopo River (Gabrielli, 2003;Prinsloo, 1994;Figures 1 and 2).…”