scholarly journals Variations in the thickness of the crust of the Kaapvaal craton, and mantle structure below southern Africa

2004 ◽  
Vol 56 (2) ◽  
pp. 125-137 ◽  
Author(s):  
C. Wright ◽  
M. T. O. Kwadiba ◽  
R. E. Simon ◽  
E. M. Kgaswane ◽  
T. K. Nguuri
Keyword(s):  
Southern Africa ◽  
Kaapvaal Craton ◽  
Mantle Structure

scholarly journals Neoarchean large igneous provinces on the Kaapvaal Craton in southern Africa re-define the formation of the Ventersdorp Supergroup and its temporal equivalents

2020 ◽  
Vol 132 (9-10) ◽  
pp. 1829-1844 ◽  
Author(s):  
Ashley Gumsley ◽  
Joaen Stamsnijder ◽  
Emilie Larsson ◽  
Ulf Söderlund ◽  
Tomas Naeraa ◽  
...  
Keyword(s):  
Mantle Plume ◽  
Southern Africa ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Kaapvaal Craton ◽  
Ionization Mass ◽  
Flood Basalts ◽  
Large Igneous Provinces ◽  
Igneous Provinces ◽  
World Class

Abstract U-Pb geochronology on baddeleyite is a powerful technique that can be applied effectively to chronostratigraphy. In southern Africa, the Kaapvaal Craton hosts a well-preserved Mesoarchean to Paleoproterozoic geological record, including the Neoarchean Ventersdorp Supergroup. It overlies the Witwatersrand Supergroup and its world-class gold deposits. The Ventersdorp Supergroup comprises the Klipriviersberg Group, Platberg Group, and Pniel Group. However, the exact timing of formation of the Ventersdorp Supergroup is controversial. Here we present 2789 ± 4 Ma and 2787 ± 2 Ma U-Pb isotope dilution-thermal ionization mass spectrometry (ID-TIMS) baddeleyite ages and geochemistry on mafic sills intruding the Witwatersrand Supergroup, and we interpret these sills as feeders to the overlying Klipriviersberg Group flood basalts. This constrains the age of the Witwatersrand Supergroup and gold mineralization to at least ca. 2.79 Ga. We also report 2729 ± 5 Ma and 2724 ± 7 Ma U-Pb ID-TIMS baddeleyite ages and geochemistry from a mafic sill intruding the Pongola Supergroup and on an east-northeast–trending mafic dike, respectively. These new ages distinguish two of the Ventersdorp Supergroup magmatic events: the Klipriviersberg and Platberg. The Ventersdorp Supergroup can now be shown to initiate and terminate with two large igneous provinces (LIPs), the Klipriviersberg and Allanridge, which are separated by Platberg volcanism and sedimentation. The age of the Klipriviersberg LIP is 2791–2779 Ma, and Platberg volcanism occurred at 2754–2709 Ma. The Allanridge LIP occurred between 2709–2683 Ma. Klipriviersberg, Platberg, and Allanridge magmatism may be genetically related to mantle plume(s). Higher heat flow and crustal melting resulted as a mantle plume impinged below the Kaapvaal Craton lithosphere, and this was associated with rifting and the formation of LIPs.

scholarly journals Eclogite and Garnet Pyroxenite Xenoliths from Kimberlites Emplaced Along the Southern Margin of the Kaapvaal Craton, Southern Africa: Mantle or Lower Crustal Fragments?

2020 ◽  
Vol 61 (4) ◽  
Author(s):  
Anton Le Roex ◽  
Christel Tinguely ◽  
Michel Gregoire
Keyword(s):  
Southern Africa ◽  
Kaapvaal Craton ◽  
Crustal Shortening ◽  
Southern Margin ◽  
Accessory Phase ◽  
Garnet Granulite ◽  
Crustal Origin ◽  
Lower Crustal ◽  
Ree Patterns ◽  
Granulite Xenoliths

Abstract Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K2O in clinopyroxene and Na2O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites. Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe–Mg exchange equilibration temperatures for the eclogites range from 815 to 1000 °C, at pressures of 1·7 ± 0·4 GPa as determined by REE partitioning, indicating that they were sampled from depths of 50–55 km; i.e. within the lower crust of the Namaqua–Natal Belt. The garnet pyroxenites show slightly lower temperatures (686–835 °C) at similar pressures of equilibration. Initial 143Nd/144Nd and 87Sr/86Sr ratios (calculated to time of kimberlite emplacement) of both lithologies overlap the field for lower crustal samples from the Namaqua–Natal Belt. Further evidence for a crustal origin is found in the similar REE patterns shown by many of the associated garnet granulite xenoliths. Garnet pyroxenites are interpreted to have a similar origin as the associated eclogites but with the mafic protolith having insufficient Na (i.e. low modal plagioclase) to allow for development of omphacitic pyroxene. Metamorphism of the mafic protoliths to these eclogites and garnet pyroxenites is inferred to have occurred during crustal shortening and thickening associated with the collision of the Namaqua–Natal Belt with the Kaapvaal craton at 1–1·2 Ga.

scholarly journals Electrical lithosphere beneath the Kaapvaal craton, southern Africa

2011 ◽  
Vol 116 (B4) ◽  
Author(s):  
Rob L. Evans ◽  
Alan G. Jones ◽  
Xavier Garcia ◽  
Mark Muller ◽  
Mark Hamilton ◽  
...  
Keyword(s):  
Southern Africa ◽  
Kaapvaal Craton
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