THEME 8: The Mokolian Era. Namaqualand Metamorphic Complex. This is a granite-gneiss complex. Includes folded and metamorphosed volcanosedimentary

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1 THEME 8: The Mokolian Era This runs from 2050 Ma (end of Bushveld Complex) to 1080 Ma (start of Pan African) Includes: Namaqualand metamorphic Complex, Natal metamorphic Complex, sedimenatery sequences of the Waterberg and Soutpansberg groups, the Wilgenhoutsdrif and Koras groups and Mokolian intrusive rocks Namaqualand Metamorphic Complex. This is a granite-gneiss complex. Includes folded and metamorphosed volcanosedimentary bodies Namaqualand Metamorphic Complex Volcano-sedimentary rocks: Marydale and Kaaien groups, Korannaland succession, Bushmanland Group, Okiep Group and Orange River Group Intrusive granites include: Vioolsdrif, Klein Namaqua, Hoogoor, Keimoes, Spektakel and Koperberg Suites 1

2 The volcano-sedimentary successions and granitic intrusions are reminiscent of greenstone belts addition of new curst to the southern edge of the Kalahari Craton. Rocks have been re-worked by subsequent (Pan African) tectonic events Namaqualand Metamorphic Complex contains many important base metal deposits (Cu-Pb-Zn), Fe, Mn, Ba e.g. Aggenys and Gamsberg Folded rocks in the Aggenys area: Rodinia assembly Natal Metamorphic Complex Very similar to Namaqualand Metamorphic Complex. Gneiss, Granite, Schist, metasediment, metavolcanics Natal Metamorphic Complex Four stratigraphic units are: Ntingwe, Mfongozi, Tugela, Mapumulo groups. Also strongly reworked later in the Pan-African 2

3 Because of the similarities between the Namaqualand and Natal Complexes, we can consider them to be a single mobile belt.the Namaqua- Natal Mobile Belt Microterranes and small plates (some of which have an older history >3.0Ga), island arcs and ophiolites that were accreted onto the southern edge of the Kalahari and Namibian Craton What else was going on at this time? Fresh sedimentation close to the Limpopo Belt.the Blouberg Formation, Waterberg Group and Soutpansberg Group Soutpansberg Group Waterberg Group 3

4 All of these rocks were deposited between 2.0 and 1.8 Ga, and relate to reactivation in the adjacent Limpopo Belt. They are continental sediments and lesser volcanics.and are red in colour Blouberg Formation Aeolian deposits in the Waterberg Group Waterberg Group Soutpansberg Group The red colour suggests that the Earth now has an oxygenated atmosphere.no more Fe in the oceans to form BIF, so O 2 enters the atmosphere 4

5 Waterberg sedimentation began in the Wilgerivier area ( Middelburg basin ) just East of Pretoria: coarse alluvial sandstones and conglomerates of the Wilgerivier Formation At a similar time, in the Blouberg area (on the Limpopo Belt) and in the Warmbaths area (Nylstroom protobasin and Alma trough) by deposition immediately adjacent to fault scarps.reactivation of the Limpopo Belt and the TML Coarse clastic granulestone and conglomerate (Blouberg Fm) All of these are coarsegrained immature sediments deposited close to their source, at the northern and southern extremes of the main basin. Movement along faults 5

6 N S N Alma trough S Blouberg Pull-apart basin Palala Shear Zone TML Nylstroom Protobasin Palala Shear Zone TML Sedimentation was then spread across a much larger area of the Main basin with the onset of rifting. Lesser conglomerates, granulestones, sandstones, shales, lavas and pyroclastics Because of tectonism (reactivation of the Limpopo Belt) at this time, a spectacular angular unconformity is developed between the Blouberg Fm and the Upper Waterberg Group Blouberg Formation (1250m) 6

7 In addition to fluvial deposits, the Waterberg also contains the world s oldest and best preserved palaeodeserts The Makgabeng Formation The Makgabeng Formation contains the earliest evidence for life in a terrestrial environment The NE corner of the Waterberg Group is unconformably overlain by the Soutpansberg Group. These form a long mountain chain from Punda Maria to Blouberg, and represent renewed rifting Sibasa Formation 7

8 Wyllie s Poort Formation So the Blouberg, Waterberg and Soutpansberg all represent reactivation of faults, especially the Limpopo Belt, between 2.0 and 1.8 Ga. Might be related to the Eburnean Orogeny, when other cratons were been added to the northern edge of the Zimbabwe Craton. This same timing for orogenic activity is also recorded in other parts of Africa Other rocks of Mokolian age: Wilgenhoutsdrif Gp: metalavas and metasediments north of Groblershoop in Northern Cape Ma, 2000m thick. Koras Gp: alluvial sedimentary rocks, lavas, pyroclastics, deposited in grabens Ma Mokolian intrusive rocks: a range of compositions and and ages. Granite, mafic/ultra-mafic layered intrusions, alkaline complexes. Most important are Pilanesberg Complex: 1850 Ma (alkaline volcanic pipe) and Phalaborwa Complex: 2049 Ma (Cu, vermiculite and Fluorite) Phalaborwa 8