Part 1

• Pilanesberg Complex


  Mesoproterozoic alkaline complex, among largest in the world
• Pilanesberg Complex


  • Volcanic Facies (trachytic and phonolitic)
  • Intrusive Facies (syenite and nepheline syenite)
  • Retains parts of its volcanic carapace, unlike other complexes
• Pilanesberg Complex is situated on the Kaapvaal Craton as part of the Bushveld Complex
• Pilanesberg Complex is part of the broader Pilanesberg Alkaline Province, which includes several smaller alkaline and carbonatite complexes in the area
• Pilanesberg Complex has potential for rare Earth elements (Zr, Nb, Th, and U) due to modern technology, with economic implications
• Agpaitic rocks


  Peralkaline igneous rock, characterized by unusual minerals like eudialyte and astrophyllite
• The evolution of alkaline magmas towards peralkaline compositions is an intriguing aspect for research studies
• The Pilanesberg Complex's unique rocks influence soil and drainage patterns in the region
• Human occupation in the Pilanesberg region spans from the Middle Stone Age to later Iron Age settlements
• Limited surface water and saline groundwater pose challenges for agriculture and livestock in the Pilanesberg region
• Fluorite occurrences in the Pilanesberg region contribute to health issues among local inhabitants
• The northeastern portion of South Africa is underlain by the Kaapvaal Craton, which experienced microcontinent accretion from 3,600 to 3,000 Ma
• Rock groups deposited on the Kaapvaal Craton

  • Pongola and Dominion Groups (3000 to 2900 Ma)
  • Witwatersrand and Ventersdorp Supergroups (2900 to 2700 Ma)
  • Transvaal Supergroups (2600 to 2100 Ma)
• The Transvaal Supergroup was invaded by magmas (2060 Ma), forming the felsic lavas, Bushveld Complex, and granites
• Lithospheric subsidence allowed the accumulation of the Waterberg Group until approximately 1,750 Ma, after which geological activity declined
• The Pilanesberg Event occurred between 1250 and 300 Ma, which is relevant to the geomorphology of the Pilanesberg region
• South Africa was covered by the Dwyka glaciation ice sheet (~300Ma), resulting in the erosion of the land surface and the formation of a relatively flat surface
• The Karoo Supergroup rocks, including temperate sandstones, mudstones, and desert sandstones, buried the glaciated surface
• The eruption of Drakensberg basaltic lavas (180 Ma) abruptly terminated sediment accumulation, and the break-up of Gondwana led to a new cycle of erosion
• GEOG211


  2024
• South Africa was covered by the Dwyka glaciation ice sheet (~300Ma) → portion of Gondwana lay over the South Pole
• Resulting in the erosion of the land surface
• Layers similar rock hardness → Formation of relatively flat surface
• Layers opposing rock hardness → Formation of ridges and valleys
• Gondwana moved slowly northward → glaciated surface buried under Karoo Supergroup rocks
• Karoo Supergroup rocks


  • Temperate Sandstones
  • Mudstones (Ecca and Beaufort Groups)
  • Desert Sandstones (Stormberg Group)
• Eruption of Drakensberg basaltic lavas → abruptly terminated sediment accumulation


  180 Ma
• The break-up of Gondwana → new cycle of erosion
• Removal of the Karoo Supergroup cover → northern Kaapvaal Craton
• Exposing the pre-Karoo land surface
• Erosion and exhumation → shaping the Pilanesberg region


  90 Ma
• Pilanesberg Alkaline Province


  Intrusive and extrusive igneous activity → north-western Kaapvaal craton and areas eastwards (1,250 Ma)
• Pilanesberg Complex


  • ~25 to 30 km in diameter
  • Intrusion aided by regional tensional forces → produced north-northwest orientated dykes (syenite and alkali gabbro) → extended for about 400 km (Witwatersrand to Botswana)
• Shand (1928)


  Suggested it was a shallow lopolith
• Lurie (1973)


  Suggested it was a tilted series of cone sheets which were intruded into a volcanic capping
• Volcanic rocks


  • Very fine-grained trachytes and phonolites
  • With sanidine phenocrysts as the only visible phase
• Intrusive rocks


  • Chemically comparable to the lavas
  • Coarser-grained and formed variably coloured syenites and foyaites
• Cauldron subsidence


  • Resulted (probably) in the downward collapse of the entire structure
  • Preserving a near-perfect circular shape within the surrounding Bushveld Magmatic Province
• Pilanesberg Geomorphology


  • Forms a nearly perfect circle with concentric rings of hills and valleys
  • Each hill is composed of a different rock type
  • Structure height ~100 to 500 m above the surrounding flat landscape
  • The highest point (~1560 m) is to the southeast = Magaliesberg
• Pilanesberg Geomorphology


  • Exhibit rectilinear slope elements
  • Prominent basal breaks of the slope
  • V-shaped valleys with underfit rivers