COMPONENT 3 : GEOLOGY AND GEOGRAPHICAL FEATURES

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1 1 COMPONENT 3 : GEOLOGY AND GEOGRAPHICAL FEATURES A BRIEF GEOLOGICAL HISTORY AND THE ORIGIN OF THE MOST IMPORTANT MINERALS Scientists believe that during the earth s history its land areas were once united into one huge continent, called Pangea. This super continent separated into two parts, namely Laurasia and Gondwana. Gondwana eventually split up about 60 million into South America, Africa, India, Australia and Antarctica Formation of the earth 4.5 billion Oldest Rocks in South Africa 3.8 billion Kaapvaal Craton billion What are cratons? DEFINITION Oldest Fossils 3.4 billion Our sun formed on the outer arm of the Milky Way and around it accumulated a disc of dust from which the earth developed as a red-hot ball. first identifiable rocks had started to form within the crust and the earth continued to cool over millions of years. Sandriver Gneiss in the Limpopo Province is the oldest rock formation in South Africa (Snyman, CP). Kaapvaal craton was stabilized and consolidated about 3100 million. It underlay the whole of the northeastern part of the country and when it was welded to the Zimbabwe Craton in the north, the so-called Limpopo belt was formed. Kernels on which continents grow. y are much older and deeper than the neighboring crust and mantle and are formed by nuclei being welded together. Fragments of the earliest part of the Earth s crust, comprising the most ancient sedimentary and volcanic rocks and the granites that intruded them (Norman & Whitfield). rocks of the Barberton Greenstone belt were formed after the first proto-foundation of the Kaapvaal craton was laid down. Microscopic single-cell blue-green algae also appeared at this time and began the process of producing oxygen from carbon dioxide through photosynthesis. Evidence of these algae is found in the Barberton Greenstone belt. Maarten de Wit proved that these are the oldest fossils dating back 3400 million.

2 2 A shallow sea /ancient lake about 3 billion Witwatersrand Supergroup interior of ancient South Africa, at this time still part of Gondwana, was submerged under a shallow sea or lake. shores of this sea were Granite Mountains containing minute amounts of gold. granite eroded quickly as there was no plant life and the waters had a ph of 3. fragments that were eroded away, accumulated on the bed of the lake forming the Witwatersrand Super group. gold bearing reefs of the Witwatersrand above led to the formation of sedimentary rock made up of various combinations of black chert or white quartz pebbles, sand and silt. Whenever the rocks were reworked, the gold was more and more concentrated in specific layers, called conglomerates. se consisted of quartz pebbles and a fine sand matrix with about grams of gold per ton, which lead to the largest and richest gold deposits on earth. A period of volcanic activity and sedimentation Ventersdorp lavas about 2.7 billion years Transvaal Supergroup About 2.2 billion years After the formation of the Witwatersrand Supergroup a period of volcanic activity followed, covering most of the sediments deposited earlier. A period of sedimentation and inter dispersed volcanic activity followed that covered most of the northern part of the old Kaapvaal Craton. In the beginning of this period, calcium-magnesium carbonates were precipitated to form the dolomites, well known for the sinkholes that appeared in them in the 1960s. After the deposition of the dolomites, sandstones and mudstones were deposited that formed over time the prominent quartzite hills and shale valleys around Pretoria of which the Magaliesberg is the most prominent. In the dolomites, the iron and manganese bearing sediments were also deposited, resulting in more of South Africa s mineral riches.

3 3 Molten magma 2 billion years Pressure started building up within the earth s mantle. Enormous amounts of molten magma were pushed at numerous intervals between the sedimentary layers of the whole Transvaal Sequence and a reservoir settled underneath the ancient lake. As the volumes of magma were considerable, cooling and crystallization were slow processes and the molten material solidified into enormous lobes of solid rock over a period of 30 million years. crystals that were significantly denser than the magma, sank through it and settled at the bottom. This caused differentiation or layers of the thick mafic intrusive bodies forming the chromium rich layers (UG2) and the famous platinum bearing Merensky reef. Thus the Bushveld Igneous Complex (BIC) was formed. Bushveld Igneous Complex and platinum Bushveld Igneous Complex (BIC) is the world s largest known deposit of platinum group metals (PGMs). PGMs namely platinum, palladium, rhodium, ruthenium, osmium and iridium occur with small amounts of gold, nickel, copper and cobalt. BIC also boasts the largest resources of chromium and vanadium in the world. It comprises a range of diverse igneous rock found in two layers the Merensky Reef (named after Hans Merensky who first discovered these deposits of platinum in 1924) and the UG2 Chromitite Layer. Erosion million years formation of mountains 400 million A long period of non-deposition followed where erosion was the main activity to shape the land. In the oceans of the Kaapvaal Craton, thick sequences of sediments and lavas accumulated in linear belts that were to become major fold mountain chains. se sediments formed the Cape Supergroup and the folding and uplifting of these formations gave rise to Table Mountain and the Cape Fold Mountains. Due to continental drift the southern tip of Africa slowly moved to the east at a rate of about 2 cm./year, resulting in the crumbling up or folding of the rocks.

4 4 Karoo Supergroup million years Climatic Change An ice age million Swamps and dinosaurs Deserts 180 million Drakensberg Coal Sedimentary and volcanic rocks of the Karoo Supergroup cover Two-thirds of South Africa over a period of 160 million years. sediments of the Karoo recorded a changing geological environment due to the migration of the ancient supercontinent of Gondwanaland from polar through tropical and finally desert environments. Meteorological conditions caused the southern hemisphere to become extremely cold and a glacial (ice) sheet starting creeping from what is today Zimbabwe, southwards across Gondwanaland. Quantities of soil and rock were absorbed by the moving glacier, the conglomeration serving as an abrasive, mixing with more debri as it went along and scraping the surface clean. debri was finally deposted as till. After about 65 million years the climate of the two hemispheres were reversed. supercontinent, Gondwana, started breaking up giving birth to Africa. At this time, South Africa became a swamp inhabited by dinosaurs and other creatures. Layers of silt and humus were deposited and lead to the formation of the Ecca Group (sedimentary rocks famous for their fossils) and coal. climate continued to change and eventually the swamps became deserts. Deep cracks/fissures started to form over most of Gondwana and basalt magma from the mantle welled up. Finally, the Karoo Sequence was capped by a layer of lava that erupted from this fissures created by the breaking up of Gondwanaland. soft Karoo deposits was eroded and left the typical flattopped hills. lava also spread further afield across the landscape, giving birth to what is now referred to as the Drakensberg. Karoo Supergroup also hosts the Karoo coal deposits, the primary energy source of Southern Africa. South Africa is the fourth largest coal producer and the second largest exporter in the world.

5 5 TIPS ON HOW TO IMPROVE YOUR KNOWLEDGE OF GEOLOGY Watch the video of the geological history of the earth at the Maropeng Visitor s Centre (Cradle of Humankind) Try and identify different types of rock and/or bring a sample to class. (Never remove samples from heritage sites). Visit the Transvaal Museum (Pretoria) geological section. Read a book on Geology. Attend a Vredefort Dome workshop or practical outing. GEOLOGICAL TIMESCALE AND THE MAJOR EVENTS IN SOUTH AFRICA S PAST Million years EON (ERA) EVENT 4500/4600 Archean (Early) Formation of the Earth Archean (Early) Barberton and other greenstone belts form and evidence of single-cell live found Archean (Late) Formation of the Witwatersrand gold-bearing conglomerate Proterozoic (Early) Transvaal stromatolitic dolomites 2200 Proterozoic (Early) Transvaal iron formations deposited Proterozoic (Early) Intrusion of the Bushveld Igneous Complex 2023 Proterozoic (Early) Vredefort meteorite impact event Proterozoic (Early) Deposito of the first Waterberg and Olifantshoek red-beds 1200 Proterozoic (Middle) Intrusion of Pilanesberg alkaline igneous complex Phanerozoic(Palaeozoic) Intrusion of the Cape granites Phanerozoic(Palaeozoic) Great Ice Age 183 Phanerozoic(Mesozoic) Karoo dolerites intruded and Drakensberg basalts erupted 65 Phanerozoic(Cenozoic) Extinction of the dinosaurs 3 Phanerozoic(Cenozoic) Development of hominids and early humans

6 6 difference between Rocks and Minerals Rocks form the hard outer crust of our planet and are made up of minerals. A mineral is homogeneous (it is the same all the way through). It is made up of elements (simple chemical substances such as silicon, aluminum and oxygen that are the building blocks of most of the rocks). A rock is mixture of minerals, for example, granite is made up of three minerals: mainly feldspar and quartz with minor amounts of mica. Classification of Rocks IGNEOUS SEDIMENTARY METAMORPHIC Cooling and crystallization of molten magma (molten rock or lava rising from deep within the Earth s crust). Granite Dolerite Basalt Kimberlite Deposited by water, wind or ice. From the breakdown of other rocks or by in situ biological or chemical accumulation Examples Sandstone Conglomerate Limestone Dolomite Re-crystillization from pre-existing rocks and melts Gneiss Schist Slate Marble Hornfels Occurrence of the following natural disasters in South Africa Earthquakes Only minor earthquakes appear in South Africa, mainly due to mining activity. In September 1969 was the only time that South Africa experienced a quake with a high rating on the Richter scale. During this quake some older buildings in Tulbach and Ceres in the Western Cape was seriously damaged. Volcanoes Only extinct ones

7 7 THE LANDSCAPE AND GEOGRAPHY Topography Landscape is dominated by a high interior plateau, rising abruptly to form a series of mountain ranges known as the Great Escarpment, before dropping to a narrow strip of coastal lowlands. Coastline: km East coast : Indian Ocean east coast has the north-to-south Mozambique/Agulhas current that provide its warm waters. West coast : Atlantic Ocean cold Benguela current sweeps up from the Antarctic along the Atlantic coast, laden with plankton and providing rich fishing grounds. se two currents have a major effect on the country's climate, the ready evaporation of the eastern seas providing generous rainfall while the Benguela current retains its moisture to cause desert conditions in the west. Natural hazards are droughts and floods Environmental Issues - Water conservation and control - River pollution - Waste - Dust and toxic gases from mining activities as well as the danger of sinkholes. SA lies between 22º and 35 S and between 17º and 32 E Tropic of Capricorn, or Southern tropic, is one of the five major circles of latitude that mark maps of the Earth. It lies south of the Equator, and marks the most southerly latitude at which the sun can appear directly overhead at noon when the southern hemisphere is tilted towards the sun to its maximum extent in December. northern hemisphere equivalent of the Tropic of Capricorn is the Tropic of Cancer. Area 1,219,090 sq km /Approximately 1.2 million km 2 (slightly less than twice the size of Texas). Ranks 25 th in the world re are only two major rivers Limpopo, a stretch of which is shared with Zimbabwe and the Orange (with its tributary, the Vaal) which runs with a variable flow across the central landscape from east to west, emptying into the Atlantic Ocean at the Namibian border. In so dry a country, dams (over 519) and irrigation are extremely important: the largest dam is the Gariep on the Orange River. No significant natural lakes; but along the coast lons and estuarine lakes longest range is the Drakensberg Mountains, stretching over an area of approximately 5000km. semicircular range starts in Mpumalanga in the north and stretches down through Kwa- Zulu Natal the Free State and the Eastern Cape.

8 8 Geographical regions Highveld Bushveld Rolling grasslands or veld. rock formations to the north are known as the Witwatersrand that is a gold-bearing rock m above sea level. North of the Witwatersrand is a dry savannah area. It consists of open grasslands with scattered trees and bushes. This area is home to one of the most important volcanic mineral complexes in world: Bushveld Igneous Complex m above sea level. Cape Middleveld Great Escarpment Great Karoo Between the Kalahari and Namib deserts. Arid and wavy plains with pans where rainfall collects. Elevation of m. southern border of Highveld gives rise to a semicircle mountain range. Drakensberg range: South Africa s largest mountain range, with the highest peaks over 3000m (in KwaZulu- Natal). highest peak is found in Lesotho (Mountain Kingdom). Cape range: Fold mountains (formed by continental crust). Forms an l-shape. North-south Cape Ranges: Cedarberg, Witsenberg and Great Winterhoek Mountains with peaks close to 2 000m East-West ranges: Swartberg and Langeberg, peaks 2 200m. Khoisan term for land of thirst. Little Karoo Lowveld Narrow strip of arid savannah between Great Karoo and the Cape East-West ranges. More temperate than the Great Karoo with a larger diversity of fauna and flora. Narrow strip between great Escarpment and ocean.