1. BASIC GEOLOGY OF SA · 2014-06-04 · 1. BASIC GEOLOGY OF SA 2 a) Brief geological history of SA...

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University of Pretoria

GEOLOGICAL PROCESSES AND MATERIALS

SGM210

25 March 2014

1. BASIC GEOLOGY OF SA

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a) Brief geological history of SA

b) Geological maps

c) Witwatersrand Supergroup

d) Transvaal Supergroup

e) Bushveld Igneous Complex

f) Karoo Supergroup

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a) Witwatersand SupergroupSingle richest gold deposit in the world.50 000 tons of Au has been mined (30% of world reserve).50% remains!!!

b) Bushveld Igneous ComplexLargest layered igneous complex in the world.85% of world’s platinum !! (and palladium, rhodium, ruthenium,

osmium and iridium = Platinum Group Metals).

c) SA first in terms of reserves of:Manganese, chrome, PGM, gold, vanadium

Also very rich in:Titanium, diamonds, uranium, nickel, phosphate, copper, zinc, lead,

iron, coal.

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d) GeologySA part of oldest intact continent on earth (The Cape Vaal Craton).SA has some of the oldest rocks on earth (Baberton).SA has some of the best preserved old rocks on earth.

e) Largest flawless diamond in the world - Cullinan

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By studying astronomy and physics (Big Bang, relativity, quantum mechanics)

and geology (stratigraphy, fossil records, radio active dating)• Old rocks lie at bottom, younger rocks above. • Intrusions are younger than the rocks into which they

intruded.• Identical fossils occur in rocks of about the same age.• Works well in igneous rocks. • Does not work in rock that recrystalised.• Does not work in sedimentary rocks.

and archeology (human history)

religious texts (?)

“In the beginning God created the heaven and the earth. And the earth was without form, and void; and the darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. And God said, Let there be light: and there was light.” Gen. 1:1-3.

“The Big Bang occurred approximately 13,7 billion years ago and the entire universe exploded from an infinitesimal singular point, cooling and expanding and developing to this very day. Earth accumulated from cosmic dust under the forces of gravity, was bombarded with meteorites, cooled and life developed gradually through evolution which is continuing today.”

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• Half-life – The amount of time needed for one half of a sample of a radioactive parent isotope to decay to its daughter isotope

• Radioactive dating – determination of the age of an object be measuring the proportions of a radioactive element and its decay product

238U 206Pb in zircon (half-life of 4.5 billion years)235U 207Pb in zircon (half-life of 700 million years)40K 40Ar (half-life of 1.25 billion years)14C 12C (half-life of 5700 years)

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238U 206Pb in zircon (half-life of 4.5 billion years)

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t (years)Using a mass spectrometer, it was determined that 5.5% of the uranium contained in a zircon crystal has been converted to lead. At formation zircon does not contain any lead. How old is the zircon crystal?

It was determined that after 15000 years only 16,14% of the original amount of 14C remains in a particular sample. What is the half-life of 14C?

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GEOLOGICAL HISTORY OF SA

• 4500 million years ago– Earth stabilises in orbit.– It was hot!!! Earth cooled down.– Heavy elements settle. Light ones float. Crust forms.– First oceans formed.– Gasses like CO2, CH4, H2O

• 3800 million years ago– Earth continues to cool down.– Volcanic outbursts – igneous rocks (Baberton)– First sedimentary rocks formed.

• 3500 million years ago– Single cell blue-green algae CO2 O2

– First granites (komatiite) intrude into crust – oldest known oceanic crust

– Stable “islands” form = cratons

• 13700 million years ago– The Big Bang

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• 3100 million years ago– Cape-Vaal craton established and stable.– Sediments from mountains deposited in shallow seas. (Fig

Tree Group, Baberton)– Witwatersrand-basin one of the first (2970 – 2714 M.A.) Au


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• 3100 million years ago– Cape-Vaal craton established and stable.– Sediments from mountains deposited in shallow seas.– Witwatersrand-basin one of the first (2970 – 2714 M.A.) Au




• 2700 million years ago– Ventersdorp lava flows out over west of Cape-Vaal craton.– Volcanic outbursts alternate with sedimentary deposits.

• 2500 million years ago– Dolomitic limestone of Transvaal & Griekwaland West basins

precipitate – algae.– O2 production accelerates.– First banded ironstone deposits form in Transvaal basin.


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• 3100 million years ago– Cape-Vaal craton established and stable.– Sediments from mountains deposited in shallow seas.– Witwatersrand-basin one of the first (2970 – 2714 M.A.) Au


• 2500 million years ago– Dolomitic limestone of Transvaal & Griekwaland Wes basins


• 2061 million years ago– Bushveld Igneous Complex flows out (85% of the world’s Pt.)– Biggest layered igneous intrusion known on earth.





• 2500 million years ago– Dolomitic limestone of Transvaal & Griekwaland Wes basins


• 2061 million years ago– Bushveld Igneous Complex flows out (85% of the world’s Pt.)– Biggest layered igneous intrusion known on earth.


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• 1100 million years ago– Sediments deposit around stable Cape-Vaal craton.– West and south of craton still unstable. – Several sedimentary deposits formed here: Gariep

Supergroup (700 M.A.), Malmesbury & Kango Groups, Nama& Vanrynsdorpgroups (600 M.A.)

– Later metamorphosed during intrusion of Cape Granites (540 M.A.)

• 400 million years ago– Cape Supergroup deposited in elongated southern ocean

(Table Mountain deposited.)

• 1900 million years ago– Massive banded ironstone deposits form = O2 now common.

• 2023 million years ago– Vredefort meteorite impact

• 1300 million years ago– Pilanesberg volcanic intrusion (Sun City)


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The Cape Supergroup

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• 183 million years ago– Wide spread basaltic lava flows cover Southern Africa (the

Drakensberg and Karoo dolerite intrusions.)– Gondwana begins to break up.

• 320 million years ago– 50 M.A. Ice age covers Gondwana - Dwyka Group– Ice Age ends and sediments begin to accumulate in Karoo

Basin for 130 million years in shallow seas, lakes and deserts. – Karoo Supergroup (60% of SA).

• 65 million years ago– Immediate extinction of the dinasours (Meteorite on Yukutan

Peninsula, Mexico???????)

• More recently...– Kalahari sands


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• 183 million years ago– Wide spread basaltic lava flows cover Southern Africa (the

Drakensberg and Karoo dolerite intrusions.)– Gondwana begins to break up.

• 320 million years ago– 50 M.A. Ice age covers Gondwana - Dwyka Group– Ice Age ends and sediments begin to accumulate in Karoo

Basin for 130 million years in shallow seas, lakes and deserts. – Karoo Supergroep (60% of SA).


Karoo Supergroup

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DRAKENSBERG – END OF THE KAROO

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• Life– 3900M.A. The late bombardment.– 3800M.A. Carbon containing deposits in Greenland

poor in 13C. (From nothing to life in just 100 million years!!! ...was there intervention????)

– 3500M.A. Single cell organisms (Baberton).– 545M.A. Shell fossils.– 450-500M.A. First fish.– 430M.A. Algae on land.– 420M.A. Insects.– 370M.A. Amfibians– 350M.A. Forests full of reptiles established on land.– 65 M.A. Extinction of the dinosaurs. – 3 M.A. Ancestors of man???


• During all of this:– continents float around on earth surface under forces of plate

tectonics;– heaving, erosion and deposition takes place;– nearly everything is broken up, mixed up and reassembled

(except the stable cratons).


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END OF HISTORY

1. BASIC GEOLOGY OF SA · 2014-06-04 · 1. BASIC GEOLOGY OF SA 2 a) Brief geological history of SA...

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