Lecture 5 Vredefort Dome PDF

VREDEFORT DOME Lecture 5 Source: http://www.hartrao.ac.za/other/vredefort/vredefort.html 1 (Accessed on 28 March 2021) Learning objectives Students must understand; The terminology Types of craters The f...

VREDEFORT DOME Lecture 5 Source: http://www.hartrao.ac.za/other/vredefort/vredefort.html 1 (Accessed on 28 March 2021) Learning objectives Students must understand; The terminology Types of craters The formation of the Vredefort dome Characteristics of the Vredefort dome The impact of the Vredefort dome on life 2 Location of the Vredefort Dome Source: https://geology.com/articles/vredefort-dome.shtml (Accessed on 28 March 2021) 3 Understanding the terminology Meteors Meteoroids Meteorites Asteroids Comets Impact craters 4 Meteoroid A meteoroid is a small rocky or metallic body in outer space. Meteoroids break down in the earth’s atmosphere, which results in a flash of light. A small body moving in the solar system that would become a meteor if it entered the earth's atmosphere. Most meteoroids that enter the atmosphere vaporize completely and never reach the Earth’s surface due to high temperatures generated when the object https://upload.wikimedia.org/ wikipedia/commons/6/63/ encounters the Earth’s Meteoroid_meteor_meteorite.gif atmosphere. 5 Meteor A meteor is a piece of rock or metal that burns very brightly when it enters the Earth's atmosphere from space. OR A visible path of a meteoroid that enters the Earth’s atmosphere (commonly known as a shooting star) leaves a “smoke trail” across the sky. A meteor is visible for a few seconds. 6  Meteor Source: https://in.mashable.com/science/3234/nasa-warns-a-major-meteo r-strike-is-on-its-way-this-is-not-a-sci-fi-movie (Accessed on 28 March 2021) 7 Leonid Meteor Source: https://commons.wikimedia.org/wiki/File:Leonid_Meteor.jpg8 (accessed on 28 March 2021) Meteorite A meteoroid that falls through the atmosphere and lands on the Earth’s surface is a meteorite. It is so large that intense friction and heating are generated as it enters the atmosphere. Meteorites are bigger than meteors. 9 Hoba Meteorite in Namibia Source: http://www.atlasobscura.com/places/hoba-meteorite- near-grootfontein-namibia 10 Asteroids An asteroid is a small rocky body orbiting the Sun. They vary in size and are found between the orbits of Mars and Jupiter. They are also known as minor planets (because they are made up of the same material as the planets, but they are smaller in size). 11 Images of asteroids Source: https://www.nasa.gov/feature/goddard/2021/how-were-the-trojan- asteroids-discovered-and-named (Accessed on 28 March 2021) 12 Comets A comet is a small, icy celestial body that glows as it warms and releases gases when travelling near the Sun. Comets are asteroid-like objects covered with ice, methane, ammonia and other compounds that develop a fuzzy, cloud-like shell called a coma, which might extend into a tail. They are referred to as dirty snowballs. They are left over from the formation of stars and planets billion years ago. As a comet’s orbit nears the Sun, the comet heats up, the ice melts, and particles break off. A comet can be visible for days or weeks. 13 Image of a comet Source: https://www.newscientist.com/article/2245355-longest-known- comet-tail-stretched-for-over-a-billion-kilometres/ 14 (Accessed on 28 March 2021) Impact Crater An impact crater is formed when an object like an asteroid or meteorite crashes into the surface of a larger solid object like a planet or a moon. There are simple and complex craters. A simple crater is a bowl-shaped depression formed when an impact breaks up the target rock and ejects it out over the surrounding land. Complex crater structures include: - a central dome - a shallow, flat floor - concentric rings of ridges around the central uplift - terraced rims. 15 Image of a simple crater (Tswaing) Source: https://www.amethyst.co.za/JhbGuide/Tswaing.htm (Accessed on 28 March 2021) 16 Images of a complex crater (Vredefort dome) The crater formed about 2023 million years ago, when a large meteorite which was about 10 km across, and travelling at more than 10 km per second (36 000 km/h) struck the Earth. Source: http://www.hartrao.ac.za/other/vredefort/vredefort.html 17 (Accessed on 28 March 2021) Vredefort Dome It is referred to as a dome because the existing rock layers were deformed into the shape of an upside-down bowl by the impact The core of the basement marks the centre of the Vredefort dome. It is well exposed at Vredefort town near Parys (little town in Free State). Surrounded by inclined rock units that dip away from the granite core in concentric circles to form a dome. The southeastern portion is not visible as it is covered by the sediments of the Karoo Supergroup. The northern half can be seen clearly. 18  Geological map of the dome structure Source: https://dl0.creation.com/articles/p134/c13429/map-Vredefort- Dome-lge.jpg 19 (Accessed on 28 March 2021) The formation of Vredefort dome Major damage occurred to the rocks when a meteorite collided with the Earth’s surface. The basement rock rose rapidly from below during the event, punching through the overlying rocks. Granite punched through the overlying stacked rocks of the Witwatersrand, Ventersdorp and Transvaal Supergroups. Fracturing and jointing in layered rocks indicate that granite was solid at the time and that the process was rapid. 20 https://geology.com/articles/images/vredefort-crater.gif 21 Characteristics of the Vredefort dome It is the largest impact crater on Earth. The original crater was about 250 to 300km wide, about 5km deep. The present structure has been altered by erosion and deposition. Due to erosion, the remaining visible structure is a partial ring of hills with a diameter of about 70km. Semi-circular ranges of hills in an arc about 8km in diameter- called the Vredefort Mountain Land. The mountainland occurred due to the presence of resistant quartzite layers of the Witwatersrand Supergroup that produces ridges. It occupies the central part of the Witwatersrand basin. It has the villages of Parys and Vredefort at the centre. It has been declared a UNESCO World Heritage Site in 2005. 22 Impact of Vredefort on Life When the meteorite hit the Earth, its debris covered the gold-bearing rock of the Witwatersrand, protecting the gold from erosion. The impact resulted in extreme faulting and folding of the Earth’s crust. It may have resulted in the mass extinction of species (dinosaur extinction is linked to the impact). Vredefort dome has great scenic beauty with abundant flora and fauna. Vredefort is also an important birding area. It is also a tourist attraction. 23 Watch: Stone From Heaven video clip https://www.youtube.com/watch?v=DjE 354S5C_Q 24 Google Earth Activity Go to the Google Earth site. Type in “Parys” in the search box Zoom in to the image and see whether you can identify the northern and western portions of the Vredefort dome which are visible. 25 Vredefort Dome: A World Heritage Site A good website for resources: http://www.vredefortdome.org/ index.html 26 How is geomorphology characterised as important in the World Heritage Site nomination? Faulting and dolomitic cave formation – Sterkfontein Caves where important finds of hominid fossils have been made. Transition between prokaryotic and eukaryotic life forms. Vredefort the largest episode of explosive energy release on the Earth’s surface. Early gold mining – shallow deposits of low grade ore. Granite quarrying Tourism 27 Reading Download the following article from Ulwazi: Vredefort Dome World Heritage Site Nomination Read the following excerpts: Pages 7-9, Sections d(i) to d(iii) Pages11-12, Section 3(b) Pages 29 – 31, Sections a - e *** Lecture ends *** 28