§ 13. Geological structure and relief. (textbook)

§ 13. Geological structure and  relief

 

1. Recall that the structure has a platform.

3. How to distinguish between plain and mountain height?

 

Geological structure. Another 180 million years ago Africa was part of ancient supermateryka Gondwana. When was split Gondwanaland, separated from it African lithospheric plate. The basis of the same modern Africa is part of this plate African-Arabian platform.

The lower part Platformfoundation - Make hard crystalline rocks with igneous and metamorphic origin. They very old age, as were formed about 3 billion years ago. At the foundation as a result of external forces (weathering, of wind, surface and ground water) formed continental sedimentary sediments, and in reducing accumulated marine sedimentary deposits. By millions of years they formed bahatokilometrovyy sedimentary cover platform.

Sedimentary cover covers the base evenly, so that over geological time platform suffered heavy slow vertical oscillating movements (raising and opuskan). In those areas which had long rose, ancient crystalline basement rocks are on the surface formed shields. But other areas platform fell, the waters of ancient seas zalyvalysya. There  foundation was covered powerful depth marine sediments, so these places platform formed plates. Through millions of years old Precambrian platform in the northwest and the south was "completed"  parts of the ocean floor, the thickness of sedimentary which breeds in zim'yalysya folds, forming folded region ..

Finally (about 60 million years ago) all African-Arabian platform intensively raised. This was accompanied giant faults. Then formed the largest onshore system East African Rift Valley (Rift). She stretched out on the 4000 km from the Suez isthmus and down the Red Sea on dry land for Zambezi River. Width Rift sometimes 120 km. These faults, like a knife, rozitnuly African-Arabian platform. Along these being felt earthquakes where and there are volcanoes.

Fig. Earth crust Africa

 

Working with map

1.     Lithospheric plate on which rests Africa?

2.     In which direction and how rate moves this plate?

3.     Where are the boundaries of lithospheric plates with respect to the mainland?

4.     What platform is the basis Africa? What part of the African lithospheric plate it takes?

5.     Which parts of Africa foundation old African-Atabian platform reaches the surface?

6.     What minerals are deposited in foundation platform?

7.     In places where African-Arabian platform was constructed orogen? In a geological period they were formed?

8.     In which part of Africa is fault zone (rift)?

 

Relief. In Africa relief predominate plain. It is caused by a platform that is the basis of almost the entire continent. The peculiarity of the African plains is that among them have dominion High Plains - high, plateau, plateaus. In those areas of the platform that geological past, rose, lie high plateauTo those who fell - Depression. Interestingly, even those areas of the platform, which fell (Eg area of the Sahara Desert) and where at first formed lowlands, is a high plain, exceeding 200 c. This is a general show of the whole of Africa in the Cenozoic. Lowlands are stretched only along narrow strips of sea. Same mountains in Africa have very small areas. Overall height above sea level continent divided into two Parts: Low Africa і High Africa.

Relief Low AfricaCovering northern and western parts of the mainland, has a height of 1000 m. In this part are large plain. Their surface is very heterogeneous: Upland alternate with lowlands and plateaus. In places where the surface crystalline rocks are foundation (panels) to the Sahara sands  rise upland Ahaggarand Tibesti with heights of 3000 meters or more.  Among the high plateau to a height of 1000 m is relatively low swampy Trench CongoThat has a concave surface. In the northwest of the mainland rises гHorae AtlasThat formed at the junction of two lithospheric plates where the crust was ere in the fold.

Altitude High AfricaCovering the eastern and southern parts of the continent, exceeding 1000 m. The highest mark is East African plateau - At large plain raised. There are extinguished Volcanoes Kenya (5199 m) і Kilimanjaro(5895 m). These volcanic mountains confined to the East African Rift Valley area. Ethiopian upland is also highly upraised (2 000 - 3 000 m) high plain, littered with extinct volcanoes. It ends abruptly in the East and West decreases to the west. The cave of the Kalahari plateau surrounded from all sides and Plateau. Mountains rise in the south of the mainland. Cape Mountlow and ploskoverhi. Drakensberg higher from coast giant they descend the stairs to the interior of the continent.

 

Fig. Cape Mount

 

Fig. Kilimanjaro

 

Task. Consider the profile and Set:

a) which corresponds to the plain area with high platforms, foundation where it reaches the surface;

b) that the plain area is responsible for the high platform that cover bedding platform.

 

Fig. Physical map of Africa

 

Working with map

1. Determine which form of relief (mountains or plains) dominate in Africa.

2. Which structures - platform or orogen - meets the flat part of Africa?

3. What are common on the mainland plains in height? Name high plateau and plateau.

4. Locate on the map lowlands, which has a negative mark height. How many feet below sea level it is? Where is common in Africa lowlands?

5. Where are the mountains? To which the height of mountains (low, medium, high) they belong?

6. Name the major landforms Low Africa. What prevailing  mark heights they have?

7. What landforms include High Africa? What marks heights they have?

8. Where is the highest point height of the African continent?

 

Minerals. Subsoil Africa's rich various minerals. Their placement is closely related to geological structure of certain parts of the continent.

Put ore minerals - Iron, copper, zinc, tin, chrome ore, Gold - confined to the old base platform, and a composite magmatic metamorphic rocks. Their largest deposits are concentrated in the south and east Africa where the foundation of lies and shallow ore is close to the surface. In particular, are deposits of gold and copper reserves are in Africa ranked first and second places in the world.

Africa is famous diamonds - the most valuable precious stones. They are used not only as fine jewelry, but also as unsurpassed in hardness material. In Africa, producing half of all diamonds in the world. They lay open on the southwest coast and in the center Africa.

Put nonmetallic minerals - Coal, oil, natural gas, phosphates - deposited in sedimentary rocks that cover a powerful cover reduced plot platform. Huge oil field discovered in the north of the Sahara and the coast Gulf of Guinea. Rich deposits of phosphates, of which produce fertilizer, concentrated in the north of the mainland. In the sedimentary series are mines and minerals that formed due to weathering of magmatic and metamorphic rocks. So Deposits of iron, copper, gold and manganese ores of sedimentary origin common in the west and southern Africa. Placement of mineral resources in Africa continue to learn.

FAQ task

1. What resulted from domination plains in Africa?

2. What rocks (sedimentary or magmatic and metamorphic) composite East African plateau? What for origin of minerals deposited there?

3. What kinds plain height corresponding sections of the exit to the surface of the foundation platform?

4. What the origin of mountain rocks composed of the Congo basin?

5. How Associated relief geological structure and location of mineral resources on the mainland?

     6. Consider why in Africa there are no high and extended mountain chains, such as Himalayas in Eurasia, the Andes in South America, North American Cordillera.