"," Minerals ". They are considered in the physical and geographical characteristics of a region.
Definition 1
Geological structure - this is the structure of the site crust, features of bedding of layers of rocks, their mineralogical composition, origin.
When studying the geological structure of continents, the concepts of "platform" and "folded area" are encountered.
On a geological time scale, the Mesozoic occurs after the Paleozoic and before the Cenozoic. The Mesozoic era is divided into Triassic, Jurassic and Cretaceous periods. Morocco, located in northwest Africa, is the subject of many expeditions. For Central Europeans, especially for a geologist, it is interesting here.
Africa has not always been a separate continent. At a geologically untimely time, about 140 million years ago, it was part of a supercontinent southern hemisphere, the so-called Gondwana, which also included South America, Australia, Antarctica and India. In the northern hemisphere, the continent of Laurasia, including today's Europe, Asia and North America, was devastated at that time. We have paleontological, sedimentological, paleomagnetic and structural-tectonic evidence of the relationship between these lands.
Definition 2
Platform Is a large, relatively immobile area of the earth's crust.
Platforms are at the core of every continent. In the relief, the platforms correspond to the plains.
Definition 3
Folded area - a movable area of the earth's crust, where active mountain-forming processes (earthquakes, volcanic eruptions) are taking place.
According to today's accepted theory of plate tectonics, Africa is part of a large African plate bounded in the west, south and southeast by mid-ocean ridges. Africa is separated from Europe by a complex folded alpine zone formed from the former territory of the Tethys Sea 30 million years ago, in the Tertiary.
A feature of Africa is the significant geological age of the main part of its territory. It is made up of a stable block that has not been influenced by any horticultural processes leading up to it; Africa is different from most other continents. Within the framework of African platform morphologically larger massifs and blocks with higher or lower elevations are more pronounced, for example, in the Moroccan territory of the West African Megablock. Blocks are laid out stacked mountain systems or orogenic zones.
In the relief, folded areas are represented by mountain systems.
Definition 4
Relief Is a set of irregularities on the earth's surface.
Definition 5
Minerals - this is the wealth of the earth's interior that can be used by man to meet his needs.
Features of the geological structure of Africa
About $ 180 million years ago, the territory of Africa was an integral part of the ancient supercontinent of Gondwana. When Gondwana split apart, the African lithospheric plate separated. At the heart of the modern territory of Africa lies a part of this plate, namely, the ancient (Precambrian) African-Arabian platform .
At first glance, individual geological units in Morocco differ not only in morphology, but also in the nature of vegetation, reflecting climatic conditions, mainly due to the distance from the Mediterranean and the altitude. Reef and Atlas are relatively young in the mountains, completed in the Tertiary. The African Alps are the southern wing of the Alpine Orogen and are associated with the Apennine region of Europe.
The Antiatlas Mountains are older - it was built and metamorphosed in the Pre-Amber, over 850 million years ago. The reef borders the northwestern edge of the African continent. It is connected to the southern Spanish mountain range, from which it is separated only by the Strait of Gibraltar. The Rifian's own zone consists mainly of a series of alternating marshes and shale. In the most high parts of this mountain range sporadically preserved tortoiseshell to Tertiary limestones, the highest is the Tertiary gluten, deposited after the creation of the plateau.
In most of the territory, active mountain building stopped another $ 1000 - $ 500 million years ago. Later, the hard core of the continent did not experience folded processes.
The lower part of the platform, that is, its foundation, is made up of crystalline rocks - basalts and granites of magmatic and metamorphic origin. They are very ancient in age. As a result of weathering, continental sediments accumulated on the basement, and marine sediments in depressions. Over millions of years, they have formed a powerful sedimentary cover on the platform. It should be noted that the sedimentary cover unevenly covers the basement, because the platform experienced several slow ups and downs over a long period of time. In those areas where a long process of uplift took place, the ancient crystalline rocks of the basement appeared on the surface, thus forming shields.
The ridge includes highly metamorphic rocks of amphibolite facets and ultrabasic rock bodies. The old crystalline substrate has been shriveled over 440 million years ago. Together with younger units, it was reworked by the Alpine orogeny in the Middle and Upper Eocene and Middle Miocene.
By the end of the Oligocene and in the Miocene, separate partial margins were formed, which included a perennial subsoil and were moved to the south. The Atlas, along with the Mesetta plateau, is part of one large unit. From the northern part, represented by the Reef, this area is separated by a tertiary moat. Each of these units has undergone a completely different geotectonic development. Unlike the Reefa, the Atlas is characterized by an uncharted black structure.
Definition 6
The shield is the place where the crystalline basement of the platform exits to the surface.
In other parts of the platform, the processes of subsidence and flooding by waters of ancient seas took place. In these places, the foundation was overlapped by a huge layer of marine sedimentary deposits, in such areas of the platform plates were formed. Millions of years later, the platform in its northwestern and southern parts was "completed" by parts of the ocean floor, while the strata of its sedimentary rocks were crumpled into folds and formed folded areas (area Atlas and Cape mountains ). More than $ 60 million years ago, the African-Arabian platform began to rise intensively. This rise was accompanied by giant fractures in the earth's crust. During these faults, the largest land-based system was formed East African faults (rifts) ... It stretches for $ 4000 $ km from the Isthmus of Suez along the bottom of the Red Sea and overland to the Zambezi River. The rift width in some places reaches $ 120 km. The above faults cut the African-Arabian platform like a knife. Along them there are earthquakes, manifestations of volcanism.
Mainly limestone - Moroccan mezet and middle atlas. The grid rises a few degrees from the coastal plain to the interior. His central part, located at an altitude of 600 m above sea level, is separated from the coastal plain by a separate line of steep slopes. The grid is filled with numerous erosional valleys, ridges and undulating ridges, among which volcanic formations also grow.
High Atlas with a length of more than 800 km. Its steep slopes are exposed and eroded, which also contributed to the Quaternary glaciation. The old bowels of the Atlantic region are composed of pre-African rocks of the African plate. On it lie rocky rocks, wrinkled and somewhat metamorphosed during the Hercynian period of orogenesis, which surfaced in some parts of the Moroccan Mesa and the High and Middle Atlas.
Relief of africa
The relief of Africa is dominated by flat areas. This is due to the fact that almost the entire continent is based on a platform. A feature of the African plains is the predominance of high plains:
- hills,
- plateau,
- plateaus.
This can be explained by the general uplift of the entire territory of Africa in the Cenozoic. The lowlands extend only in narrow strips, mainly along the sea coasts.
Younger sedimentation began here in the pre-Triassic Permian. First, continental layers of colorful shale with gypsum and basalt intrusions were deposited. During the jury period when the Atlas was submerged Mediterranean Sea, on the underwater platforms, powerful positions of limestone and dolomite were created. Greater sea coverage during the Upper Cretaceous, spanning the Mediterranean through the High and Middle Atlas to the Low Atlas. The total sediment thickness is up to 10 km. Sedimentary layers penetrate into veins of gaber, dolerite, and subvolcanic rocks of preclass age.
Largest plains located in the north and western parts mainland. Their surface is very heterogeneous. At the same time, the alternation of uplands with lowlands and plateaus is characteristic of Africa. In places where crystalline basement rocks emerge on the surface, Ahaggar and Tibesti highlands , with a height of more than $ 3000 m. Among the high plateaus (up to $ 1000 m) lies the Congo swampy depression. The Kalahari depression is also surrounded on all sides by plateaus and plateaus.
Then the deposited layers were shriveled during the Oligocene and Miocene period, creating a series of synclinal and anticline. Also participated in the ice season mountain glaciers... Intensive rock modeling is still ongoing. Gravitational instability caused by deep erosion leads to rotation, rock formation and massive landslides. For example, the upper part of the Ifni Valley on the southern side of the Jebel Tubkal massif is completely covered by huge boulders. In addition, Ifni Lake owes its destructive rock material to its origins.
A relatively small area in Africa is occupied by mountains. The highest marks are East african plateau ... On it are the extinct Kenya ($ 5199 m) and Kilimanjaro ($ 5895 m) - highest point Africa.
These volcanic mountains are confined to the East African Rift Valley. Ethiopian highlands with numerous extinct volcanoes it is raised by $ 2000- $ 3000 m. It drops off abruptly in the east and descends with ledges in the west. In the northwestern part of the mainland rise Atlas Mountains (or Atlas Mountains), formed at the junction of two lithospheric plates, in the place where the earth's crust was crumpled into folds. In the south of the mainland, low and flat-topped Cape Mountains ... They look like cups turned upside down (hence the name). Dragon mountains - higher, from the coast they descend in giant ledges to the inland regions of the mainland.
Another ditch in the Ait-Mizan valley has created a large accumulation of rubble on which the village of Imlil and the surrounding settlements stands. The buildings, built with local materials to raise a field without vegetation, almost match the reddish clay and debris.
On the Jebel Toubkal exit road, you can see abundant Jurassic and Cretaceous limestones, dolomites and swamps and Triassic "red" - continental deposits, mainly sandstones, colored iron oxides - with volcanic rocks. There are also abundant rocks of magma - gabra and dolerite.
Minerals
The bowels of Africa are rich in a variety of minerals, their location is closely related to the geological structure of the continent. Deposits of ore minerals are confined to the ancient foundation of the platform. In particular, this applies to gold and ores such as:
Calcareous limestone from the central High Atlas has arisen in shallow lagoons and under marine conditions, mainly on the heights of the seabed. These organisms received up to gigantic... In addition to corals, algae, and to a lesser extent lilies, molluscs and molluscs, rocks are composed of chemically precipitated substances.
An example is the Upper Devonian gray-black limestone with large cross-sections of animal shells completely replaced by calcite. Airplanes, built in horizontally laid layers, collapse in mountain slides. On steeply inclined layers of different elasticity, selective erosion - under the action of secondary streams - creates the so-called gradients and goats. If the layers are slightly tilted, so-called "snakes" are created.
- iron,
- copper,
- zinc,
- pewter,
- chrome.
The largest deposits are concentrated in the south and east of Africa, in places of shallow bedding. There, in particular, are significant deposits gold and copper , according to the amount of their reserves, Africa occupies the first and second places in the world, respectively. The bowels of the continent are rich and uranium ores ... Africa is famous for deposits diamonds - valuable precious stones.
On the way south, slightly behind Erfoud, the landscape changes again. Only the "pistons" that traverse desolate desert plains instead of roads prove the presence of man. We must cross a strip of stone deserts or hammocks to reach the goal of our erg Chebbi wandering dunes. Sand dunes- an exciting creation of nature. To create them, even a tiny obstacle is enough, behind which sand accumulates. Someone who experienced only a weak sandstorm, when brutally flying sand beads painfully tormented the body despite weak clothing, he did not say that all the dunes can move.
Remark 1
They are used not only for the manufacture of expensive and exquisite jewelry, but also as materials, unsurpassed in their hardness. Half of the world's diamonds are mined in Africa.
Their deposits were discovered at southwest coast and in the center of the mainland. Deposits of nonmetallic minerals occur in sedimentary rocks that cover the lowered areas of the platform with a thick cover. These breeds in Africa include:
This migration occurs at a rate of 15-20 m per year. Small regular ripples on the surface of the dunes - windy or aeolian - are similar to underwater sobbing at the intersection of two different dense and changing velocities of the moving medium in this case of air and sand.
They also move in the direction of the wind. They are the result of the appearance of aqueous solutions that precipitate certain substances, most often iron and manganese oxides. We see columns of water splashing vertically. These are artesian wells, one of the few water sources in dry areas. Water trapped in a permeable horizon between two impermeable positions acts by hydrostatic pressure on its overburden surface; if its level is below the free level in the area of penetration, then the excess pressure created by the difference between the two levels leads to its spontaneous exit.
- coal,
- natural gas,
- oil,
- phosphorites and others.
There are huge deposits in the north of the Sahara and on the shelf of the Gulf of Guinea. Developed deposits of phosphorites, widely used in the production of fertilizers, are located in the north of the continent. The sedimentary strata also contain ore fossils that were formed as a result of the weathering of igneous and metamorphic rocks. For example, in the southern and western regions Africa's known deposits iron, copper, manganese ores and gold of sedimentary origin.
In central and southern Morocco, roads are curved with many river gorges and canyons. Picturesque are, for example, the Dades Valley Gorge, the Todry River Canyon and, above all, the Ziz River Canyon, reminiscent of the Grand Canyon in Colorado. They are formed in dry and desert climates by rapidly cutting rivers in the bowels or in areas where rainwater quickly flows into the ground due to the high carrying capacity of the substrate.
In the south, the so-called gypsum rose is an important article of stall sellers; they are concretes of gypsum crystals, spherical, elliptical or irregular, which are formed in sand by crystallization from solutions saturated with calcium sulfate. Sandy grains offer little resistance to crystallization, they are pushed aside, and only a small part is enclosed in crystals. In all parts of the country, polished spherical shapes with irregular stripes of yellow and yellow-brown color are sold, consisting of calcite or aragonite - the so-called onyx marble.
09.11.2015.
Lesson number 18 7 cl.
Lesson topic. Geological structure. East African faults of the earth's crust.
The purpose of the lesson: Formation of students' knowledge about the features of the geological structure and relief of the continent of Africa.
Tasks: to form knowledge about the features of the relief of Africa; antiquity of the mainland; predominance of plateaus;
In the High Atlas, stall counters overflow with samples of ore minerals, crystals or artificially colored quartz in the so-called geodesic spherical crystals inside. There are also agates, as well as azure and malachite. Denudation - an abundance of outcasts, the removal of hidden hard rocks.
Plate tectonics is a tectonic concept that explains all tectonic phenomena by the movement and interaction of lithospheric plates with modern continents. The platform is a large stabilized area of the earth's crust with very weak tectonic and magmatic activity, without continuous folds.
Developing, develop skills for independent and group work.
Equipment: textbooks, workbooks, alases and contour maps.
Lesson type: learning new material.
During the classes
1. Organizing time
2. Updating basic knowledge pupils
Frontal work on teacher issues:
What platform lies at the base of the continent?
Which card will we use?
Determine the age of folding on the map.
Remember what is called relief.
What landforms do you know?
How do they differ in height?
How is the relief depicted on the map?
Africa - part of which ancient continent?
What is a platform?
3. Motivation learning activities
Technique "Attractive target"
The teacher summarizing the students' knowledge notes that Africa is one of the most high continents the world. Why is Africa considered the treasure of humanity?
What are the main features of the relief of the African continent? (since at the base of the continent lies the ancient African-Arabian platform, the relief is dominated by plains, mainly plateaus, with protrusions of the crystalline basement; there are few lowlands; extended and high mountains no, they have already collapsed, only the Atlas Mountains in the northwest stand out, the Cape Mountains in the south and the Drakensberg Mountains in the southeast).
4. Learning new material
Teacher's word
Geological structure. As early as 180 million years ago, Africa was part of the ancient supercontinent Gondwana... When the split of Gondwana took place, African lithospheric plate. At the heart of modern Africa lies part of this slab African-Arabian platform.
Lower part platform – foundation- They are solid crystalline rocks of magmatic and metamorphic origin. They are very ancient in age, because they were formed about 3 billion years ago. On a foundation due to action external forces(weathering, work of the wind, surface and ground waters) formed continental sedimentary deposits, and in the depressions accumulated marine sedimentary deposits. For millions of years, they formed a multi-kilometer sedimentary cover platforms.
The sedimentary cover covers the basement unevenly, since during geological time, the heavy platform underwent slow vertical oscillating movements (ups and downs. shields... Other parts of the platform sank, flooded with the waters of the ancient seas. There, the foundation was overlapped by a thick layer of marine sedimentary deposits, therefore, in these places, platforms were formed slabs... Millions of years later, the ancient Precambrian platform in the northwest and south was "completed" with parts of the ocean floor, the sedimentary rocks of which were winterized in folds, forming folded regions ..
Finally (about 60 million years ago), the entire African-Arabian platform was intensively rising. This was accompanied by giant fractures in the earth's crust. Then the largest system on land was formed East African rifts(rifts ). It stretches for 4,000 km from the Isthmus of Suez under the Red Sea and further overland to the Zambezi River. The rifts are 120 km wide in places. These faults, as if with a knife, cut through the African-Arabian platform. Along them earthquakes make themselves felt, in some places volcanoes are active.
Rift Valley
crust, a system of large faults (faults) and grabens (rifts), developed against the background of the latest uplifts in East Africa. Extends in the meridional direction from the northern edge of the Red Sea to the lower reaches of the river. Zambezi; also includes the graben of the Red Sea with branches (the Gulf of Suez and the Gulf of Aqaba) and the graben of the Gulf of Aden. North of the Gulf of Aqaba h. R. continues through the Dead Sea and the valley of the river. Jordan to the foot of the Taurus Mountains parallel to the Mediterranean coast of the Arabian Peninsula. Within Africa, it consists of 2 branches. The continuation of the Red Sea graben is the Afar graben in Ethiopia and then a strip of grabens passing east of Lake Victoria, past the volcanoes Elgon, Kenya, Kilimanjaro, from the basin of Lake Rudolf to Lake Nyasa. Roughly parallel to this Eastern Rift from the western side of Lake Victoria, through Lakes Albert, Edward, Kivu, Tanganyika, Rukwa to the northern end of Lake Nyasa, the Western Rift can be traced. South of Lake Nyasa V. z. R. follows along the graben of the river valley. Wider to r. Zambezi.
V. z. R. in its present form began to form in the Oligocene, simultaneously with the growth of large uplifts and mountain building in the eastern part of Africa and Arabia. At the same time, the newest faults partially used the directions of more ancient faults, up to the Precambrian. The movements along the faults led to a powerful outbreak of volcanic activity, which peaked in the Neogene and continued until the modern era; all active volcanoes Africa (except Cameroon) are located in this zone. The seismicity of the zone indicates the latest movements along the faults. V. z. R. is part of the Rift world system (See. Rift world system) and bears great similarity to ocean rifts. The common reason for the development of rifts, volcanism and seismicity in the zone is, according to some geologists, the decompaction of the subcrustal matter of the upper mantle due to an increased heat flow from deeper bowels of the Earth; others associate these phenomena with the expansion of the earth's crust (see. Tectonic hypotheses).
Lit .: Dixie F., The Greats African faults, per. from English, M., 1959; Milanovskiy EE, Basic features of the structure and formation of the rift system of East Africa and Arabia, “Bulletin of Moscow State University. Geology ", 1969, v. one.
Rice. The structure of the earth's crust in Africa
Working with the map
1. On which lithospheric plates does Africa lie?
2. In what direction and at what speed is this plate moving?
3. Where are the boundaries of the lithospheric plates in relation to the mainland?
4. What platform is at the heart of Africa? What part of the African lithospheric plate does it occupy?
5. In what parts of Africa does the foundation of the ancient African-Arabian platform come to the surface?
6. What minerals lie in the platform foundation?
7. In what places was the African-Arabian platform completed with folded areas? In what geological period did they form?
8. In what part of Africa is the rift zone?
5. Consolidation of the studied material
Technique "Catch the cartographer's mistake"
The student (teacher) shows and names the mountains, plains, volcanoes of Africa, sometimes deliberately making mistakes. Students express their agreement or disagreement.
- EXERCISE MINUTE -
6. Lesson summary
Pupils take stock of the results on their own, answering the questions: What new things did they learn about Africa in the lesson?
Reception "Calling associations"
Children take turns calling and pronouncing those concepts and names that arose with the word "Africa". After that, without looking at the atlas, they apply the main landforms and minerals to outline map.
7. Homework
Work out the text of the paragraph.
Complete the table.
