§ 3. The structure of the crust and relief (textbook)

§ 3. Structure of the Earth crust and relief


1. Remember what the earth's crust.

2. What is different from the mainland oceanic crust?

3. What distinguish landforms?


STRUCTURE The crust. As is well known, crust - Is the top layer of our planet. Together with top of the mantle it forms lithosphere - Solid shell of the Earth. There are two main types of crust. Continental crustconsists of three layers (sedimentary, granite, basalt). Oceanic crust formed only two layers (sedimentary and basaltic) and very thin. This type of crust is just under zapadynamy oceans.

Scientists believe the planet first formed oceanic crust type. Under the influence of processes occurring in the depths Earth, it potovschuvalasya and on its surface formed fold - mountain area. Over billions of years of Earth's crust has been subjected to lasting change: rozlamuvalasya on huge chunks, prohynalasya cavity, curved around the corner, not yet acquired a modern look.


Fig. Structure of the Earth crust


MOVEMENTS lithospheric particleboards. According to the theory of movement of lithospheric plates based on the hypothesis of drifting continents, Earth's crust along with part upper mantle is a solid surface of our planet. It is broken by deep breaks for huge blocks - lithospheric plates. Most plates include both the mainland and oceanic earth measles. Their thickness of 60 - 100 km.

Lithospheric plates can move around slowly viscous mantle surface (Asthenosphere), like giant ice surface water. The speed of their movement seems meager - a few centimeters a year. However, this movement going on for hundreds of millions of years ago at a time slab moved thousands of kilometers. Thus, modern accommodation and continents oceans - the result of a long horizontal movement of lithospheric plates. These movements also lead to the fact that at the interface between slabs in some places is their impact, while others - rozsuvannya.

Because of collisiontwo lithospheric plates with their mainland crust edges with all piled in sedimentary rocks zmynayutsya fold, creating mountains ranges. If the converging plates, one of the ocean, and the second to the mainland bark, the first and sags like dives under the mainland. This upraised edge of continental crust zmynayetsya in folds, forming the mountains, along coasts have a chain of islands and deep troughs.

At rozsuvanni lithospheric plates on them within the cracks. This happens mostly on the ocean with a thin crust - in Rift Valley - Longitudinal crevices (Width of several tens of kilometers) that separate Mid-ocean ridges - Huge underwater mountain building. Cracks on the surface of molten magma rises bottom. In its cooling magmatic rocks occur strip young crust. She gradually proliferation in both sides of the deep fault that her father, increasing edges of lithospheric plates. Consequently Oceanic bed expands. At the bottom Ocean is like a giant conveyor belt that moves a lot with young bark from their place of origin to the ocean surrounding hinterland. The speed of their movement small, and way long. Therefore, these sites reach the coast in 15 - 20 million years. Having gone this way, they fall into deep troughs and diving on the mainland, immersed in mantle from which they formed in the central parts of the Mid-ocean ridges.

SUSTAINABLE And movement areas of the earth's crust. Movement of lithospheric plates indicate that at Earth surface is relatively steady and moving plot.

Relatively stable areas of the earth cortex is called platforms. It is the oldest age-aligned plot lithospheric plates. They underlie the continents and ocean trenches. Platforms have a two-layer structure. Lower tier - the foundation formed crystalline magmatic and metamorphic rocks. Upper - sedimentary cover, bedding, that seems to cover the top cover foundation. Sometimes the hard crystalline rocks are the foundation from under unconsolidated sediment cover on the surface of the platform. Such areas are called shields. Land cover is closed is called - plates (Not to be confused with lithospere plates). Зand geological age wasozriznyayut old and young platform. Ancient Platforms formed in ancient geological times - in Archean and Proterozoic era, ie Precambrian. Age of base of 1.5 - 4 billion years. Foundation young Platforms only formed 0.5 billion years ago.

Between relatively stable areas of the earth's crust placed unstable areas - moving Zones.They coincide with places faults on land and in oceans (in Mid-oceanic ridges and deep gutters). In these  narrow, but extended thousands of kilometers areas crowded volcanoes and earthquakes often occur. Therefore they are called seismic belts.

ACCOMMODATION Topography. The relief is closely related to the structure the crust. The modern look of its highest form the landforms - performances of continents and ocean basin, mountains and vast plains. They formed as a result of movements lithospheric plates. In placing the relief forms on the surface Earth is a certain regularity.

Speeches continents meet crust mainland type, and ocean trenches - dissemination of oceanic crust. Great Plains placed on the old platforms. Of of the platform on which piece is plain depends on its height: on billboards often lying hills and plateaus, on the stove - lowland.

Mountains  land and Mid-oceanic ridges and deep troughs on the ocean floor are located in mobile zones on the boundaries of lithospheric plates. On dry land, when confronted lithospheric plates at their edges breed zmynayutsya in folds - formed folding region. This emerging youth folded mountains. Gradually, over millions of years, they destroyed. Subsequent movements of the earth's crust breaks break them into separate blocks. For these faults are vertical displacement: if one area rises relatively nearby, they formed HorstIf omitted - graben. It formed fold-hat mount.

CHANGE Relief. The main reason for diversity relief is the interaction of internal and external forces acting simultaneously.

The internal forces are mainly created in large form relief. External forces are (weathering, water working fluid, wind, underground waters, glaciers, sea surf) destroy rocks and carry debris from some areas of the earth's surface to the other, where their deposition and accumulation. Changing the terrain of the Earth occurs continuously. Changing contours of the mountains, their height, aligned hills filled decrease. Even though very slowly changing shape of continents.

The relief of the planet was formed long time. This horotvorennya periods alternated with periods of less active movements of the earth crust when ridges destroyed by external processes and transformed into Plain.

AS READ CARD "Earth crust. In topic maps "Structure crust displays the location of lithospheric plates and their direction and speed movement. On the plates are highlighted platform and folding area. They better studied and more reliably shown on land. As seen from the map, the core of modern continents most ancient form Precambrian platform. Their frame platform and youth field folding that formed in the coming era. Often on the map "structure of the Earth cortex " provides a special scale - geochronological tableThat displays snippets of geological time (geological era periods), which corresponds to a certain stage of crust (age horotvorennya).

The map on the bottom of the seas and oceans marked oceanic platform seredynnookeanichni ridges, deep grooves, fracture zones. Hatching and badges marked zone earthquakes and volcanoes. In mistseznahodzhennya deposits of different origin (Sedimentary, magmatic, metamorphic) minerals indicate standard icons.


Fig. Geochronological table


Working with map

1.     Name and show the large lithospheric plates. What type of crust they formed?

2.     Determine the direction and moved South American African, Eurasian and Indo-Australian plate.

3.     Determine which lithospheric plates and move into areas with the greatest speed.

4.     Where are the boundaries of lithospheric plates? What are the processes and phenomena have their limits? Explain why within the Pacific Ring of Fire focuses 80% modern volcanoes.

5.     Name the Atlantic islands, which lie on the boundaries of lithospheric plates. What are the islands of the ocean beyond?

6.     Give examples of neighborhood deep trenches and island arcs. What natural processes and phenomena occur near them?

7.     What landforms occur on the boundaries of lithospheric plates on the earth? Point specific examples.

8.     Name the ancient (Precambrian) platform.

9.     Areas of folding periods which are on the Eurasian Plate?

FAQ task

1. What crust mainland type different from oceanic crust type?

2. What are the implications of convergence and rozsuvannya lithospheric plates?

3. What structure have a platform? What distinguished platform with age? Name, using the map "structure of the Earth cortex, the most ancient and young platforms.

4. Decide on a map where located seredynnookeanichni ridges, chains of islands and deep troughs.

5.     What are the patterns in placing forms of relief?