1、The Structure of the Earth and Plate TectonicsStructure of the Earth The Earth is made up of 3 main layers: Core Mantle CrustInner coreOuter coreMantleCrustThe Crust This is where we live! The Earths crust is made of:Continental Crust- thick (10-70km)- buoyant (less dense than oceanic crust) - mostl
2、y oldOceanic Crust- thin (7 km)- dense (sinks under continental crust)- youngHow do we know what the Earth is made of? Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy Acquisition: land, air, sea and satellite Geological surveys: fieldwork, boreholes, minesWhat is Plate Tectonic
3、s?If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.Plate Tectonics The Earths crust is divided into 12 major plates which are moved in various directions. This plate motion causes them to collide, pull apart, or scrape against e
4、ach other. Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.World PlatesWhat are tectonic plates made of? Plates are made of rigid lithosphere.The lithosph
5、ere is made up of the crust and the upper part of the mantle.What lies beneath the tectonic plates? Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.Plate Movement “Plates” of lithosphere are moved around by the underlying hot mantle convection cellsPractical Exercise
6、1Supercontinents!What happens at tectonic plate boundaries? Divergent Convergent TransformThree types of plate boundary Spreading ridges As plates move apart new material is erupted to fill the gapDivergent BoundariesAge of Oceanic CrustCourtesy of www.ngdc.noaa.gov Iceland has a divergent plate bou
7、ndary running through its middleIceland: An example of continental rifting There are three styles of convergent plate boundaries Continent-continent collision Continent-oceanic crust collision Ocean-ocean collisionConvergent Boundaries Forms mountains, e.g. European Alps, HimalayasContinent-Continen
8、t CollisionHimalayas Called SUBDUCTIONContinent-Oceanic Crust Collision Oceanic lithosphere subducts underneath the continental lithosphere Oceanic lithosphere heats and dehydrates as it subsides The melt rises forming volcanism E.g. The AndesSubduction When two oceanic plates collide, one runs over
9、 the other which causes it to sink into the mantle forming a subduction zone. The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep!Ocean-Ocean Pla
10、te Collision Where plates slide past each otherTransform BoundariesAbove: View of the San Andreas transform faultPractical Exercise 2Where will the UK be in:1,000 years?1,000,000 years?1,000,000,000 years?whats the connection?Volcanoes and Plate TectonicsVolcanism is mostly focused at plate marginsP
11、acific Ring of Fire- Subduction - Rifting - HotspotsVolcanoes are formed by:Pacific Ring of FireHotspot volcanoes Hot mantle plumes breaching the surface in the middle of a tectonic plateWhat are Hotspot Volcanoes?Photo: Tom Pfeiffer / The Hawaiian island chain are examples of hotspot volcanoes.The
12、tectonic plate moves over a fixed hotspot forming a chain of volcanoes.The volcanoes get younger from one end to the other.whats the connection?Earthquakes and Plate Tectonics As with volcanoes, earthquakes are not randomly distributed over the globe At the boundaries between plates, friction causes
13、 them to stick together. When built up energy causes them to break, earthquakes occur.Figure showing the distribution of earthquakes around the globeWhere do earthquakes form? Figure showing the tectonic setting of earthquakesPlate Tectonics Summary The Earth is made up of 3 main layers (core, mantle, crust) On the surface of the Earth are tectonic plates that slowly move around the globe Plates are made of crust and upper mantle (lithosphere) There are 2 types of plate There are 3 types of plate boundaries Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates
