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Plate Tectonics EARTH; once upon a time How did it form to the current day earth? http://www.classzone.com/books/earth_scien ce/terc/content/visualizations/es0806/es0806 page01.cfm?chapter_no=visualization Tectonics Plates • Earth’s crust is now broken to several pieces called crustal or tectonic plates • Each plate has an average thickness of 100km and is composed of both continental and oceanic crust • Plate movement results in various landform appearance Tectonics Plates • 9 major plates have been identified: Eurasian plate Philippine plate Indo-Australian plate Pacific plate North American plate African plate South American plate Nazca plate Antarctic plate Causes of Plate Movements • Convection currents in the athenosphere • Currents circulate near the base of the lithosphere, cause drag on the bottom of the plates, causing them to move over the surface of the Earth. http://www.classzone.com/books/earth_science/terc/content/visualizations/es0805/es0 805page01.cfm?chapter_no=visualization Plate movements and boundaries • As the plates move, they interact with each other at their boundaries. • 3 types of boundaries: Divergent Plate Boundaries Convergent Plate Boundaries Transform Fault Boundaries Plate movements and boundaries Divergent Plate Boundaries Plate movements and boundaries Convergent Plate Boundaries Plate movements and boundaries Transform Fault Boundaries Divergent Plate Boundaries • Zones of Tension • Occurs mostly beneath oceans, few occur within continents • Convection currents diverge (moving apart), the plates are pulled apart • Magma from mantle wells up to fill gap between separating plates. Divergent Plate Boundaries • Cooling and solidification of magma on earth’s surface • Constructive margins formed, where new sea floor (ocean crust )is generated. • New sea floor appears as series of ridges • Sea floor spreading occurs – As plate pulls apart again and new cracks appear, more magma rises to fill gaps creating more sea floor Divergent Plate Boundaries • Rocks found further away from ridge proves that new sea floor is created continuously • Example of divergent plate boundary : Mid-Atlantic Ridge, East African Rift Valley OLDER ROCKS YOUNGER ROCKS OLDER ROCKS RIDGES MAGMA http://whs.moodledo.co.uk/file.php/1365/EarthSystems/Earth%20Systems/Rift%20Valleys%20t o%20Oceans.swf Convergent Plate Boundaries • Zones of Compression • Convection currents converge (coming together), the plates come together • Three types of convergent boundaries Oceanic and Continental plate collide Oceanic and Oceanic plates converge Continental and Continental plates collide OceanicContinental • Known as destructive margins • Continental plate which is less dense will ride over oceanic plate • Oceanic plate Subducts (forced downwards the mantle), forming a deep elongated trough (ocean trench) • Volcanoes form in subduction zone • As oceanic plates sink deeper, it gradually melts and becomes magma http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0 804page01.cfm?chapter_no=visualization OceanicContinental http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0 804page01.cfm?chapter_no=visualization Oceanic-OCEANIC • Less dense oceanic plate ride over more dense oceanic plate • More dense oceanic plate subducts, formation of ocean trench • Magma is force through overriding oceanic plate, forming a chain of volcanic islands • Example: line of islands running from the Aleutians, Japan and down through Philippines Oceanic-OCEANIC ContinentalContinental • Collision results in massive land form • No Subduction • Fold Mountain Range tend to form • Example: the Himalayan Fold Mountain Range ContinentalContinental Transform fault boundaries • Also known as conservative margins • Two plates slide past each other • Fault-line created Continental Plate or Oceanic Plate Continental Plate Fault-line Transform fault boundaries • Example of a transform fault boundary is the San Andreas Fault http://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0 804page01.cfm?chapter_no=visualization Results of Plate Movements • Folding and Faulting • Earthquakes • Volcanoes Folding • When 2 plates collide, the rock strata (layers) will bend and warp as they are compressed • Features of folding: Synclines (downfold) and anticlines (upfold) ANTICLINE SYNCLINE Folding • Place where rock strata band over is called hinge line • The rock strata on either sides of the hinge is called limbs HINGE LINE LIMBS LIMBS Folding • Types of fold : • Symmetrical fold – both limbs of equal gradient • Assymmetrical fold- one limb steeper than the other • Recumbent fold- Limbs are nearly parallel • Overthrust old- One limb pushed forward so forcefully that the rocks may fracture, and it overrides the other limb. When the overriding limb becomes detached from the main fold, it is called a nappe Folding SYMMETRICAL ASYMMETRICAL NAPPE RECUMBENT Folding • Large scale folding will lead to formation of Fold Mountains • Examples of fold mountains: The Himalayas The Andes The Zagros of Iran http://www.classzone.com/books/earth_science/terc/content/visualizations/es110 5/es1105page01.cfm?chapter_no=visualization Faulting • Displaces rocks along a crack or fault line • Occurs in 3 ways: • Normal fault • Reverse fault • Tear fault • Can give rise to block mountains and rift valleys Normal fault • When rock strata are under tension caused by forces acting in opposite directions • Tension causes the rock strata to stretch and crack, developing a normal fault • One block of land then moves down (downthrown block) to form an escarpment • Example: The Tenton Mountain in Wyoming USA NORMAL FAULTS Reverse fault • When rock strata are compressed • Forces pushing towards each other causes the rock strata to fold, giving rise to reverse fault • One block of land moves up (upthrown block) against the direction of the fault, creating an overhanging scarp • The overhanging scarp collapses due to gravity, weathering and erosion, and produce a gentler slope • Example: Sierra Nevada Mountains of California RESULT FAULTS Tear fault • Also known as wrench fault or strike-slip fault • When plates slip past each other horizontally • Tensional or compressional forces act on the rock strata giving rise to tear faults • Big tear faults are known as transcurrent faults • Example: San Andreas Fault in the United States TEAR FAULT Block Mountains • Block raised between 2 parallel fault lines is called a block mountain • If surface is horizontal, it is termed as a horst • if block is tilted, it is termed tilt block • Examples of faulted blocks: • Hawkes bay in New Zealand HORST Rift valleys • Also known as a graben • Formation can be due to: land between two parallel lines sink land on either side of the two parallel lines are unpthrown above the central block of land two plates pull apart • Example: The East African Rift Valley The Red Sea GRABEN http://www.iris.washington.edu/gifs/animations/faults.htm http://www.classzone.com/books/earth_science/terc/content/visualizations/es11 03/es1103page01.cfm?chapter_no=visualization Earthquakes • Vibrations in earth’s crust caused by sudden release of energy • Energy released in the form of seismic waves and that radiate out from the epicentre • Point below the epicentre is called the point of origin where the earthquake originated from http://www.pbs.org/wnet/savageearth/animations/earthquakes/index.html Earthquakes • Two types of seismic waves: • P- waves (Compression waves) alternately compress and release rocks in the direction the waves are moving • S- waves (Shear waves) move rocks perpendicularly to the direction the waves are moving Earthquakes http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es10 02page01.cfm?chapter_no=visualization Earthquakes • Major earthquake zones: • Pacific Ring of Fire -Along the edge of the Pacific Ocean • Trans-Eurasian Belt –Where the Indo-Australian Plate and African Plate meet the Eurasian Plate Earthquakes http://www.classzone.com/books/earth_science/terc/content/visualizations/es1005/es1 005page01.cfm?chapter_no=visualization http://www.classicalarchives.com/eq/ EFFECTS OF Earthquakes • Displacement of earth’s crust • When earthquakes occur in the ocean floor: Tsunamis (huge tidal waves) • Devastation of cities and loss of lives VOLCANOES volcanoes • Found along plate boundaries or hotspots • Can be found on land or under water • Volcanoes on land : often form flat cones and the expulsions build up over the years. • Volcanoes under water: often form rather steep pillars and in due time break the ocean surface in new islands. volcanoes • Vulcanicity: when magma is forced towards earth’s surface from within the earth • Hotspot volcanoes: where the location has vulcanism for a long period of time • Example of hotspot volcano: Java Island in Indonesia http://www.classzone.com/books/earth_science/terc/content/visualizations/es0904/es0904pag e01.cfm?chapter_no=visualization volcanoes • Most volcanoes on the land are formed at destructive plate margins: • Oceanic crust melt, reduced density force the newly formed magma to rise. • As magma rises it rises up through weak areas in the continental crust, eventually erupting as one or more volcanoes. volcanoes • For example, Mount St. Helens is found inland from the margin between the oceanic Juan de Fuca Plate and the continental North American Plate. volcanoes http://www.classzone.com/books/earth_science/terc/content/visualizations/es0902/es0902pag e01.cfm?chapter_no=visualization References. • • • • • • • • • • • • • • • • • • • • • • • • • • • • http://www.lostrivers.ca/points/pangaea.gif http://www.cotf.edu/ete/images/modules/msese/earthsysflr/EFPlateP2.gif http://www.oera.net/How2/PlanetTexs/EarthMap_2500x1250.jpg http://www2.jpl.nasa.gov/galileo/wedges/images/plat.gif http://stloe.most.go.th/html/lo_index/LOcanada4/403/images/4_1.jpg http://lacreekfreak.files.wordpress.com/2008/11/wsci_03_img0412-san-andreas-fault1.jpg http://www.yosemite.ca.us/library/geologic_story_of_yosemite/images/28.jpg http://geomaps.wr.usgs.gov/parks/pltec/ocnvsocn289x151.gif http://www.adventure-india-tour.com/about-himalayas/gifs/himalayan-mountain-ranges.jpg http://geomaps.wr.usgs.gov/parks/pltec/converge.html http://dl.coastline.edu/classes/telecourses/geology100/IntroLecture_files/image005.jpg http://depts.washington.edu/explore/images/maps/250px-Pangaea_continents.png http://www.sedl.org/scimath/pasopartners/dinosaurs/continent2.gif http://2.bp.blogspot.com/_osP51C3atIY/Rf7Z34zK7PI/AAAAAAAAAr4/F2WdWu92P0g/s200/oceanic-subd-ridge.png http://www.emporia.edu/earthsci/amber/students/grunz/antsyn.gif http://www.whoi.edu/cms/images/s-p_waves_73570.jpg http://i243.photobucket.com/albums/ff24/terryhallinan/800px-Pacific_Ring_of_Fire-1-1.png http://www.enchantedlearning.com/subjects/volcano/gifs/ringoffirecolor.GIF http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/study/Images/ReverseFault.gif http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/study/Images/HorstGraben_2.gif http://www.geocities.com/yingzyingz/faulttear.gif http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/study/Images/NormalFault.gif http://www.tinynet.com/faultimages/graben.gif http://www.3mfuture.com/images/tsunami_wave_coming_now_too_late.jpg http://depts.washington.edu/qrc/mht1.jpg http://www.pacificislandtravel.com/nature_gallery/volcanoes2.gif http://www.tolkienforums.com/Mount_Doom.jpg http://www.malapascua.de/Volcanoe-Map/Mayon__Philippines/Vulkan_MAYON-3/Mayon_Volcano_Eruption_by_Night.jpg The End.
