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PLATE TECTONICS

PLATE TECTONICS. UPPS! MY CONTINENT IS MOVING…. Earth’s internal layers. Compositional layers. Crust : dense rocks , rich in silicon and alumninium . (Granite in Continental crust , basalt in oceanic crust ) Mantle : denser rocks , peridotite and magnesium Core : iron.

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PLATE TECTONICS

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  1. PLATE TECTONICS UPPS! MY CONTINENT IS MOVING…

  2. Earth’sinternallayers

  3. Compositionallayers • Crust: dense rocks, rich in silicon and alumninium. (Granite in Continental crust, basalt in oceaniccrust) • Mantle: denserrocks, peridotite and magnesium • Core: iron

  4. Physicallayers • Lithosphere: rigidsurface • Asthenosphere: ductile and partiallymolten • Lowermantle: solidbut flexible and ductile • Core: moltenouterlayer and a solidinnerpart.

  5. Seismicdiscontinuities • There are twotypes of internalseismicwaves: • Primarywaves (P): thefastest and thefirsttoreachthesurface. Theymovethroughsolid and liquids. • Secondarywaves (S): slower and movetrhroughsolids. Seismometers record vibrationscausedbyseismicwaves. Changes in thewavesspeedindicate a change in thecomposition of the material they’re travelling through.

  6. Refraction of seismicwaves

  7. Discontinuityboundaries • TheMohorovicicdiscontinuity: (MOHO) Marks theboundarybetweencrust and mantle. • The Gutenberg discontinuity: S-wavescan’ttravelanyfurther and desappear, but P-waves are strongly refractes and slowdown. Limitbetweenmantle and outercore.

  8. Seismicvelocity

  9. Themovement of continents • XIX and XX centuries: controversyaboutthe geological hisotory of continents. • Alfred Wegener(Germanmeteorologist) collectedevidencestoexplainthesimilarities in theshape of African and South American coastlines. Theory of Continental drift (1912).

  10. Continental DriftTheory • Continents, made of lightercrust, slidover a continuousthickerlayer. Thislayermade up theoceanfloor and continuedunderthecontinents. • Around 200 m y ago, allthecontinentswerejoinedforminPangea (thewholeEarth)

  11. Evidencestoprovetheexistence of Pangea • Paleolithicevidence: identicalfossils of land-basedorganisms. • Geological evidence: continentsfitalongtheircoastlines and continental shelves. • Paleoclimaticevidence: glacial morraines in thecontinentsthatweresituated in thesouth pole of Pangea.

  12. TheTheory of PlateTectonics • Seismic and volcanicbelts: earthquakeswerelocated in narrowbandswhichalsocontainareaswherevolcanoes are concentrated. • The geological activitycausedbytheEarth’sinternalenergyisconcentrated in trenches, mid-oceanridges and youngmountainranges.

  13. Distribution of Earthquakes

  14. Lithosphericplates • A lithosphericplateis a fragment of thelithosphere. Eachplateisseparatedby a seismicbelt. • Classificationcriteria: • Size: 8 large and manymicroplates • Type of lithosphere: oceanic, continental, and mixedplates. • Dependingontheboundariesthere are varyinglevels of risk of Earthquakesorvolcanoeseruptionsoccurring.

  15. Types of plateboundaries(edges): • Divergentboundaries (constructive): zoneswheretwoplatesmoveaparttocreate a new oceaniclithosphere. Ex: Mid-atlanticridge • http://www.kidsgeo.com/geology-for-kids/0045-divergent-boundaries.php

  16. Convergentboundaries (destructive): zoneswheretwocontinentscollideorsubductionzoneswheretheoceanfloorgoesintothemantle. The Mariana Trench in thePacificOcean. • http://www.kidsgeo.com/geology-for-kids/0046-convergent-boundaries.php

  17. Transformboundaries (passive): these are fractures , or transforma faultswheretwoplatesslidehorizontallyaganisteachother. (Seismicactivity)

  18. Allboundaries

  19. Allplates

  20. http://www.kidsgeo.com/geology-for-kids/0044-plate-boundaries.phphttp://www.kidsgeo.com/geology-for-kids/0044-plate-boundaries.php

  21. Subductionzones • Itoccurs at trencheswhenanocanplatecollideswithanotherplate and isforceddownintothemantle. Types: • Subductionunderthe continental lithosphere: anandeanmontainrangeisformedor more material isaddedtothelandmass. West coast of SourhnAmerica • Subductionundertheoceaniclithosphere: itcreatesanarc of volcanicislandsontheupperplate. Pacificislands

  22. Convergent

  23. Theoceanfloor • 1960:oceanographic surveyships: Oceanfloormappingusingsonar • Details of theoceanfloor: • Mid-oceanridge: it has a central channelknown as a rift, crossedby perpendicular fractures calledtransformfaults. • Trenches: narrow and deepchannelsfoundnexttocontinentsorvolcanicislandarcs.

  24. Theoceanfloorismade up of volcanicrockscovered in marine sediments. Theserocks are veryyoung, lessthan 180 million • years. • http://video.nationalgeographic.com/video/news/environment-news/us-ocean-floor-mapping-vin/

  25. The Wilson Cycle • John Tuzo Wilson (1903-93) suggestedthattherehavebeentwocyclicalprocesses of rifting and reuniting of supercontinentsduringEarths’shistory. • Continental rifting • Extension of theoceanbasin • Closing of theoceanbasin • Continental collision

  26. Theevolution of platetectonics • Original orclassicexplanation: • Convectioncurrentin theasthenosphere cause tectonicplatemovement. Currents are generatedbydifferences in density (temperatures9 • Lithospherefloatsontheasthenosphere • Wherehotcurrentsascend and separate, ridges are formed. • Wherecurrentscool and descend, trenches are formed.

  27. Evolution of platetectonics • Currentexplanation: • Theasthenosphereisnottheonly place wherconvectioncurrentshavebeendetected: • belowsubductionzones • Hot spots of mantle(occasionally) In additiontoconvectioncurrents, there are twoforceswhich cause movement in thelithosphere: • Force of gravitypullsdownbothsides of elelvatedringes • Once a plateisbeingsubducted, theweight of sinkingplatespullsitdownlower.

  28. Theoceanicfloor….magma flowingout of theridge

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