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I.Geology B.Plate Tectonics 2.Mid-Ocean Ridge System Discovered from sea floor mapping with SONAR during and after World War IIDiscovered from sea floor.

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Presentation on theme: "I.Geology B.Plate Tectonics 2.Mid-Ocean Ridge System Discovered from sea floor mapping with SONAR during and after World War IIDiscovered from sea floor."— Presentation transcript:

1 I.Geology B.Plate Tectonics 2.Mid-Ocean Ridge System Discovered from sea floor mapping with SONAR during and after World War IIDiscovered from sea floor mapping with SONAR during and after World War II Largest geological feature on EarthLargest geological feature on Earth Ridges displaced in some areas by transform faultsRidges displaced in some areas by transform faults 3.Trenches Conspicuous sea floor featuresConspicuous sea floor features Especially common in the Pacific OceanEspecially common in the Pacific Ocean

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3 Fig. 2.5

4 I.Geology C.Plate Tectonics - Evidence 1.“Ring of Fire” Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenchesGeological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenches

5 Fig. 2.6

6 I.Geology C.Plate Tectonics - Evidence 1.“Ring of Fire” Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenchesGeological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenches 2.Closer to ridges Younger rockYounger rock Thinner covering of sedimentThinner covering of sediment 3.Magnetic anomalies Caused by magnetic field reversalsCaused by magnetic field reversals Symmetrical on either side of ridge axisSymmetrical on either side of ridge axis

7 Fig. 2.7

8 I.Geology D.Plate Tectonics - Mechanism 1.Sea-Floor Spreading Mid-ocean ridges contain rifts where two pieces of crust are moving apart and new oceanic crust is being created (spreading rate ca cm y -1 )Mid-ocean ridges contain rifts where two pieces of crust are moving apart and new oceanic crust is being created (spreading rate ca cm y -1 ) As rift widens, hot mantle material rises through rift, cools and solidifies to form new oceanic crustAs rift widens, hot mantle material rises through rift, cools and solidifies to form new oceanic crust Ridges = spreading centersRidges = spreading centers Theory generated by induction explains observationsTheory generated by induction explains observations Younger rock closer to ridgesYounger rock closer to ridges Thinner sediment closer to ridgesThinner sediment closer to ridges Patterns of magnetic anomaliesPatterns of magnetic anomalies

9 Fig. 2.8

10 I.Geology D.Plate Tectonics - Mechanism 1.Sea-Floor Spreading Lithosphere made up of lithospheric platesLithosphere made up of lithospheric plates Plates may contain continental crust, oceanic crust, or bothPlates may contain continental crust, oceanic crust, or both Plates rest on asthenosphere (plastic upper mantle)Plates rest on asthenosphere (plastic upper mantle) Plate boundaries correspond to locations of mid-ocean ridges and to trenchesPlate boundaries correspond to locations of mid-ocean ridges and to trenches Not all plates completely characterized yetNot all plates completely characterized yet Fig. 2.9

11 I.Geology D.Plate Tectonics - Mechanism 2.Subduction Old crust destroyed when one plate dips below anotherOld crust destroyed when one plate dips below another Oldest oceanic crust ~200 million years oldOldest oceanic crust ~200 million years old Denser plate subducted beneath less dense plateDenser plate subducted beneath less dense plate Locations – oceanic trenches = subduction zonesLocations – oceanic trenches = subduction zones Recycles crust and supports volcanic activityRecycles crust and supports volcanic activity May result from collisions betweenMay result from collisions between Continental plate and oceanic plate (oceanic plate subducted; usually forms volcanoes)Continental plate and oceanic plate (oceanic plate subducted; usually forms volcanoes) Two oceanic plates (denser plate subducted; usually forms island arc)Two oceanic plates (denser plate subducted; usually forms island arc)

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14 I.Geology E.Geological History 1.Continental Drift All continents joined together ~200 myaAll continents joined together ~200 mya Pangaea – “supercontinent”Pangaea – “supercontinent” Panthalassa – single ocean  Pacific OceanPanthalassa – single ocean  Pacific Ocean Tethys Sea – Shallow sea between Eurasia & Africa  Mediterranean SeaTethys Sea – Shallow sea between Eurasia & Africa  Mediterranean Sea Sinus Borealis  Arctic OceanSinus Borealis  Arctic Ocean Laurasia separated from Gondwana ~180 myaLaurasia separated from Gondwana ~180 mya

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20 Global Plate Tectonics Jurassic to Present Day By L.A. Lawver, M.F. Coffin, I.W.D. Dalziel L.M. Gahagan, D.A. Campbell, and R.M. Schmitz  2001, University of Texas Institute for Geophysics February 9, 2001

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44 We wish to thank the PLATES’ sponsors for their support: Conoco, TotalFinaElf, Exxon-Mobil, Norsk Hydro, and Statoil.

45 For more information, contact: Lisa M. Gahagan Institute for Geophysics 4412 Spicewood Springs Rd., Bldg. 600 Austin, TX

46 Earth – Future Drift

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50 Link

51 I.Geology F.Geological Provinces 1.Continental Margins Boundaries between continental and oceanic crustBoundaries between continental and oceanic crust Accumulate sediment deposits from rivers and streamsAccumulate sediment deposits from rivers and streams a.Continental shelf b.Continental slope c.Continental rise 2.Deep-Ocean Basins 3.Mid-Ocean Ridges 4.Hot Spots

52 Fig. 2.17

53 I.Geology F.Geological Provinces 1.Continental Margins a.Continental shelf Shallowest part of continental marginShallowest part of continental margin Underlie ~8% of ocean surfaceUnderlie ~8% of ocean surface Richest, most productive parts of oceanRichest, most productive parts of ocean Some parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyonsSome parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyons

54 Fig California Coastline Monterey Canyon

55 I.Geology F.Geological Provinces 1.Continental Margins a.Continental shelf Shallowest part of continental marginShallowest part of continental margin Underlie ~8% of ocean surfaceUnderlie ~8% of ocean surface Richest, most productive parts of oceanRichest, most productive parts of ocean Some parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyonsSome parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyons Varies in width from 1 km (Pacific coast of S Am) to 750+ km (Arctic coast of Siberia)Varies in width from 1 km (Pacific coast of S Am) to 750+ km (Arctic coast of Siberia) Ends at shelf break, usually at m but up to 400+ m depth.Ends at shelf break, usually at m but up to 400+ m depth.

56 I.Geology F.Geological Provinces 1.Continental Margins b.Continental slope Transition from continent to oceanTransition from continent to ocean Furrowed with submarine canyons in many areasFurrowed with submarine canyons in many areas Canyons channel sediment and debris to deep sea floorCanyons channel sediment and debris to deep sea floor c.Continental rise Accumulated sediment, including deep-sea fansAccumulated sediment, including deep-sea fans May be extensive in areas where large rivers discharge into oceanMay be extensive in areas where large rivers discharge into ocean

57 I.Geology F.Geological Provinces 1.Continental Margins d.Active margins Geologically activeGeologically active Usually subduction or transform faultUsually subduction or transform fault Steep, rocky shorelineSteep, rocky shoreline Narrow continental shelfNarrow continental shelf Steep continental slopeSteep continental slope Usually lack well- developed continental riseUsually lack well- developed continental rise Sediment removed by geological activitySediment removed by geological activity Fig. 2.20

58 I.Geology F.Geological Provinces 1.Continental Margins e.Passive margins Not geologically activeNot geologically active Flat coastal plainFlat coastal plain Wide continental shelfWide continental shelf Gentle continental slopeGentle continental slope Usually well-developed continental riseUsually well-developed continental rise Fig. 2.20

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60 I.Geology F.Geological Provinces 2.Deep-Ocean Basins Mostly between 3000 and 5000 mMostly between 3000 and 5000 m Predominantly abyssal plain

61 I.Geology F.Geological Provinces 2.Deep-Ocean Floor Mostly between 3000 and 5000 mMostly between 3000 and 5000 m Predominantly abyssal plain Seamounts – Undersea mountains Guyots – Flat-topped seamounts Rises – Large table-like features Common in Pacific

62 California Coastline Monterey Canyon Fig. 2.19

63 I.Geology F.Geological Provinces 3.Mid-Ocean Ridges Central region – rift valleyCentral region – rift valley Fractures allow sea water to seep into crustFractures allow sea water to seep into crust

64 Fig. 2.23

65 I.Geology F.Geological Provinces 3.Mid-Ocean Ridges Central region – rift valleyCentral region – rift valley Fractures allow sea water to seep into crustFractures allow sea water to seep into crust Water is heated by rock and rises back to surface of sea floorWater is heated by rock and rises back to surface of sea floor Hot water picks up dissolved minerals (iron, manganese, sulfides)Hot water picks up dissolved minerals (iron, manganese, sulfides) Hot, mineral-rich water contacts cold sea waterHot, mineral-rich water contacts cold sea water Precipitate formsPrecipitate forms Black smokersBlack smokers May be very hot (350 o C or more)May be very hot (350 o C or more)

66 Fig. 2.25


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