Geology

Plate TectonicsMid-Ocean Ridge SystemDiscovered from sea floor mapping with SONAR during and after World War IILargest geological feature on EarthRidges displaced in some areas by transform faultsTrenchesConspicuous sea floor featuresEspecially common in the Pacific Ocean

http://www.ngdc.noaa.gov/mgg/image/global_topo_large.gif

Fig. 2.5

Geology

Plate Tectonics - EvidenceRing of FireGeological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenches

Fig. 2.6

Geology

Plate Tectonics - EvidenceRing of FireGeological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges and with trenchesCloser to ridgesYounger rockThinner covering of sedimentMagnetic anomaliesCaused by magnetic field reversalsSymmetrical on either side of ridge axis

Fig. 2.7

Geology

Plate Tectonics - MechanismSea-Floor SpreadingMid-ocean ridges contain rifts where two pieces of crust are moving apart and new oceanic crust is being created (spreading rate ca. 2-18 cm y-1)As rift widens, hot mantle material rises through rift, cools and solidifies to form new oceanic crustRidges = spreading centersTheory generated by induction explains observationsYounger rock closer to ridgesThinner sediment closer to ridgesPatterns of magnetic anomalies

Fig. 2.8

Geology

Plate Tectonics - MechanismSea-Floor SpreadingLithosphere made up of lithospheric platesPlates may contain continental crust, oceanic crust, or bothPlates rest on asthenosphere (plastic upper mantle)Plate boundaries correspond to locations of mid-ocean ridges and to trenchesNot all plates completely characterized yetFig. 2.9

Geology

Plate Tectonics - MechanismSubductionOld crust destroyed when one plate dips below anotherOldest oceanic crust ~200 million years oldDenser plate subducted beneath less dense plateLocations oceanic trenches = subduction zonesRecycles crust and supports volcanic activityMay result from collisions betweenContinental plate and oceanic plate (oceanic plate subducted; usually forms volcanoes)Two oceanic plates (denser plate subducted; usually forms island arc)

Fig. 2.10

Fig. 2.11

Geology

Geological HistoryContinental DriftAll continents joined together ~200 myaPangaea supercontinentPanthalassa single ocean Pacific OceanTethys Sea Shallow sea between Eurasia & Africa Mediterranean SeaSinus Borealis Arctic OceanLaurasia separated from Gondwana ~180 mya

Fig. 2.14

Fig. 2.14

Fig. 2.14

Fig. 2.14

Fig. 2.14

Global Plate Tectonics

Jurassic to Present DayByL.A. Lawver, M.F. Coffin, I.W.D. DalzielL.M. Gahagan, D.A. Campbell, and R.M. Schmitz2001, University of Texas Institute for GeophysicsFebruary 9, 2001

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

For more information, contact:Lisa M. GahaganInstitute for Geophysics4412 Spicewood Springs Rd., Bldg. 600Austin, TX 78759plates@ig.utexas.edu

Earth Future Drift

Earth Future Drift

Earth Future Drift

Earth Future Drift

Earth Future DriftLink

Geology

Geological ProvincesContinental MarginsBoundaries between continental and oceanic crustAccumulate sediment deposits from rivers and streamsContinental shelfContinental slopeContinental riseDeep-Ocean BasinsMid-Ocean RidgesHot Spots

Fig. 2.17

Geology

Geological ProvincesContinental MarginsContinental shelfShallowest part of continental marginUnderlie ~8% of ocean surfaceRichest, most productive parts of oceanSome parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyons

Fig. 2.19California CoastlineMonterey Canyon

Geology

Geological ProvincesContinental MarginsContinental shelfShallowest part of continental marginUnderlie ~8% of ocean surfaceRichest, most productive parts of oceanSome parts exposed during times of low sea level and eroded by rivers and glaciers now are submarine canyonsVaries in width from 1 km (Pacific coast of S Am) to 750+ km (Arctic coast of Siberia)Ends at shelf break, usually at 120-200 m but up to 400+ m depth.

Geology

Geological ProvincesContinental MarginsContinental slopeTransition from continent to oceanFurrowed with submarine canyons in many areasCanyons channel sediment and debris to deep sea floorContinental riseAccumulated sediment, including deep-sea fansMay be extensive in areas where large rivers discharge into ocean

Geology

Geological ProvincesContinental MarginsActive marginsGeologically activeUsually subduction or transform faultSteep, rocky shorelineNarrow continental shelfSteep continental slopeUsually lack well-developed continental riseSediment removed by geological activityFig. 2.20

Geology

Geological ProvincesContinental MarginsPassive marginsNot geologically activeFlat coastal plainWide continental shelfGentle continental slopeUsually well-developed continental riseFig. 2.20

Fig. 2.20

Geology

Geological ProvincesDeep-Ocean BasinsMostly between 3000 and 5000 mPredominantly abyssal plain

Geology

Geological ProvincesDeep-Ocean FloorMostly between 3000 and 5000 mPredominantly abyssal plainSeamounts Undersea mountainsGuyots Flat-topped seamountsRises Large table-like featuresCommon in Pacific

California CoastlineMonterey CanyonFig. 2.19

Geology

Geological ProvincesMid-Ocean RidgesCentral region rift valleyFractures allow sea water to seep into crust

Fig. 2.23

Geology

Geological ProvincesMid-Ocean RidgesCentral region rift valleyFractures allow sea water to seep into crustWater is heated by rock and rises back to surface of sea floorHot water picks up dissolved minerals (iron, manganese, sulfides)Hot, mineral-rich water contacts cold sea waterPrecipitate formsBlack smokersMay be very hot (350 oC or more)

Fig. 2.25