Geology Plate Tectonics Mid-Ocean Ridge System

I.I. GeologyGeology

B.B. Plate TectonicsPlate Tectonics2.2. Mid-Ocean Ridge SystemMid-Ocean Ridge System

• Discovered from sea floor mapping with SONAR Discovered from sea floor mapping with SONAR during and after World War IIduring and after World War II

• Largest geological feature on EarthLargest geological feature on Earth• Ridges displaced in some areas by Ridges displaced in some areas by transform transform

faultsfaults3.3. TrenchesTrenches

• Conspicuous sea floor featuresConspicuous sea floor features• Especially common in the Pacific OceanEspecially common in the Pacific Ocean

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

Fig. 2.5

I.I. GeologyGeology

C.C. Plate Tectonics - EvidencePlate Tectonics - Evidence1.1. ““Ring of Fire”Ring of Fire”

• Geological activity (e.g. earthquakes, Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges volcanoes) associated with mid-ocean ridges and with trenchesand with trenches

Fig. 2.6

I.I. GeologyGeology

C.C. Plate Tectonics - EvidencePlate Tectonics - Evidence1.1. ““Ring of Fire”Ring of Fire”

• Geological activity (e.g. earthquakes, Geological activity (e.g. earthquakes, volcanoes) associated with mid-ocean ridges volcanoes) associated with mid-ocean ridges and with trenchesand with trenches

2.2. Closer to ridgesCloser to ridges• Younger rockYounger rock• Thinner covering of sedimentThinner covering of sediment

3.3. Magnetic anomaliesMagnetic anomalies• Caused by magnetic field reversalsCaused by magnetic field reversals• Symmetrical on either side of ridge axisSymmetrical on either side of ridge axis

Fig. 2.7

I.I. GeologyGeology

D.D. Plate Tectonics - MechanismPlate Tectonics - Mechanism1.1. Sea-Floor SpreadingSea-Floor Spreading

• Mid-ocean ridges contain Mid-ocean ridges contain riftsrifts where two pieces where two pieces of crust are moving apart and new oceanic crust of crust are moving apart and new oceanic crust is being created (spreading rate ca. 2-18 cm yis being created (spreading rate ca. 2-18 cm y-1-1))

• As rift widens, hot mantle material rises through As rift widens, hot mantle material rises through rift, cools and solidifies to form new oceanic crustrift, cools and solidifies to form new oceanic crust

• Ridges = Ridges = spreading centersspreading centers• Theory generated by induction explains Theory generated by induction explains

observationsobservations• 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

Fig. 2.8

I.I. GeologyGeology

D.D. Plate Tectonics - MechanismPlate Tectonics - Mechanism1.1. Sea-Floor SpreadingSea-Floor Spreading

• LithosphereLithosphere made up of made up of lithospheric plateslithospheric plates• Plates may contain continental crust, oceanic Plates may contain continental crust, oceanic

crust, or bothcrust, or both• Plates rest on Plates rest on asthenosphereasthenosphere (plastic upper (plastic upper

mantle)mantle)• Plate boundaries correspond to locations of Plate boundaries correspond to locations of

mid-ocean ridges and to trenchesmid-ocean ridges and to trenches• Not all plates completely characterized yetNot all plates completely characterized yet

Fig. 2.9

I.I. GeologyGeology

D.D. Plate Tectonics - MechanismPlate Tectonics - Mechanism2.2. SubductionSubduction

• Old crust destroyed when one plate dips below Old crust destroyed when one plate dips below anotheranother

• 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 = Locations – oceanic trenches = subduction zonessubduction 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 Continental plate and oceanic plate (oceanic plate subducted; usually forms volcanoes)plate subducted; usually forms volcanoes)

• Two oceanic plates (denser plate subducted; Two oceanic plates (denser plate subducted; usually forms island arc)usually forms island arc)

Fig. 2.10

Fig. 2.11

I.I. GeologyGeology

E.E. Geological HistoryGeological History1.1. Continental DriftContinental Drift

• All continents joined together ~200 myaAll continents joined together ~200 mya• Pangaea – “supercontinent”Pangaea – “supercontinent”• Panthalassa – single ocean Panthalassa – single ocean Pacific Ocean Pacific Ocean• Tethys Sea – Shallow sea between Eurasia & Tethys Sea – Shallow sea between Eurasia &

Africa Africa Mediterranean Sea Mediterranean Sea• Sinus Borealis Sinus Borealis Arctic Ocean Arctic Ocean

• Laurasia separated from Gondwana ~180 myaLaurasia separated from Gondwana ~180 mya

Fig. 2.14

Fig. 2.14

Fig. 2.14

Fig. 2.14

Fig. 2.14

Global Plate TectonicsGlobal Plate Tectonics

Jurassic to Present DayJurassic to Present Day

ByByL.A. Lawver, M.F. Coffin, I.W.D. DalzielL.A. Lawver, M.F. Coffin, I.W.D. DalzielL.M. Gahagan, D.A. Campbell, and R.M. L.M. Gahagan, D.A. Campbell, and R.M. SchmitzSchmitz2001, University of Texas Institute for 2001, University of Texas Institute for GeophysicsGeophysicsFebruary 9, 2001February 9, 2001

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

For more information, For more information, contact:contact:Lisa M. GahaganLisa M. GahaganInstitute for GeophysicsInstitute for Geophysics4412 Spicewood Springs Rd., 4412 Spicewood Springs Rd., Bldg. 600Bldg. 600Austin, TX 78759Austin, TX 78759plates@ig.utexas.eduplates@ig.utexas.edu

Earth – Future Drift

Earth – Future Drift

Earth – Future Drift

Earth – Future Drift

Earth – Future Drift Link

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces1.1. Continental MarginsContinental Margins

• Boundaries between continental and oceanic Boundaries between continental and oceanic crustcrust

• Accumulate sediment deposits from rivers and Accumulate sediment deposits from rivers and streamsstreams

a.a. Continental shelfContinental shelfb.b. Continental slopeContinental slopec.c. Continental riseContinental rise

2.2. Deep-Ocean BasinsDeep-Ocean Basins3.3. Mid-Ocean RidgesMid-Ocean Ridges4.4. Hot SpotsHot Spots

Fig. 2.17

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces1.1. Continental MarginsContinental Margins

a.a. Continental shelfContinental 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 Some parts exposed during times of low sea

level and eroded by rivers and glaciers now are level and eroded by rivers and glaciers now are submarine canyonssubmarine canyons

Fig. 2.19

California Coastline

Monterey Canyon

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces1.1. Continental MarginsContinental Margins

a.a. Continental shelfContinental 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 Some parts exposed during times of low sea

level and eroded by rivers and glaciers now are level and eroded by rivers and glaciers now are submarine canyonssubmarine canyons

• Varies in width from 1 km (Pacific coast of S Am) Varies in width from 1 km (Pacific coast of S Am) to 750+ km (Arctic coast of Siberia)to 750+ km (Arctic coast of Siberia)

• Ends at Ends at shelf breakshelf break, usually at 120-200 m but up , usually at 120-200 m but up to 400+ m depth.to 400+ m depth.

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces1.1. Continental MarginsContinental Margins

b.b. Continental slopeContinental slope• Transition from continent to oceanTransition from continent to ocean• Furrowed with submarine canyons in many Furrowed with submarine canyons in many

areasareas• Canyons channel sediment and debris to deep Canyons channel sediment and debris to deep

sea floorsea floorc.c. Continental riseContinental rise• Accumulated sediment, including Accumulated sediment, including deep-sea fansdeep-sea fans

• May be extensive in areas where large rivers May be extensive in areas where large rivers discharge into oceandischarge into ocean

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces1.1. Continental MarginsContinental Margins

d.d. Active marginsActive margins• Geologically activeGeologically active

• Usually subduction or Usually subduction or transform faulttransform fault

• Steep, rocky shorelineSteep, rocky shoreline• Narrow continental shelfNarrow continental shelf• Steep continental slopeSteep continental slope• Usually lack well-Usually lack well-

developed continental developed continental riserise

• Sediment removed Sediment removed by geological activityby geological activity

Fig. 2.20

I.I. GeologyGeology

F.F. Geological Geological ProvincesProvinces

1.1. Continental MarginsContinental Marginse.e. Passive marginsPassive margins• Not geologically activeNot geologically active• Flat coastal plainFlat coastal plain• Wide continental shelfWide continental shelf• Gentle continental Gentle continental

slopeslope• Usually well-Usually well-

developed continental developed continental riserise

Fig. 2.20

Fig. 2.20

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces2.2. Deep-Ocean BasinsDeep-Ocean Basins

• Mostly between 3000 and 5000 mMostly between 3000 and 5000 m• Predominantly abyssal plain

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces2.2. Deep-Ocean FloorDeep-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

California Coastline

Monterey Canyon

Fig. 2.19

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces3.3. Mid-Ocean RidgesMid-Ocean Ridges

• Central region – Central region – rift valleyrift valley• Fractures allow sea water to seep into crustFractures allow sea water to seep into crust

Fig. 2.23

I.I. GeologyGeology

F.F. Geological ProvincesGeological Provinces3.3. Mid-Ocean RidgesMid-Ocean Ridges

• Central region – Central region – rift valleyrift 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 Water is heated by rock and rises back to surface of sea floorsurface of sea floor

• Hot water picks up dissolved minerals (iron, Hot water picks up dissolved minerals (iron, manganese, sulfides)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 May be very hot hot (350 (350 ooC or more)C or more)

Fig. 2.25