The Structure of the Earth andPlate Tectonics
Structure of the Earth
•The Earth ismade up of 3main layers:
–Core
–Mantle
–Crust
Inner core
Outer core
Mantle
Crust
Pink Slip Questions!
•Which layer or Earth is a liquid?
•Which layer of Earth has the greatesttemperature?
The Crust
•This is where we live!
•The Earth’s crust is madeof:
Continental Crust
- thick (10-70km)- buoyant (less densethan oceanic crust)- mostly old
Oceanic Crust
- thin (~7 km)- dense (sinks undercontinental crust)- young
What is Plate Tectonics?
•If you look at a map of the world, you may notice that some of thecontinents could fit together like pieces of a puzzle.
Plate Tectonics
•The Earth’s crust is divided into 12 majorplates which are moved in various directions.
•This plate motion causes them to collide, pullapart, or scrape against each other.
•Each type of interaction causes acharacteristic set of Earth structures or“tectonic” features.
•The word, tectonic, refers to the deformation ofthe crust as a consequence of plateinteraction.
World Plates
What are tectonic plates made of?
•Plates aremade of rigidlithosphere.
The lithosphere ismade up of thecrust and the upperpart of the mantle.
What lies beneath the tectonic plates?
•Below thelithosphere(which makesup the tectonicplates) is theasthenosphere.
Plate Movement
•“Plates” of lithosphere are moved around bythe underlying hot mantle convection cells
Convection
•convection, is the transfer of heat fromone place to another by the movementof fluids.
What happens at tectonicplate boundaries?
•Divergent
•Convergent
•Transform
Three types of plate boundary
•Spreading ridges
–As plates move apart new material is erupted tofill the gap
Divergent Boundaries
Pink Slip Questions!
•_________ is aprocess that occursat mid-ocean ridges,where new oceaniccrust is formedthrough volcanicactivity and thengradually movesaway from the ridge.
•The ocean will getbigger if the________________consumes theoceanic crust_____________then the__________produces it.
Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
Pink Slip Question
•How was the last image evidence ofsea-floor spreading?
•There are three styles of convergentplate boundaries
–Continent-continent collision
–Continent-oceanic crust collision
–Ocean-ocean collision
Convergent Boundaries
•Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
Himalayas
•Called SUBDUCTION: Is the processwhere one plate sinks under another.
Continent-Oceanic Crust Collision
•Oceanic lithospheresubducts underneath thecontinental lithosphere
•Oceanic lithosphere heatsand dehydrates as itsubsides
•The melt rises formingvolcanism
•E.g. The Andes
Subduction
•When two oceanic plates collide, one runs over theother which causes it to sink into the mantle forminga subduction zone.
•The subducting plate is bent downward to form a verydeep depression in the ocean floor called a trench.
•The worlds deepest parts of the ocean are foundalong trenches.
–E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision
•Where plates slide past each other
Transform Boundaries
Above: View of the San Andreastransform fault
…what’s the connection?
Volcanoes and PlateTectonics…
•Composite Cone
•Cinder Cone
•Shield
Three Types of Volcanoes
Each are different because of the way they eruptor the types of materials they erupt and theirshape
Composite Cone
*Most explosive eruptions
*built of lava, cinders, and ash.
*The size increases after an eruption.
*Also called strato volcano.
*Serves as a transportation system formagma to rise to the surface from deepwithin Earth’s crust.
*Can be so powerful that part of the volcanocan be blown away, reshaping the mountain
Cinder Cone
*Formed by lava fragments called cinders
*Has only one vent in which magma can flow
*Lava fragments burst into the air and thenfall into the vent of the volcano.
*Have steep sides
*Not as large as composite or shieldvolcanoes.
Shield
*Look like shields with their gentle slopingsides
*Slopes are caused by eruptions
Eruptions usually have fluid lava which flowsfrom it.
*Lava flows not only from the top but alsofrom the cracks in the ground.
*Slow to erupt so usually animals and peoplehave enough time to escape.
*Some of the largest volcanoes in the world
Volcanism ismostlyfocused atplatemargins
Pacific Ring of Fire
Pacific Ring of Fire
Hotspotvolcanoes
•Hot mantle plumes breaching thesurface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain areexamples of hotspot volcanoes.
The tectonic plate moves over a fixed hotspotforming a chain of volcanoes.
The volcanoes get younger from one end to the other.
…what’s the connection?
Earthquakes and PlateTectonics…
•As with volcanoes, earthquakes are notrandomly distributed over the globe
•At the boundaries between plates, frictioncauses them to stick together. When built upenergy causes them to break, earthquakesoccur.
Figure showingthe distribution ofearthquakesaround the globe
Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
Earthquakes may help uspredict…
• Earthquakes may also occur in volcanicregions and are caused there both bytectonic faults and by the movement ofmagma (hot molten rock) within thevolcano. Such earthquakes can be anearly warning of volcanic eruptions.
Plate Tectonics Summary
•The Earth is made up of 3 main layers (core,mantle, crust)
•On the surface of the Earth are tectonicplates that slowly move around the globe
•Plates are made of crust and upper mantle(lithosphere)
•There are 2 types of plate
•There are 3 types of plate boundaries
•Volcanoes and Earthquakes are closelylinked to the margins of the tectonic plates
Double Pink Slip Question!
•What is the root cause of bothvolcanoes and earthquakes?