Download - Structure of the Earth Tectonics
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Chapter 22ISCI 2001
Structure of the EarthTectonics
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Structure of the Earth
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Crust(1). Thin, brittle
Oceanic Basalt rock (dark); greater
densityContinental
Granitic rock (lighter); less dense
Less dense than mantle Floats
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Mantle• (1). Most of the volume (82%)
and mass (65%)– Thickest layer
• (2). Rich in Si and O– Contains Fe, Mg, Ca (causes increased
density)• Density increased by weight of crust also
• (3). Hotter than crust– High pressure
• Caused by radio active decay of elements • Flow of heat from core
• (4). Regions – Upper Mantle – Lithosphere
• Stiff, cool – similar to crust (forms one layer together)
– Asthenosphere• Solid, plastic (solid flow)
• (5). Upper Mantle– Solid and rigid – Plastic but not as much as upper mantle
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Core Consist of:
Metallic Fe2x dense as mantle
(2). Inner CoreSolid 4000 to 7000 C
Radioactive elements Earth development; matter hitting the surface Core sinking to the center
(3). Outer CoreFlows due to less pressure Rotation of Earth stirs up core material
Produces magnetic field (flowing electrical charge)
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Plate Tectonics(1). Continents sit atop of tectonic ‘plates’
What are the plates made of?What is a continent?
(2). PlatesConsist of mantle and the crust (lithosphere) Plates move atop the asthenosphere (plastic)
Continents move because they are embedded into the plates
(3). Plate boundaries and continents Continents and plates do not have the same boundaries
(overlapping) Figure 22.18A lot of action occurs at the plate boundaries!
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Plates
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How were the Plates Discovered?
(1). Alfred Wegener Proposed the theory of “Continental Drift”
Continents are in motion; drifting over geologic time
Pangea (figure 22.8)Same fossils found in several different
continentsMatching rocks on both sides of Atlantic
Ocean
(2). Evidence for CDSeafloor SpreadingMagnetic Stripes
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Pangea
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Evidence for Continental Drift –Seafloor Spreading
(1). Magma flows out of breaks in lithosphereNew lithosphere is formed and old lithosphere
will be recycled back in trenches (22.16)Mid-ocean ridge
Pushes the continents in specific directions
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Evidence – Magnetic Stripes (1). Lava contains Fe and magnetite (Fe and
O)Crystals are magnetic – line up with the
magnetic field of the EarthCrystals point North and south / cool and freeze and
become locked inContains a record of the history of the magnetic field of
the Earth Gives a striped, bar pattern (22.17)Alternates normal (today’s field) and reversed field from
years ago. Runs along the spreading seafloor
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How do the Plates Move?(1). As magma is heated deep in the Earth it
moves upward via convection currents (22.21)Hot rocks from lower mantle move upward cool in the
upper mantle and returnHit the lithosphere and can crack it – seafloor
spreading Plates move atop ‘convection cells’
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ISCI 2001Chapters 22-24
Plate Tectonics
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Plate Activities – Divergent Plate Boundaries
(1). Plates may ‘diverge’Plates move apart
Lava fills spaces in between
(2). What types of structures are produced?Volcanic mountainsRift valleys
(3). Examples Mid-Atlantic Ridge Great Rift Valley (Africa near Nairobi
Kenya)
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Seafloor Spreading Rift Valley in Kenya
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Mid-Atlantic Ridge
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Convergent Boundaries
(1). When two plates collideOne plate usually subducts Most dense or oldest plates
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Oceanic – Oceanic
Trench formation (Marianas Trench)11,000 m or 7.0 miles deep
Pacific and Phillipine Plates collide Formation of volcanic islands or arcs
Subduction plate mantle rock melts comes to the surface and cools
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Marianas Trench
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Oceanic – Continental
Oceanic – Continental Oceanic basaltic plate (more dense) subducts under granitic continental plate
Mantle rock melts, magma rises and cools forms island chains
Volcanic Arcs (Peru)
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Oceanic – Continental
The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form the towering peaks of the Andes, as seen here in the Pachapaqui mining area in Peru.
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Continental – Continental
Continental – Continental Massive plate collisions (both granitic)
No subduction, why?Both have same density
Massive mountains are formedHimalayas
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Continental – Continental
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Transform Plate Boundaries (1). ‘Sliding Plate’ Boundaries
Slipping of plates causes ‘faults’
(2). Slipping causes plate movementsBoundaries move in opposite directions
against each other
(3). Where are they normally found?Mostly ocean basinsContinental plate: San Andreas Fault
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San Andreas Fault
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Faults Parts of a Fault Normal Faults
Dip-slip Reverse Faults Strike-Slip
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Types of Faults
(1). Dip-Slip (See figure 24.5)Hanging wall and vertical wall move
vertically along the fault plane Movement is vertical
(2). Strike-SlipMovement is horizontal San Andreas Fault motion
(3). ObliqueMove horizontally and vertically
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Slip-DipConjugate Normal faults, Canyonlands National Park, Utah
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Fault Types
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Folding(1). Bending in Rock layers
Caused by compression
(2). Results Anticlines or synclines
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(1). Folded MountainsDuring formation continental crust thickens
and wrinkles into vertical folds from compressionAppalachians, Rockies and Himalayas
(2). Unwarped Domed shaped
Single anticline (crust is heaved upwards; no folds produced)
Adirondack mountains NY
(3). Fault-BlockLand is ‘uplifted’ , stretched and elongated Very steep profileTetons (Wyoming); Sierra Nevada (California)
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Mountain FormationFolded Mountain – Antarctica
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Mountain Formation
Adirondack Mountains – unwarped
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Mountain Formation- (Fault-Block)
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(1). EarthquakesTransform faults
Compression and tension caused by stress of plate movements -- SlippingFocus location
Rock is snapped or broken releasing ‘elastic’ energy
(2). TypesIntraplate (10%)
Away from plate boundaries New Madrid, Missouri
Interplate (90%)Plate boundaries
Transform plates (mild Eqs)Subduction zones (strong)
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Earthquakes
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Subduction Zones – Ring of Fire!
80% of all interplate EQs occur here
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Powerful Interplate EQs and Tsunamis
(1). Coast of Sumatra Indian and Burma Plate collision Megathrust quake
100 billion tons of TNT
(2). Production of a Tsunami Quake took place in the Indian oceanAs subduction occurred
The seafloor bent as the other plate sankStress caused rock to snap and thrust
upwardsForce caused water to creat large wave30m +/- above sea level
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Earthquakes – San Francisco 1906
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Magnitude of Earthquakes –Richter Scale (1). Logarithmic scale
Each point represents a 10-fold increase in quake shaking strengthMeasures shaking Also indicates 30 fold increase in energy
output 1 thru 10
Examples 1906 San Francisco (8.2)Sumatran 2004 (9.0)
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Richter Scale
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Tsunami
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Sumatra EQ and Tsunami
184,000 People died
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Surface and Ground Water
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Watershed
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Ocean Floor
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Surface Water – Surface Processes
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Glaciers