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Evidence
Theory
Types of Plate Boundaries
Evidence
Theory
Types of Plate Boundaries
Plate Tectonics
Tony K. Hariadi
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What defines Plate Tectonics?
Earths surface is made up of rigid
plates Plates do not deform internally;
deformation is at boundaries
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Early 1500's mapping coast of S America
Francis Bacon: Match with Africa
Plate Tectonics discovery
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1912: AlfredWegenerFirst Proposed that Plates Move
ContinentalDrift
Not believed Rates Too Fast Continents "sail" through oceans??? NOT
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New Technologies afterWWII
Sonar
Magnetometers
Nuclear monitoring
led to mid-1960's:
Plate Tectonic Revolution
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Sonar maps of sea floor
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The Sea Floor
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Nuclear Monitoring global earthquake catalogs
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Earthquakes 30 days
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Magnetometers ages of sea floor
Magnetic Reversals
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Rock Magnetism Some minerals magnetize
Rocks record field when they form
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Observe: Magnetic Polarity Flips
every 0.2 50 Ma
(Ma = million years)
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Pattern of Reversals is distinct
N
N
N
S
S
normal
reversed
normal
lavas
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Vine-Mathews (1963):Magnetic stripes on sea floor
M
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Crust
Forms at Ridge, cools, freezes Mag. Field
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Magnetic Field Flips "recorded"
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... leaving magnetic "stripes" on sea floor
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lineation
age
Age of Oceans from Magnetic Stripes
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Plates travel: 1-20 cm/yr RELATIVE to each other
2 cm/yr
18 cm/yr
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Action is at boundaries
Continents along for the ride
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ConvectionFlow of material when heated
1. Heated from below
2. Yellow stuff heats--> less dense
--> RISES!
3. Yellow stuff cools--> denser
--> SINKS!
Lava Lamp
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Plate Tectonics
Earths Lava Lamp:
Driven by Earth Heat
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km
100 km
1000C
C
Temperature
HEAT : Earth is Hotter Deeper
Depth
InEarth
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C
km
Heat in Earth
Coldand
Strong
Temperature
Depth
Hot andWeak
Lithosphere
Astheno-sphere
~100
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mid-ocean
ridge
subductionzone
Plate Boundaries
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Divergent
Convergent
Transform
3 Plate Types of Plate Boundaries
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Divergent
Mid-Ocean Ridge
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Ridges
Depth shallowest atridge axis
Symmetric
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North Mid-AtlanticRidge Bathymetry
fracturezone
rift valley
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Rifts: Continental Divergent Margins
Basin and Range -- a Rift
10
mm/yr
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San Andreas Fault
Big Earthquakes,No Volcanoes
Offsets
Transform
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Transform
San Andreas Fault
Big Earthquakes,No Volcanoes
Offsets
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Big Transform
Faults
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Subduction Zones
Convergent
100 kmbig quakes!
oceanic
trench
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North Pacific
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Aleutian ArcAnchorage
trench
bulldozed
wedge
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arctrench
East Aleutians
Side View, real data
wedge
0
50km
N
100
-100 -50 0 km 50 100 150
1985 198319741993
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Nicaragua Arc
Momotombo Momotombito
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BU seismic experiment, 2004
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BU seismic experiment, 2004
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Continental CollisionsThick Crust too light to subduct
collision
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An Example: India-Eurasia
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Everest
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Hawaiian Chain: not a plate boundary?
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NOT Plate Boundaries
Observe: volcanoes in age order parallel trends
0 Ma1
2
3age
What's up?
Hot Spots
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Hot spots have DEEP sources, below plates
plate
plate moves
hot spot stays put
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Observe: All hotspots fixed to each other
Hotspots give ABSOLUTE Motion of plates
0 Ma2 Ma
200 km2 Ma
= 10 cm/yr
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