basic natural sciences - tectonics

8/8/2019 Basic Natural Sciences - Tectonics

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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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