What we’ll learn today:!

1. List the three types of tectonic plate boundaries!2. Describe the processes occurring at ocean-continent and

ocean-ocean convergent boundaries!3. Describe the origin of the Himalayas!4. Describe the San Andreas transform fault!5. Describe where earthquakes tend to occur and why!

Learning Objectives (LO)!

Lecture 11: Plate Tectonics II!No Homework!!** Chapter 3 **!

Three types of plate boundaries

•  Divergent (move apart)

•  Convergent (come together)

•  Transform (move side by side)

• Plates move apart • Spreading centers

• Examples - Mid Atlantic Ridge

- East Pacific Rise

East Pacific Rise

Divergent Boundary

As two plates continue to move apart, the rock in the seafloor grows older as its distance from the rift zone increases

Mid-Ocean Ridge Spreading Center

Paleomagnetism at Divergent Plate Boundaries

•  Two plates pull apart!•  New molten material rises

through Rift Zone!•  Like conveyer belts, the newer

crust travels away from the center on each side. !

•  Oceanic crust records reversed and normal polarity episodes!

Three types of plate boundaries

•  Divergent (move apart)

•  Convergent (come together)

•  Transform (move side by side)

• Plates collide • Subduction zones • We observe: 1) Trench 2) Volcanoes 3) Earthquakes

1 2

3

- Sumatran Coast

- Alaskan Coast

• Examples - Peru-Chilean Coast

Ocean-continent convergent boundary

Plate of oceanic crust collides with plate of continental crust. Oceanic crust is subducted (goes under) continental plate.!

Fig.4.15a!

Pacific Plate

Ocean-ocean convergent boundary

Two oceanic crust plates collide. Older, denser plate usually subducts, site of Island Arc formation.!

• Old oceanic lithosphere is more dense than continental lithosphere -- so it sinks

litho

sphe

re

asthenosphere

volcano chain

trench

Example: India - Asia collision is forming the Himalayas

collison zone

Continent-continent convergent boundary !OROGENESIS

Megathrust Earthquakes Occurs when “locked” subduction zone ruptures

1.  Strain accumulates. 2.  Crust shortens. 3.  Uplift occurs. 4.  Plates unlock. 5.  Crust extends rapidly,

culminating in a megathrust earthquake

Megathrust Earthquakes

Megathrust Earthquakes: Tsunamis

Three types of plate boundaries

•  Divergent (move apart)

•  Convergent (come together)

•  Transform (move side by side)

• Plates slide by • Transform faults • We observe: 1) Offset surface features 2) Earthquakes

• Examples - San Andreas Fault

strike-slip faulting

- North Anatolian Fault (Turkey)

Pacific Plate

North American Plate

Oceanic Fracture Zone Transform Boundary with inactive (fracture zone)!

and active (transform fault) portions.!

Hotspots

Fig.4.20!

- sometimes marked by chain of islands -  less common than plate-boundary volcanoes - different composition (deep source)

hot spot trail

Fig.4.22a!

Hot (not molten) rising plume

lithosphere

V1

V1

melting at base of crust

V1

Fig.4.22b!

• Island chain formed by Pacific plate moving over stationary hot spot

• Kauai (oldest); Big Island (youngest)

• Island chain extends north to Emperor Seamount Chain (under water)

Fixed hot spot

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.!

Plate tectonics explains chains of volcanic islands

Hot Spots

Plates have divergent, convergent, and transform boundaries.

the “Ring of Fire” the most seismically and volcanically active zone in the world.

• Earth’s crust is divided into plates • Plates move relative to one another at 1-15 cm/yr • Plate interiors are largely undisturbed • Deformation is concentrated at plate boundaries

Consequences: • Plate tectonics constantly change Earth’s surface • Earthquakes occur mostly at plate boundaries • Volcanoes occur mostly at plate boundaries

Why is Plate Tectonics Important?

• For us: delivers earthquakes and volcanoes

• For Earth: helps Earth cool - spreading centers, hotspots give off heat - subduction allows recycling of cold material

• Plate tectonics effectively “stirs” outer layer of Earth

Plate Movement Powers the Rock

Cycle

What you should know from today:!

1. List the three types of tectonic plate boundaries!2. Describe the processes occurring at ocean-continent and

ocean-ocean convergent boundaries!3. Describe the origin of the Himalayas!4. Describe the San Andreas transform fault!5. Describe where earthquakes tend to occur and why!

Action Items for Tuesday, Oct. 6

1.  Read Chapter 3-5 to 3-10 2.  Complete homework assignment #10