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Learning Objectives (LO)!

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

What we’ll learn today:!

1. List the three types of tectonic plate boundaries! 2. Describe the processes occurring at - and ocean-ocean convergent boundaries! 3. Describe the origin of the ! 4. Describe the San Andreas transform ! 5. Describe where tend to occur and why! 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 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 travels away from the center on each side. ! • records reversed and normal polarity episodes! Three types of plate boundaries • Divergent (move apart) • Convergent (come together) • Transform (move side by side) • Plates collide 1 2 • zones • We observe: 3 1) 2) Volcanoes 3) Earthquakes

• Examples - Peru-Chilean Coast - Alaskan Coast - Sumatran Coast Ocean-continent

Plate of oceanic crust collides with plate of . 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 Arc formation.!

trench chain

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

Example: - Asia collision is forming the Himalayas 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 Megathrust Earthquakes Megathrust Earthquakes: 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 strike-slip 2) Earthquakes faulting

• Examples - San Andreas Fault - North Anatolian Fault (Turkey)

Pacific Plate

Oceanic Zone

Transform Boundary with inactive ()! and active () portions.! Hotspots Fig.4.20!

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

hot spot trail Fig.4.22a!

V1 lithosphere melting at base Hot (not molten) of crust V1 rising plume

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 Chain (under ) Fixed hot spot Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.! explains chains of volcanic islands Hot Spots Plates have divergent, convergent, and transform boundaries.

the “” the most seismically and volcanically active zone in the world. • ’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 Action Items for Tuesday, Oct. 6

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

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!