Learning Objectives (LO)! Lecture 11: Plate Tectonics 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 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!
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)
1 2 3 Plates collide Subduction zones We observe: 1) Trench 2) Volcanoes 3) Earthquakes Examples - Peru-Chilean Coast - Alaskan Coast - Sumatran 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.!
trench volcano chain lithosphere asthenosphere Old oceanic lithosphere is more dense than continental lithosphere -- so it sinks
collison zone Example: India - 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 earthquake
Megathrust Earthquakes
Megathrust Earthquakes: Tsunamis
Three types of plate boundaries Divergent (move apart) Convergent (come together) Transform (move side by side)
strike-slip faulting Plates slide by Transform faults We observe: 1) Offset surface features 2) Earthquakes Examples - San Andreas Fault - North Anatolian Fault (Turkey)
North American Plate Pacific 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! V1 lithosphere melting at base of crust V1 Hot (not molten) rising plume V1
Fig.4.22b! Island chain formed by Pacific plate moving over stationary hot spot Kauai (oldest); Big Island (youngest) Fixed hot spot Island chain extends north to Emperor Seamount Chain (under water)
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
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!