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) • Plates collide 1 2 • Subduction zones • We observe: 3 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) • Plates slide by • Transform faults • We observe: 1) Offset surface features strike-slip 2) Earthquakes faulting • 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 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 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 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!.