lecture 11: plate tectonics ii no homework! ** chapter 3 ... · copyright © 2014 john wiley &...
TRANSCRIPT
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)
Divergent Boundary
As two plates continue to move apart, the rock in the seafloor grows older as its distance from the rift zone increases
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.!
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
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
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)
Oceanic Fracture Zone Transform Boundary with inactive (fracture zone)!
and active (transform fault) portions.!
Fig.4.20!
- sometimes marked by chain of islands - less common than plate-boundary volcanoes - different composition (deep source)
hot spot trail
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
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
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