Lecture 5

Plate Tectonics: Part 2

Major Tectonic Plates

• List of Major Plates:

  • Arabian Plate

  • Philippine Plate

  • Juan de Fuca Plate

  • Caribbean Plate

  • Cocos Plate

  • Pacific Plate

  • African Plate

  • Nazca Plate

  • South American Plate

  • Scotia Plate

  • Antarctic Plate

  • Australian-Indian Plate

Plate Movement and Speed

• Speed Categories:

  • Less than 3 cm/year

  • 3 to 9 cm/year

  • More than 9 cm/year

Game Plan

• Topics Covered:

  • Plate Boundaries

  • Divergent

  • Convergent

  • Transform

  • Processes at Plate Boundaries

  • Earthquakes

  • Volcanoes

Reminders/Announcements

• Module 2 Activity is available today; comments due by Wednesday 9/17.

• Quiz 2 available today; due Thursday 9/18.

• Material for the quiz includes Plate Tectonics, covering Lectures 4 & 5.

Learning Outcomes

At the end of this lecture, students should be able to:

• Describe the three different types of plate boundaries and the effects on the crust at each.

• Sketch each type of boundary and provide examples.

• Identify types of plate boundaries based on surface features.

• List other geological processes occurring at different plate boundary types.

• Explain the connection between plate tectonics and the occurrence of earthquakes and volcanoes.

• Analyze how plate tectonics serves as a unifying theory in geology.

Types of Plate Boundaries

Divergent Boundaries

• Definition: Plates move apart, leading to the upwelling of material from the Mantle to create new sea floor.

• Characteristics:

  • New oceanic crust formation

  • Rifting due to tensional stress

  • Earthquakes typical along these boundaries

  • Rift volcanoes may develop in weakened crust.

Convergent Boundaries

• Definition: Plates collide, resulting in one plate being subducted into the Mantle.

• Categories:

  1. Oceanic-Continental

  2. Oceanic-Oceanic

  3. Continental-Continental

• Characteristics:

  • Compression leads to thrust faults.

  • Earthquakes and mountain building processes occur.

  • Depending on the type, subduction processes may result in volcanic activity or mountain formation.

Transform Boundaries

• Definition: Plates slide past each other, not creating or destroying lithosphere.

• Characteristics:

  • Shearing forces cause earthquakes along strike-slip faults.

  • Links mid-ocean ridges to convergent boundaries.

Global Notes on Plate Boundaries

Divergent Boundaries

• Formation: Hot material wells up, causing faulting and cracking as tension develops.

• Example Locations:

  • Mid-Atlantic Ridge (oceanic-oceanic)

  • East African Rift (continent-continent)

• Rifting Process:

  • Initial uplift and faulting lead to new ocean basins.

  • Example: The breakup of Pangea resulted from rifting processes.

Convergent Boundaries

• Oceanic-Continental Collision:

  • Denser oceanic plate subducts beneath lighter continental plate, forming a trench.

  • Volcanic mountain belts develop as subducting plates melt and generate magma.

  • Example: Andes Mountains (Nazca Plate and South American Plate).

• Oceanic-Oceanic Collision:

  • Older, denser plate subducts beneath the younger plate, creating volcanic island arcs.

  • Example: Mariana Islands (Mariana Trench).

• Continental-Continental Collision:

  • Forms mountain ranges where two continental plates collide and crumple without subduction.

  • Example: Himalayas (India-Asia collision).

Transform Boundaries

• Example: San Andreas Fault in California, with significant lateral movements.

• Characteristics:

  • Movement leads to various geological features but not the creation of new crust.

Earthquakes and Volcanoes

How Earthquakes Occur at Plate Boundaries

• Plates get stuck at edges due to friction, storing energy.

• Strain builds until friction is overcome, resulting in a fault slip, which releases energy as seismic waves, causing ground shaking.

Locations of Earthquakes and Volcanoes

• Correlation: Most earthquakes and volcanoes are located at plate boundaries, following specific patterns associated with the type of boundary.

• Seismic Activity: Wadati-Benioff zone signifies increasing depth of earthquakes away from subduction zones.

Summary of Processes at Plate Boundaries

Volcanoes and Plate Tectonics

• Volcano Formation:

  • Occurs at rifts, subduction zones, and hot spots.

  • Types of volcanoes:

  1. Island Arc Volcanoes: All active, formed from subduction.

  2. Hotspot Volcanoes: Active at one site above mantle plume, e.g., Hawaiian Islands.

Conclusion

• Understanding plate tectonics is crucial in explaining geological processes like earthquakes, mountain formation, and volcanism.