Mechanical Layers and Plate Tectonics

Introduction

• Plate tectonics explains several geological phenomena:
  • Volcanism
  • Earthquakes
  • Mountain belts
  • Fossil and paleo-climate mysteries
• Key question: What is a tectonic plate?

Tectonic Plate

• Defined as a piece of Earth's rigid solid lithosphere.
  • Composed of crust + uppermost mantle.
• There are 7 major and about 20 minor plates.
• Plates move relative to one another atop the flowing asthenosphere.

Earth's Layers

Compositional Layers (Review)

• Crust
  • Made of granite (continental) or basalt (oceanic)
• Mantle
  • Composed of peridotite
• Core
  • Consists of iron and nickel

Mechanical Layers

• Lithosphere
  • Brittle solid, breaks under stress
• Asthenosphere
  • Plastic solid, flows under stress
• Mesosphere
  • More rigid than the asthenosphere but flows slowly
• Outer Core
  • True liquid, flows
• Inner Core
  • Solid, does not flow

Characteristics of Earth's Layers

• Temperature increases toward the center of the Earth, increasing likelihood of melting.
• Pressure increases toward the center, increasing likelihood of solidification.
• Composition changes affect the state (solid, liquid) at various temperatures and pressures.

Focus of the Unit: Lithosphere and Asthenosphere

• Lithosphere
  • Composed of the crust and upper mantle.
  • Rigid, brittle, behaves elastically (can snap).
• Asthenosphere
  • Located directly below the lithosphere.
  • Behaves plastically (flows like ooblek, a non-Newtonian fluid).