crust deformation and pangaea

Crust Deformation in Earth Science

General Concepts

  • Earth’s crust shape is constantly changing due to deformation, which involves bending, tilting, and breaking.

  • Deformation occurs as a result of stress caused by pressure from plate movement.

Types of Stress

  • The three main types of stress affecting the crust are:

    • Compression

    • Tension

    • Shearing

Compression

  • Definition: Rocks are squeezed together, resulting in elevation changes.

  • Location: Occurs at convergent boundaries.

Tension

  • Definition: Rocks are pulled apart, leading to thinning.

  • Location: Occurs at divergent boundaries.

Shearing

  • Definition: Rocks are pushed horizontally in opposite directions, twisting, bending, or breaking.

  • Location: Occurs at transform boundaries.

Responses to Stress

  • Rocks can respond to stress in three ways:

    • Fold

    • Fracture

    • Fault

Folding

  • Definition: Permanent bending of rock under extreme stress, without breaking.

  • Types of folds:

    • Anticline: A fold that bends upward.

    • Syncline: A fold that bends downward.

Fracture

  • Definition: The rock breaks, but pieces on either side do not move.

Fault

  • Definition: The rock breaks, and pieces on either side of the break do move.

Types of Faults

  • Normal Fault: One side drops down; occurs along divergent boundaries due to tension stress.

  • Reverse/Thrust Fault: One side moves up; occurs along convergent boundaries due to compression stress.

  • Strike-Slip Fault: Rocks slide horizontally; occurs along transform boundaries due to shearing stress.

Continental Drift Theory

Introduction to Alfred Wegener

  • 1912: Wegener first presented his hypothesis on continental drift.

  • 1915: Published The Origin of Continents and Oceans detailing his theory.

  • Wegener was a German geophysicist and meteorologist.

Evidence for Continental Drift

  • Continental Fit: Continents resemble jigsaw puzzle pieces, notably South America and Africa's coastlines match.

  • Supercontinent Pangaea: Proposed that all continents were once part of this landmass.

  • Over millions of years, continents have drifted to their current positions.

Timeline of Continental Drift

  • Pangaea existed approximately 250 million years ago (Permian period).

  • Breakup Timeline:

    • Triassic (200 Mya): Formation of Laurasia and Gondwanaland.

    • Jurassic (145 Mya): Further continental separation.

    • Cretaceous (65 Mya): Continents continued to drift, resembling today's configuration.