Plate Tectonics and Geological Deformations Explained

Divergent Boundaries

This occurs when a stream of magma rises to encounter a plate, breaking it up and separating it into two fragments.

Convergent Boundaries

These occur when two plates collide against each other.

Oceanic and Continental Plates

The oceanic plate sinks beneath the continental plate in a process called subduction.

Continental Plates

If two continental plates collide, they form intracontinental mountain ranges.

Two Oceanic Plates

When two oceanic plates collide, subduction occurs, with one sliding below the other to form a volcanic island arc.

Transform Boundaries

Plates slide laterally without climbing over one another, causing the formation of large faults.

Deformations and Scales

• Mesotectonics: Structures between 1m and 1km in length.
• Macrotectonics: Structures between 1km and 1000km in length.

Types of Deformations

• Folds: When rocks are plastic, undulations form, known as folds.
• Fractures:
  • Fault: Rupture of fragile rocky material with displacement of blocks.
  • Jointing: Rupture of fragile rocky material without displacement of blocks.

Anatomy of Folds

• Hinge: Points at which the slope of the fold changes.
• Axial Plane: Imaginary plane passing through the hinges.
• Fold Axis: The line where the axial plane intersects the terrain.
• Flanks: The lateral sides of the fold on both sides of the hinge.

Types of Folding

• Anticlines: The oldest strata are in the center and the most modern are on the flanks.
• Synclines: The oldest strata are on the flanks and the most modern are in the center.

Joints and Faults

Joints: Characterized by a separation or crack in the rock between blocks, but with no displacement.

Faults:

• High Lip: The displaced block is sunken.
• Low Lip: The block is facing upward.
• Fault Jump: The shift occurred between the two fault lips.
• Fault Plane: The surface on which displacement of the lips has occurred.
• Normal Fault: Produced by distension forces of separation.
• Reverse Fault: Occurs because of compression forces.
• Horizontal Fault: Occurs when forces act in the same direction, causing horizontal displacement between blocks.