Overview
This lecture focuses on crustal deformation, plate boundaries, rock stress, faults and folds, and introduces key terms relevant to plate tectonics and rock metamorphism.
Crustal Deformation and Plate Boundaries
- Deformation of the crust occurs when plates collide, divide, or slide past each other.
- Divergent boundaries occur when plates pull apart, forming new crust.
- Convergent boundaries happen when plates collide, creating trenches and mountains.
- Transform boundaries involve plates sliding laterally past each other.
Faults and Folds
- Faults are fractures in rock where one block moves relative to another during earthquakes.
- Folds occur when rock layers bend without breaking due to immense pressure.
- Faults and folds result from different types of stress on rocks.
Types of Plate Movements and Stresses
- Tensional stress pulls rocks apart.
- Compressional stress pushes rocks together.
- Shear stress causes rocks to slide past one another along planes.
Types of Faults
- Normal fault: hanging wall moves down relative to foot wall.
- Reverse fault: hanging wall moves up over foot wall.
- Strike-slip fault: rocks slide past each other horizontally.
- Oblique fault: movement is both vertical and horizontal.
Metamorphism and Crust Movement
- Metamorphism starts at temperatures of 100–150°C in unstable protoliths.
- Earth's crust is made of large slabs (tectonic plates) that move due to internal heat (convection currents).
Convection and Plate Tectonics
- Convection involves heat transfer through fluid movement, driving plate movement.
- Example: a cork placed in heated water moves due to convection currents beneath it.
Key Terms & Definitions
- Fault — a crack in the Earth's crust where movement has occurred.
- Fold — a bend in rock layers due to pressure and high temperature.
- Divergent Boundary — plates move apart.
- Convergent Boundary — plates move toward each other.
- Transform Boundary — plates slide sideways past each other.
- Tensional Stress — stress that stretches rock apart.
- Compressional Stress — stress that squeezes rock together.
- Shear Stress — stress causing rocks to slide parallel to each other.
- Protolith — the original, unmetamorphosed rock from which a metamorphic rock forms.
- Metamorphism — process where rock changes form due to heat and pressure.
- Foot Wall — block below the fault.
- Hanging Wall — block above the fault.
Action Items / Next Steps
- Complete the activity: Describe convection using the cork-in-water analogy.
- Answer the guide questions on types of plate movements and stress.
- Review key fault types and their characteristics.