Plate Tectonics Overview

Study Notes

Tectonic plates, not continents, move at 1 to 10 centimeters per year, floating on the asthenosphere.
Approximately 20 lithospheric plates exist, interacting in various ways.

The regions where tectonic plates interact are called plate boundaries.
Plate boundaries are critical because they are often sites of earthquakes and volcanic activity, with most seismic events occurring at three types: divergent, convergent, and transform.

Occurs when two plates move away from each other, creating a gap or rift.
Produces mid-ocean ridges and continental rift zones.
Example: Iceland sits on a divergent boundary between the North American Plate and the Eurasian Plate.
Example: East Africa Rift Valley, a continental rift.

Two plates move toward each other, forming subduction zones or orogenic belts.
Subduction Zone: One plate moves beneath another, leading to volcanic activity.
- Example: Mariana Trench formed by oceanic-oceanic convergence.
Oceanic-Continental Convergence: An oceanic plate collides with a continental plate, leading to trench formation and volcanism.
- Examples: Andes Mountains in South America, Cascade Range in North America.
Continental-Continental Convergence: Both continental plates collide and push upwards, forming large mountain ranges.
- Examples: Himalayas, European Alps formed from the collision of Africa and Eurasia.

Plates slide past each other, causing earthquakes without forming mountains or volcanoes.
Example: San Andreas Fault.

Divergent: Plates moving apart (e.g., mid-ocean ridges like Iceland, continental rift zones like the African Rift Valley).
Convergent: Plates moving together, resulting in:
- Oceanic-Oceanic (e.g., Japanese Islands)
- Oceanic-Continental (e.g., Andes and Cascades)
- Continental-Continental (e.g., Himalayas).
Transform: Plates slide against each other (e.g., San Andreas Fault).
Hotspots, which are not located at plate boundaries, provide insights into plate motion.

Plate movement is driven by mantle convection as the plastic asthenosphere flows.
Mechanisms include slab pull at subduction zones, ridge push at mid-ocean ridges, and rising mantle plumes.