There are two primary types of lithospheric plates: continental and oceanic.
Understanding Lithospheric Plates
The Earth's lithosphere, which is the rigid outer layer, is broken into several large and small plates. These plates are not uniform in composition or thickness. Their differences lead to diverse geological features and processes.
Continental Lithosphere
- Composition: Primarily composed of felsic rocks (like granite) which are less dense and thicker.
- Thickness: It's typically thicker, resembling a thick oak block with a thick cork “crust,” as described in the provided reference. The average thickness ranges from 100 to 200 km but can be thicker under mountain ranges.
- Age: Generally older than oceanic lithosphere.
- Density: Lower density due to its composition.
- Example: The plate underlying the continents of North America and Europe.
Oceanic Lithosphere
- Composition: Primarily composed of mafic rocks (like basalt) which are denser and thinner.
- Thickness: It's thinner, similar to a thinner oak block with a thinner pine “crust,” according to our reference. It typically ranges from 50 to 100 km in thickness.
- Age: Relatively younger and is constantly being created and destroyed at plate boundaries.
- Density: Higher density than continental lithosphere due to its composition.
- Example: The Pacific Plate which makes up the floor of most of the Pacific Ocean.
Comparison Table
| Feature | Continental Lithosphere | Oceanic Lithosphere |
|---|---|---|
| Composition | Felsic rocks (like granite) | Mafic rocks (like basalt) |
| Thickness | Thicker (100-200 km or more) | Thinner (50-100 km) |
| Age | Generally older | Relatively younger |
| Density | Lower density | Higher density |
| Description | Thick oak block with thick cork “crust” | Thinner oak block with thinner pine “crust” |
Implications
The differences in density and thickness between these plate types have several implications:
- Subduction: Oceanic lithosphere is denser and tends to subduct (sink) beneath continental lithosphere at convergent plate boundaries.
- Buoyancy: Continental lithosphere is more buoyant and remains on the surface, leading to the formation of continents.
- Plate Boundaries: These differences play a significant role in the formation of various geological features like mountains, volcanoes, and trenches.
