There are two primary types of lithosphere: oceanic lithosphere and continental lithosphere.
Oceanic Lithosphere
Oceanic lithosphere underlies the ocean basins. Key characteristics include:
- Composition: Primarily composed of basalt and gabbro, which are denser than the rocks that make up continental lithosphere.
- Thickness: Generally thinner than continental lithosphere, typically ranging from 50 to 100 kilometers thick. The thickness increases with distance from mid-ocean ridges as it cools and ages.
- Density: Higher density contributes to its lower elevation compared to continental lithosphere.
- Age: Relatively young compared to continental lithosphere, with the oldest oceanic lithosphere being around 200 million years old. This is due to the process of subduction where oceanic lithosphere is recycled back into the mantle.
- Location: Found under all the major ocean basins.
- Formation: Formed at mid-ocean ridges through seafloor spreading.
Continental Lithosphere
Continental lithosphere forms the landmasses of Earth. Key characteristics include:
- Composition: Predominantly composed of granite and other felsic rocks, which are less dense than the rocks forming oceanic lithosphere.
- Thickness: Significantly thicker than oceanic lithosphere, ranging from 100 to 200 kilometers. It is also composed of the continental crust and the uppermost part of the mantle.
- Density: Lower density results in its higher elevation compared to oceanic lithosphere.
- Age: Much older than oceanic lithosphere, with some parts dating back over 4 billion years.
- Location: Forms the continents and their associated continental shelves.
- Stability: Includes a stable cratonic portion (shields and platforms) that are resistant to deformation, and more tectonically active regions such as mountain belts.
| Feature | Oceanic Lithosphere | Continental Lithosphere |
|---|---|---|
| Composition | Basalt, Gabbro | Granite, Felsic rocks |
| Thickness | 50-100 km | 100-200 km |
| Density | Higher | Lower |
| Age | Younger (up to 200 my) | Older (up to 4 billion y) |
| Formation | Mid-ocean Ridges | Various tectonic processes |
In summary, the lithosphere consists of two main types: oceanic, which is thinner, denser, and younger, and continental, which is thicker, less dense, and older. Their differences in composition, thickness, and density determine their respective elevations and roles in plate tectonics.
