There are two primary types of lithosphere: oceanic lithosphere and continental lithosphere. They differ significantly in their composition, thickness, density, and age.
Oceanic Lithosphere
- Composition: Primarily composed of mafic rocks like basalt and gabbro.
- Thickness: Generally thinner than continental lithosphere, ranging from about 50 to 100 km.
- Density: Denser than continental lithosphere due to its composition.
- Age: Relatively young; most oceanic lithosphere is less than 200 million years old. This is because oceanic lithosphere is constantly being created at mid-ocean ridges and destroyed at subduction zones.
- Location: Found beneath the oceans.
- Formation: Formed at mid-ocean ridges through seafloor spreading.
Continental Lithosphere
- Composition: Primarily composed of felsic rocks like granite.
- Thickness: Considerably thicker than oceanic lithosphere, averaging around 150 km, but can be over 200 km thick under mountain ranges.
- Density: Less dense than oceanic lithosphere due to its composition.
- Age: Much older than oceanic lithosphere; some continental rocks are over 4 billion years old. Continental lithosphere is more stable and less prone to destruction compared to oceanic lithosphere.
- Location: Forms the continents and continental shelves.
- Formation: Formed through a complex process of accretion and orogenesis (mountain building).
Comparison Table
| Feature | Oceanic Lithosphere | Continental Lithosphere |
|---|---|---|
| Composition | Mafic (basalt, gabbro) | Felsic (granite) |
| Thickness | 50-100 km | ~150 km (can exceed 200 km) |
| Density | Higher | Lower |
| Age | Younger (typically < 200 million yrs) | Older (up to 4 billion+ years) |
| Primary Location | Ocean basins | Continents |
| Formation Process | Seafloor spreading | Accretion and orogenesis |
In summary, the lithosphere is divided into two main types: oceanic and continental. They differ in composition, thickness, density, and age, impacting their behavior and role in plate tectonics.
