The primary difference between continental and oceanic lithosphere lies in their composition, thickness, density, and age.
Composition and Structure
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Continental Lithosphere: Primarily composed of granitic rocks, which are rich in silicates and aluminum (SIAL). It is significantly thicker than oceanic lithosphere.
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Oceanic Lithosphere: Primarily composed of basalt rocks, which are rich in silicates and magnesium (SIMA). It is thinner and denser than continental lithosphere.
Key Differences Summarized
| Feature | Continental Lithosphere | Oceanic Lithosphere |
|---|---|---|
| Composition | Primarily granitic (SIAL - Silicates and Aluminum) | Primarily basaltic (SIMA - Silicates and Magnesium) |
| Thickness | Typically 100-200 km (can be thicker under mountain ranges) | Typically 5-100 km |
| Density | Lower (approximately 2.7 g/cm³) | Higher (approximately 3.0 g/cm³) |
| Age | Much older; can be billions of years old | Relatively young; generally less than 200 million years |
| Buoyancy | More buoyant (sits higher on the asthenosphere) | Less buoyant (sits lower on the asthenosphere) |
| Major Elements | Silicon, Aluminum, Oxygen | Silicon, Magnesium, Iron, Oxygen |
Detailed Comparison
Composition
The continental lithosphere's granitic composition gives it a lower density than the oceanic lithosphere. The oceanic lithosphere is composed of basalt, which results from the cooling of magma at mid-ocean ridges.
Thickness and Density
Continental lithosphere is significantly thicker (averaging around 150 km) than oceanic lithosphere (averaging around 75 km). The greater thickness and lower density of continental lithosphere are why continents "float" higher on the semi-molten asthenosphere compared to oceanic plates. This difference in buoyancy is crucial for the existence of continents above sea level.
Age
Oceanic lithosphere is constantly being created at mid-ocean ridges and destroyed at subduction zones, resulting in a relatively young age (typically less than 200 million years). In contrast, continental lithosphere can be billions of years old, with some continental rocks dating back nearly 4 billion years.
In summary, the continental and oceanic lithosphere differ significantly in their composition, thickness, density, and age. These differences determine their behavior and interaction within the Earth's plate tectonic system.
