Continental lithosphere can be described as a rigid outer layer of Earth, primarily composed of a relatively light granitic crust underlain by a denser mantle peridotite layer.
Composition and Structure
The continental lithosphere is distinct from oceanic lithosphere due to its composition and thickness. It is generally older and thicker, extending deeper into the Earth's mantle. Specifically:
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Crust: The continental crust ranges in thickness from approximately 20 to 35 miles (32 to 56 kilometers). It's predominantly composed of granitic rocks, which are relatively low in density compared to other Earth materials. This is what makes the continents "float" higher on the mantle.
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Mantle Lithosphere: Beneath the crust lies a layer of heavy mantle peridotite, extending approximately 60 to 80 miles (96 to 128 kilometers). Peridotite is rich in olivine and pyroxene, making it significantly denser than the granitic crust.
Key Characteristics
Here's a summary of the key characteristics of continental lithosphere:
| Feature | Description |
|---|---|
| Composition | Granitic crust overlying peridotite mantle |
| Thickness | Varies, generally 80 to 115 miles (128 to 185 kilometers) total |
| Density | Relatively lower density compared to oceanic lithosphere |
| Age | Older on average than oceanic lithosphere |
| Tectonic Role | Forms a major part of tectonic plates and participates in plate tectonics |
| Isostasy | Exhibits isostatic balance, meaning it "floats" on the asthenosphere due to density differences |
Tectonic Plates
It's crucial to remember that the continental crust and the underlying mantle lithosphere together form a tectonic plate. These plates move and interact with each other, causing earthquakes, volcanic activity, and the formation of mountains. The differences in density and thickness between continental and oceanic lithosphere significantly influence these interactions.
In conclusion, continental lithosphere is a layered structure consisting of a less dense, thick granitic crust atop a denser mantle peridotite layer, forming a cohesive unit within a tectonic plate. This combination dictates the overall physical and chemical properties, influencing its behavior in geological processes.
