The lithospheric mantle, a key component of the Earth's outer shell, exhibits distinct characteristics that set it apart from the asthenosphere and deeper mantle regions.
Key Characteristics of the Lithospheric Mantle:
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Compositionally Distinct: The continental lithospheric mantle (CLM), in particular, is considered a chemically distinct reservoir compared to the rest of the mantle. This chemical heterogeneity is significant because it influences magmatism and provides valuable insights into Earth's history. It is composed of mostly peridotite, an ultramafic rock, but its specific composition can vary geographically.
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Relatively Small Volume: The CLM makes up a relatively small percentage (approximately 2.5%) of the total mantle volume.
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Rigidity and Strength: Compared to the underlying asthenosphere, the lithospheric mantle is more rigid and stronger. This is largely due to lower temperatures, which prevent it from deforming as easily.
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Location and Extent: The lithospheric mantle lies directly beneath the crust and, together with the crust, forms the lithosphere. The thickness of the lithospheric mantle varies; it can be hundreds of kilometers thick beneath continents and significantly thinner beneath oceanic regions.
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Role in Magmatism: The chemical composition of the lithospheric mantle influences the composition of magmas generated in both continental and oceanic settings. It is a source reservoir for various elements and isotopes that can be traced in volcanic rocks.
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Preservation of Chemical Heterogeneity: The lithospheric mantle is more effective at preserving chemical heterogeneity compared to other parts of the mantle. This makes it a valuable source of information about the Earth's evolution and past tectonic events.
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Thermal Boundary Layer: The lithospheric mantle acts as a thermal boundary layer between the cooler crust and the hotter asthenosphere. This temperature gradient affects heat flow within the Earth.
In summary, the lithospheric mantle is a rigid, chemically distinct layer that plays a crucial role in plate tectonics, magmatism, and the thermal structure of the Earth. Its unique characteristics make it a key area of study for understanding the Earth's past and present.
