Continental lithosphere formation fundamentally occurs when the mantle lithosphere becomes denser than the underlying deep mantle rocks. This density difference initiates a process called delamination.
Here's a breakdown of the process:
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Mantle Lithosphere Density: The mantle lithosphere, the rigid outermost shell of the Earth beneath the continental crust, can become denser due to cooling and compositional changes.
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Delamination: When the mantle lithosphere is heavier than the asthenosphere (the hotter, more ductile part of the upper mantle), it sinks or detaches from the base of the continental plate in a process termed "delamination." Think of it as a dense layer peeling off.
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Upwelling of Warm Mantle: The delaminated layer is replaced by an upwelling of hotter mantle material from below.
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Thermal Effects on Crust: This upwelling warm mantle heats the overlying crust.
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Isostatic Uplift and Extension: The warming leads to thermal expansion and isostatic uplift (the rising of land masses due to decreased weight). It can also cause crustal extension (stretching) and possibly gravitational collapse.
In essence, continental lithosphere formation is an ongoing cycle of thickening, densification, delamination, and replacement by warmer, buoyant mantle material that ultimately shapes the continents.
