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How do folding and overthrusting thicken Earth’s crust and build mountain ranges?
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continental landform
Davis's proposed landscape-development states. The morphology shown is not actually time-indicative. For example, A could be a gully system in soft sediment or a canyon such as the Royal Gorge in Colorado, which is millions of years old. The ridge-ravine topography of B would normally develop under humid conditions, but the river meandering on alluvium indicates a prior or extraneous non-humid aggrading mechanism. The riverine plain of C implies a complex history of planation and aggradation in a current fluvial mode.
Folding and overthrusting thicken the Earth’s crust and build mountain ranges primarily through horizontal crustal shortening. When two lithospheric plates converge, the buoyant continental crust resists being carried deep into the asthenosphere. Instead, slices of crust are scraped off and stacked on top of one another, effectively thickening the crust and elevating the terrain.123
This process involves several key mechanisms:
- Folding: Layers of sedimentary rock are compressed into linear anticlines and synclines. In deeper, hotter regions, rocks may appear to flow into large folds rather than bending.3
- Overthrusting: Through ramp overthrusts, large slices of crystalline rock are torn from the basement and thrust upward onto the intact continent. This displacement can uplift rocks by 10 to 20 kilometers, creating high-relief mountain ranges.3
- Crustal Stacking: As one continent plunges beneath another, multiple slices of material are removed and stacked, which increases the vertical thickness of the crust.3
These tectonic processes elevate land faster than erosion can wear it down, resulting in the formation of major mountain belts.2