M4 ErosionSedimentationExhumation Cycle

Topic

The erosion-sedimentation-exhumation cycle links tectonic uplift, surface denudation, sediment transport and deposition in basins, and the isostatic response—which, in turn, feeds back into that same tectonic uplift. This cycle is the mechanism by which continental crust is recycled, mountains are built and destroyed, and sediments come to record the entire tectonic and climatic history of their source region.

Tectonic uplift increases the slope of the rising terrain; this steeper slope accelerates the rate of erosion, and the resulting removal of rock mass relieves the load on the lithosphere, triggering isostatic rebound. For every meter of rock removed by erosion, the lithosphere rebounds by seventy-five to eighty-five centimeters—depending on the relative densities of the eroded rock and the underlying mantle—and this isostatic rebound further uplifts the terrain. This creates a self-reinforcing cycle in which the total exhumation vastly exceeds the initial tectonic uplift that triggered the process.

This coupling between erosion and isostatic response drives the phenomenon of continuous exhumation—a process detected by thermochronology even in mature mountain ranges, long after active subduction has ceased pushing them upward.

River incision into a streambed follows a well-established principle: the incision rate depends on the river's drainage basin area (a proxy for discharge volume) and the slope of the channel at that specific point. When the incision rate exactly matches the rate of tectonic uplift, the system reaches a steady state that determines the equilibrium elevation of the entire mountain range. The sediment production generated by erosion, and the transport of that sediment into a foreland basin or onto a continental margin, follow diffusion and advection laws that are strongly dependent on the region's climate; this—together with the previously described isostatic rebound and fluvial incision—completes the cycle linking tectonic uplift and erosion with which this description began.

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