the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 May 2025
Deformation and exhumation in thick continental crusts induced by valley incision of elevated plateaux
Abstract. Surface processes such as erosion and sedimentation play a critical role in crustal deformation, particularly in actively deforming orogenic belts. While these processes have been extensively studied in large-scale erosive and tectonically active regions, the specific effects of valley incision on crustal deformation, especially in tectonically inactive regions, remain poorly understood. In this study, we hypothesize that crustal deformation induced by valley incision is primarily governed by three parameters: incision velocity, crustal thickness, and the elevation difference between the plateau and the valley base level. Using two-dimensional thermo-mechanical models, we investigate the influence of valley incision on crustal deformation and exhumation by varying these parameters. Our results show that valley incision alone can induce significant crustal deformation, associated with lateral viscous flow in the lower crust leading to near-vertical channel flow and extensional brittle deformation in the upper crust below the valley. This deformation leads to lower crust exhumation, within a 10 Myr timeframe, if crustal thickness is greater than 50 km, the initial plateau elevation is greater or equal to 2 km, and the long-term effective erosion rate exceeds 0.5 mm.yr-1. Furthermore, while the onset of lower crust exhumation is primarily controlled by the initial plateau elevation, the total amount of exhumed lower crust after 10 Myr strongly increases with the initial thickness of the lower crust which favors viscous flow. We also show that despite the simplified tectonic context of our models, the first-order results align well with observations from natural systems. These findings offer new insights into the coupling between surface processes and deep crustal dynamics, highlighting the potential for valley incision to drive substantial crustal deformation and promote lower crustal exhumation.
- Preprint
(2049 KB) - Metadata XML
-
Supplement
(1556 KB) - BibTeX
- EndNote
Status: open (until 27 Jun 2025)
-
RC1: 'Comment on egusphere-2025-1962', Carole Petit, 06 Jun 2025
reply
This is an original study on the effect of large valley incision on lower crust exhumation in the context of a continental plateau underlain by a thick continental crust with very low ductile resistance. The authors conclude that, under certain conditions (high plateau elevation, thick crust, large incision rate and prolonged incision history), river incision can lead to exhumation of the ductile lower crust beneath the valley axis. The article is well-written, has high-quality illustrations, and I agree with the main interpretation of the model results. However, I have several criticisms that should be addressed prior to publication, this is why I ask for major revisions although I think that they will be relatively easy to address. My comments to the authors are as follows:
- I understand that in nature, crustal thickness and plateau elevation can vary widely. However, in your case, since you assume constant crust and mantle densities, there should be a linear relationship between these two parameters due to isostasy. This means that you cannot arbitrarily choose both crustal thickness and plateau elevation independently. For example, if we assume a mean crustal thickness of 35 km for sea-level elevation, then local isostasy (neglecting density changes due to temperature and pressure and including the plateau in the total crustal thickness) would give approximately the following values: a 1 km-high plateau corresponds to a total crustal thickness of 42 km, 2 km corresponds to 49 km, and 3 km to 56 km. How, then, can you justify a 65 km-thick crust with a 3 km-high plateau, as shown in Figure 2a, using your chosen densities, without introducing a significant initial isostatic imbalance? Am I missing something here?
- I find one of your results particularly interesting — that surface uplift can be decoupled from the lithospheric response, and that crust-mantle decoupling explains why the Moho remains stable while the lower crust migrates toward zones of lower pressure. Could this behavior explain the very low effective elastic thickness often inferred from the isostatic response of the lithosphere to surface processes? In other words, could this be explained by a situation where only the upper crust effectively responds?
- Yield stress envelope in Figure 2b: there appears to be no strength in the mantle, which seems surprising. With the dry olivine rheology you use, I would expect some resistance.
- I'm generally not in favor of requesting additional model runs in modeling papers, as this can easily become an endless process. However, I am somewhat puzzled by the fact that you don’t really discuss your choice of an extremely weak and thick lower crust, which leads to strong convection and very rapid ductile flow. While I understand this may be a deliberate choice, I think it would be helpful to include a comment on how this specific rheology — which possibly resembles that of an orogenic crust — may not represent the "average" continental crust. Out of curiosity, I would be very interested to see how the system behaves with a more resistant (mafic) lower crust and/or a colder lithosphere. For instance, you could add another dimension to your parameter space in Figure 11, for instance by representing the effect of the thickness and/or average viscosity of the ductile crust and the comparison to natural settings.
- By the way, you should clearly define in the main text what you mean by "lower crust." In your model, you designate crust below 10 km depth as the lower crust, but it shares the same rheological properties as the upper crust. In the literature, "lower crust" can refer either to the ductile portion of the crust — as you do here — or to the more mafic and mechanically stronger part of the continental crust. While this is briefly explained in a figure, it would be helpful to clarify this choice explicitly in the main text to avoid confusion.
- Along the same lines, I’m not sure that such an overthickened and weak crust could remain stable without collapsing, unless it's being artificially supported by the model boundaries. This issue is not visible in your setup because you impose a constant crustal thickness and therefore remove any lateral pressure gradients (except the ones due to valley incision). But from a large-scale geodynamic perspective, the configuration might not be entirely realistic — especially if we consider that real-world plateaus are not laterally infinite. That said, since your model already shows lower crustal flow driven solely by valley incision, I can only imagine how much flow would occur if this plateau were adjacent to a region of much lower elevation and much thinner crust.
Citation: https://doi.org/10.5194/egusphere-2025-1962-RC1
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 85 | 27 | 11 | 123 | 11 | 7 | 6 |
- HTML: 85
- PDF: 27
- XML: 11
- Total: 123
- Supplement: 11
- BibTeX: 7
- EndNote: 6
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1