The relief is not just a matter of crust. The coat, which is located underneath, also has its say. It is notably capable of influencing the relief by creating uplifts or, on the contrary, basins that can reach two kilometers in amplitude.
Mountains, basins, plains… The relief which marks our landscape results from the movements of the tectonic plates which cause the massesmasses continental, but also processes of erosion and alteration, which plane the summits and move the sedimentary particles. We therefore tend to consider that topography is only influenced by the evolution of the earth’s crust, that is to say the envelope solidsolid the outermost part of the globe. We forget, however, that the coatcoat which is underneath also plays a role.
An effect of the mantle hidden in the relief of the crust
The influence is certainly more subtle, and is only seen on large wavelengthswavelengths. Thanks to geodetic and gravimetric studies, we know that surface topography is the result of a sum of several components. There is therefore the crustal component, which is based on the local thickness of the crust and isostasy (i.e. the floating effect of the crust above the mantle), but also a mantle component. , which is based on anomaliesanomalies thermals of the coat. This mantle component is difficult to observe at first glance. It only appears when the crustal component is subtracted from the topography. In certain cases, we can thus see the appearance of a “residual topography”, which is linked to the influence of the mantle.
Topographic variations of up to 2 km
A new study has just highlighted this residual topography on a global scale, based on the analysis of 26,725 points measuring the thickness of the earth’s crust. The results published in the journal Journal of Geophysical Research: Solid Earth show that if this influence of the mantle is often visible at the level of plate boundaries, it is also present inside the plates, where it can produce topographic variations of the order of two kilometers (uplifts or troughs) and which can extend over hundreds or even thousands of kilometers. This residual topography is linked to variations in temperature but also in chemical structure inside the mantle. A warm anomaly in the mantle will lead to an uplift, and a cold anomaly to a lowering of the crust. These new results could provide a better understanding of certain geological processes, notably the presence of magmatism in these regions far from plate margins.
