Lithological control on the post-orogenic topography and erosion history of the Pyrenees

Abstract

Numerous studies on active mountain ranges have demonstrated the interaction between tectonics and climate in shaping topography. Here we explore how variations in rock types have affected the topographic development of the Pyrenees since cessation of orogenesis ca. 20 Ma. Our study is based on a multidisciplinary approach and integrates topographic analyses, rock strength measurements and thermal modelling of low-temperature thermochronological data published across the Central Pyrenees. Results indicate a strong influence of rock strength in determining the post-orogenic morphology of the Pyrenees. We observe a correlation between rock strength and the normalized channel steepness index (ksn) of the different lithologies. Moreover, the highest topography is dominated by the Variscan plutonic massifs which have highest rock strength. Consequently, the drainage divide appears to track the position of these massifs. Abrupt deceleration of exhumation recorded in inverse modelling of low-temperature thermochronologic data suggests that the exhumation of the Variscan massifs also played role in lowering in erosion rates over the massifs during orogenesis.

26Al/10Be ratios reveal the source of river sediments in the Kimberley, NW Australia

“…While in tectonically active landscapes denudation and sediment transport processes are controlled by the competing influence of tectonic and climatic forcings (e.g., Roe et al, 2008), our study adds to an increasing list (e.g., Nott et al, 1996a, Jansen et al, 2010Scharf et al, 2013;Bernard et al, 2019) showing that in many post-orogenic terrains lithology exerts the dominant control. These actively retreating scarps located along major northsouth homoclinal ridges in the Kimberley plateau, are major factors in landscape denudation, showing the importance of geological structures, lithology, and jointing scale on the dominant erosion processes and spatial distribution of sediment supply.…”

“…These actively retreating scarps located along major northsouth homoclinal ridges in the Kimberley plateau, are major factors in landscape denudation, showing the importance of geological structures, lithology, and jointing scale on the dominant erosion processes and spatial distribution of sediment supply. While in tectonically active landscapes denudation and sediment transport processes are controlled by the competing influence of tectonic and climatic forcings (e.g., Roe et al, 2008), our study adds to an increasing list (e.g., Nott et al, 1996a, Jansen et al, 2010Scharf et al, 2013;Bernard et al, 2019) showing that in many post-orogenic terrains lithology exerts the dominant control.…”

Rock strength and structural controls on fluvial erodibility: implications for drainage divide mobility in a collisional mountain belt

“…This model predicts that a geologically instantaneous capture of the Upper Tennessee River catchment by the Lower Tennessee River occurred at 9 Ma, which has led to a shift in the drainage divide and explains observed subsequent topographic rejuvenation in the landscape visible today. In the Pyrenees, Bernard et al (2019) show the drainage divide follows the position of high-strength, high-elevation plutons in the crystalline basement in the centre of the belt, suggesting a direct lithological control on the position of the central drainage divide. These field studies demonstrate the drainage divide can be mobile in near-horizontal sedimentary stratigraphy of mountain belts and is likely to move to the centre of highly resistant plutons as they get exhumed in the axis of a collisional mountain belt.…”

“…Bedrock erodibility is expected to play a significant role in drainage divide reorganisation since heterogeneous exhumation of weak and strong substrates can enhance and suppress erosion respectively (Giachetta et al, 2014;Gallen, 2018) and cause topographic rejuvenation, for example through the exhumation of a basement palaeosurface (Strong et al, 2019). This is especially the case in postorogenic settings where erosion is dominant over crustal thickening (Gallen, 2018;Bernard et al, 2019). However, the magnitude of erodibility variation within a mountain belt, and the mobility of the drainage divide as rivers erode through its stratigraphy are still relatively unexplored.…”

Rock strength and structural controls on fluvial erodibility: Implications for drainage divide mobility in a collisional mountain belt

“…This model predicts 67 that a geologically instantaneous capture of the Upper Tennessee River catchment by the Lower 68 Tennessee River occurred at 9 Ma, which has led to a shift in the drainage divide and explains 69 observed subsequent topographic rejuvenation in the landscape visible today. In the Pyrenees, 70 Bernard et al (2019) show the drainage divide follows the position of high-strength, high-elevation 71 plutons in the crystalline basement in the centre of the belt, suggesting a direct lithological control 72 on the position of the central drainage divide. These field studies demonstrate the drainage divide 73 can be mobile in near-horizontal sedimentary stratigraphy of mountain belts and is likely to move to 74 the centre of highly resistant plutons as they get exhumed in the axis of a collisional mountain belt.…”