Preprints
https://doi.org/10.5194/esurf-2020-68
https://doi.org/10.5194/esurf-2020-68

  25 Aug 2020

25 Aug 2020

Review status: a revised version of this preprint was accepted for the journal ESurf and is expected to appear here in due course.

Growing topography due to contrasting rock types in a tectonically dead landscape

Daniel Peifer1,2, Cristina Persano1, Martin D. Hurst1, Paul Bishop1, and Derek Fabel3 Daniel Peifer et al.
  • 1School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, UK
  • 2CAPES Foundation, Ministry of Education of Brazil, Brasilia – DF 70040-020, Brazil
  • 3Scottish Universities Environmental Research Centre, East Kilbride, G75 0QF, UK

Abstract. Many mountain ranges survive in a phase of erosional decay for millions of years (Myr) following the cessation of tectonic activity. Landscape dynamics in these post-orogenic settings have long puzzled geologists due to the expectation that topographic relief should decline with time. Our understanding of how denudation rates, crustal dynamics, bedrock erodibility, climate, and mantle-driven processes interact to dictate the persistence of relief in the absence of ongoing tectonics is incomplete. Here we explore how lateral variations in rock type, ranging from resistant quartzites to less-resistant schists and phyllites and up to the least-resistant gneisses and granitic rocks, have affected rates and patterns of denudation and topographic forms in a humid semitropical, high-relief, post-orogenic landscape in Brazil where active tectonics ended hundreds of Myr ago. We show that denudation rates are negatively correlated to topographic relief, channel steepness and modern precipitation rates. Denudation instead correlates with inferred bedrock strength, with resistant rocks denuding more slowly relative to more erodible rock units, and suggest that the efficiency of fluvial erosion varies primarily due to these bedrock differences. Variations in erodibility continue to drive contrasts in rates of denudation in a tectonically inactive landscape evolving for hundreds of Myr, suggesting that equilibrium is not a natural attractor state and that relief continues to grow through time. Over the long timescales of post-orogenic development, exposure at the surface of rock types with differential erodibility can become a dominant control on landscape dynamics by producing spatial variations in geomorphic processes and rates, promoting the survival of relief, and determining spatial differences in erosional response timescales long after cessation of mountain building.

Daniel Peifer et al.

 
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Status: closed
Status: closed
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Printer-friendly Version - Printer-friendly version Supplement - Supplement

Daniel Peifer et al.

Daniel Peifer et al.

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Short summary
Plate tectonics drives the formation of mountain ranges. Yet when tectonic forces cease, mountain ranges persist for hundreds of millions of years, forming major Earth surface features. Our contribution presents denudation rate estimates from one such ancient mountain range that show that denudation is strongly tied to rock type. Resistant rocks are denuding more slowly despite having much steeper topography and contrasts in rock type cause increasing relief in the absence of active tectonics.