Geomorphology of active fold-and-thrust belts and plateaux:
unravelling tectonic and climatic controls

Abstract

Orogenic belts on Earth are varied, complex and are areas of seismic and landslide hazard. Understanding them means assessing relative tectonic (active faulting, deformation style, strain rate), climatic (precipitation, glaciation) and erosional (fluvial erosion, lithology) controls. Climatic and tectonic controls are interlinked and understanding the relative importance of each is important for understanding the global landscape system.

Geomorphic indices capture the landscape response to competition between climate and tectonics and reflect the spatial distribution of erosion. They can be applied over remote and large-scale geographic areas. I use geomorphic indices (hypsometric integral (HI), elevation-relief ratio (ZR), surface roughness (SR) and normalised channel steepness (ksn)) to identify areas of active deformation and erosion, highlight landscape variations and I interpret the results for potential tectonic and climatic drivers. Geomorphic indices are also compared to active strain rate, calculated from published geodetic data. High HI, SR and low ZR are found to occur in landscapes overlying areas of brittle crustal deformation (seismogenic faulting) in the Qilian Shan, Himalaya, Andes and Zagros.

In the central-eastern Tibetan Plateau geomorphic indices and precipitation data are used to identify a broad ˜WSW-ENE trending transition in the landscape where changes in landscape and precipitation are grouped and in alignment. I argue that this geomorphic-climatic transition zone represents a change from incised to non-incised landscapes, the location of which is controlled by the western extent of the East Asian summer monsoon rainfall. This modern pattern is consistent with a model of early Cenozoic growth of the eastern Tibetan Plateau, superimposed by incision driven by Miocene monsoon intensification; this model is supported by published erosion rate and thermochronology data.

Precipitation and strain rate are found to be strong controls on landscapes when fold-and-thrust belts are compared but are not found to be major controls on landscape within individual fold-and-thrust belts. Climate (precipitation) is found to be more strongly correlated with geomorphic indices than tectonics (strain rate) and this result has implications for further work in understanding climate-tectonic-landscape relationships.