Lateral variations in lower crustal strength control the temporal evolution of mountain ranges: examples from south‐east Tibet

Penney, Camilla and Copley, Alex (2020) Lateral variations in lower crustal strength control the temporal evolution of mountain ranges: examples from south‐east Tibet. Geochemistry, Geophysics, Geosystems. ISSN 1525-2027 DOI

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Plain Language Summary - Abstract below The rocks which make up the Earth's continents move and change shape in response to tectonic forces. How rocks respond to these forces depends on their material properties, which can vary in space and time. These material properties, therefore, control the shape of mountain ranges, and how mountains grow. This study investigates why some mountain ranges have steep fronts, whilst others have gentle gradients. We look at how regions made up of strong rocks (such as the Sichuan Basin) affect the shape and growth of adjacent mountain ranges. We find that mountain ranges with steep fronts can form when weaker rocks move over stronger ones. Recent measurements of oxygen in ancient soils suggests that parts of the south‐eastern margin of the Tibetan Plateau (between the Sichuan Basin and the Central Lowlands of Myanmar) have been high since about 50 million years ago, and that the area has risen more slowly than has previously been estimated. In south‐east Tibet, the pattern of earthquakes, and how fast the mountains have grown, can be explained by these strong areas, without invoking complicated material properties in the mountain ranges. Such strong regions may be important in controlling the shape of mountain ranges globally. Abstract Controversy surrounds the rheology of the continental lithosphere, and how this rheology controls the evolution and behaviour of mountain ranges. In this study, we investigate the effect of lateral contrasts in the strength of the lower crust, such as those between cratonic continental interiors and weaker rocks in the adjacent deforming regions, on the evolution of topography. We combine numerical modelling with recently published results from stable‐isotope palaeoaltimetry in south‐east Tibet. Stable‐isotope palaeoaltimetry in this region provides constraints on vertical motions, which are required to distinguish between competing models for lithosphere rheology and deformation. We use numerical modelling to investigate the effect of lateral strength contrasts on the shape and temporal evolution of mountain ranges. In combination with palaeoaltimetry results, our modelling suggests that lateral strength contrasts provide a first‐order control on the evolution of topography in south‐east Tibet. We find that the evolution of topography in the presence of such strength contrasts leads to laterally‐varying topographic gradients, and to key features of the GPS‐ and earthquake‐derived strain‐rate field, without the need for a low‐viscosity, lower‐crustal channel. We also find that palaeoaltimetric samples may have been transported laterally for hundreds of kilometres, an effect which should be accounted for in their interpretation. Our results are likely to be applicable to the evolution of mountain ranges in general, and provide an explanation for the spatial correlation between cratonic lowland regions and steep mountain range‐fronts.

Item Type: Article
Uncontrolled Keywords: 2020AREP; IA76
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
Journal or Publication Title: Geochemistry, Geophysics, Geosystems
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 23 Dec 2020 21:14
Last Modified: 10 Jun 2021 00:01

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