Lateral Variations in Lower Crustal Strength Control the Temporal Evolution of Mountain Ranges: Examples From South‐East Tibet

Abstract

Controversy surrounds the rheology of the continental lithosphere, and how this rheology controls the evolution and behavior 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 modeling 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 modeling to investigate the effect of lateral strength contrasts on the shape and temporal evolution of mountain ranges. In combination with palaeoaltimetry results, our modeling 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 kilometers, 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.

Post‐50 Ma Evolution of India‐Asia Collision Zone From Paleomagnetic and GPS Data: Greater India Indentation to Eastward Tibet Flow

“…Figure 2b highlights the fact that a strong compression is located along the Himalayan compressive front, and a positive dilatation rate affects the central Tibetan Plateau. In central Tibet, the strain rate axes show an E–W to NW–SE oriented extension, in agreement with an E‐SE‐ward directed gravitational flow of the Tibetan crust (Copley & McKenzie, 2007; Penney & Copley, 2021). The geodetic velocity field with respect to Tibet‐fixed (Figure 2b) and the Quaternary slip rates highlight that the Xianshuihe‐Xiaojiang fault system absorbs most of the deformation induced by the large‐scale CW rotation around the EHS (Wang et al., 2021).…”

Impact of Decelerating India‐Asia Convergence on the Crustal Flow Kinematics in Tibet: An Insight From Scaled Laboratory Modeling

“…Our model experiment strongly supports the hypothesis proposed by several earlier workers that the eastward flows encountered a resistance from the mechanically strong Sichuan basin in eastern Tibet (Clark et al., 2005; Cook & Royden, 2008; Penney & Copley, 2021). The Sichuan basin thus acted as a crucial factor in forcing the crustal flows to take a clockwise turn around the EHS (Figure 10c).…”

Southeastern Tibetan Plateau Growth Revealed by Inverse Analysis of Landscape Evolution Model

“…A progressive southeastward growth from the central plateau since the Paleogene is in agreement with synthesized structural analyses (Li, Wang et al, 2015;Wang et al, 2014) and compiled thermochronologic ages (Li et al, 2019;Figure S1 in Supporting Information S1), showing a younging trend from the central plateau (with almost exclusively Paleogene ages) to the SE plateau margin (with ages extending up to the Pliocene). Our modeling results, showing gradual propagation rather than initial wholesale uplift (e.g., for 𝐴𝐴 𝐴𝐴𝑓𝑓 ≈ 20 Ma and 𝐴𝐴 𝐴𝐴𝑖𝑖 − 𝐴𝐴𝑓𝑓 ≈ 0 in Figure S3 in Supporting Information S1) in SE Tibet, are also consistent with various geodynamic models which suggest that the plateau expanded progressively in an outward propagation sequence characterized by successive marginal uplift (e.g., Penney & Copley, 2021;Wolf et al, 2021). This outward propagation with deeply incised valleys is also consistent with the early Oligocene diversification of Alpine flora linked to joint uplift and monsoonal intensification in central Tibet (Ding et al, 2020), followed by the late Miocene development of SE Tibet biodiversity hotspots (e.g., the Hengduan mountains) that have been genetically linked to orogenesis and habitat segmentation by incising drainages (e.g., Xing & Ree, 2017).…”