How Continuous Are the “Relict” Landscapes of Southeastern Tibet?

Abstract

Pervasive low-relief, high-elevation surfaces separated by incised canyons are common
\nacross the Southeastern margin of the Tibetan Plateau and have been used to define the
\nnature of crustal deformation that drove plateau growth. A common assumption is that
\nthese surfaces were once part of a continuous low-relief paleotopography that has
\nundergone surface uplift and dissection. Recent research, however, has questioned
\nthis assumption and the derived geodynamic models, which suggests that these
\nsurfaces formed in situ through drainage network reorganization and the piracy of
\nupstream drainage area. Here, we test the continuity of the low-relief surfaces across
\nSE Tibet using a new inversion scheme that also illuminates the nature of conflicting
\nhypotheses. Our analysis is based on combining the local information contained in maps of
\nnormalized channel steepness with the more distributed and integrated information
\ncontained in maps of normalized landscape response time. This allows us to model
\nthe formation of a hypothetical landscape prior to rock uplift and dissection. We find that
\nlarge variations in channel steepness are required along the trunk channels within the
\ninferred paleotopography. This is inconsistent with a low-relief surface prior to surface uplift
\nand indicates that a surface interpolated between remnants cannot be used to robustly
\nmeasure geodynamic processes in space and time. Furthermore, our inverse framework
\nhighlights many different solutions to this ill-posed problem and thus provides an
\nexplanation as to why the topography alone cannot be used to provide a unique
\nsolution to the debate.

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