Topographic rejuvenation of an elevated post-rifting landscape with low contrasting rock strength(Southeast Brazil)

Post-rifting and dead orogens landscapes have presented topographic rejuvenation long after intense tectonic activity ceased, resulting in relief growth in a topography that was expected decay.In addition, there is compelling evidence of low denudation rates in tropical post-orogenic landscapes, mainly related to low-relief uplands capped with duricrusts.Thus, understanding the evolution of these landscape settings has proven enigmatic. Recent studies have invoked the contrasting rock strength as primary factor for such topographic rejuvenation. In contribution to this issue, we investigated the topographic signals in a post-orogenic and post-rifting Brazilian landscape with low contrasting rock strength, the Southern Espinhaço Range(SER). In order to reveal potential relief growth, we explored interactions between drainage signatures, topographic metrics, bedrock inheritance and duricrusts. We extracted local relief, hillslope angle, and normalised channel steepness, and performed knickpoint and stream profile analysis to explore spatial variations in topography of the study area. Our findings suggest that the post-rifting evolution of the study area is dictated by episodic uplift and base level fall events coupled with favored stress concentrator zones, which accelerate channel incision and trigger ongoing dismantling of duricrusts. Knickpoints at high elevation separate a relict low-relief landscape upstream, capped by either Fe or Al duricrusts, from a transient adjustment zone downstream, indicating that records of different boundary conditions coexist in the landscape. This study shows a contradiction between low denudation rates and topographic rejuvenation even in a low contrasting rock strength domain. We have found that interactions between surface processes and pre-existing weakness zones likely occur in the SER, highlighting how enigmatic and complex long-term landscape evolution can be in ancient post-orogenic and post-rifting settings.