Impact of tectonic topographic rejuvenation in landscapes with high bedrock/duricrust strength: Insights from geomorphic evidence in a post-rifted region (SE Brazil)
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2023-08-15
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The evolution of Cenozoic relief in post-rifted and post-orogenic landscapes reveals enigmatic and intricate dynamics. Unsteady conditions long after the cessation of ongoing tectonics have been reported in these landscapes with evidence for relief growth rather than the expected slow topographic decay. Various controlling factors (e.g., lithology and isostasy) have been invoked to explain their geomorphic evolution; however, topographic rejuvenation controls remain puzzling, particularly within intraplate landscapes. Here, we investigated topographic rejuvenation, exploring the interactions between the river long profiles of the drainage network, the broader landscape topography, and their collective relationships with the strength of the bedrock and duricrust soils that cap the land surface in the Southern Espinhaço Range of Brazil. This is a humid tropical post-orogenic and post-rifted landscape characterised by resistant bedrock and duricrusts, despite some rock-type strength variability. We show robust evidence for a first-order control exerted by the lithology/rock strength. However, results revealed an overall non-collinearity between the transformed river profiles. These profiles displayed knickpoints separating upstream low-relief uplands capped by Fe/Al duricrusts from an incised downstream transient landscape associated with uplift/base-level fall. Regionally, the river profiles display an asymmetric pattern of relief growth with an eastward gain in elevation and fault-controlled dismantling of duricrusted surface that cannot be explained exclusively by bedrock strength variations. This spatial configuration suggests that links exist between the internal and external factors that collectively control the landscape development. The interplay between faulting/dismantling of the duricrusts and river incision/topographic patterns provides compelling evidence for Pliocene tectonic/topographic rejuvenation. Our findings are consistent with a pattern of regional surface uplift related to combined flexural isostasy and far-field stress interactions. Collectively, our study demonstrates that lithology, as a first control factor on topographic rejuvenation, is not exclusive to post-orogenic landscapes with strongly heterogeneous bedrock. The bedrock/duricrust strength acts in combination with locally inherited discontinuities and large-scale tectonics/flexural isostasy. Such interactions add significant complexity to the evolution and rejuvenation of post-rifted landscapes, particularly within intraplate settings.
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Duricrust, Post-orogenic landscape, Rock strength, Tropical highland
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Geomorphology, v. 435.