Erosion and development of granitic inselbergs in cratonic zones: insights from the Quixadá/Quixeramobim Complex, NE Brazil
Bibliographic record
Abstract
The origin of inselbergs is classically linked to long-term episodic exposure, alternating between the deepening of the weathering mantle and the regolith stripping driven by differential erosion. However, a better understanding of denudation patterns and exposures ages in granite landscapes is hindered by key gaps arising with this assumption: i) the absence of sedimentary markers or their dating; ii) the scarcity of quantified denudation rates to reconcile with classical models of evolution in cratonic zones. To address these gaps, in-situ produced 10Be and 26Al in river-borne sediments, bedrocks, and sedimentary deposits can be compared and analyzed to quantify the role played by differential erosion in the evolution of granitic inselbergs and to unravel complex exposure histories. Previous studies quantifying erosion in granitic landscapes have focused on small inselberg groups or isolated high inselbergs, comparing rock surfaces without integrating sedimentary covers or basin-averaged denudation, thereby limiting regional-scale understanding. In this study, we paired 10Be and 26Al in quartz from sands and rocks collected across watersheds, colluvial-eluvial sediments, and inselbergs. Denudation rates were combined to reconstruct the history of inselbergs in a tropical semiarid setting.Using this approach, we selected the Quixadá/Quixeramobim Complex (NE Brazil), a globally significant inselberg field with 561 units, renowned for its diverse granite landforms in cratonic and semiarid areas. These landforms rise 1-410 m above the Surface Sertaneja (160-240 m). Within the plutons, the erosion surface is ~20 m lower than in adjacent regions, where metamorphic rocks and colluvial-eluvial covers are found.Our results show that colluvial-eluvial covers exhibit higher cosmogenic nuclide concentrations than bedrocks, with values at least twice as high as those in watersheds. Conversely, catchments experience faster erosion than bedrocks. All bedrocks and 60% of the catchments are plotted within the steady-state erosion island, whereas Cenozoic covers display low 26Al/10Be ratios. Average exposure ages suggest a Pleistocene age (1.0-1.4 Ma) for sedimentary covers. This reflects a general denudation pattern where inselbergs and sedimentary surfaces are preserved while the regional erosion surface is progressively stripped.Assuming no erosion for sedimentary covers and continuous denudation, the differential denudation obtained between inselberg top and basin-averaged rates indicates that ~20 Ma is required to grow a 175 m-high inselberg, and ~50 Ma for a 400 m-high inselberg. These results highlight the utility of cosmogenic techniques in measuring denudation rates and improving the understanding of processes that govern origin and development of inselbergs.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".