Shortening of Archaean and Paleoproterozoic continental lithospheres: large strains, but no orogeny
Bibliographic record
Abstract
Shortening of Archaean and Paleoproterozoic continental lithospheres: large strains, but no orogeny Denis Gapais1, Jonathan Poh1, Philippe Yamato1, Thibault Duretz1, Florence Cagnard2 (1) Géosciences Rennes, UMR CNRS 6118, Université de Rennes 1, 35042 Rennes cedex, France (2) Bureau de Recherche Géologique et minière, 3 avenue Claude-Guillemin, BP 36009 45060 Orléans Cedex 2, France Denis.gapais@univ-rennes1.fr, jonathanpoh87@gmail.com, philippe.yamato@gmail.com, thibault.duretz@univ-rennes1.fr, f.cagnard@brgm.fr In many ancient deformation belts of Archaean and Paleoproterozoic age (e.g. Terre Adélie in East Antarctica, Finnish Svecofennides in Southern Finland, Murchison Belt in South Africa, Thompson Nickel Belt in Manitoba, Dharwar Craton in western India, Abitibi sub-Province in Québec, Trans-Hudson belt of Canada, Trans-Amazonian belt of Suriname), latest recorded deformations are compressive or transpressive. In these belts that involved hot and weak continental crusts, deformations are distributed with basically vertical tectonics and important crustal thickening. On the other hand, there is no evidence of syn-orogenic extension or late-orogenic collapse, as classically observed in modern orogens where extensional detachments are widespread. Analogue and numerical models emphasize that shortening of weak and hot lithospheres basically favour downward motions, which result in limited topographies. Field evidence further point to metamorphic isogrades rather parallel to the Earth surface at belt scale. Hence, metamorphic conditions are rather monotonous at the scale of individual belts, with limited metamorphic jumps and typical P-T paths with no significant adiabatic retrograde segments. Consistently, localized deep detrital sedimentary basins like foreland or intra-mountain basins, are not documented. Sedimentary records rather suggest distributed sedimentation processes. In addition, several lines of evidence tend to point out that cooling of ancient hot deformation belts was rather slow, which is consistent with distributed topographies and long-lasting erosion-driven exhumation processes. On these bases, we propose that gravity-driven collapse had no reason to occur in ancient hot deformation belts because important topographic gradients and orogeny could not develop as observed in modern mountain chains.
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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) | 0.006 | 0.001 |
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".