Metamorphism overprint in mafic–ultramafic cumulates in the Mangabal and Americano do Brasil complexes, Brasilia Belt, Brazil
Bibliographic record
Abstract
The Americano do Brasil and Mangabal complexes belong to a cluster of Neoproterozoic mafic–ultramafic intrusions in the southern Goiás Magmatic Arc in Brazil. Both complexes were highly deformed and metamorphosed under amphibolite facies, leaving few igneous relict domains. We have documented the mineralogy and texture of the poorly exposed rocks of the Americano do Brasil and Mangabal complexes. We use diverse analytical methods, encompassing petrography, mineral chemistry, geochemistry and thermodynamic modelling, with the principal objective of elucidating the intricacies of secondary alteration processes and offering insights into the complex metamorphic history of the complexes. The rocks of both complexes show intense amphibolitization associated with the most highly metamorphosed rocks. The construction of pseudosections suggests a temperature between 670 and 710°C and pressure up to 7.5 kbar at amphibolite facies conditions. In some amphibolite samples, we note unusual minerals such as kyanite, sillimanite, muscovite, silvialite (a sulfate-rich member of calcic scapolite) and/or anhydrite. We attribute some unusual assemblages to open system behaviour during metamorphism, probably related to metasomatism surrounding diorite veins that are inferred to have released fluids rich in CO 2 , Ca and SO 3 . However, this open system behaviour and fluid circulation do not seem to favour Ni–Cu mineralization.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".