Petrochronological constraints and tectonic implications of Tonian metamorphism in the Embu Complex, Ribeira Belt, Brazil
Bibliographic record
Abstract
The Embu Complex of the Ribeira Belt, southeast Brazil, provides records of orogenic processes within the time period between Rodinia break-up and West Gondwana assembly. Recent studies have questioned the accretionary setting for the belt, suggesting an intracontinental setting. In this paper, we present new petrological, U–Pb and Rb–Sr data from metasedimentary rocks of the Embu Complex, discussing the implications for the tectonic evolution from Rodinia to West Gondwana in the Ribeira Belt. Sillimanite, sillimanite–K-feldspar and cordierite zones represent the high-grade metamorphic zones for the metamorphic event identified in the southern portion of the Embu Complex. Petrological and thermodynamic modelling data indicate that the high-grade metamorphic rocks of the complex attained conditions between 750–805 °C and 3.6–9.2 kbar. Monazite and zircon U–Pb data indicate that the high-grade metamorphic event occurred between 810–760 Ma, concomitant with igneous activity recorded during this period. In addition, zircon and apatite U–Pb ages, as well as, biotite and muscovite Rb–Sr ages, between 675–550 Ma record a slow cooling rate of 4.4 °C/Ma for the period between 675–640 Ma, and a late stage of shear zones development. These results reinforce the accretion of distinct units within the Ribeira Belt during the Neoproterozoic Era.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 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) | 0.002 | 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".