PETROLOGY OF THE NEOPROTEROZOIC ITARANTIM NEPHELINE SYENITE BATHOLITH, SAO FRANCISCO CRATON, BAHIA, BRAZIL
Bibliographic record
Abstract
The Itarantim nepheline syenite batholith, with an area of 230 km2, is located at the extreme south of the Southern Bahia Alkaline Province, in Brazil. It has a Pb–Pb zircon age of 721 ± 3 Ma, and consists of the Serra do Rancho Queimado facies of pyroxene-bearing nepheline syenite, and the Serra do Felissimo facies of biotite-bearing nepheline syenite, surrounded by fenite. The two facies have diffuse contacts, and occur along oriented NE–SW bands. The mineralogical and geochemical evolution of the pyroxene syenites was controlled by fractional crystallization, but the biotite-bearing nepheline syenites, whose evolution involves decreasing SiO2 and strong increases in Na2O (up to 9.6%) and Al2O3 (up to 23.5%) contents, probably evolved by open-system behavior with peralkaline fluids. This is indicated by the presence of fenites, and by the strong enrichment in Zr (up to 5100 ppm), Hf (up to 141 ppm), Th (up to 117 ppm), U (up to 74 ppm), Ta (up to 169 ppm) and Nb (up to 1372 ppm) in dyke rocks. The eNd(T) values of the rocks, between +0.6 and +3.0, and eSr(T) values, between − 6.3 and − 12.7, lie along the mantle array, whereas geochemical characteristics are similar to those of OIB. The δ13C values, between − 6.37 and − 6.83‰, and δ18O values, between 6.48 and 6.98‰ in interstitial carbonates, show that even the late magmatic fluids retain a mantle signature. The anorogenic character, the mantle signatures, and the age of the batholith show that it was emplaced during the breakup of Rodinia.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".