Geochemical and temporal provinciality of the magmatism of the eastern Parnaíba Basin, NE Brazil
Bibliographic record
Abstract
Abstract This paper presents new field, petrographic, geophysical, geochemical and geochronological data for the felsic and mafic magmatism of the eastern Parnaíba Basin, integrating previously published data with new surface data acquired within the scope of the Cooperation Program developed by UERJ-Petrobras. New precise 40 Ar– 39 Ar Cambrian ages ( c. 508–506 Ma) were obtained for the felsic volcanic to subvolcanic rocks associated with intracontinental rift sediments in the São Raimundo Nonato area in the SE of the basin. The new results include the detection of three different basic magmatic pulses at c. 181, 126 and 118 Ma, related, respectively, to Central Atlantic Magmatic Province magmatism, the Sardinha large igneous province and the break-up period for the equatorial basins. The eastern side of the basin contrasts with the western side and shows a predominance of outcropping sills of Sardinha age. Most of these rocks are quartz tholeiites, but two samples ( c. 118 Ma) are olivine tholeiites. This paper provides the first description of a clear chemical provinciality of the Sardinha tholeiitic magmatism in the eastern Parnaíba Basin, similar to that described in the Paraná Basin. Low-TiO 2 suites, independent of age, occur on the northwestern side of the Senador Pompéu–Coccoci lineament, whereas high-TiO 2 suites, including the Ceará Mirim dyke swarm in the basement to the east, are located SE of this lineament. The duality of geochemical signatures reproduces the basement signatures of the opposite sides of the Senador Pompéu suture zone, suggesting, at least in part, that the composition of the sub-lithospheric continental mantle of these two domains played a part in the development of Cretaceous magmatism in the Parnaíba Basin. Supplementary material: Geophysical and geochemical data provided by Petrobras and subsequent analysis. Supplementary material available online at https://doi.org/10.6084/m9.figshare.c.4117985
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".