New Ar-Ar geochronology of the Catanda carbonatitic magmatism (Angola) and implications on its origin
Bibliographic record
Abstract
The Catanda Complex is one of the few examples of extrusive carbonatitic volcanoes in the world, and the only one known in Angola. It occurs along the Lucapa corridor that runs SW-NE across Angola. Kimberlitic, alkaline (mostly syenitic to ijolitic terms) and carbonatitic intrusions mark this corridor out that runs SW-NE across Angola. This magmatism was previously related to the Mesozoic continental rifting and the opening of the South Atlantic Ocean. However, recent geochronology from the carbonatitic volcanics of the Catanda Complex indicates that these volcanic rocks are much younger (0.56-0.78 Ma), and related to the Pleistocene reactivation of Mesozoic structures coeval with the formation of the East African rift. Newly acquired Ar39-Ar40 geochronology during the PLANAGEO project illustrates the complexities of dating these carbonatitic melts. The whole-rock Ar-Ar spectra shows a U-shape pattern indicative of excess-Ar with a series of well-defined steps at 471 ± 28 Ma and 210 ± 6 Ma, confirmed by the intercepts of their separate Ar-isochrons. The geological significance of these dates is questionable, but this Ar-spectra could indicate the presence of older Ar reservoirs. A phlogopite separate from the same sample does provide a reliable spectra with an Ar-Ar plateau age of 3.01 ± 0.53 Ma and a concordant Ar-isochron age of 2.83 ± 0.66 Ma. This age is slightly older than the previously reported ages suggesting the existence of several carbonatitic magmatic pulses in the Catanda area during the Pliocene-Pleistocene.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".