Preliminary Ar-Ar geochronology of Mesozoic alkaline-carbonatitic to tholeiitic magmatism in the Quilengues area, SW Angola
Bibliographic record
Abstract
New geochronological data have been obtained on kimberlitic units related to the Bonga carbonatite massif and basaltic dikes in the Quilengues region of southwestern Angola as part of the National Geological Plan of Angola (PLANAGEO). Ar-Ar dating of mineral separates (phlogopite, amphibole) indicates distinct intrusion pulses for the alkaline-carbonatite magmas of the Bonga Complex (155.2 ± 2.9 Ma) and a NNE-SSW dike assemblage (124.7 ± 2.2 Ma). These ages agree with those reported from coeval volcanic materials in the coastal region, suggesting a direct correlation with lithospheric destabilisation processes induced by the ascent of deep melts, during incipient to progressive stages of the Atlantic rifting and Pangea’s breakup. The basaltic dikes may represent the feeding channels of mantle-derived melts that extruded as Large Igneous Provinces (LIPs), forming the Paraná-Angola-Etendeka Province. The spatio-temporal relationships of the studied bodies are consistent with the intrusion of mantle melts during the early stages of rifting, in directions equivalent to the Lucapa structure and the Atlantic margin. The new age data reinforce the existing dataset of Jurassic-Cretaceous alkaline-carbonatite and bimodal (alkaline to tholeiitic) pulses in Angola and their South American counterparts. A structural control is also suggested, with the later alkaline pulses emplaced along ~E-W directions, related to the progress of rifting and the action of deep transform faults during continental breakup.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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".