Mineralogical and geochemical characteristics of the NNW-NNE trending Libiri doleritic dyke swarm of the Paleoproterozoic Liptako basement (West Niger): Genesis and magmatic evolution
Bibliographic record
Abstract
The NNW-NNE Libiri doleritic dyke swarm of the Liptako region of West Niger is one of multiple mafic dyke swarms that crosscut the Birimian formations of the Léo-Man shield in the West African Craton. This NNWNNE trending swarm consists of two different groups based on mineralogy and geochemical composition. Both groups have a matching assembly of minerals (ferro-edenite, pyroxene, plagioclase, biotite, apatite, chlorite, grains with granophyric texture and titanomagnetite-ilmenite). In detail Group I dykes have a distinct intergranular texture and some particular minerals (bytownite, pigeonite, clinoenstatite and sanidine) that differ from those in Group II dykes which have a partially preserved ophitic texture and less calcic plagioclases (albite to labradorite). Variation in Mg# and differentiation index (DI) indicate that Group I (Mg# = 55–65, DI = 16.26–20.19) is more primitive in composition than Group II (Mg# = 30–35, DI = 22.82–50.00). REE and other incompatible element values are elevated in Group II compared to Group I, and the REE slopes are parallel one to each other, which suggests that the two groups are co-genetic and that Group II units are more evolved magmas from Group I. The presence of negative Nb and Ta values normalized to primitive mantle in both groups and the La n /Yb n (4.73–6.21) ratios suggests that the magma was formed by partial melting of hydrated garnet lherzolite from the lithospheric mantle, modified by interaction with previously metasomatized lithosphere in subduction setting. Alteration minerals such as ferro-edenite, biotite, epidote and chlorite on augite crystal margins indicate later deuteric alteration or low grade late magmatic metamorphism. Petrography and chemistry of a sample SD (Samira Dyke, a sample from the Libiri pit in the Samira gold mine, which was previously dated at 1791 ± 3 Ma and belong to Group II dykes) suggests the entire swarm of NNW-SSE to NNE-SSW trending dykes belong to the Libiri swarm of a plume-generated Large Igneous Province that extends into formerly adjacent Sarmatia (Baltica) and Amazonia.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| 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 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".