Petrology and geochronology of Mesoproterozoic mafic–intermediate plutonic rocks from Mitwaba (D. R. Congo): implications for the evolution of the Kibaran belt in central Africa
Bibliographic record
Abstract
Mesoproterozoic supracrustal rocks in the Kibaride belt (southeast Congo) were intruded by mafic–intermediate plutonic rocks. These igneous rocks were affected by greenschist- to amphibolite-facies metamorphism during the Mesoproterozoic Kibaran orogenesis. U–Pb single zircon dating of the Mitwaba mafic–intermediate plutonic rocks yields an emplacement age of 1.38 Ga. The compositions of the Mitwaba mafic–intermediate plutonic rocks range from gabbro to diorite and show the following elemental concentrations: SiO2: 49–58 wt%, TiO2: 0.53–0.92 wt%, A2O3: 13.1–18.68 wt%, Zr: 45–142 ppm, Y: 13–43 ppm. Mg no. 40–66 indicates variable degrees of fractionation of the magmas. The rocks are marked by high and variable Th/Ta (3–14), La/Nb (2–5) and low Ce/Pb (0.3–12.8) and Ti/V (10–19). Chondrite-normalized REE patterns exhibit enrichment in LREE relative to HREE ((La/Yb)N=2.9–5.8). Primordial mantle-normalized spider diagrams show negative slopes with gradual decrease from LIL to HFS elements and are marked by Nb and Ti negative anomalies. Immobile trace-element contents indicate a continental arc setting for these mafic–intermediate igneous rocks. They are inferred to have originated from a mantle wedge enriched by fluid from a subducting slab, with possibly an additional contribution from subducted sediments. Low, sub-chondritic Nb/Ta ratios in these mafic rocks support this interpretation. A model involving underplating of mafic–intermediate arc magma into the crust, triggering partial melting of Mitwaba group metasedimentary rocks during the accretionary stage of the Kibaran orogeny, is proposed to explain the coeval emplacement of mafic–intermediate arc magmas and peraluminous S-type granitoids in the Kibaride belt of central Africa.
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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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| 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".