High-precision U–Pb dating and Hf isotopes of MARID zircons reveals multi-source, prolonged metasomatism of the Kaapvaal sub-continental lithospheric mantle
Bibliographic record
Abstract
Abstract Mica-amphibole-rutile-ilmenite-diopside (MARID) xenoliths are unique examples of phlogopite-dominated mantle metasomatism hypothesized to correlate geochemically and petrologically to kimberlite and carbonate-rich olivine lamproite (formerly group II kimberlite) magmatism. Here, we investigate the linkage between MARID metasomatism and alkaline magmatism using multiple analytical techniques: in situ trace element major phase and zircon geochemistry, in situ Hf isotope and U–Pb zircon geochemistry and geochronology, and high-precision isotope dilution U–Pb zircon geochronology. We find that most zircons in the studied MARID suite from Kimberley (South Africa) crystallized over a protracted interval in the Late Cretaceous coeval with regional kimberlite volcanism, with one sample yielding Neoproterozoic and Mesoproterozoic dates that are broadly coeval with Proterozoic tectono-magmatic events. Notably, we observe that older metasomatic compositions and ages in zircon are not obscured by mantle storage or later metasomatic events. Our findings confirm that some MARID-like metasomatism occurred as early as the Proterozoic, evolving to form a viable lithospheric mantle source for carbonate-rich olivine lamproites. Zircon geochemistry and geochronology also document that MARID precursors are infiltrated and modified by later Cretaceous kimberlitic melts, resulting in their diverse geochemical and isotopic compositions.
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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 | 0.000 | 0.000 |
| 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 | 0.000 |
| 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 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".