Sr-Nd-Pb isotopes of fluids in diamond record two-stage modification of the continental lithosphere
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Bibliographic record
Abstract
High-density fluid (HDF) microinclusions in diamonds allow direct investigation of deep carbon- and water-rich fluids that influence the properties of Earth’s mantle. Identifying the sources and evolution of such fluids in the context of different potential mantle reservoirs is difficult due to the limited radiogenic isotope data. Here, we report Sr-Nd-Pb isotope compositions of silicic to low-Mg carbonatitic HDFs in a suite of diamonds from a single source in Canada. Relationships between isotopes and trace element compositions indicate the contribution of two distinct sources within the continental lithosphere: one with relatively primitive isotopic compositions characterised by εNd of −0.2, <sup>87</sup>Sr/<sup>86</sup>Sr of 0.7044 and <sup>206</sup>Pb/<sup>204</sup>Pb of 17.52, and another with more unradiogenic εNd < −16 and radiogenic <sup>87</sup>Sr/<sup>86</sup>Sr and <sup>206</sup>Pb/<sup>204</sup>Pb > 0.713 and 18.3, respectively. We suggest that the latter reflects an old metasomatic event in the continental lithosphere involving fluid addition from a subducting slab, most probably in the Paleoproterozoic. HDFs formed and their host diamonds crystallised in a more recent metasomatic event, indicated by the unaggregated nitrogen of the diamonds, where fluids from both sources mixed. HDFs from Canada, Botswana, and Congo have comparable isotope-trace element relationships, suggesting contributions of similar sources in distinct lithospheric provinces worldwide.
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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 | 0.001 |
| 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) | 0.002 | 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 it