Sublithospheric diamonds extend Paleoproterozoic record of cold deep subduction into the lower mantle
Bibliographic record
Abstract
Cold deep subduction – a hallmark of modern-style plate tectonics – is the dominant mechanism for recycling crustal materials into Earth's deep mantle, potentially changing its composition, heat budget and dynamics. The onset of cold deep subduction remains contentious and is largely constrained by crustal rocks, despite subduction being driven by mantle processes. Here we use the chemical and chronological information from sublithospheric mantle-derived minerals entrapped in diamonds from the DO-27 kimberlite, Slave Craton, Canada, to better constrain the timing and products of cold deep subduction reaching Earth's lower mantle. DO-27 sublithospheric diamonds preserve a complete lower mantle mineral assemblage: Ca-silicates (retrogressed CaSi-perovskite) ± enstatite (retrogressed bridgmanite) ± ferropericlase. The high Mg#s (molar Mg/(Mg+Fe)) of retrogressed bridgmanite (median Mg#=95) and ferropericlase (median Mg#=86) implicate a harzburgitic host rock for the diamonds. This strongly melt-depleted signature contrasts with the high abundance of Ca-silicate inclusions, some of which are variably enriched in incompatible elements and have enriched Sr-Nd-Pb isotopic signatures that collectively indicate the host rock was metasomatized by carbonatitic melts released from a relatively cold subducting slab in the lower mantle. The U-Pb systematics of the Ca-silicates define two ages of diamond crystallisation: 998 ± 18 Ma and 1679 ± 13 Ma. This is the first direct evidence of cold deep subduction in Earth's lower mantle at ∼1.7 Ga (Paleoproterozoic), in agreement with the oldest crustal low-temperature, high-pressure eclogites and is much earlier than previous Neoproterozoic estimates.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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) | 0.005 | 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".