Modelling Partial Melting in Sinking Greenstone Belts With Implications for Archaean Continental Crust Formation
Bibliographic record
Abstract
Abstract Tonalite–trondhjemite–granodiorite (TTG) gneisses are the dominant component of Archaean continental crust, with their parent magmas generally thought to have formed due to the partial melting of hydrated basalts; however, this process typically produces melts with a notably lower Mg # than most natural TTGs. By contrast, ultramafic volcanic rocks commonly preserved in Archaean greenstone belts may represent an alternative source of TTG magma that has been largely overlooked. Here, we use petrological modelling to investigate anatexis of komatiites and komatiitic basalts from the Warrawoona Group of the Pilbara craton. In all cases, komatiite is refractory and generates no melt within the pressure‐temperature range considered. Komatiitic basalts, however, could produce 20–25 vol. % of MgO‐rich melts during greenstone belt sinking and hot subduction. Anatexis of komatiitic basalts generates melt fractions too depleted in large ion lithophile elements to represent natural TTGs; however, hybridization of melts produced by partial melting of tholeiitic basalts and komatiitic basalts during crustal overturn would generate magma that resembles natural TTGs. All calculated melts are felsic in composition, and TTGs with high Mg # could have been generated entirely within the crust, with no requirement for the assimilation of mantle materials. By contrast, Archaean sanukitoids require some assimilation of mantle materials with crustal melts, indicating that the oldest sanukitoids preserved in each Archaean craton may record temporary and localized subduction on the early earth. The ubiquitous occurrence of sanukitoids worldwide by c . 2.7 Ga may provide a minimum age for the onset of global plate tectonics.
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".