Formation of Diatexite Migmatite and Granite Magma during Anatexis of Semi-pelitic Metasedimentary Rocks: an Example from St. Malo, France
Bibliographic record
Abstract
Abstract Petrological and geochemical variations are used to investigate the formation of granite magma from diatexite migmatites derived from metasedimentary rocks of pelitic to greywacke composition at St. Malo, France. Anatexis occurred at relatively low temperatures and pressures (<800°C, 4–7 kbar), principally through muscovite dehydration melting. Biotite remained stable and serves as a tracer for the solid fraction during melt segregation. The degree of partial melting, calculated from modal mineralogy and reaction stoichiometry, was <40 vol. %. There is a continuous variation in texture, mineralogy and chemical composition in the diatexite migmatites. Mesocratic diatexite formed when metasedimentary rocks melted sufficiently to undergo bulk flow or magma flow, but did not experience significant melt–residuum separation. Mesocratic diatexite that underwent melt segregation during flow generated (1) melanocratic diatexites at the places where the melt fraction was removed, leaving behind a biotite and plagioclase residuum (enriched in TiO2, FeOT, MgO, CaO, Sc, Ni, Cr, V, Zr, Hf, Th, U and REE), and (2) a complementary leucocratic diatexite (enriched in SiO2, K2O and Rb) where the melt fraction accumulated. Leucocratic diatexite still contained 5–15 vol. % residual biotite (mg-number 40–44) and 10–20 vol. % residual plagioclase (An22). Anatectic granite magma developed from the leucodiatexite, first by further melt–residuum separation, then through fractional crystallization. Most biotite in the anatectic granite is magmatic (mg-number 18–22).
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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 | 0.001 |
| 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) | 0.001 | 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 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".