Decoupling of Zr-Hf during contact metamorphic anatexis of metabasalts and timing of zircon growth, Sudbury, Canada
Bibliographic record
Abstract
Whole-rock Zr-Hf systematics combined with zircon petrography, geochronology, and geochemistry in partially melted mafic rocks offer new insights into Zr-Hf decoupling processes during metamorphism. Zirconium and Hf are frequently used to interpret the petrogenesis of mafic igneous rocks, but their behavior during dehydration and partial melting is still controversial. The contact aureole of the 1850 Ma Sudbury Igneous Complex (SIC, Canada) includes pyroxene hornfels facies metabasalts with systematically strong negative whole-rock Zr/Zr* (down to 0.25) and Zr/Hf (down to 29.7) anomalies. This signature only occurs in the highest grade portions of the aureole where partial melting occurred proximal to the SIC, and indicates that Zr-Hf decoupling is linked to partial melting and melt segregation. In this zone, the metabasalts contain intergranular melt with rare interstitial and poikilitic zircon grains yielding an 1850 ± 24 Ma U-Pb age, connecting zircon growth to partial melting processes. In addition, zircon texturally overgrows the peak contact metamorphic mineral assemblage and locally shows straight crystal faces in microleucosomes. This is consistent with zircon crystallizing from trapped melt and in agreement with models suggesting that metamorphic zircon does not necessarily grow during peak pressure-temperature conditions. The apparent requirement for melt to facilitate zircon growth and Zr-Hf mobility illustrates the importance of melting for understanding zircon and Zr-Hf behavior in mafic rocks. An increased understanding of whole-rock Zr-Hf decoupling combined with zircon analysis provides the opportunity of better constraining high-temperature crustal processes involving silicate melts.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 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) | 0.003 | 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".