High-pressure Cu–Fe–S Phase Equilibria: some Experimental and Thermodynamic Constraints on Sulfides in Subduction Zones and the Lithospheric Mantle
Bibliographic record
Abstract
Abstract High-pressure phase relations for much of the Cu–Fe–S system have not previously been determined experimentally. Experimental studies have concentrated on low-pressure phase relations and cannot explain high-pressure sulfide mineral inclusion assemblages in some natural blueschists and eclogites. In particular, the coexistence of pyrite + covellite at 1·0 GPa, and pyrite + bornite at 1·9 GPa, observed in New Caledonian rocks, is precluded by tie-lines between S and bornite, and S and the intermediate solid solution (iss), in the published low-pressure experimental topologies at corresponding temperatures. In addition, the Cu content (up to ∼10 at%) of pyrrhotite in eclogite exceeds the experimentally determined maximum for Cu in solid solution with pyrrhotite at low pressures and at corresponding temperatures. We have performed six experiments in which natural chalcopyrite starting material was equilibrated at conditions ranging from 1·0 to 1·7 GPa and 500 to 650 °C. At 1 GPa chalcopyrite is replaced by iss. The iss phase undergoes a terminal breakdown reaction between 1·0 and 1·7 GPa, being replaced by a new assemblage of bornite, pyrite, and pyrrhotite. Our experimental results confirm predictions from the SUPCRT thermodynamic database (Johnson et al., 1992; Computers & Geosciences 18, 899–947) but not that of Robie & Hemingway (1995; US Geological Survey Bulletin 2131). The former database is therefore recommended for calculation of high-pressure sulfide phase relations. Chalcopyrite and its high-temperature, low-fS2 equivalent, iss are not stable at pressures corresponding to much of blueschist–eclogite-facies metamorphism. These results are also applicable to sulfide assemblages in the lithospheric mantle along both oceanic and continental geotherms; the subsolidus Cu-rich mineral in the lithosphere at depths of 30 to >65 km must be bornite–digenite solid solution (bn-ss) rather than iss as is commonly assumed.
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How this classification was reachedexpand
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 | 0.000 |
| 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".