Petrogenesis of Secondary Diatexites and the Melt Budget for Crustal Reworking
Bibliographic record
Abstract
Abstract This study investigates the petrogenesis of diatexite migmatites and leucogranites in a granulite facies terrain and quantifies the melt budget for it. The anatectic rock types in the Ashuanipi Subprovince are: (1) melt-depleted orthopyroxene metatexite migmatite, (2) secondary diatexite migmatite formed where anatectic melt intruded, entrained and accumulated in the metatexite, and (3) leucogranite. The FeO, MgO, TiO2, Cr, Co and Sc contents of the diatexites are controlled by the fraction of entrained metatextite. However, most diatexites and many leucogranites are richer in (Na2O+CaO) but depleted in K2O relative to an anatectic melt + metatexite mixture. This, and the predominance of plagioclase + orthopyroxene frameworks in the diatexites, indicates loss of fractionated melt. Mass-balance models using the metatexite and compositions of fractionated melts and crystallised solids obtained from simulated crystallisation of the anatectic melt indicate that ‘typical’ diatexite formed by mixing ∼40% metatexite with ∼60% anatectic melt, and then when 8 to 30% crystallised, most (>73%) of the remaining melt was expelled, likely by shear-enhanced compaction. The processes making the diatexites and leucogranites expelled ∼50% of the initial amount of melt; some formed the K2O-rich leucodiatexites and leucogranites in the terrain, but most escaped. A melt budget for the present Ashuanipi surface made by combining mass-balance calculations and the area of each rock type reveals that it once held 3.05 times more melt than was generated there. The adjacent Opinaca Subprovince contains 10 times more leucogranite than partial melting there produced; moreover, its leucogranites are compositionally similar to fractionated melts expelled from the Ashuanipi. Combining these crustal levels and assuming a gradient of 30oC km-1, then ∼400 000 km3 of melt representing >68% of the total generated during crustal reworking in the Ashuanipi remained in the middle crust where temperatures were above the solidus.
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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".