Continental collisional effects on magma source redox state and water content: Insights from thermodynamic modeling
Bibliographic record
Abstract
Abstract Arc magmas are typically more oxidized and hydrous than postcollisional magmas, but the geochemical signatures reflecting these critical differences remain poorly understood. This study examines variations in the redox state and water content of magmatism in the West Kunlun Orogenic Belt, northwestern Tibetan Plateau, using Rhyolite-MELTS and Perple_X thermodynamic modeling. We identified closely comparable samples from two distinct magmatic episodes: a Late Ordovician to Early Silurian episode (ca. 444–441 Ma), comprising Datong monzonite-syenites and Kangxiwa monzogranites; and a Late Silurian to Early Devonian episode (ca. 420–409 Ma) comprising Saitula monzonites and North Kudi syenogranites. Elemental and Sr-Nd-Hf-O isotopic data indicate that both intermediate rock series (i.e., Datong monzonite-syenites and Saitula monzonites) formed through fractional crystallization of mantle-derived basaltic magmas, while the granitic rock series (i.e., Kangxiwa monzogranites and North Kudi syenogranites) formed through partial melting of metasedimentary rocks. Despite their similar sources and petrogenetic processes, the two magmatic episodes display distinct compositional characteristics. For instance, the Datong monzonite-syenites exhibit lower TiO2 and higher Nb/Ta ratios, as well as depleted Zr and Hf than the Saitula monzonites. Similarly, the Kangxiwa monzogranites show lower K2O, higher CaO, and consequently lower K2O/CaO ratios than the North Kudi syenogranites. Thermodynamic and trace-element modeling indicate that such differences may arise from variations in oxygen fugacity and water content. Late Ordovician to Early Silurian magmas formed under more oxidizing and hydrous conditions (H2O = ~4 wt%, ΔQFM [quartz-fayalite-magnetite] = +1.0–+2.0), whereas Late Silurian to Early Devonian magmas crystallized in a more reduced, anhydrous environment (H2O = ~1 wt%, ΔQFM = −0.5 to +0.5). Combined with existing data, our results are consistent with continental collision in the West Kunlun Orogenic Belt at ca. 430–420 Ma. This study highlights how variations in the geodynamic setting influence magma differentiation, specifically through changes in the redox state and water content of magmas between subduction and postcollisional settings. Furthermore, our findings provide a potential timing constraint for continental collision in other orogenic belts.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".