<b>Titanomagnetite Rims on Hornblende Phenocrysts in Intermediate Subvolcanic Intrusions, Torud–Ahmad Abad Magmatic Belt, Iran: Examination of</b> <b>Devolatilization and Oxidation Processes</b>
Bibliographic record
Abstract
Abstract Mafic to felsic adakitic intrusive and extrusive rocks in the Torud–Ahmad Abad magmatic belt occur south-southeast of Shahrood (north of the Central Iran Zone). These adakites, in the form of dykes and other hypabyssal igneous bodies, are emplaced into late Neoproterozoic amphibolite and mylonitized granites and a thick sequence of Paleocene to middle Eocene volcanic and volcano-sedimentary rocks. These high silica and low silica adakites (HSA and LSA) span a range of lithologies including basaltic andesite, andesite, trachyandesite, dacite, trachydacite, and dacite. The adakites are composed mainly of calcic pyroxene, Ca-Na amphibole, and plagioclase phenocrysts, with minor biotite and titanomagnetite. In these intrusions, iron-titanium oxides crystallized late (within the groundmass) or occur as secondary phases. One of the interesting features of these rocks is the opacitization (magnetite rich selvage) of ferromagnesian phenocrysts, such as hornblende, which is a localized replacement reaction. The intensity and color of these opacitized margins depend on the extent of titanomagnetite-magnetite formed. The SEM-EDS analysis results show that most of magnetite formed at temperatures >500°C related to pressure quenching of the melt due to emplacement and differential volcanic degassing. The phenomenon of opacitization is due to decreasing stability of Fe2+ and hydrous ferromagnesian phenocrysts, such as amphiboles, to form less hydrous to anhydrous pseudomorphs (selvage) in the near-surface environment with oxidative reactions linked to pressure quenching and differential devolatilization of H2 from the melt during hypabyssal emplacement. The rapid decrease in pressure during magma ascent causes hornblende instability and thus helps to create these opaque rims (opacitized) on ferromagnesian phases (magnetite and titanomagnetite-rich assemblage). Hornblende breakdown - destabilization increases due to melt degassing - devolatilization [decrease in P(H2O)] during the process of ascent—emplacement with reduction of magmatic total pressure (decompression) and/or melt oxidation due to differential degassing of H2.
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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 | 0.000 |
| 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) | 0.001 | 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".