Partial Melting in the Higher Himalayan Crystallines of Eastern Nepal: the Effect of Decompression and Implications for the ‘Channel Flow’ Model
Bibliographic record
Abstract
Partial melting of deep continental crust may occur during either prograde heating or decompression. Although the effect of temperature on crustal melting has been widely investigated, few experimental studies have addressed the question of the influence of pressure on crustal anatexis. To understand the influence of decreasing pressure on partial melting processes, the thermodynamic approach of isochemical phase diagrams has been applied to garnet–K-feldspar–kyanite–sillimanite anatectic gneisses (Barun Gneiss) from the Higher Himalayan Crystallines (HHC) of eastern Nepal. The main melt-producing reactions, the amount of melt produced during heating vs decompression, and the effects of melt loss on the mineral assemblages and compositions have been investigated along four ideal P–T trajectories, dominated by either heating or decompression. Based on these results, the observed microstructures and mineral compositions of the Barun Gneiss have been interpreted in terms of melt-producing vs melt-consuming reactions (e.g. growth of peritectic garnet with preserved ‘nanogranite’ inclusions vs microstructures related to back-reactions between solids and melt), and used to derive the metamorphic evolution of the studied samples. The P–T pseudosection modelling predicts that at least 15–20 vol. % of melt was produced at peak P–T conditions through dehydration melting of both muscovite and biotite, and that melt production was mainly triggered by heating, with or without the combined effect of decompression. The preserved granulitic peak metamorphic assemblage, however, is consistent with a significant loss of most of this melt. The P–T evolution inferred for samples from different, strategically located, structural levels of the Barun Gneiss is consistent with the expectations of a ‘channel flow’ model, including: (1) the clockwise shape of the P–T paths; (2) the estimated P at peak T (new data: 10–8 kbar at 800°C; model: 13–7 kbar at 800°C); (3) the decreasing P structurally upward, which defines a ‘normal’ metamorphic sequence, in contrast to the inverted metamorphic sequence occurring in the lowermost Main Central Thrust Zone; (4) the nearly isothermal exhumation of the structurally lowest sample, reflecting the progressive exhumation of rocks that have been entrained in the deep, high-T region of the channel, versus the nearly isobaric heating of the structurally uppermost sample, reflecting the evolution of those rocks that flowed outwards with the underlying channel.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".