Superhydrous magmas, flat subduction, and cool transcrustal continental arc batholiths
Bibliographic record
Abstract
Abstract Pressure-temperature arrays from several iconic continental arc granitoid batholiths define cool, hydrous adiabatic ascent paths extending to depths >60 km, constrained between the 5 and 15 wt% H2O granite liquidus curves. These paths differ significantly from those of many volcanic arc magmas, which typically form by mantle decompression melting during normal steep subduction. The Cretaceous Fiordland arc, New Zealand, preserves a deep crustal hot zone (DCHZ) of hydrous hornblende gabbros and diorites that was thickened during ongoing magmatism and burial to depths of 50–60 km. Published tomographic imaging suggests that this mantle-dominated (stage 1) magmatic flareup coincided with a transition from normal to flat-slab subduction, which ultimately terminated Fiordland magmatism. In other continental arcs, the return to normal subduction mode (slab steepening) restores normal-thickness (~30–35 km) arc crust. This process destroys the thickened DCHZ through hydrous fluxed melting, generating superhydrous granitoid arc magmas during a crust-dominated (stage 2) flareup. Dense garnet-pyroxenite initially forms as a residue but is progressively removed by vigorous corner flow in the mantle wedge. Once lower-crustal, hydrous fluxed melting is established, ascending granitoid magmas remain cool and near water saturated because water is incrementally degassed as pressure decreases, which explains the high H2O content in many arc melt inclusions. This hydrous melting mechanism establishes cool, transcrustal continental arc batholiths even when episodically rejuvenated by hot, hydrous mafic infusions during mantle decompression melting, which again dominates crustal heat transfer (but not granitoid magma temperature) as the mantle wedge reopens during the transition back to normal-mode subduction.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".