Bibliographic record
Abstract
It is well recognized that active arc volcanism at nearly all subduction zones requires temperatures greater than 1200°C in the subarc mantle, despite the underthrusting cool subducting plate. In this study, we document evidence that high upper mantle temperatures are not restricted to the arc but usually extend for several hundred kilometers across the back arc, even in areas that have not undergone extension. For 10 circum‐Pacific back arcs where there has been no significant recent extension, we have compiled observational constraints on the thermal structure using a number of independent indicators of mantle temperature, including surface heat flow, seismic velocity, and xenolith thermobarometry. The observations indicate uniformly high temperatures in the shallow mantle and a thin lithosphere (1200°C at ∼60 km depth) over back‐arc widths of 250 to >900 km. Similar high temperatures are inferred for extensional back arcs of the western Pacific and southern Europe, but the thermal structures are complicated by extension and spreading. A broad hot back arc may be a fundamental characteristic of a subduction zone that places important constraints on back‐arc mantle dynamics. In particular, the thermal structure predicted for slab‐driven corner flow is inconsistent with the observed uniformly high back‐arc temperatures. We favor the alternate model that heat is rapidly carried upward from depth by vigorous thermal convection in the back‐arc upper mantle. Such convection may be promoted by low viscosities, resulting from hydration by fluids from the subducting plate. Following subduction termination, we find that the high temperatures decay over a timescale of about 300 Myr.
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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 | 0.001 | 0.001 |
| 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".