Does Underthrusting Crust Feed Magmatic Flare‐Ups in Continental Arcs?
Bibliographic record
Abstract
Abstract Episodic magmatic flare‐ups are documented in many continental arcs worldwide. Yet, the causes of such episodicity and the sources feeding the flare‐ups are not well‐understood. In this study, we use a 1‐D numerical model and scaling analysis to assess the mass balance and thermodynamic feasibility of generating arc magma as a result of partial melting of underthrusted retro‐arc lower crust. Results show the magma volumetric flux or magmatic thickening rate, is directly correlated with the crustal underthrusting rate and the relative timescales of heat transfer and underthrusting. For a continental arc with dimensions similar to the Sierra Nevada arc in California, we show with a constant underthrusting rate of 5 km/Myr, the magmatic thickening rate is 0.1–0.3 km/Myr. This is slightly below the baseline of arc magma thickening rate (∼0.3 km/Myr) from the mantle wedge and accounts for 10%–30% of the magmatic thickening rate during a flare‐up. The cumulative volume of magma generated from the partial melting of a 20‐km‐thick underthrusted lower crust is on the order of 105 km3, about 10%–40% of the estimated magma volume generated during a flare‐up. Therefore, we argue partial melting of underthrusted lower crust plays a partial or subsidiary role in driving a magmatic flare‐up event. Additional melts from the mantle and/or other crustal sources are needed to achieve the observed magmatic output during flare‐ups. The arc root developed by partial melting of the underthrusted crust reduces the time needed to obtain the critical thickness for root foundering, thus influencing the tempo of arc magmatism.
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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 | 0.001 |
| 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".