Crust‐Derived CO<sub>2</sub> Production From a Shallow Pluton in Limestone Is Driven by Metamorphic Decarbonation, Not Assimilation
Bibliographic record
Abstract
Abstract Traditionally, it is assumed that contributions of crust‐derived CO 2 emissions at arc settings are minor, but this requires well‐constrained field studies to determine the extent of magma‐carbonate reaction and concomitant C released. The Jurassic Bonanza arc on Vancouver Island (Canada) was built on a Triassic limestone platform and makes for an ideal setting to examine arc magma‐carbonate interactions beneath an island arc. We examine how km‐scale magma bodies might react with carbonate from a well‐constrained study of a gabbro pluton that intrudes limestone. The pluton shows muted to nil carbonate interaction preserving primary igneous 87 Sr/ 86 Sr values (∼0.703) except for a thin (<2 m wide) marginal gabbro (∼0.706) in contact with a decarbonized metamorphic aureole. A lack of 87 Sr/ 86 Sr or δ 18 O cpx enrichment in gabbro ∼10 to >1,000 m from the contact suggests that any reaction with limestone wallrock is limited to at most the outer ∼10 m of the pluton. More enhanced magma‐carbonate interaction and CO 2 production occurs via a network of shallow dikes and sills (<0.2 GPa) compared to deeper plutons, consistent with experimental data showing increased carbonate assimilation at shallower depths (≤0.5 GPa). Plutons are an important heat source to release CO 2 from carbonate wallrock by contact metamorphism, where >89% of crust‐derived CO 2 is liberated by wallrock decarbonation and <11% is liberated by magma that assimilated limestone. Nonetheless, we show that neither magmatic nor metamorphic crust‐derived CO 2 contributions compare to mantle‐derived CO 2 . Our study places realistic and quantitative limits on arc‐derived CO 2 from upper crustal limestone sources.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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 | 0.001 |
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 teacher head, 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".