CO2 transport at shallow depths in arc magmas: evidence from unique orbicular dikes in the Jurassic Bonanza arc, Vancouver Island, Canada
Bibliographic record
Abstract
A growing body of evidence suggests the interaction between arc magmas and crustal carbonates may play a large role in outgassed CO 2 at arcs. We examine magma–carbonate interactions within the shallow (< 0.2 GPa) crust in the Jurassic Bonanza arc on Vancouver Island, a well-exposed island arc crustal section. Detailed mapping in the Merry Widow mountain area revealed unique, late-stage orbicular mafic dikes that only occur above the stratigraphic level of subsurface carbonates. The orbicular dikes are primitive, show physical and chemical evidence of interaction with limestone, including high CaO/SiO 2 and low REE (~ 10–20× chondrite) that correlate with orbicule abundance, and are geochemically discordant from other rocks of the Bonanza arc. The orbicules have identical intergranular textures to the host melt but markedly higher Ca/Si. Simple binary mixing and MELTS modeling indicates the orbicular dike compositions are a mixture of a primitive hydrous arc basalt with 3–25% limestone addition. Comparisons to published experimental data on basalt–calcite reaction suggest some of the dike compositions result from > 25% calcite assimilation, producing up to 11 wt% CO 2 , orders of magnitude higher than the CO 2 solubility of the parent melt (0.11 wt% CO 2 ). We interpret the orbicules as Ca-rich hybrid melts produced from limestone assimilation that did not homogenize with the host dike magma and underwent crystallization during rapid ascent, possibly propelled by the excess CO 2 . Our results inform on the amount and mechanism of CO 2 transport at low crustal pressures (< 0.5 GPa) in island arcs built on carbonate platforms. We estimate the CO 2 flux of the Jurassic Bonanza arc to have ranged from 0.14 to > 1.16 Tg CO 2 /year during its ~ 34 Myr lifespan.
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 | 0.002 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".