The role of scapolite-bearing granulites in sequestering and releasing sulfur: Implications for S isotope signatures of crustal fluids during lower-crustal exhumation
Bibliographic record
Abstract
To understand sulfur and carbon sequestration and release within the continental crust, scapolite minerals from a variety of granulite facies rocks were analyzed for their elemental composition and S isotope signatures. These high-grade scapolites host significant amounts of SO 3 and CO 2 , up to approximately 5 wt% and 3 wt%, respectively, with δ 34 S VCDT from −3 to +10 ‰, and formed in relatively oxidizing environments characterized by low a H 2 O in which scapolite may form as a primary igneous mineral or via metamorphic reactions involving sulfides and silicates. The range of scapolite sulfur isotope compositions mirrors those observed in mantle xenoliths, suggesting transport of S from the mantle into the lower crust via fluids and melts. Although scapolite’s contribution to the global S and C cycles may be modest, it is significant in the context of sulfur fluxing from the mantle to the lower crust, particularly in its oxidized form. We estimate that at least 10 % of lower crustal sulfur is sequestered within scapolite. The exhumation of scapolite-bearing lower crustal rocks can therefore liberate substantial quantities of sulfur species and CO 2 , which may serve to both supply and compositionally buffer retrograde metamorphic fluids. These fluids may exhibit a range of S isotope compositions from mantle-like (δ 34 S VCDT ≈ 0 ‰) to relatively 34 S-enriched signatures. Consequently, retrograde fluids may have S isotope signatures indistinguishable from those of mantle fluids, even in the absence of direct mantle S input during fluid formation. Exhumation of scapolite-bearing lower crust may facilitate element mobilization through S and Cl complexing, particularly with respect to base metals, within exhumed lower crustal sections, thus providing sources of metals and fluids in mid- to high-grade metamorphic rocks. Globally, scapolite-bearing lower crust may help balance the global sulfur cycle through catch-and-release from scapolite.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| 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".