Enrichment of immobile elements in synmagmatic fractures
Bibliographic record
Abstract
Useful minerals containing rare Earth elements (REE) and metals are sourced from magma bodies, but exactly how these elements initially leave the magma is not well known. Here we present textural and chemical analyses of mineral-filled fracture bands within the rhyolitic Sandfell laccolith exposed in eastern Iceland. The fracture fillings showcase dynamic and complex textures and imply multiple energy levels during precipitation. The dominant mineral phases are Fe- and Mg-oxides, Mn carbonate, and La/Ce oxide. The textures they present are comb, laminate, radial, and a rounded reworked clastic texture filling the tips. Microtomography images of hand-samples show the fractures are stretched-penny shaped, and contain 80 vol% fillings and 20 vol% void space. The connectivity of fractures within one band is limited to 1-3 neighbours, via small oblique fractures joining two main fractures together. µXRF measurements revealed distinct halos of 0.8 wt% Fe depletion surrounding each facture, and within the fracture-fill a strong enrichment in an unusual suite of elements including Fe, Mn, Cl, Zn, Cr, Y, Ce, and La. This assemblage is puzzling, as many of these elements are typically carried by fluids which have strong alteration effects on the surrounding rock, and there is a lack of this kind of alteration at Sandfell. Our working hypothesis is that the formation of the fractures provided a degassing pathway through the impermeable magma. However, the nature and the composition of the magmatic volatiles are as yet unknown. The minimal connectivity between fractures (at hand-sample scale) suggests fluid would have travelled through the length of one to three fractures until intersecting with another fracture band system, and minerals precipitated along the way. Given the ubiquitous occurrence of the fracture bands within the laccolith, this small-scale process compounds into large amounts of mass transfer overall. The fractures at Sandfell may be a snapshot of the initial process of removing incompatible elements from silicic magma.
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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 | 0.000 |
| 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 | 0.000 |
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".