The Zebra granitic pegmatite, San Luis, Argentina
Bibliographic record
Abstract
ABSTRACT We describe an unusual example of rhythmically layered peraluminous granitic pegmatite locally developed in the intragranitic Potrerillos NYF pegmatites derived from the A-type host granites of the Las Chacras–Potrerillos batholith, Sierra de San Luis, Argentina. The strikingly rhythmic layers in the Zebra pegmatite consist of units of albite–K-feldspar–quartz–K-feldspar–albite, with accessory tourmaline and minor muscovite. The layers crystallized from a boron-bearing melt ponded and thermally insulated in the intermediate zone. A layer of low albite 1–2 cm thick was followed by coarser-grained K-feldspar, then well-ordered microcline, which gives way to quartz grains, also coarser-grained, in optical continuity. Zoned prismatic crystals of schorl nucleated in the feldspathic layer in random orientation. Muscovite is scarce. The rock has a granitic composition enriched in Rb, Cs, and B, and is depleted in the rare-earth elements compared to its precursor. We contend that the normative composition, 35.3% Or, 38.1% Ab, and 21.3% Q, was close to the eutectic in the granite system modified by dissolved H2O, F, and B, at a P(H2O) close to 3.5 kbar and a temperature in the range 575–600 °C. Repeated incursions from the field of Ab + Or to the field of quartz and back again as the melt was producing bubbles of H2O can account for the rhythmic crystallization and the local truncation or merging of the feldspathic layers. Occasional larger crystals of K-feldspar may have become detached from the wall or roof of the chamber.
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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 | 0.000 | 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) | 0.002 | 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".