Three-Phase Perthite and the Progressive Predominance of Albite in the Cap de Creus LCT Pegmatite Swarm, Catalunya, Spain
Bibliographic record
Abstract
Abstract The Cap de Creus swarm of 400 or so dikes is a well-known and well-exposed LCT granitic pegmatite in Catalunya, northeastern Spain. Four categories of dikes are recognized across the zoned metamorphic belt, from Type-I pegmatites in the sillimanite-K-feldspar zone to Type-IV in the chlorite-muscovite zone. The dikes were emplaced close to 299 million years ago, and a fluid-circulation event dated at 292 m.y. accompanied the intrusion of the nearby Roses granite. We chose 20 representative samples (six from Type I, five from Type II, five from Type III, and four from Type IV) to determine how closely the feldspar assemblages had achieved equilibrium compositionally and structurally. We acquired step-scanned X-ray diffraction scans of the 20 samples and refined the spectra using the Rietveld full-pattern approach. In the time available, the magmatic K-feldspar equilibrated fully compositionally with albite down to a low temperature. Structurally, the pseudomonoclinic K-feldspar (now orthoclase) did invert to well-ordered microcline in the time available only in rare cases. Also present are imperfectly ordered microcline and relict orthoclase. The progression of Al–Si order in K-feldspar requires repeated solution-and-redeposition steps. Dissolution in the ambient aqueous fluid is very sluggish in peraluminous systems like this one. As a result, eleven of the 20 samples contain three-phase perthite (Mcc + Or + Ab), which is clearly a metastable assemblage. The presence of CO2 in the fluid phase hindered progress in the ordering reaction. In the transition from Type-I to Type-IV dikes, the proportion of K-feldspar progressively decreases, such that albite eventually predominates or becomes the only feldspar to coexist with muscovite. The steady buildup of albite at the expense of K-feldspar is a predictable result of ionic equilibria in the system K2O–Na2O–Al2O3–SiO2–H2O. In most cases, the assemblage crossed the K-feldspar-out curve before the ordering reaction was complete.
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 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 | 0.002 | 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 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".