MINOR-ELEMENT SYSTEMATICS OF FLUORAPATITE AND ZIRCON INCLUSIONS IN ALLANITE-(Ce) OF FELSIC VOLCANIC ROCKS FROM THREE OROGENIC BELTS: IMPLICATIONS FOR THE ORIGIN OF THEIR HOST MAGMAS
Bibliographic record
Abstract
We have investigated allanite phenocrysts and the apatite and zircon inclusions they contain from three localities: (1) SK100 ash beds, Niigata, Japan, (2) the youngest Toba Tuff (YTT), Sumatra, Indonesia, and (3) the Bishop Tuff (BST) in eastern California, to gather geochemical inferences about the magmas from which these phases crystallized using an electron microprobe. Back-scattered electron (BSE) images reveal the presence of euhedral crystals of apatite (5–30 μm) and zircon (5–20 μm) incorporated into euhedral phenocrysts of allanite. Textural evidence suggests that apatite, zircon and allanite crystallized in that order. Furthermore, the chondrite-normalized REE pattern of apatite inclusions in these allanite phenocrysts resembles that of apatite in syenites and unfractionated carbonatites. This characteristic suggests that apatite inclusions crystallized from relatively alkaline magmas rich in REE, CO32− and PO43−. Such a magmatic signature could perhaps represent that of a boundary-layer melt. In addition, the F/Cl and Mn/Fe values of the apatite inclusions imply that the relative SiO2 contents of such magmas increase in order SK100 → YTT → BST. Variations in Y and Hf contents and Zr/Hf value among the zircon inclusions also show that they crystallized from mafic (SK100), intermediate (YTT), and felsic (BST) magmas. The host rocks are similar to magnetiteseries granites from Japan, according to two characteristics of the allanite: (1) appreciable amounts of Mg (0.078–0.165 apfu ) and Ti (0.057–0.137 apfu ) and (2) chondrite-normalized REE pattern. The petrogenetic processes envisaged for crystallization of allanite phenocrysts and their apatite and zircon inclusions can explain differences in (1) the REE pattern between allanite and apatite, (2) variations in minor elements among allanite, apatite and zircon, and (3) occurrences of minerals associated with the allanite phenocrysts.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| 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".