A LA-ICP-MS EVALUATION OF Zr RESERVOIRS IN COMMON CRUSTAL ROCKS: IMPLICATIONS FOR Zr AND Hf GEOCHEMISTRY, AND ZIRCON-FORMING PROCESSES
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
The results of ~4000 LA–ICP–MS analyses in 152 thin sections from common crustal rocks reveal that several rock-forming minerals contain tens to a few thousand ppm of Zr. The highest concentrations of Zr are found in xenotime, followed by titanite, ilmenite, rutile, allanite, amphibole, clinopyroxene, garnet, magnetite and, less commonly, plagioclase, K-feldspar and orthopyroxene. Olivine, cordierite, biotite, muscovite, apatite, epidote and monazite have low levels of Zr (<5 ppm, generally <1 ppm). The minerals with the highest K D Hf/ K D Zr are titanite (2.5), orthopyroxene (2.0), amphibole and clinopyroxene (1.8), and epidote and rutile (1.6–1.7). Ilmenite, magnetite, the feldspars and apatite have K D Hf/ K D Zr ≈1, and values less than one were found in xenotime and zircon (0.8), garnet (0.7), and allanite (0.6). The most important implications of these results follow. First, the growth of a Zr-bearing phase during partial melting does not influence the Zr concentration of the melt, but increases the fraction of zircon that can be dissolved at a given temperature. This accelerates the disappearance of zircon from the protolith or, in melts already segregated, the dissolution of inherited zircon. The effect will be more marked in metaluminous magmas precipitating amphibole and titanite than in any other type of magma. Second, the presence of Zr-bearing phases has little influence of the zircon-saturation “geothermometer”. It may cause somewhat higher (20–30°C) results in metaluminous rocks, but has no effect on peraluminous rocks. Third, the uptake of Zr by major minerals in crystallizing magmas may reduce both the concentration of Zr in the melt available to form zircon and the temperature at which zircon begins to precipitate. Mineral–melt reactions involving Zr-bearing phases may lead to zircon grains with complicated patterns of zoning and texturally discordant zones, apparently diachronous. Fourth, higher-than-chondrite Zr/Hf fractionates may arise from titanite, amphibole or clinopyroxene fractionation, but this requires very little or no crystallization of zircon. Significantly lower-than-chondrite Zr/Hf magmas only result from zircon fractionation. Lastly, two new examples of mineral reactions that involve the formation of a mass-balancing accessory phase, useful for high-resolution geochronology, are described: the formation of xenotime as a product of the breakdown of garnet in amphibolite-grade metapelites, and the subsolidus growth of a new rim on zircon included in Zr-bearing feldspars.
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.
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 | 0.000 | 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) | 0.000 | 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 it