Timing and conditions of UHP metamorphic and metasomatic processes in the subducting Farallon plate revealed by eclogite and omphacitite xenoliths of the Navajo volcanic field (USA)
Bibliographic record
Abstract
Abstract Eclogite and omphacitite xenoliths of the Navajo Volcanic Field (NVF) provide a unique opportunity to study processes in an oceanic slab down to subarc depths. However, ambiguities remained about protolith origin, prograde metamorphic conditions, and metasomatic processes, which we address here with new geothermobarometric and in-situ U-Pb data. The earliest garnet (53.4 ± 4.8 Ma), omphacite, and phengite generations yielded conditions of 2.4–3.3 GPa, 400–540 °C. Zircon cores (87−37 Ma 206Pb/238U dates) yielded higher Th/U ratios (0.1–0.6) than zircon mantles (65−30 Ma and Th/U < 0.1). Rutile dates cluster at 32.3 ± 1.2 to 28.4 ± 1.9 Ma. The Th/U ratios suggest magmatic growth of the zircon cores, which we consider a strong argument that the NVF eclogites and omphacitites were at least partly derived from Cretaceous Farallon oceanic crust. Rare relic Proterozoic zircon can be explained by inheritance, or by derivation of some xenoliths from the Proterozoic North American lithosphere. Regardless of protolith origin, the rocks were brought to depth by the Farallon slab and resided at lawsonite eclogite facies conditions for a ca. 20–25 Myr interval bracketed by the garnet and rutile dates, during which they experienced two (likely ultra-high pressure) metasomatic events. Firstly, Na-Si-rich fluids, likely derived from metasedimentary rocks, caused growth of Na-rich omphacite. A second metasomatic episode through serpentinite-derived fluids happened just prior to ~ 30 Ma xenolith exhumation as part of the “Great Hydration Event” that affected the Colorado Plateau.
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 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".