Cerium Oxidation State in Silicate Melts and the Application to Ce-in-Zircon Oxygen Barometry
Bibliographic record
Abstract
Through measurements of cerium redox equilibrium in silicate melts, and an internally-consistent model for zircon-melt partitioning of Ce, a calibration for estimating the redox conditions during zircon crystallization is presented. To quantify Ce4+/Ce3+ in natural magmas, Ce doped silicate glasses ranging in composition from basalt to rhyolite (± H2O) at 0.001 and 1 GPa, under fO2 conditions varying from FMQ –6.0 to +8.4 (where FMQ is the fayalite-magnetite-quartz oxygen buffer), and temperatures from 1200 to 1500°C were synthesized. \nSamples were analyzed using both synchrotron-based Ce M4,5-edge x-ray absorption near edge structure (XANES) spectroscopy and traditional wet chemical techniques. Based on comparison to potentiometric determinations of Ce4+/Ce3+ in digested portions of our samples, Ce4+ was found to have a greater fluorescence yield (FLY) response to the incident radiation in the M4,5-edge XANES region than Ce3+. A correction to M-edge determined Ce4+/Ce3+ ratios as follows: \nCe4+/Cetotal=587.7[Ce4+/Cetotal+/-5%]XANES^A(+/-0.004) (0<Ce4+/Cetotal<0.4) \nwhere the exponent A is a function of the number of non-bridging oxygens per tetrahedrally-coordinated cation (NBO/T) for a given glass composition, [Ce4+/Cetotal]XANES is the contribution from Ce4+ to the M4,5-edge area over the total area of the M4,5-edge, and Ce4+/Cetotal is the actual fraction of Ce4+ in the sample. \nFor a given melt composition, the change in Ce4+/Ce3+ with fO2 follows the thermodynamically predicted trend assuming simple oxides as melt species. In addition to fO2, melt composition and water content have been found to be secondary controls on Ce4+/Ce3+, with more depolymerized melts and hydrous compositions favoring the stabilization of Ce3+. The Ce4+/Ce3+ ratio can be expressed through the equation, \nlog(Ce4+/Ce3+)=1/4logfO2+5705(+/-257)/T-0.8694(+/-0.005)NBO/T-3.856(+/-0.049)xH2O-3.889(+/-0.102) \nwhere T is in Kelvin, and xH2O is the mole fraction of water in the melt. \nUsing this model, fO2 for samples from the Bishop tuff (USA), Toba tuff (Indonesia) and Nain plutonic suite (Canada), have been calculated and are in excellent agreement (typically within 0.5 log units) with independent estimates. Using the composition of the Jack Hills Hadean zircons, combined with estimates of parental magma composition, the fO2 during zircon crystallization was determined to be between FMQ -1.0 to +2.5, suggesting that relatively oxidized magmatic source regions, similar to 3.5 Ga komatiite suites, existed by ~4.4 Ga.
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 | 0.000 | 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 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".