Calibrating chemical abrasion: Its effects on zircon crystal structure, chemical composition and U Pb age
Bibliographic record
Abstract
The present sub-permil precision of single zircon chemical abrasion, isotope-dilution, thermal ionisation mass spectrometry (CA-ID-TIMS) U Pb dates often reveals age dispersions that are outside of analytical uncertainty. Interpreting these complex age distributions requires the ability to distinguish between protracted crystallization of zircon over a few 100 kyr, age bias due to radiation damage induced Pb-loss, and analytical artefacts. This is a particularly critical issue when a number of these factors occur together. To ensure geologically meaningful results, the complete eradication of Pb-loss is of paramount importance. The impact of Pb-loss can be removed by chemical abrasion (CA) applied prior to the dissolution of zircon. However, CA is an empirical approach that is used without a detailed understanding of how the temperature applied during the annealing step, or the temperature and duration of the partial dissolution step affect the radiation-damaged zones. In addition, the conditions of the CA procedures differ between laboratories making comparisons of age data problematic. This study presents an experimental approach to quantify how chemical abrasion affects the crystal structure and the chemical composition of zircon as well as its U Pb age. For this experiment, we have chosen the Plešovice reference zircon, because of its known variation in trace element concentrations and especially the presence of domains rich in actinides. We performed CA experiments under different temperature-time conditions on fragmented Plešovice crystals. These were compared in respect to the changes in trace element concentration, lattice order and U Pb date. The most reliable U Pb results are obtained by chemically abrading Plešovice fragments at 210 °C for 12 h. Additionally, we demonstrate that the Plešovice zircon cannot be considered homogenous at the current level of precision achieved by CA-ID-TIMS dating due to a natural age variation at the ~900 kyr scale.
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 | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 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".