Complementarity of Hf isotopes from detrital and igneous zircon: an example from the Central Gneiss Belt, Grenville Province, Ontario
Bibliographic record
Abstract
Combined U–Pb and Hf isotopic analysis of detrital and igneous zircon provides information about variations in crustal addition versus reworking through time. However, whereas detrital zircon data from only a few samples can provide information about extended periods of orogenic activity, this approach lacks the geological context that comes with studying igneous zircon and may not record mid- and deep-crustal sources or sources isolated from sites of deposition. Conversely, igneous zircon is likely to miss sources that were removed by later tectonic activity, but which may be preserved in the detrital record. The Central Gneiss Belt of the southwest Grenville Province in Ontario has a relatively well-understood orogenic architecture and records active-margin growth and reworking between ca. 1900 and 1200 Ma. We present U–Pb and Hf isotope data of zircon from 30 orthogneiss samples ranging in age from ca. 1750 to 1250 Ma, covering all tectonostratigraphic levels of the Central Gneiss Belt. As expected, the detrital and igneous datasets display many of the same overall features, such as crustal growth along the southwest Laurentian active margin; however, there are also some distinct differences. In particular, sedimentation appears to have taken place near the active margin, with little or no input from distal inboard sources, thus missing this significant component of reworked crust. This study highlights the need for a combination of detrital and igneous samples to provide the most complete picture of long-lived accretionary orogenic systems.
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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 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".