Detrital zircon age and Hf isotopic studies for metasedimentary rocks from the Chinese Altai: Implications for the Early Paleozoic tectonic evolution of the Central Asian Orogenic Belt
Bibliographic record
Abstract
The Chinese Altai, a typical region of the Central Asian Orogenic Belt (CAOB), has been envisaged as subduction‐accretion complex or Precambrian microcontinent. Thick metasedimentary rocks crop out extensively in the Central Altai and Qiongkuer domains, but their depositional age is not well constrained. Most workers have regarded these sedimentary rocks as passive continental margin sediments deposited on a Precambrian microcontinent. However, our studies of U‐Pb and Hf isotopes of detrital zircons separated from these rocks reveal that a predominant population has 206 Pb/ 238 U ages between 460 and 540 Ma and most grains of this population possess positive ɛ Hf (t) values. Zircons of the population have oscillatory zoning, possess high Th/U ratios, and are enhedral to subhedral crystals with sharp edges, showing short distance of transportation from an igneous provenance. The above results indicate that these metasedimentary rocks were deposited on an active continental margin not prior to the Middle Ordovician. Therefore the Chinese Altai orogen was an active continental margin in the Early Paleozoic, which is inconsistent with a Precambrian microcontinent model and reveals an arc accretionary history.
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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 | 0.001 |
| 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".