Early Mesozoic tectonic transition of the eastern South China Block: constraints from Late Triassic Dashuang complex in eastern Zhejiang Province
Bibliographic record
Abstract
The Mesozoic tectonic transition from the Palaeo-Tethys tectonic regime to the Palaeo-Pacific tectonic regime in the eastern South China Block has long been debated. Geochemical and zircon U–Pb–Hf isotopic studies were conducted on the Dashuang complex in the eastern Zhejiang Province. The Dashuang complex consists mainly of quartz syenite in the northwestern part and quartz monzonite in the southeastern part. New laser ablation inductively coupled plasma mass spectrometry zircon U–Pb data show that the quartz syenite, the quartz monzonite, and its chilled margin (fine-grained granite) crystallized at 235 ± 4 Ma, 232 ± 3 Ma, and 230 ± 1 Ma, respectively. The Dashuang complex intrudes into the Chencai Group gneiss that postdated ~646 Ma and underwent anatexis at 443 ± 14 Ma. The quartz monzonite shows A-type granite affinity, characterized by high K2O + Na2O and Zr + Nb + Ce + Y, high FeOT/(MgO + FeOT) and Ga/Al ratios, an enrichment in light rare earth elements, and depletions in Ba, Sr, and Eu. The quartz monzonite has zircon εHf(t) values of −14.2 to –11.9 and two-stage model ages of 1788–1922 Ma. Zircon εHf(t) values of the chilled margin (fine-grained granite) and wall rock (gneiss) are scattered (−18.2 to –6.3 and −19.5 to 10.2). The corresponding two-stage model ages are 1482–2133 Ma and 1184–2471 Ma, respectively. The Dashuang complex was derived mainly from partial melting of Neoproterozoic clastic rocks in the Cathaysia Block. Geochemical data indicate that the quartz monzonite formed in a post-collision extensional environment. These results, considered with previous data, indicate that the transition from the Palaeo-Tethys to the Palaeo-Pacific tectonic regimes of the eastern South China Block occurred during the Late Triassic (225–215 Ma).
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 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".