Continuous crustal thinning of the North China Craton in the Early Cretaceous: Evidence from A-type granites
Bibliographic record
Abstract
Widespread crust-derived granitoids in North China provide evidence of Mesozoic lithospheric thinning and destruction of the North China Craton. However, the link between lower crust and lithospheric mantle reactivation remains poorly understood. We present whole-rock geochemistry and zircon O-Hf isotopes for Early Cretaceous peralkaline A-type granites (i.e., Xiwanzi, Xiangshan, and Yansehu) from the Yanshan Mountains of the eastern block of the North China Craton. The Xiwanzi granite has a U-Pb age of 134.3 ± 0.4 Ma, with homogeneous whole-rock Nd isotopes [εNd(t) = −7.7 to −7.5] but highly variable zircon O-Hf isotopes [δ18O = 5.1‰ to 7.2‰ and εHf(t) = −7.7 to +9.6]. Such isotopic variations likely resulted from a hybrid juvenile source consisting of partial melting of newly underplated basaltic rocks derived from both the metasomatized ancient and juvenile sub-continental lithospheric mantle. In contrast, the Xiangshan (117.4 ± 1.0 Ma) and Yansehu (116.3 ± 1.4 Ma) granites have relatively uniform isotopic compositions [whole-rock εNd(t) = −12.2 to −10.8, zircon δ18O = 5.2‰ to 6.4‰, and εHf(t) = −17.1 to −4.7], close to those of the Proterozoic mafic granulite xenoliths from the ancient lower crust. The isotopic variations of the Early Cretaceous A-type granites suggest a continuous change in the melting model from the underplated juvenile lowermost crust to the overlying ancient lower crust at high temperatures in an extensional environment. Our results indicate that A-type granites can be used to probe the nature and reactivation of the lower crust of an Archean craton. Significantly, large-scale continuous thinning of lower continental crust provides key insights into the generation of the widespread Mesozoic crust-derived granitoids in North China.
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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 | 0.001 | 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".