Geochronology and geochemistry of granites from the Hengjian area, Qinling Orogenic Belt: Implications for the Late Palaeozoic tectonic evolution of the North Qinling Terrane, China
Bibliographic record
Abstract
The North Qinling Orogen underwent subduction and collision processes during the Palaeozoic, but the tectonic framework remains unclear. To investigate the tectonic evolution of the North Qinling Orogen, we selected the Devonian granites from the northeastern margin of the North Qinling Terrane. Integrated petrographic, geochemical, and geochronological studies, as well as Sr–Nd–Hf isotopic analyses, were carried out on the newly identified Devonian granites from the Hengjian area in the northeastern North Qinling Terrane, Qinling Orogenic Belt. Zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating reveals that these granites were crystallized at 396–387 Ma. The granite samples are metaluminous to weakly peraluminous (A/CNK = Al 2 O 3 /(CaO+Na 2 O+K 2 O) = 0.86 to 1.12), with high SiO 2 (60.6–76.5 wt%) and high total alkaline (Na 2 O + K 2 O = 8.45–11.0 wt%) contents. The granites are enriched in Th, rare‐earth element, Zr, and Hf and depleted in Sr, Nb, Ta, P, Eu, and Ti. They are characterized by high Zr + Nb + Ce + Y contents (511–990 ppm) and 10,000*Ga/Al ratios (2.71–3.32), as well as high zircon‐saturation temperatures ( T Zr = 819–885°C, average = 845°C), which indicate that they are typical A‐type granites. The granites have low Y/Nb (0.39–0.67) and Yb/Ta (0.56–0.83) ratios, resembling those of the A 1 ‐type granite, which indicates that they are formed in anorogenic settings. They also have low ( 87 Sr/ 86 Sr) i ratios (0.7055–0.7071) and negative ε Nd ( t ) values (−10.1 to −8.40) and variable zircon ε Hf ( t ) values (−8.46 to +14.7), with the two‐stage model ages of 2.0–1.8 Ga and 1.9–0.4 Ga, respectively. These geological features suggest that the granites of the Hengjian area were most likely generated by partial melting of mafic lower crust induced by asthenospheric ascent. The A‐type granites were generated in a continental rift environment during 396–387 Ma, corresponding to the closure of the Shangdan Ocean and the opening of the Palaeo‐Tethyan Ocean during the Early Devonian.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".