Geochronology and geochemistry of basalts from the Yingchuan Formation, eastern Jiangnan Orogen: Implications for the Neoproterozoic tectonic evolution of the South China Block
Bibliographic record
Abstract
The Neoproterozoic magmatism along the Jiangnan Orogen preserves significant information for understanding the tectonic evolution of the South China Block (SCB). We conducted a systematic zircon U–Pb geochronological and whole‐rock geochemical study on the basalts from the Yingchuan Formation in the eastern Jiangnan Orogen, SCB. The basalts yielded a weighted mean 206 Pb/ 238 U age of 817 ± 13 Ma, enriched in Rb, Th, U, LREE and HFSE (e.g., Zr and Ti). The basalts have positive ε Nd (t) (+1.9 to +2.1) and high ( 87 Sr/ 86 Sr)i (0.69853–0.70737), indicating a slightly depleted mantle source. The high La/Nb (2.14–2.35) and La/Ta (28.6–33.3) ratios indicate a lithospheric mantle source for the basalts. Their high Ba/Yb (7.85–44.3) and Th/Yb (0.59–0.74) ratios and high absolute Nb contents (7.64–11.6 ug/g) indicate that the lithospheric mantle source has been metasomatized by melts and fluids derived from a subducted slab. The basalts are characterized by (La/Yb) N ratios (3.0–3.5) and Sm/Nd ratios (0.24–0.26), comparable to intra‐continental back arc basin basalts (BABBs). Their Ta/Yb (0.14–0.16) and Th/Yb (0.59–0.74) ratios are similar to those of Okinawa Trough basalts and contemporary mafic rocks formed in the back‐arc basin in the Jiangnan Orogen. Combined with their source features, we propose that the basalts were formed in a back‐arc basin setting. The identification of BABBs from the Yingchuan Formation shows that there were Neoproterozoic back‐arc basins in the south‐eastern Yangtze Block, indicating that the final assembly between the Yangtze and Cathaysia blocks did not occur before ca. 817 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 | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 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".