LA‐ICPMS zircon U–Pb dating of the Heilongjiang Complex in the Luobei area: New constraints for the late Palaeozoic‐Mesozoic tectonic evolution of Jiamusi Block, NE China
Bibliographic record
Abstract
The Heilongjiang Complex is a sequence of high‐pressure (HP) metamorphic rocks that are distributed along the N‐S suture zone between the Jiamusi and Songliao blocks in NE China. In this study, we investigated samples from Luobei in order to understand the geochronological and tectonic framework of the Heilongjiang Complex. The Heilongjiang Complex consists of two‐mica schist, muscovite‐albite schist, quartz schist, plagioclase gneiss, granitic gneiss, serpentinite, blueschist, greenschist, amphibolite, and marble. LA‐ICP‐MS dating of all samples shows a range of protolith ages from 435 to 210 Ma. These data, together with a 492 ± 6 Ma age from a granite gneiss sample in the Yilan area, indicate that the protoliths of the Heilongjiang Complex were formed over a protracted time span from ~490 to ~210 Ma. In addition, five zircon grains in two samples contain metamorphic rims that yield ages of 197 ± 2 Ma. These results, when combined with field evidence that the Heilongjiang Complex is overlain by Middle Jurassic strata, indicate it was metamorphosed between ~210 and 197 Ma and not in the Cretaceous as previously considered. This line of evidence, plus the occurrence of late Palaeozoic arc‐affinity volcanic rocks in the eastern margin of the Jiamusi Block and syn‐collisional Mesozoic volcanic rocks in the Zhangguangcai and Lesser Xing'an ranges, suggests the Heilongjiang Complex was a result of Panthalassa subduction during the late Palaeozoic and Paleo‐Pacific subduction during the Mesozoic.
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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 | 0.000 |
| 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".