Ar–Ar dating and Sr–Nd–Pb isotopic character of Paleogene basalts from the Xialiaohe Depression, northern Bohai Bay Basin: implications for transformation of the subcontinental lithospheric mantle under the eastern North China Craton
Bibliographic record
Abstract
Paleogene basalts are widely distributed in the Xialiaohe Depression, which lies in the northern part of the Bohai Bay Basin, the second largest petroleum-bearing basin of China, in the northeastern part of the North China Craton. The basalts mainly occur in three formations: the Paleocene Fangshenpao Formation (PFF), the Eocene Shahejie Formation (ESF), and the Oligocene Dongyin Formation (ODF). The PFF is dominated by tholeiites, whereas the ESF and ODF are characterized by alkaline basalts with minor tholeiites. These basalts contain generally lower contents in large-ion lithophile elements (LILEs) and most high-field-strength elements (HFSEs) relative to ocean-island basalts (OIBs), except for positive anomalies for Ba, Sr, Eu, and Ti, and are characterized by OIB-like Sr and Nd isotopic compositions and by abnormally low radiogenic lead isotopic composition. They display a positive correlation between 206 Pb/ 204 Pb and 143 Nd/ 144 Nd, and a negative correlation between 206 Pb/ 204 Pb and 87 Sr/ 86 Sr. The geochemical characteristics of these basalts are quite different from that expected from magmas derived from crustal contamination or melting from a uniform asthenospheric mantle source, but is consistent with derivation from newly formed lithospheric mantle. Combined with the geochemical character of the ESF and ODF basalts, we ascribe the abnormally low radiogenic lead isotopic composition for the Paleocene PFF basalts to newly formed lithospheric mantle that originated from recycling of delaminated thickened lithosphere in Late Mesozoic, including a lower crustal component.
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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 | 0.000 | 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".