Revisiting early Neoproterozoic mafic sills in the North China Craton
Bibliographic record
Abstract
Neoproterozoic Large Igneous Provinces (LIPs) continue to receive worldwide attention due to their genetic links with supercontinent dispersal and use in paleocontinental reconstructions, formation of ore deposits, climate shifts, and biological extinctions. However, their utility is hampered by a lack of high precision geochronology. Here we present a new U-Pb ID-TIMS baddeleyite age for a Neoproterozoic mafic sill intrusion in the North China Craton (NCC). A mafic intrusion within the Huaibei/Huaihe Group of Xuhuai Basin, previously dated between 915 Ma and 900 Ma (U-Pb zircon/baddeleyite LA-ICP-MS) gives a baddeleyite age of 906.5 ± 1.1 Ma. Given the wide occurrence of 915–900 Ma mafic intrusions dated previously, this new age potentially suggests a widespread ca. 907 Ma mafic intrusive event across NCC. Furthermore, this baddeleyite age constrained the Huaibei/Huaihe Group to have deposited in an age span of 1121–907 Ma. Apatite grains from the mafic sills have also been dated by U-Pb LA-ICP-MS, which produced dates that range from 984 ± 64 Ma to 930 ± 57 Ma, with errors similar to previous zircon/baddeleyite U-Pb LA-ICP-MS dates, indicating the feasibility of apatite U-Pb geochronology to constrain the timing of mafic intrusions. REE distribution patterns coupled with the Sr/Y-LREE discrimination plots demonstrate a primary origin for the dated apatite grains. Apatite crystallized from mafic magmas following earlier crystallization of feldspar that incorporated significant amounts of Eu. Recalculation of nearly 600 radio-isotopic data points on Neoproterozoic mafic intrusions in the NCC yield three age peaks at ca. 940 Ma, ca. 915 Ma and ca. 885 Ma, respectively. The major age peak at ca. 915 Ma is broadly consistent with our U-Pb ID-TIMS baddeleyite age that is suggestive of the main episode of mafic intrusion. Further high precision U-Pb ID-TIMS geochronology is necessary to precisely constrain the timing of the ca. 940 Ma and ca. 885 Ma mafic intrusions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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 teacher head, 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".