Late Paleo-to early Mesoproterozoic mafic magmatism in the SW Yangtze Block: Mantle plumes associated with Nuna breakup?
Bibliographic record
Abstract
Numerous late Paleoproterozoic to early Mesoproterozoic mafic magmatic rocks are exposed in the southwestern Yangtze Block of South China, corresponding to the early breakup of the Nuna supercontinent. The geochronological data reveal three episodes of mafic magmatism at ~1740 Ma, 1700 Ma and 1500 Ma. The two older generations have MORB-like Nb/Ta ratios and superchondritic Nd-Hf isotopes, indicating that they were likely derived from partial melting of asthenospheric mantle. In contrast, the ~1500 Ma mafic rocks possess OIB-like Nb/Ta (16.7-19.1) and Zr/Hf (41.0-45.1) ratios, ε<sub>Nd</sub> (t) values (-0.8 to +0.1) and ε<sub>Hf</sub> (t) values (-3.3 to +8.4), suggesting that they originated from a mantle plume. These three pulses of mafic magmatic activity in the Yangtze Block have geochemical features (such as TiO<sub>2 </sub>contents, Nb/Y and La/Yb values), similar to coeval mafic rocks in Siberia and Laurentia, consistent with detrital zircon provenance studies which show a spatial linkage of the Yangtze Block with northern Laurentia and southern Siberia in the Nuna configuration. Taking all synchronous mafic magmatism into account, a mantle plume beneath southern Siberia initiated at ~1750 Ma forming a broad region of mafic magmatism that extended into the Yangtze Block and resulted in lithospheric extension. The Yangtze Block was possibly the nearest neighbor to western part of the Siberian Craton at ~1500 Ma. It subsequently drifted from the Nuna supercontinent induced by the ~1500 Ma Kuonamka mantle plume, heralding a period of limited magmatic activity and tectonic quiescence that extended throughout the remainder of the Mesoproterozoic.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.011 | 0.050 |
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; both teacher heads agree on what is shown here.
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".