The ∼860 Ma mafic dikes and granitoids from the northern margin of the Yangtze Block, China: A record of oceanic subduction in the early Neoproterozoic
Bibliographic record
Abstract
There are voluminous Neoproterozoic arc-related volcano-sedimentary sequences and small intrusions on the northern margin of the Yangtze Block, South China. The understanding the origin of the Sanligang granitoid intrusion and the spatially associated mafic dikes in the region is crucial for unraveling the tectonic evolution and continental crust growth processes in the Yangtze Block. Zircon U–Pb dating suggests that the mafic dikes (ca. 871 Ma) and granitoids (ca. 860 Ma) are contemporaneous. The mafic dikes have low SiO 2 (45.37–46.55 wt.%), K 2 O (0.32–0.82 wt.%) and Na 2 O (2.01–2.85 wt.%), and are characterized by enrichment in large ion lithophile elements (LILEs) and depletion in high-field strength elements (HFSEs), suggesting that their mantle source was modified by subducted materials. The Sanligang granitoids have intermediate to high SiO 2 (60.35–71.38 wt.%), intermediate K 2 O (1.38–3.67 wt.%) and Na 2 O (3.97–5.33 wt.%), and high MgO (1.03–3.16 wt.%). They show LREE-enriched REE patterns (La/Yb N = 7.2–12.3) with no or minor negative Eu anomalies. Their primitive mantle-normalized trace element patterns are characterized by enrichment of LILEs and depletion of HFSEs. Both the mafic dikes and granitoids share similar zircon ɛ Hf ( t ) values (+10.5 to +12.9, +7.9 to +11.7, respectively), whole-rock initial 87 Sr/ 86 Sr ratios (0.7051–0.7057, 0.7033–0.7041, respectively) and ɛ Nd ( t ) values (+4.0 to +7.1, +3.4 to +4.9, respectively), suggesting that the granitoids were generated by partial melting of juvenile basaltic crust. High Mg# values (49–58) in the granitoids may have resulted from assimilation of residual mafic minerals in their source region. Based on its arc-related geochemical affinity and contemporaneous arc-related magmatism, the Sanligang pluton is proposed to be generated in a Neoproterozoic arc setting during crustal growth and reworking. The early Neoproterozoic assemblage from the Sangligang–Sanyang fault belt provides an important record of oceanic slab subduction in the northern margin of the Yangtze Block.
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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 | 0.003 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".