Metamorphic P-T-t paths of high-pressure felsic and pelitic from the Qianlishan Complex and tectonic implications for the Khondalite Belt in the North China Craton
Bibliographic record
Abstract
The Khondalite Belt is an east-west-trending Paleoproterozoic continental-continental collisional belt, separating the Western Block of the North China Craton into the Yinshan Block and the Ordos Block from north to south. In the past years, extensive metamorphic and geochronological investigations for pelitic granulites have been carried out in the Khondalite Belt. However, felsic granulites attract just a little attention although they are widely exposed in the field and potentially preserve key high-pressure information, thus hindering better understanding of the tectonic processes and settings of this critical area. In this study, a link between ‘inter-layered’ felsic and pelitic granulites from the Qianlishan Complex of the Khondalite Belt was established based on comprehensive metamorphic analysis. Three distinct metamorphic stages including peak pressure (M1), post-peak decompression (M2) and late retrograde cooling (M3) stages have been identified in the felsic and pelitic granulites. Felsic granulites experienced high-pressure metamorphism up to ~12 kbar, while estimated peak pressure for pelitic granulites is 11-15 kbar. The decompression stage (M2) is represented by cordierite + sillimanite symplectite and/or cordierite coronae with conditions of 5.7-6.5 kbar/800-835 °C in pelitic granulites, and by garnet-sillimanite assemblages formed at conditions of >6.5 kbar/810-865 °C in felsic granulites. The later cooling stage (M3) is indicated by sub-solidus biotite-quartz-plagioclase symplectite and later melt crystallization. Clockwise P-T paths involving near-isothermal decompression and near-isobaric cooling were defined by these mineral assemblages and approximate P-T conditions, which suggest a continent-continent collisional event. SIMS zircon U-Pb dating yields a consistent metamorphic age of ~1.95 Ga from felsic granulites, interpreted as the timing of peak metamorphism. The results, combined with previously reported data, suggest that the Khondalite Belt formed by collision between the Yinshan and Ordos blocks at ~1.95 Ga.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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 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".