Geology of the Liuyuan Complex, NW China: A Permian back-arc basin ophiolite at the southern edge of the Central Asian orogenic belt
Bibliographic record
Abstract
Located in the southern margin of the Central Asian orogenic belt, the stratigraphy and tectonic setting of the mafic 290−280 Ma Liuyuan Complex have been controversial for decades, with workers arguing for a forearc ophiolite or a continental rift setting. Here, we present the results of a detailed field study, where the Liuyuan Complex was subdivided into troctolite, melatroctolite, layered gabbro, varitextured olivine gabbro, hornblende gabbro, plagiogranite, sheeted dike, and mafic tectonite, in addition to previously identified and studied basalt and chert. All contacts between the igneous facies are intrusive, with gabbroic rocks separated from the overlying basalt by a well-developed and laterally continuous sheeted dike complex. Based on their geochemical affinities, two groups of basalt were identified: group I (low-TiO2) and group II (high-TiO2). A modeled liquid line of descent, assuming perfect mineral fractionation, with a liquidus temperature of 1212 °C, pressure of 1 kbar, fO2 at the quartz-fayalite-magnetite (QFM) buffer, and initial melt H2O of 0.5 wt%, provides an excellent fit to group I lavas, with group II basalts interpreted as having formed from a distinct arc source. The stratigraphy, extended trace-element patterns, and tectonic fingerprinting of the lavas suggest the Liuyuan Complex formed as an ophiolite in a fast-spreading back-arc basin, a setting inconsistent with previously proposed tectonic models for the southern Central Asian orogenic belt. We expand on a tectonic model that proposes the Liuyuan Complex formed as a back-arc to the recently identified Ganquan arc. The back-arc basin was then consumed in a north-dipping subduction zone beneath the active margin of composite Siberia. The magmatic center of this arc migrated southward, likely caused by slab roll-back, with the Liuyuan Complex becoming the basement of an arc. Exhumation of the Liuyuan Complex took place by 267 Ma, as constrained by the age of a subaerial dacite that unconformably overlies the basalts of the Liuyuan Complex.
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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 | 0.001 | 0.001 |
| 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".