Early Paleozoic Continental Arc Mafic Magmatism in the North Qaidam Tectonic Belt: Implications for Subduction of the Proto-Tethyan Oceanic Lithosphere
Bibliographic record
Abstract
Abstract The North Qaidam tectonic belt is characterized by the development of high-pressure to ultrahigh-pressure eclogite formed during deep subduction of the continental lithosphere. However, the tectonic processes that occurred prior to continental collision/subduction are relatively poorly studied and this leads to controversy over the evolutionary history of the North Qaidam tectonic belt. In this contribution, we present an integrated study of field observations, petrography, geochronology, and geochemistry (whole-rock major elements, trace elements, and Sr–Nd isotopes as well as zircon Lu–Hf isotopes) of continental arc mafic rocks in the North Wulan metamorphic complex to track Proto-Tethyan oceanic subduction and the nature of metasomatism of the mantle wedge. Zircon U–Pb geochronology demonstrates that continental arc mafic rocks crystallized at ca. 483–472 Ma. Mafic intrusions are enriched in light rare earth elements and large ion lithophile elements but are depleted in high field strength elements; these are typical features of arc-related magmatic rocks. They have relatively radiogenic Sr–Nd–Hf isotope compositions, with relatively high initial 87Sr/86Sr ratios of 0.710363 to 0.719404, low εNdt values of -7.77 to -2.30, variable zircon εHft values ranging from -8 to +2.8, and the single-stage Hf model ages of ca. 1.4–1.0 Ga. These features suggest that the mafic intrusions were sourced from ancient subcontinental mantle that was modified by subducted oceanic slab-derived components. The modified mantle source was generated by the interaction between subcontinental lithospheric mantle peridotite in the overlying mantle wedge and hydrous fluid and felsic melt that were derived from a subducted oceanic slab and seafloor sediments with ancient terrestrial origin in the rutile stability field. Crust-mantle interaction transferred the subducted crustal geochemical signatures to the mantle source during subduction of the Proto-Tethyan oceanic lithosphere. Retreat and rollback of the Proto-Tethyan oceanic slab triggered asthenosphere upwelling and the partial melting of metasomatized and enriched fertile lithospheric mantle to form continental arc mafic magmas in the North Qaidam tectonic belt. Combined with the coeval LP-HT metamorphism, the North Wulan metamorphic complex records the early Paleozoic tectonic evolution of a continental arc-back-arc system, and these continental arc mafic rocks record the subduction of the Proto-Tethyan oceanic lithosphere.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".