Mesozoic intracontinental ductile shearing along the Paleozoic Shangdan suture in the Qinling Orogen: Constraints from deformation fabrics and geochronology
Bibliographic record
Abstract
Abstract The Qinling Orogen, located between the North and South China Blocks, records subduction-collisional orogeny along the Paleozoic Shangdan and Triassic Mianlue sutures, and Mesozoic intracontinental orogenesis, which all played an important role in building the present tectonic framework and topography. The strike-slip Shagou ductile shear zone that overprints the Paleozoic Shangdan suture between the North and South Qinling Belts is crucial for understanding the Mesozoic intracontinental deformation in the Qinling Orogen. The microstructures, asymmetrical fabrics, and kinematic vorticities (0.81–0.95) suggest sinistral simple shear. The quartz c-axis patterns from felsic mylonites exhibit Y-maximum fabrics, indicating the activity of prism slip, while those from amphibole-rich mylonites display both Y-maximum and Z-maximum fabrics showing the combined activity of prism and basal slip systems. In the mafic mylonites, the plagioclase fabrics were induced by combined (010)[100] and (001)[100] slip systems, while the amphibole fabrics were probably related to anisotropic growth or passive rotation of rigid clasts. Equilibrium P–T conditions of 4.28–6.12 kbar and 646–727 °C estimated from geothermobarometry suggest that the main deformation occurred under amphibolite facies conditions at middle–lower crustal depths. Zircon U-Pb ages constrain their protolith rocks to have crystallized at 816 ± 25 Ma and 726–718 Ma, while the intense mylonitization and sinistral shearing occurred at ca. 200–187 Ma. A U–Pb zircon age of 132 ± 3 Ma from a granitic dike cutting the foliation and an amphibole 40Ar/39Ar plateau age of 119.0 ± 0.9 Ma from mylonites together suggest that the Shagou shear zone evolved through decompression and exhumation stages in the time period of 132–119 Ma.
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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 | 0.001 | 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".