Metamorphic evolution of high-pressure garnet amphibolite from the Eastern Himalayan Syntaxis: Implications for the mechanism of crustal thickening and exhumation of southern Lhasa terrane during late Cretaceous
Bibliographic record
Abstract
This study presents a comprehensive metamorphic study of geochronology, petrography, mineral chemical, and P-T path for late Cretaceous high-pressure garnet amphibolite from the southern Lhasa terrane of the Eastern Himalayan Syntaxis. Mineral textures and reaction relationships suggest that these rocks have experienced three metamorphic stages (M1-M3). The M1 stage is characterized by peak mineral assemblages of Grt + Hb + Ab + Ru + Ms + Qz, followed by the post peak (M2) assemblages of Grt + Hb + Pl + Ep + Bi + Ru + Qz in the matrix. Late retrograde stage (M3) is defined by Hb + Pl coronae surrounding garnet porphyroblasts, indicating a decompression process. These mineral compositions in combination with whole-rock phase equilibria modelling of high-pressure garnet amphibolite give P-T conditions of three metamorphic stages at 14-19 kbar/660-720 ℃ (M1), 8-10 kbar/650-660 ℃ (M2), and <7 kbar/<600 ℃ (M3), respectively. In summary, a P-T path involving a near-isothermal decompression process and late cooling accompanied by decompression has been reconstructed for high-pressure garnet amphibolite. Moreover, SIMS zircon U-Pb dating results show that metamorphic zircons yield a concordant age of ~90 Ma, suggesting a peak metamorphic age. The results indicate that the southern Lhasa terrane underwent a sequence of tectonometamorphic processes that were initiated by crustal thickening (M1) of up to 60 km at 90 Ma, followed by rapid exhumation along a subduction channel to the depth of 32-26 km (M1-M2) and later slow uplift (M2-M3).
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".