Structural framework, protolith affinity, and <i>P-T-t-D</i> evolution of the metasediments exposed in the Lalong dome, eastern Himalaya: Evidence of the upper South Tibetan detachment system in the northern Himalaya
Bibliographic record
Abstract
Abstract The North Himalayan gneiss domes serve as a type example of domal culminations that record the complex crustal thickening, metamorphic, and magmatic histories of continental collisional processes. While the basic geological information about the North Himalayan gneiss domes has been established, there have been multiple different mechanisms put forth to explain their development. This study investigates the Lalong dome in southern Tibet using detailed field observations, structural kinematics, petrology, phase equilibrium modeling, and new monazite, titanite, and detrital zircon U-Th-Pb geochronology. These data are used to construct pressure-temperature-time-deformation (P-T-t-D) paths, which confirm the overprinting of ca. 27–26 Ma Barrovian-type metamorphism (565–620 °C, 7.4–8.5 kbar, ~23 °C/km) by younger 23–20 Ma Buchan-type metamorphism (530–660 °C, 3.5–5.5 kbar, ~40 °C/km). The Buchan-type metamorphism is directly related to granite emplacement in the dome core, which is also associated with contemporaneous skarnization (590–700 °C) and enrichment of Li, Be, and Sn. Biotite in situ Rb-Sr dates of ca. 13 Ma are interpreted to reflect cooling within the dome. Detrital zircon dates and metamorphic conditions are consistent with Tethyan Himalayan sequence (THS) affinity for mantle schists and skarns within the Lalong area. Finally, a top-to-the-north extensional structure, interpreted to be equivalent to the upper South Tibetan detachment system (upper STDS), was identified within the THS rocks in the Lalong dome. The data and observations collected as part of this study are interpreted to reflect a magmatic diapirism origin for the Lalong dome with horizontal stretching and vertical thinning facilitated by the upper STDS. In the Early Miocene Himalaya, shallower extensional structures were active simultaneously with crustal shortening at depth and crosscut the stratigraphic boundary into the THS, providing chances for high-silica magma emplacement into much shallower levels.
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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 | 0.000 | 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".