Northern Provenance of the Gondwana Formation in the Lesser Himalayan Sequence: Constraints From 40Ar/39Ar Dating of Detrital Muscovite in Darjeeling-Sikkim Himalaya
Bibliographic record
Abstract
Single-grain 40Ar/39Ar dates are reported for detrital white mica from low-grade meta-arkose samples from the Gondwana Formation in the Darjeeling-Sikkim Himalaya. The majority (61%) of single grains from five samples yielded dates of ~480 Ma. The remaining grains yielded dates between ~590 and 1700 Ma, and a few grains were younger than 480 Ma. These data suggest that the source of the Gondwana sedimentary rocks in the Himalaya lay to the north, in contrast to the previously held view that it was in the south. This also indicates that the Cambro-Ordovician granites, extensively present in the Himalayan metamorphic core, the Greater Himalayan Sequence, were exposed at the surface in the Permian in a mountain range to the north of the Permian continental rifts. Preservation of the original muscovite ages and the absence of evidence of a thermal overprint during the Himalayan orogenesis indicate that the burial temperatures of the Gondwanan sedimentary rocks, located at the base of the Lesser Himalayan Sequence, did not exceed 400 °C.
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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 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".