Structural and metamorphic architecture of the Zanskar Himalaya, Suru Valley region, NW India: Implications for the evolution of the Himalayan metamorphic core
Bibliographic record
Abstract
Abstract New 1:50,000-scale geological mapping in the Zanskar Himalaya of NW India, covering 2,400 km2, is integrated with structural and petrographic analysis to document the evolution and key tectonometamorphic relationships within the Himalayan metamorphic core. The integrated dataset constrains the regional three-dimensional geology and relationships between lithostratigraphy, folds, faults, deformation fabrics, metamorphic isograds, and growth of porphyroblasts within the context of five main deformation phases. Following the initial collision of India and Asia, NW–SE-oriented deformation is recorded by D1 (greenschist-facies) fabrics and D2 (greenschist- to amphibolite-facies) fabrics. D2 represents the main tectonometamorphic deformation phase associated with crustal thickening and produced the dominant regional penetrative fabric through crenulation and transposition of D1 fabrics. Thrust-sense D2 fabrics were reactivated during D3 as the Greater Himalayan Sequence was exhumed along the normal-sense Zanskar Shear Zone, which is part of the South Tibetan Detachment System. D3 fabrics, associated with movement on the Zanskar Shear Zone, were temporally continuous with crenulation and mesoscale folding, recording progressive kilometer-scale backfolding and backthrusting toward the NE between the Greater Himalayan Sequence–Tethyan Himalayan Sequence and the adjacent Indus Suture Zone. Finally, D4 and D5 are recorded as kilometer-scale open folding of older planar and linear structures. The orientation of mineral isograd surfaces ranges from subparallel to oblique with respect to D2 planar structural elements. The growth of pelitic and metabasic peak metamorphic phases from greenschist to upper-amphibolite facies is synchronous with or postdates D2 fabrics. D3 fabrics wrap thermal peak porphyroblasts and realign linear mineral phases. Tectonic thinning adjacent to D3 normal faults is documented by reduced structural spacing of isograds and alignment of isograd surfaces parallel to the faults. D4 and D5 structures modify the trace of all regional metamorphic isograds. Collectively, these observations imply that the thermal peak of metamorphism was reached after the main phase of deformation (D2), and predated movement on the Zanskar Shear Zone (D3). The results document numerous classical elements of collisional orogenesis, including implied clockwise P-T paths, polyphase deformation, and a complete Barrovian metamorphic isograd sequence supplemented by complementary metabasic isograds. The Zanskar Himalaya, unlike other areas of the Himalayan metamorphic core, records metamorphic conditions primarily attained following substantial crustal thickening rather than during subsequent decompression and exhumation. The reduced expression and/or discontinuous nature of exhuming fault systems, which produces variable levels of crustal exposure, may account for this lateral heterogeneity across the mountain belt. Deciphering the complex kinematics of continental tectonics requires the integration of observations and data over large length scales and a range of structural 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 | 0.001 | 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) | 0.001 | 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".