Subducting Indian Lithosphere Controls the Deep Carbon Emission in Lhasa Terrane, Southern Tibet
Bibliographic record
Abstract
Abstract The India‐Asia orogenic zone is considered to participate significantly in the Earth's geological carbon budget. However, the carbon cycling process at orogenic belts with ongoing continental subduction is poorly constrained. Here, new He‐C‐N systematics of hydrothermal gases in Lhasa terrane are reported to explore carbon cycling and the role of the subducting Indian slab. Except for samples where the CO 2 content and C isotopic signature were modified by calcite precipitation, gas samples in Lhasa terrane display low 3 He/ 4 He ratios of 0.015–0.895 R A but with increasing mantle‐helium input from south to north. Our modeling results show that the continuous subduction of the Indian continental slab has caused high Th‐U contents and time‐integrated 4 He production rates in the present mantle wedge beneath the Lhasa terrane. The N‐S helium isotopic trend can be interpreted as a northward‐decreasing mantle enrichment. Compared to volatiles showing crustal helium but mantle‐like δ 13 C ratios, mantle‐helium‐richer fluids display heavier δ 13 C ratios, higher CO 2 / 3 He and molar C/N values, indicating a substantial carbonate input. We propose that the heavier carbon isotopes are inherited from the carbonated‐enriched mantle (CEM) rather than the carbonate assimilation of the overlying continental crust. Combined with an eastward increase in dip angle of the Indian lithosphere, we suggest that the slab rollback has caused asthenosphere heat flow and consequent decarbonation in CEM beneath northern and eastern Lhasa terrane, leading to enhanced isotopically heavier carbon release. Our study highlights the controlling role of subducting Indian lithosphere on the regional distribution of volatiles in the Lhasa terrane.
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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 | 0.001 | 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".