Geochemistry of adakites and rhyolites from the Neoarchaean Gadwal greenstone belt, eastern Dharwar craton, India: implications for sources and geodynamic setting
Bibliographic record
Abstract
Adakite and rhyolite volcanic flows with different petrographic and geochemical characteristics have been identified from the Neoarchaean Gadwal greenstone terrane of the eastern Dharwar craton, India. These are part of the bimodal basalt–felsic association that dominates the belt, which includes previously documented boninites and Nb-enriched basalts. Adakites plot in the MgO–SiO2field of Cenozoic adakites, distinct from high-Mg andesites, and have low Yb (1.2 ppm) and fractionated rare-earth elements (REE) (La/Ybn = 16) of Cenozoic counterparts. They also possess the Cr/Ni (1.3–4.0), Nb/Ta (8.6–12.8), and Zr/Sm (33–58) ratios distinctive of adakites from recent oceanic arcs. Zero to positive Eu anomalies contrast with negative Eu present in older Dharwar cratonic crust, such that crustal contamination is unlikely, endorsing an intraoceanic setting. Cenozoic oceanic adakites may form by slab melting, then hybridizing to variable degree with wedge peridotite, and Gadwal adakites are also interpreted to be slab melts. Rhyolites have greater SiO2, highly incompatible elements (Th, La, Zr), and higher Yb (2.41 ppm) contents than adakites, with fractionated REE and pronounced negative Eu anomalies; they are comparable to FI type rhyolites of other Archean greenstone belts, likely melts of thick mafic crust at ~40 km with residual garnet, in an extensional setting. Consequently, the switch from arc basalts and boninites to adakites, Nb-enriched basalt, and rhyolites in the Gadwal terrane signifies a transition from slab dehydration-wedge melting to slab melting-wedge hybridization, possibly triggered by ridge subduction or flattening of the slab, as well as crustal melting. These new observations endorse the emergence of complex arc magmatism in Neoarchean terranes.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| 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".