Mineralogy of K-Rich Rocks from the Jharia Basin in Jharkhand: Indications for Cretaceous Lamproite Magmatism in Eastern India
Bibliographic record
Abstract
Abstract Potassic dikes of early Cretaceous age (ca. 115 Ma) are emplaced in the Gondwana sedimentary basins of the Damodar valley in eastern India. Two potassic dikes in the Jharia basin (Ena and Moonidih) are characterized by the presence of olivine macrocrysts and phenocrysts, together with microphenocrysts of olivine, phlogopite–biotite, ilmenite, and apatite. These are set in a groundmass of phlogopite, apatite, ilmenite, spinel, and K-feldspar. Microphenocrystal and groundmass Al-Na-poor diopside and Al-poor Ti-rich amphibole are present in the Ena dike, whereas rutile, pyrite, galena, Zr-Ti-rich garnet, and quartz are minor phases occurring in the Moonidih dike. Two populations of relatively fresh olivine (I and II) are found in the Ena dike, in contrast to the Moonidih dike, where olivine macrocrysts and microphenocrysts are completely replaced by secondary magnesite, serpentine, and talc. The occurrence of fresh olivine in the Ena dike is reported for the first time in the Jharia basin. High forsterite (Fo) and Ni together with low Ca and Mn contents of the olivine-I macrocrysts suggest a mantle-derived xenocrystic origin. In contrast, the olivine-II population has high Ca and Mn, but relatively low Fo and Ni, suggesting a magmatic origin. Rimward decreasing Al and increasing Fe contents in zoned phlogopite crystals, plus the presence of groundmass spinel with compositions along the titanomagnetite trend (T2), indicate the lamproitic affinity of the K-rich dike rocks. Using a mineralogical-genetic classification scheme, the Ena and Moonidih dikes are classified as olivine-phlogopite-diopside-apatite-amphibole-feldspar lamproite and olivine-phlogopite-apatite-feldspar lamproite, respectively. We use the compositional variations of phlogopite, amphibole, apatite, and spinel to understand better the magmatic evolution and crystallization history of these potassic dikes. The Cretaceous lamproite magmatic event in eastern India was sourced from ancient metasomatized lithospheric mantle, with low-degree partial melting either triggered in the periphery of the impinging Kerguelen mantle plume head or induced by distant subduction.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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 teacher head, 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".