Unraveling the Protracted Magmatic Evolution in the Central Urumieh–Dokhtar Magmatic Arc (Northeast Saveh, Iran): Zircon U-Pb Dating, Lu-Hf Isotopes, and Geochemical Constraints
Bibliographic record
Abstract
Cenozoic plutonic rocks in northeast Saveh, part of the central Urumieh–Dokhtar Magmatic Arc (UDMA) in Iran, comprise monzonite, monzodiorite, gabbro, and gabbrodiorite. Geochemical, zircon U-Pb geochronology, and Hf isotopic data reveal that these plutonic rocks belong to a medium-K calc-alkaline, metaluminous series with arc-related signatures. Zircon U-Pb ages (ca. 60 to 3 Ma) indicate prolonged magmatic evolution from the Middle Paleocene to the Middle Pliocene. Contrary to earlier reports of a 15 Ma period of reduced magmatic activity (ca. 72–57 Ma), our data indicate a shorter interval (ca. 10–12 Ma) during which magmatic activity decreased significantly. Key magmatic pulses occurred during the Late Eocene (ca. 40–47 Ma), Early Miocene (ca. 23–18 Ma), and Late Miocene–Pliocene (ca. 11–5.2 Ma), with geochemical data indicating a subduction-related origin. The most recent magmatic pulses in the central UDMA, potentially extending across the entire UDMA, are dated between 5 and 2.5 Ma, identified in a cluster of zircons from gabbroic rocks, which could correspond to the concluding stages of slab steepening related to continental subduction. Zircon εHf(t) values (−11.43 to 12.5) and geochemical data suggest fractional crystallization, crustal assimilation, and mantle-derived melts. The clinopyroxene crystallization temperatures (1150–1200 °C) and supporting geochemical data imply that magma was produced in a metasomatized spinel–lherzolite mantle at depths <80 km. This generation is associated with asthenospheric upwelling and slab rollback, which, in turn, triggered the partial melting of the lithosphere and fueled the region’s magmatic activity.
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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) | 0.002 | 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".