Detrital zircon resolve longevity and evolution of silicic magmatism in extinct volcanic centers: A case study from the East Fjords of Iceland
Bibliographic record
Abstract
Breiðuvík and Kækjuskörð are two neighboring extinct eruptive centers in the East Fjords of Iceland. Together, they compose the second-largest volume of silicic rock in the country (after Torfajökull, an active volcanic system in southern Iceland). We use ages and compositions of detrital zircon collected from two riv-ers, the Stóraá and Krossá-Kækjudalsá, to investigate the origins and longevity of silicic magmatism at Breiðuvík-Kækjuskörð. Zircon populations from the two catchments have identical median U-Pb dates (12.9 Ma), O isotopes (d18O Vienna standard mean ocean water = 3.1‰ versus 3.3‰), and Hf isotopes (İHf = 14.7). We interpret coherence of zircon elemental and isotopic compositions to indicate that a signifi cant volume of relatively uniform silicic material was produced in close temporal and spatial proximity between 11.2 ± 0.7 Ma and 15.0 ± 0.9 Ma (all errors are 1ı), dominated by assimilation–fractional crystallization processes. To test the robustness of this longevity estimate, we applied Monte Carlo modeling to the Breiðuvík-Kækjuskörð detrital zircon results and found the age span to be statistically resolvable at ³2.8 m.y. While this lifespan is comparable to those of large mafi c-silicic volcanic systems that have described in other settings glob-ally, it is the longest reported estimate for any Icelandic volcano, where typical longevity is thought to be ~0.5–1.5 m.y. The ³2.8 m.y. lifespan we present for Breiðuvík-Kækjuskörð is a conservative assessment, because the dates used in this study only represent the zircon-saturated period of magmatic activity. This study demonstrates that detrital zircon analysis of volcanigenic sediment pro-vides an effi cient and powerful tool that can illuminate histories of zircon-satu-rated magmatism at targeted volcanic centers and systems. This approach can be particularly valuable in dominantly mafi c provinces where silicic material is subordinate (e.g., ocean islands, fl ood basalt provinces), where glaciation, ero-sion, or alteration has transformed the landscape, or in areas that are inaccessi-ble (e.g., obscured by glacial ice)
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| 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".