127-4 Old Bedrock or Young Volcano?: Searching for Insights into the Esjufjöll Magmatic System using Moraine Material at Jökulsárlón, Iceland

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session

Presenting Author:

Gabby Montano

Authors:

Montano, Gabby¹, Knittel, Beck², Banik, Tenley J.³, Carley, Tamara L.⁴, Popa, Razvan-Gabriel⁵, Bachmann, Olivier⁶, Blum, Tyler⁷

Abstract:

The Öræfajökull Volcanic Belt (ÖVB) of southeastern Iceland comprises three off-rift volcanoes: Öræfajökull, Snæfell, and Esjufjöll. Esjufjöll, the middle volcano of the ÖVB, is relatively understudied due to its location beneath the Vatnajökull ice cap. We hypothesize that Breiðamerkurjökull outlet glacier’s moraines at Jökulsárlón, a large glacial lagoon, contain material from Esjufjöll’s subaerial nunataks and subglacial edifice. Esjufjöll zircon crystals from nunataks are young (~228–316 ka) and have significantly lower d¹⁸O (-1–2 ‰; Driggs et al., 2023) than zircon from the other ÖVB systems (~3.0–4.5‰; Carley et al., 2011; Banik et al., 2021) and average Iceland zircon (~3.0‰; Carley et al., 2014). The e_Hf of Esjufjöll zircons range from 11.3–18.9 (median 13.2; Banik et al., 2024) which is slightly lower than typical Icelandic zircon (median 14.5; Carley et al., 2020), but is similar to the e_Hf range of Snæfell (13.3–17.8; Banik et al., 2021). Five silicic clasts from an ice-margin moraine on the northwestern shore of Jökulsárlón were selected for zircon separation. Three clasts have ages ranging from 1.5–2.8 Ma. One clast has zircon crystallization dates of 4.8–6.3 Ma (median ~5.4 Ma; consistent with regional bedrock), the remaining clast has zircon ranging from ~300–550 ka (median ~440 ka; overlapping with, but extending beyond, the previously observed age of Esjufjöll zircon). Median values from each clast range in d¹⁸O from ~2.3–3.4 ‰ (n=106), indicating small-scale petrogenetic involvement of low d¹⁸O altered crust. Median e_Hf from each clast ranges from 14.3–15.4 (n=93), deviating from the range previously observed in zircon from Esjufjöll nunataks; e_Hf increases as the clasts become younger. Interestingly, zircon from the youngest clast has high e_Hf (15.3) but median d¹⁸O (3.1‰). This trend broadly indicates a change in petrogenic processes and/or source material over time. Based on these data, it is probable that the majority of the sampled clasts at Jökulsárlón are derived from older, underlying, bedrock. Conversely, the youngest clast preserves an earlier portion of a longer, more complicated, magmatic history at Esjufjöll than previously understood. This study provides insight into the unexpected, and kickstarts a larger investigation into what lies beneath the ice of the ÖVB.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9811

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