Origin of Silicic Magmatism at the Katla Volcanic Complex, South Iceland

<h2>Data Description</h2><p dir="ltr">Data presented in Excel and PDF format to accompany the paper "Origin of Silicic Magmatism at the Katla Volcanic Complex, South Iceland" by Troll et al. (2025), published in G-Cubed. </p><p dir="ltr">The files contain whole-rock major and trace element data from XRF and ICPMS analyses originally published in Lacasse et al. (2007) and Budd et al. (2015) as well as modelling parameters for the Magma Chamber Simulator used in the study. Link to the accompanying article: <a href="https://doi.org/10.1029/2025GC012319 " rel="noreferrer" target="_blank">Origin of Silicic Magmatism at the Katla Volcanic Complex, South Iceland</a></p><h2>Abstract</h2><p dir="ltr">The Katla volcano is a bimodal caldera complex within Iceland's basalt-dominated Eastern Volcanic Zone. To unravel the petrogenesis of silica-rich rocks from Katla, we provide new δ¹⁸O values for almost 60 basaltic, intermediate, and high-silica eruptive rocks, including a number of partially melted felsic xenoliths. The basaltic samples display a range in bulk-rock δ¹⁸O values from +4.3 to +8.5‰ (<i>n</i> = 17) and the sparse intermediate samples from +4.1 to +5.9‰ (<i>n</i> = 3). In turn, silicic rock samples and feldspar separates range from +2.7 to +6.4‰ (<i>n</i> = 38), whereas felsic xenoliths yield the lowest values from −4.9 to −2.3‰ (<i>n</i> = 4). The majority (95%) of the Katla silicic volcanics have δ¹⁸O values below typical MORB (i.e., ≤5.0‰), ruling out an origin via closed-system fractional crystallization from the basaltic magmas. We utilized the new δ¹⁸O values to model possible assimilation and fractional crystallization (AFC) scenarios. The results indicate an early stage of FC/AFC at deep- to mid-crustal levels, followed by assimilation of low-δ¹⁸O hydrothermally altered sub-volcanic materials similar to the low-δ¹⁸O felsic xenoliths at shallow crustal levels. Such a two-stage magma evolution is consistent with available geophysical and geobarometry studies at Katla, indicating mid- to deep-crustal and shallow-crustal magma domains. Importantly, mafic rocks dominantly show MORB-like δ¹⁸O values, whereas low δ¹⁸O values occur essentially in silicic rocks only. This implies that the low-δ¹⁸O values at Katla are imposed by interaction with the Icelandic crust rather than reflecting low δ¹⁸O mantle sources.</p>