Insights into crustal assimilation by Icelandic basalts from boron isotopes in melt inclusions from the 1783–1784 Lakagígar eruption

摘要: Abstract The boron isotope system has great potential for tracing alteration and assimilation in basaltic systems due to the very low concentrations of B mantle-derived melts strong isotopic contrast between mantle surface materials. However, variability ratios basalts can also be interpreted reflect inputs from enriched regions mantle, as extent heterogeneity with respect remains poorly delineated. We have determined fresh, glassy, plagioclase-hosted melt inclusions unaltered scoriaceous matrix glasses four localities associated 1783–1784 Lakagigar (Laki Fissure) eruption, Iceland. Boron range 0.59 1.25 ppm inclusions, 1.25 1.65 ppm glasses, while δ 11 NBS-951 ranges −7.8‰ −16.5‰ −10.5‰ −16.9‰ glasses. In previous studies other fissure swarms Iceland ( Gurenko Chaussidon, 1997 , Chem. Geol. 135 21–34), display a significant at constant K 2 O wt.%, which is more consistent addition by altered basalt than it mixing depleted sources. Assimilation freshwater-altered crustal materials depth may impart light signature such that observed tephra host Considering previously studied Icelandic basalts, together volatile equilibration depths we propose (a) magmas formed beneath assimilated ∼5–20% crust ∼3–4 km or more, probably during magma accumulation sills boundaries low-density hyaloclastite layers; (b) subsequently underwent extensive homogenization prior quite possibly within chamber Grimsvotn central volcano, assimilating an additional ∼10% time, total up 30% assimilation. hypothesize volatiles including H O, CO S, F, Cl, were responsible majority considerable casualties attributed added isotopically hydrothermally