Recent volatile evolution in the magmatic system of Hekla volcano, Iceland

Details Recent volatile evolution in the magmatic system of Hekla volcano, Iceland Recent volatile evolution in the magmatic system of Hekla volcano, Iceland

Mar 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007e%26psl.255..373m&link_type=abstract

Earth and Planetary Science Letters, Volume 255, Issue 3-4, p. 373-389.

Computer Science

7

Scientific paper

Estimates of the volatile budgets for volcanic eruptions are often based on volatile concentrations measured in melt inclusions (MIs) versus groundmass glass. Here, we present new measurements and estimates of pre-eruptive volatile concentrations in magma from the Hekla volcano in Iceland based on MIs in recent basalts and basaltic icelandites from the 2000 eruption. The last eruption at Hekla occurred from 26 February to 8 March, 2000. It began with a short sub-Plinian phase followed by lava effusion that produced 0.17 km3 of basaltic icelandite. Volatile (S, Cl, F and H2O) and major element concentrations were measured in MIs trapped in olivine and plagioclase phenocrysts contained in the basaltic icelandite from the 2000 eruption and in basalt erupted in 1913 from a fissure adjacent to the Hekla volcano. Same elements were measured in the groundmass glass from the 2000 tephra. The observed compositional range of MIs from the basalt (MgO ≤ 7.73%) to the basaltic icelandite (MgO ≥ 2.51%) is readily explained by fractional crystallisation, allowing the prediction of the evolution of dissolved volatile concentrations within the magma plumbing system beneath Hekla. The incompatible behaviour of the volatile elements controls their concentrations in MIs during the crystal fractionation, and consequently the highest concentrations are found in the most evolved basaltic icelandite MIs, with the notable exception of sulphur. Volatile concentrations in the basaltic MIs exhibit strong linear correlations with K2O and this relationship can be used to estimate the theoretical “expected” volatile contents in the basaltic icelandite melt just prior to eruption. Such an approach avoids underestimation of the pre-eruptive volatile contents measured in MIs and improves constraints on the volatile mass release into the atmosphere. The difference of volatile contents between “expected” concentrations and those present in the groundmass, scaled to the mass of erupted magma, yields maximum atmospheric mass loading of 0.10 Mt HCl, 0.17 Mt HF and 3.77 Mt SO2 during the 2000 Hekla eruption, whereas calculations using the measured values in the inclusions give a significant lower mass yields of 0.05 Mt HCl, 0.17 Mt HF and 0.6 Mt SO2. These results are discussed and compared to the data derived from remote sensing and snow (proxy of the gas phase) measurements.

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