Origin of volatiles emitted by Plinian basaltic eruptions of Chikurachki volcano, Kurile arc, Russia: trace element, boron and sulphur isotope constraints

Gurenko, A.; Belousov, A.; Kamenetsky, V.; Zelenski, M.

Авторы: Gurenko A., Belousov A., Kamenetsky V., Zelenski M.
Журнал: Chemical Geology
Номер: 478
Год издания: 2018
Издательство: Elsevier BV
Местоположение издательства: Netherlands
Первая страница: 131
Последняя страница: 147
DOI: 10.1016/j.chemgeo.2017.10.009
Аннотация: Chikurachki is a 1816-m high stratovolcano on Paramushir Island, Kurile arc, Russia, which has repeatedly produced highly explosive eruptions of mafic composition. The present work is aimed at constraining the origin of volatile components (CO2 , H2 O, F, S, and Cl), along with B and S isotopic compositions in a series of phenocryst-hosted melt inclusions and groundmass glasses from basaltic andesite pyroclasts of the 1853, 1986, and prehistoric Plinian eruptions of the volcano. The ranges of volatile concentrations in melt inclusions (47–1580 μg/g CO 2, 0.4–4.2 wt% H2O, 399–633 μg/g F, 619–3402 μg/g S and 805–1240 μg/g Cl) imply a sudden pressure release from ~460 through ~35 MPa that corresponds to ~1.2–16-km-depth range of magma ascent upon decompression. We conclude that rapid ascent of the volatile-rich basaltic magmas from ~16-km initial depth accompanied by near-surface bubble nucleation and growth, and subsequent magma fragmentation appear to be a primary reason for the Plinian character of the Chikurachki eruptions. Significant negative correlations of S with K, Zr, Nb, Ba, La, Ce, Pr (R = −0.8 to −0.9), no clear relationships of S with H2O, CO2 and Cl, but strong positive correlations of S/K 2O with H2O/K 2O, Cl/K 2O and F/K2O preclude magma degassing to be the only process affecting volatile concentrations dissolved in the melt. The δ34 S values of the studied inclusion and groundmass glasses range from −1.6 to +12.3‰, decrease with decreasing S, show significant positive correlations with H 2 O/K2O, Cl/K2 O and F/Zr, and negative correlations with a number of incompatibletrace elements. Neither open- nor close-system magma degassing can account for the observed range of δ34 S. The δ11 B values of the melt inclusions range from −7.0 to +2.4‰ with 13–23 μg/g B. The relationships of δ11 B with B/K 2O and B/Nb are inconsistent with magma contamination at shallow crustal depths. Linear character of 1/S vs. δ34 S relationship suggests two-component mixing. The possible mixing end-members could be the magmas having similar major and trace element compositions, but strongly contrasting volatile contents and S isotopes.Based on the behaviour of fluid-mobile vs. fluid-immobile incompatible trace elements, we conclude that the subduction component likely represents a mixture of subduction sediment-derived melt with up to 60% of slab-derived fluid. Admixture of ~1–8% of the inferred subduction component to the depleted mantle wedge source is required to account for the compositional range of the Chikurachki melt inclusions, and ~0.4–10% to constrain the composition of Kurile arc mafic magmas.
Добавил в систему: Белоусов Александр Борисович

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Origin of volatiles emitted by Plinian basaltic eruptions of Chikurachki volcano, Kurile arc, Russia: trace element, boron and sulphur isotope constraintsстатья

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