Naslov
Nucleation and growth of bubbles on plagioclase crystals during experimental decompression
(Nucleation and growth of bubbles on plagioclase crystals during experimental decompression degassing of andesitic melts)

Autori
Pleše, Pia ; Higgins, M.D. ; Baker, D.R. ; Kudrna Prašek, Marko

Izvornik
Journal of Volcanology and Geothermal Research (0377-0273) 388 (2019); 106679, 16

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Experimental degassing ; 3DBubble nucleation ; Plagioclase

Sažetak
TThe nucleation, growth and attachment/detachment of gas bubbles on crystals in silicate melts is one ofthe key drivers of volcanic eruptions and can greatly influence their explosivity. Formerly, oxides wereconsidered the best candidates for heterogeneous bubble nucleation, but recent studies showed that sil-icate crystals can also be bubble nucleation sites at 1 atmosphere (atm). This study examines whetherbubbles can nucleate on plagioclase crystal surfaces during decompression, which is a more commonnatural situation than 1 atm degassing. Experimental samples were synthesised from andesitic rock pow-der, H2O and plagioclase seed crystals, and melted and decompressed in a piston-cylinder apparatus. Theproducts were imaged with 3D X-ray computed tomography. Due to partial melting, the plagioclase crys-tals developed sieve rims and rough crystal-melt interfaces. All plagioclase crystals in all samples werecovered with bubbles. Bubble size distribution comparisons between bubbles in contact with plagioclaseand bubbles in the melt, show that bubbles belong to two populations, generated by two different events, one of which is heterogeneous nucleation on plagioclase crystal surfaces and the other is homogeneousnucleation within the melt, the latter potentially accompanied by heterogeneous nucleation on oxidemicrolite surfaces. The calculated attachment force between the bubbles and the plagioclase surface isstronger than the detachment force ; hence, such bubbles would remain attached during crystal move-ments. In our experiments, the net buoyancy of the bubble- crystal aggregates indicates that they couldsink in an andesitic melt. Our findings highlight the need to reconsider the role of plagioclase crystals inmagmatic degassing and shows interesting possibilities for magma mixing- triggered degassing.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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