Research output: Contribution to Journal/Magazine › Journal article › peer-review
Conduit- to localized-scale degassing during Plinian eruptions : insights from major element and volatile (Cl and H2O) analysis within Vesuvius AD79 pumice. / Shea, Thomas; Hellebrand, Eric; Gurioli, Lucia et al.
In: Journal of Petrology, Vol. 55, No. 2, 2014, p. 315-344.Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Conduit- to localized-scale degassing during Plinian eruptions
T2 - insights from major element and volatile (Cl and H2O) analysis within Vesuvius AD79 pumice
AU - Shea, Thomas
AU - Hellebrand, Eric
AU - Gurioli, Lucia
AU - Tuffen, Hugh
PY - 2014
Y1 - 2014
N2 - Textural investigations of the AD 79 Vesuvius pumice emphasize the complexity of magma degassing and crystallization during the eruption, which emitted two types of pumice (white and gray) associated with different magma bodies of phonolitic and tephriphonolitic compositions respectively. These studies proposed that velocity gradients caused spatial variations in degassing within the ascending magma column at both the conduit and the localized scale. To validate this hypothesis, analyses of volatiles (Cl, H2O) and major elements in pumice glasses and melt inclusions were performed using high spatial resolution tools (microRaman spectrometry and electron microprobe) and combined with major element and volatile concentration profiles and maps. The results indicate that the melt phase differentiated through degassing-induced crystallization of leucite, and that the gray pumice magma was efficiently homogenized prior to degassing. Because Cl diffuses more slowly than H2O during fast ascent, it behaves as an incompatible element and can be used as a tracer of crystallization and H2O degassing. We emphasize the importance of strain localization in generating zones of preferential exsolution and permeable pathways for gases, and establish degassing scenarios that incorporate the effects of shear-zones.
AB - Textural investigations of the AD 79 Vesuvius pumice emphasize the complexity of magma degassing and crystallization during the eruption, which emitted two types of pumice (white and gray) associated with different magma bodies of phonolitic and tephriphonolitic compositions respectively. These studies proposed that velocity gradients caused spatial variations in degassing within the ascending magma column at both the conduit and the localized scale. To validate this hypothesis, analyses of volatiles (Cl, H2O) and major elements in pumice glasses and melt inclusions were performed using high spatial resolution tools (microRaman spectrometry and electron microprobe) and combined with major element and volatile concentration profiles and maps. The results indicate that the melt phase differentiated through degassing-induced crystallization of leucite, and that the gray pumice magma was efficiently homogenized prior to degassing. Because Cl diffuses more slowly than H2O during fast ascent, it behaves as an incompatible element and can be used as a tracer of crystallization and H2O degassing. We emphasize the importance of strain localization in generating zones of preferential exsolution and permeable pathways for gases, and establish degassing scenarios that incorporate the effects of shear-zones.
KW - magma
KW - degassing
KW - crystallization
KW - Vesuvius
KW - AD 79 pumice
KW - volatiles in glass
KW - chlorine
KW - shear-zones
U2 - 10.1093/petrology/egt069
DO - 10.1093/petrology/egt069
M3 - Journal article
VL - 55
SP - 315
EP - 344
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 2
ER -