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The role of magma mixing/mingling and cumulate melting in the Neapolitan Yellow Tuff caldera-forming eruption (Campi Flegrei, Southern Italy)
Author(s)
Language
English
Obiettivo Specifico
2V. Struttura e sistema di alimentazione dei vulcani
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/173(2018)
Pages (printed)
id 45
Issued date
2018
Abstract
Understanding the mechanisms responsible for the generation of chemical gradients in high-volume ignimbrites is key to
retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the
last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi
Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear
compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor
magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions
of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic
sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1)
a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by
clinopyroxene, plagioclase and oxides with minor sanidine and biotite; (2) a hotter and more mafic magma from recharge
providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived
from remelting of low temperature mineral phases (i.e., sanidine and biotite) within the cumulate crystal mush. We suggest
that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene,
plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison
between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing
remobilized portions of a “mature” (i.e., sanidine dominated) cumulate residue, allows evaluation of the capability of crystal
mushes of becoming eruptible upon recharge.
retrieve information on the processes that control the maturation and eruption of large silicic magmatic reservoirs. Over the
last 60 ky, two large ignimbrites showing remarkable zoning were emplaced during caldera-forming eruptions at Campi
Flegrei (i.e., Campanian Ignimbrite, CI, ~ 39 ka and Neapolitan Yellow Tuff, NYT, ~ 15 ka). While the CI displays linear
compositional, thermal and crystallinity gradients, the NYT is a more complex ignimbrite characterized by crystal-poor
magmas ranging in composition from trachy-andesites to phonolites. By combining major and trace element compositions
of matrix glasses and mineral phases from juvenile clasts located at different stratigraphic heights along the NYT pyroclastic
sequence, we interpret such compositional gradients as the result of mixing/mingling between three different magmas: (1)
a resident evolved magma showing geochemical characteristics of a melt extracted from a cumulate mush dominated by
clinopyroxene, plagioclase and oxides with minor sanidine and biotite; (2) a hotter and more mafic magma from recharge
providing high-An plagioclase and high-Mg clinopyroxene crystals and (3) a compositionally intermediate magma derived
from remelting of low temperature mineral phases (i.e., sanidine and biotite) within the cumulate crystal mush. We suggest
that the presence of a refractory crystal mush, as documented by the occurrence of abundant crystal clots containing clinopyroxene,
plagioclase and oxides, is the main reason for the lack of erupted crystal-rich material in the NYT. A comparison
between the NYT and the CI, characterized by both crystal-poor extracted melts and crystal-rich magmas representing
remobilized portions of a “mature” (i.e., sanidine dominated) cumulate residue, allows evaluation of the capability of crystal
mushes of becoming eruptible upon recharge.
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