Abstract
New geochemical and Sr-isotope data have been acquired on samples
representative of volcanic units erupted inside the resurgent Campi
Flegrei caldera (CFc) over the past 12 ka. These data, integrated
with previous published petrological, and with newly acquired geochronological,
volcanological and geothermal data, shed light on the nature and
timing of the processes that controlled the evolution of the Phlegraean
magmatic system. In the past 12 ka, three isotopically and geochemically
distinct magmatic components were erupted at the CFc as either homogeneous
or mixed magma batches. One component, Campanian Ignimbrite component
(CIc) (87Sr/86Sr=0.70735-0.70740), is similar to the trachytic magma
extruded during the first phase of the Campanian Ignimbrite (CI)
eruption (37 ka). A second component, Neapolitan Yellow Tuff component
(NYTc) (87Sr/86Sr=0.70750-0.70757), is similar to the latitic-alkali-trachytic
magma batches extruded during the course of the Neapolitan Yellow
Tuff (NYT) eruption (12 ka). A third component, Minopoli component
(MIc) (87Sr/86Sr \~ 0.7086), is similar to the trachybasaltic magma
of the Minopoli 2 (MI) eruption (9.7 ka). These components were erupted
as either single batches of magma, or mixed CI-NYT or MI-NYT batches
of magma, through vents located either along the structural boundary
of the NYT caldera or inside the NYT caldera, mainly on portions
of the resurgent block under extensional stress. The CI and NYT components
represent residual portions of older, large-volume magma reservoirs
which have fed eruptions since about 60 and 15 ka, respectively.
The least-evolved MI component was erupted only during the 12-9.5
ka and 8.6-8.2 ka epochs of activity, through vents located on a
NE-SW regional fault system. This component could represent a deeper
reservoir tapped by the NE-SW regional fault system reactivated after
the NYT caldera collapse. Deeper MI and shallower CI and NYT magmatic
systems interacted by mixing among batches of magma during their
rise to surface. Overall, the data suggest that the CFc magmatic
system today is characterized by the presence of two larger, independent
reservoirs, filled by residual portions of the CI and NYT magmas.
These generated many smaller, shallower pockets of evolved magma,
that fed most of the eruptions that occurred in the CFc over the
past 12 ka. Moreover, a deeper reservoir (MI), tapped by the NE-SW
regional fault system, provided batches of less-evolved magma that
mixed with magma present in the shallower pockets.
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