Publication Date:
2017-04-04
Description:
The Campi Flegrei volcanic district (Naples
region, Italy) is a 12-km-wide, restless caldera system that
has erupted at least six voluminous ignimbrites during the
late Pleistocene, including the [300 km3 Campanian
ignimbrite (CI) which originated from the largest known
volcanic event of the Mediterranean region. The Breccia
Museo (BM), a petrologically heterogeneous and stratigraphically
complex volcanic deposit extending over
200 km2 in close proximity to Campi Flegrei, has long
remained contentious regarding its age and stratigraphic
relation to the CI. Here, we present crystallization and
eruption ages for BM plutonic ejecta clasts that were
determined via uranium decay series and (U–Th)/He dating
of zircon, respectively. Despite mineralogical and textural
heterogeneity of these syenitic clasts, their U–Th zircon
rim crystallization ages are indistinguishable with an
average age of 49.7 ± 2.5 ka (2r errors; mean square of
weighted deviates MSWD = 1.2; n = 34). A subset of
these crystals was used to obtain disequilibrium-corrected
(U–Th)/He zircon ages which average 41.7 ± 1.8 ka
(probability of fit P = 0.54; n = 15). This age closely
overlaps with published CI 40Ar/39Ar eruption ages
(40.6 ± 0.1 ka) after recalibration to recently revised flux
monitor ages. Concordant eruption ages for BM and CI
agree with previous chemostratigraphic and paleomagnetic
correlations, suggesting their origin from the same eruption.
However, they are at variance with recalibrated
40Ar/39Ar ages which have BM postdate CI by 3 ± 1 ka.
BM syenites show similar geochemical and Sr–Nd isotopical
features of pre-caldera rocks erupted between 58
and 46 ka, but are distinctive from subsequent calderaforming
magmas. Energy-constrained assimilation and
fractional crystallization modeling of Nd–Sr isotopic data
suggests that pre-caldera magmas formed a carapace of
BM-type intrusions in a mid-crust magma chamber
(C8 km depth) shielding the younger CI magma from
contamination by Hercynian basement wall rocks.
An *41–50 ka hiatus in crystallization ages implies rapid
solidification of these pre-CI intrusions. This argues against
protracted pre-eruptive storage of a large volume of CI
magma at shallow crustal levels.
Description:
Published
Description:
953
Description:
1V. Storia e struttura dei sistemi vulcanici
Description:
JCR Journal
Description:
restricted
Keywords:
Pleistocene
;
Zircon
;
Geochronology
;
Tephra
;
04. Solid Earth::04.04. Geology::04.04.02. Geochronology
;
04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology
;
04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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