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- Title
Crystallization and eruption ages of Breccia Museo (Campi Flegrei caldera, Italy) plutonic clasts and their relation to the Campanian ignimbrite.
- Authors
Gebauer, Samantha; Schmitt, Axel; Pappalardo, Lucia; Stockli, Daniel; Lovera, Oscar
- Abstract
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 km 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 km 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 (2σ 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 Ar/Ar 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 Ar/Ar 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 caldera-forming 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 (≥8 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.
- Subjects
PHLEGRAEAN Plain (Italy); CRYSTALLIZATION; VOLCANIC eruptions; BRECCIA; IGNEOUS intrusions; IGNIMBRITE
- Publication
Contributions to Mineralogy & Petrology, 2014, Vol 167, Issue 1, p1
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-013-0953-7