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Correlating the Campanian Ignimbrite using matrix glass geochemistry and morphology
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  • Rose Gallo,
  • Kayla Iacovino,
  • Michael Ort,
  • Aurora Silleni,
  • Agnese Barbero,
  • Roberto Isaia
Rose Gallo
Northern Arizona University

Corresponding Author:[email protected]

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Kayla Iacovino
Jacobs Technology, NASA Johnson Space Center
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Michael Ort
Northern Arizona Univ
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Aurora Silleni
Roma Tre University
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Agnese Barbero
University of Turin
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Roberto Isaia
National Institute of Geophysics and Volcanology
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Abstract

The Campanian Ignimbrite was emplaced during the 39-ka caldera-forming eruption of Campi Flegrei near Naples, Italy. This eruption deposited a trachytic ignimbrite up to 80 km from the caldera and co-ignimbrite fallout more than 2300 km to the northeast. The pyroclastic density current was dilute and mobile, overtopping kilometer-high mountains up to 60 km from the vent. Stratigraphic units within the proximal and distal deposits of the Campanian Ignimbrite have never been definitively correlated due to their very dissimilar appearances and the lack of medial exposure. Correlation of the ignimbrite, specifically which proximal units formed simultaneously with the majority of the distal deposits, is necessary to understand the events that formed this dilute current. The co-ignimbrite lag breccia (Breccia Museo), which represents the caldera collapse, and an earlier eruptive phase that formed a high-grade ignimbrite (Piperno) are potential proximal correlates to the main distal ignimbrite unit. Juvenile matrix material includes pumice and scoria fragments and bubble-wall shards. A distal outcrop at 970 m asl, thought to represent deposits from the upper transport system of the main pyroclastic flow, is dominated by bubble-wall shards. At all other sites, most juvenile ash shards show textures similar to associated pumice lapilli. We suggest that much of the ash was from abrasion of pumice, but the upper current had few pumice clasts and thus less abrasion-derived ash. Preliminary analyses indicate that early units have limited chemical compositional ranges (predominantly Na2O 4-7% and K2O 5-9%), whereas the Piperno and the dominant distal unit both have a broader geochemical range that extends to roughly 9% Na2O and 2% K2O. The uppermost proximal unit has the most extreme compositions, approximately 2-6% Na2O and 6-11% K2O. These observations are consistent with the source of the eruption being either a large stratified magma chamber that underwent pre-eruptive mingling, or several semi-isolated magma bodies. Proximal deposits include spatter from local vents that may have tapped isolated magma bodies. Study of pyroclasts from the Campanian Ignimbrite allow both correlation of proximal and distal deposits and a characterization of some aspects of the pyroclastic current.