RECONSTRUCTING THE MAGMATIC ARCHITECTURE AND REFINING THE AGE OF THE PERMIAN ORA IGNIMBRITE USING ZIRCON

Understanding the storage, transport, and evolution of magmas before eruption is crucial for hazard mitigation from catastrophic caldera-forming eruptions. We investigate these questions for the supereruption-sized (>1,300 km3), crystal-rich (~40%) Ora Ignimbrite located in northern Italy and aim to refine the existing understanding of eruption timing, which is currently dated as 277 ± 2 Ma (intracaldera) and 274.1 ± 1.6 Ma (outflow) by single-crystal ID-TIMS of zircon from bulk ignimbrite (Marocchi et al., 2008).

This study focuses on fiamme from from two relatively crystal rich (~40%) units: an intracaldera vitrophyre and an outflow vitrophyre. We are analyzing glass and separating zircons from individual fiamme to allow us to place zircon compositions and ages in the context of any compositional differences among fiamme, which have been previously identified (Chiaro, 2019). By analyzing only zircon hosted in fiamme, we ensure zircon ages collected reflect the magma erupted during the ignimbrite forming event. We use electron dispersive spectroscopy (EDS) and laser ablation induction coupled plasma mass spectroscopy (LA-ICPMS) to assess major and trace element compositions of fiamme glasses and sensitive high-resolution ion microprobe spectrometry (SHRIMP-RG) for U-Pb ages and trace element compositions of zircon.

Fiamme glass analyses in this study reveal distinct compositional differences between crystal rich outflow and crystal rich intracaldera fiamme, including higher Silica (~78 wt. % SiO2) and lower Sr (< 5 ppm) and Ba (< 20 ppm) in outflow fiamme than intracaldera fiamme (~77 wt. % SiO2; Sr < 20 ppm; Ba < 70 ppm). Zircon analyses for trace elements and ages from these individual fiamme will refine the chemical and temporal history of these magmas and allow us to more fully elucidate the magmatic architecture of this supervolcanic system.