GNGTS 2022 - Atti del 40° Convegno Nazionale

100 GNGTS 2022 Sessione 1.2 high crystallinity (24-62% crystals) and contain pl+amph+bt+opx+Fe-Ti ox+ap+zr±qtz. Notably, large and strongly resorbed quartz crystals are abundant in the pre-caldera lavas and scarce or absent in the caldera-forming tuff and post-caldera lavas. Bulk-rock composition of pumices and lavas varies from andesitic to dacitic, while the matrix glass in the pumices is rhyolitic. Trace element composition of glass (e.g., positive Eu anomalies) indicate resorption of feldspars. Crystallization ages of the youngest zircons in pre-caldera lavas overlap with eruption ages (~250 ka) while crystallization ages of the youngest zircons in the caldera-forming tuff and post-caldera lavas are significantly older (~100 ka) than the eruption ages (~50 and ~16 ka, respectively). Ti-in-zircon thermometry combined with zircon geochronology (Fig. 1) show that the Singkut magma body experienced a heating phase which started approximately upon eruption of the pre-caldera lavas and continued at least until the eruption of the post-caldera lavas. Such prolonged heating event determined progressive melting of the least refractory mineral phases (mostly quartz and feldspars) and hampered zircon crystallization for ~50 ky before the caldera-forming eruption and ~80 ky before the effusion of the post-caldera lavas. Heating was likely due to an increase of the recharge flux in the magma reservoir which reduced the crystallinity of the crystal mush and promoted remobilization and eruption of the Singkut magma body. References Ferry J. M. and Watson E. B.; 2007: New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr- in-rutile thermometers . Contrib. to Mineral. Petrol. 154, 429-437.