Tracing magmatic genesis and evolution through single zircon crystals from successive supereruptions from the Socorro Caldera Complex, USA

High-Precision U-Pb Geochronology of an Ignimbrite Flareup in a Silicic Large Igneous Province (Chon Aike, Patagonia)

“…Finally, previous work has indicated that magma genesis within similar volume ignimbrite flare-ups becomes increasingly juvenile over Myr time scales, indicative of evolution and hybridization of the lower crust (e.g., Gaynor et al, 2023), however the new data presented from the CASP indicates that the EQC produced ignimbrites largely over 1.035 ± 0.200 Myr. Our results suggest that once readily fusible melting domains are exhausted, the ignimbrite flare-up(s) may cease.…”

“…3A), which are often larger than the lifetime of a liquid for a given magmatic system (e.g., Cashman et al, 2017). There are potential geological mechanisms for such large ranges in zircon dates in a single sample, such as recycling of antecrystic (i.e., zircon crystallized from earlier phases of the same magmatic system) or xenocrystic (i.e., zircon inherited at depth and/or assimilated from wall rock; e.g., Miller et al, 2007) zircon grains into younger felsic magmas, and/or mixing of age domains between older zircon material with the younger overgrowths (e.g., Gaynor et al, 2022bGaynor et al, , 2023. Furthermore, there are also analytical artifacts inherent with in-situ techniques that can also cause dispersed U-Pb dates within individual samples, including unmitigated Pb-loss or unresolved discordance due to greater analytical uncertainties (e.g., Chelle-Michou et al, 2014;Gaynor et al, 2022b).…”

“…These complicated age spectra are increasingly recognized in volcanic rocks, due to analytical improvements in CA-ID-TIMS analyses (e.g., Gaynor et al, 2023 and references therein). Various models used for interpreting similar age spectra in igneous rocks include: (1) the youngest grain reflects the last period of crystallization, whereas older grains are antecrystic; (2) the spectrum reflects the full duration of magma crystallization; and/or (3) the age spectrum is complicated by the presence of old antecrystic and/or xenocrystic grains and some grains experienced Pb-loss, thus the full spectrum potentially includes ages that do not reflect the evolution of a eruptive melt of interest (e.g., Gaynor et al, 2023;Samperton et al, 2015;Szymanowski et al, 2019).…”

Identifying crustal contributions in the Patagonian Chon Aike Silicic Large Igneous Province

“…5 ) than the corresponding phenocrystic quartz (all < 1.0‰). One explanation for the divergence in isotopic equilibrium could be that zircon records a longer history of magmatic evolution (i.e., saturation prior to quartz) and/or some of the zircon grains are antecrystic and recycled from an earlier phase of magmatism (e.g., Miller et al 2007 ; Gaynor et al 2023 ). However, based on petrographical observations, we determine that quartz was not a late-stage crystallizing phase.…”

Supplemental Material: Recommendations for the reporting and interpretation of isotope dilution U-Pb geochronological information

“…This can be quantified and modeled to some extent, and such attempts show that the duration of true mineral crystallization will be longer than the measurement indicates, by an amount of time that depends on factors such as mineral growth rate, nucleation rate, and grain armoring (Curry et al, 2021;Klein and Eddy, 2023). Subtle xenocrystic cores within dated minerals can also skew data sets toward older dates such that the average has no geologic significance (Gaynor et al, 2023). Similarly, subtle Pb-loss may skew the interpretation of the youngest dates.…”