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1. Petrogenesis and Geodynamic Evolution in the Northern Westfjords, Iceland, Elucidated by Iceland's Oldest Silicic Rocks

   https://doi.org/10.1029/2022JB026265  

   Banik, Tenley J.; Coble, Matthew A.; Miller, Calvin F.; Fisher, Christopher M.; Jordan, Brennan T.; Vervoort, Jeffrey D.; Carley, Tamara L. (June 2023, Journal of Geophysical Research: Solid Earth)

   Abstract Iceland's oldest silicic rocks provide unique insight into the island's early crustal evolution. We present new zircon U‐Pb ages bolstered with zircon trace element and isotopic compositions, and whole rock Nd, Hf, and Pb isotope compositions, from three silicic magmatic centers—Hrafnsfjörður, Árnes, and Kaldalón—to understand the petrogenesis of large silicic volcanic centers in the northern Westfjords, Iceland. Our data confirm Hrafnsfjörður as the oldest known central volcano in Iceland (∼14 Ma) and establish an older age for Árnes (∼13 Ma) than previously estimated. We also report the first U‐Pb zircon dates from Kaldalón (∼13.5 Ma). Zircon oxygen isotope compositions range from δ¹⁸O∼+2 to +4‰ and indicate involvement of a low‐¹⁸O component in their source magmas. Hrafnsfjörður zircon Hf (mean sampleε_Hf∼ +15.3–16.0) and whole rock Hf and Nd (ε_Hf = +14.5 to +15;ε_Nd = +7.9 to +8.1) isotopic compositions are more radiogenic than those from Árnes (zircon sampleε_Hf∼ +11.8–13; whole rockε_Hf = +12.8 to +15.1;ε_Nd = +7.3 to +7.7), but Hrafnsfjörður whole rock Pb isotope compositions (^208/204Pb = 37.95–37.96;^206/204Pb = 18.33–18.35) are less radiogenic than those from Árnes (^208/204Pb = 38.34–38.48;^206/204Pb = 18.64–18.78). Kaldalón has zircon Hf isotope compositions ofε_Hf∼+14.8 and 15.5 (sample means). These age and isotopic differences suggest that interaction of rift and plume, and thus the geodynamic evolution of the Westfjords, is complex. Isotopic compositions of Hrafnsfjörður and Árnes support involvement of an enriched mantle (EM)‐like mantle component associated with a pulsing plume that resulted in variable spreading rates and magma fluxes and highlight the heterogeneity of the Icelandic mantle. 

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2. Anatectic melting or extreme fractionation? Chemical and temporal evolution of Quaternary small-volume, high-silica rhyolites from Mineral Mountains, Utah, USA

   https://doi.org/10.46427/gold2022.8923  

   Rivera, Tiffany; Jicha, Brian (June 2022, Goldschmidt 2022)

   The origins and evolution of small-volume, high-silica intercontinental rhyolites have been attributed to numerous processes such as derivation from granitic partial melts or small melt fractions remaining from fractional crystallization. Investigations into the thermo-chemical-temporal evolution of these rhyolites has provided insights into the storage and differentiation mechanisms of small volume magmas. In the Mineral Mountains, Utah, high-silica rhyolites erupted through Miocene granitoids between ca. 0.8 and 0.5 Ma, and produced numerous domes, obsidian flows, and pyroclastic deposits. Temporally equivalent basalts erupted in the valleys north and east of the Mineral Mountains, hinting at a potential relationship between mafic and felsic volcanic activity. Here we test competing hypotheses. Are the rhyolites products of extreme fractionation of the coeval basalts? Or do they represent anatectic melts of the granitoids through which they erupted? We address these questions through modeling with new whole rock geochemical data and zircon trace element chemistry, thermometry, and U/Pb LA-ICPMS dates. We couple these data with new 40Ar/39Ar eruption ages to improve upon the volcanic stratigraphy and address the recurrence interval for the most evolved rhyolites. Geochemical data from zircon crystals extracted from six domes suggest increasing differentiation with age and eruptive location, however there is minimal evidence for recycling of earlier crystallized zircon. These data suggest that magma batches were isolated from one another and zircon nucleation and crystallization occurred close to the eruption, thus limiting the residence time of the magmas. These data also perhaps suggest that the magmas were generated in small batches within each of the granitoids rather than from a large crystal mush body underlying the region, as seen at large silicic systems. Our preliminary geochemical models and zircon petrochronology eliminate extreme fractionation and favor local anatectic melting of different granitoids as a mechanism to produce chemical signatures observed in the Quaternary rhyolites in the Mineral Mountains. 

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3. Age of the magma chamber and its physicochemical state under Elbrus Greater Caucasus, Russia using zircon petrochronology and modeling insights

   https://doi.org/10.1038/s41598-023-36793-y  

   Bindeman, I. N.; Melnik, O. E.; Guillong, M.; Utkin, I. V.; Wotzlaw, J.-F.; Schmitt, A. K.; Stern, R. A. (December 2023, Scientific Reports)

   Abstract Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U–Th–Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km 3 /1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km 3 , temporally oscillating δ 18 O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km 3 of melt in a vertically extensive system) and the potential for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by ~ 10 3 to 10 5  years reflecting protracted dissolution–crystallization histories. 

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4. Reconciling early Deccan Traps CO ₂ outgassing and pre-KPB global climate

   https://doi.org/10.1073/pnas.2007797118  

   Hernandez Nava, Andres; Black, Benjamin A.; Gibson, Sally A.; Bodnar, Robert J.; Renne, Paul R.; Vanderkluysen, Loÿc (March 2021, Proceedings of the National Academy of Sciences)

   A 2 to 4 °C warming episode, known as the Latest Maastrichtian warming event (LMWE), preceded the Cretaceous–Paleogene boundary (KPB) mass extinction at 66.05 ± 0.08 Ma and has been linked with the onset of voluminous Deccan Traps volcanism. Here, we use direct measurements of melt-inclusion CO₂concentrations and trace-element proxies for CO₂to test the hypothesis that early Deccan magmatism triggered this warming interval. We report CO₂concentrations from NanoSIMS and Raman spectroscopic analyses of melt-inclusion glass and vapor bubbles hosted in magnesian olivines from pre-KPB Deccan primitive basalts. Reconstructed melt-inclusion CO₂concentrations range up to 0.23 to 1.2 wt% CO₂for lavas from the Saurashtra Peninsula and the Thakurvadi Formation in the Western Ghats region. Trace-element proxies for CO₂concentration (Ba and Nb) yield estimates of initial melt concentrations of 0.4 to 1.3 wt% CO₂prior to degassing. Our data imply carbon saturation and degassing of Deccan magmas initiated at high pressures near the Moho or in the lower crust. Furthermore, we find that the earliest Deccan magmas were more CO₂rich, which we hypothesize facilitated more efficient flushing and outgassing from intrusive magmas. Based on carbon cycle modeling and estimates of preserved lava volumes for pre-KPB lavas, we find that volcanic CO₂outgassing alone remains insufficient to account for the magnitude of the observed latest Maastrichtian warming. However, accounting for intrusive outgassing can reconcile early carbon-rich Deccan Traps outgassing with observed changes in climate and atmospheric pCO₂. 

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5. Volumetric extrusive rates of silicic supereruptions from the Afro-Arabian large igneous province

   https://doi.org/10.1038/s41467-021-26468-5  

   Thines, Jennifer E.; Ukstins, Ingrid A.; Wall, Corey; Schmitz, Mark (November 2021, Nature Communications)

   Abstract The main phase of silicic volcanism from the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km³dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of voluminous silicic magma generation and emplacement. Here were report high-precision²⁰⁶Pb/²³⁸U zircon ages and show that the largest sequentially dated eruptions occurred within 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding the highest known long-term volumetric extrusive rate of silicic volcanism on Earth. While these are the largest known sequential silicic supereruptions, they did not cause major global environmental change. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating⁴⁰Ar/³⁹Ar data with our²⁰⁶Pb/²³⁸U ages to yield new constraints on the duration of the C11n.1r Subchron. 

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