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1. Hot and Heterogenous High‐ ³ He/ ⁴ He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island

   https://doi.org/10.1029/2019GC008654  

   Willhite, Lori N.; Jackson, Matthew G.; Blichert‐Toft, Janne; Bindeman, Ilya; Kurz, Mark D.; Halldórsson, Sæmundur A.; Harðardóttir, Sunna; Gazel, Esteban; Price, Allison A.; Byerly, Benjamin L. (December 2019, Geochemistry, Geophysics, Geosystems)

   Abstract The Icelandic hotspot has erupted basaltic magma with the highest mantle‐derived³He/⁴He over a period spanning much of the Cenozoic, from the early‐Cenozoic Baffin Island‐West Greenland flood basalt province (49.8R_A), to mid‐Miocene lavas in northwest Iceland (40.2 to 47.5R_A), to Pleistocene lavas in Iceland's neovolcanic zone (34.3R_A). The Baffin Island lavas transited through and potentially assimilated variable amounts of Precambrian continental basement. We use geochemical indicators sensitive to continental crust assimilation (Nb/Th, Ce/Pb, MgO) to identify the least crustally contaminated lavas. Four lavas, identified as “least crustally contaminated,” have high MgO (>15 wt.%), and Nb/Th and Ce/Pb that fall within the mantle range (Nb/Th = 15.6 ± 2.6, Ce/Pb = 24.3 ± 4.3). These lavas have⁸⁷Sr/⁸⁶Sr = 0.703008–0.703021,¹⁴³Nd/¹⁴⁴Nd = 0.513094–0.513128,¹⁷⁶Hf/¹⁷⁷Hf = 0.283265–0.283284,²⁰⁶Pb/²⁰⁴Pb = 17.7560–17.9375,³He/⁴He up to 39.9R_A, and mantle‐like δ¹⁸O of 5.03–5.21‰. The radiogenic isotopic compositions of the least crustally contaminated lavas are more geochemically depleted than Iceland high‐³He/⁴He lavas, a shift that cannot be explained by continental crust assimilation in the Baffin suite. Thus, we argue for the presence oftwogeochemically distinct high‐³He/⁴He components within the Iceland plume. Additionally, the least crustally contaminated primary melts from Baffin Island‐West Greenland have higher mantle potential temperatures (1510 to 1630 °C) than Siqueiros mid‐ocean ridge basalts (1300 to 1410 °C), which attests to a hot, buoyant plume origin for early Iceland plume lavas. These observations support the contention that the geochemically heterogeneous high‐³He/⁴He domain is dense, located in the deep mantle, and sampled by only the hottest plumes. 

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2. Testing the Recycled Gabbro Hypothesis for the Origin of “Ghost Plagioclase” Melt Signatures Using ⁸⁷ Sr/ ⁸⁶ Sr of Individual Olivine‐Hosted Melt Inclusions From Hawai'i

   https://doi.org/10.1029/2020GC009260  

   Anderson, O. E.; Jackson, M. G.; Rose‐Koga, E. F.; Marske, J. P.; Peterson, M. E.; Price, A. A.; Byerly, B. L.; Reinhard, A. A. (April 2021, Geochemistry, Geophysics, Geosystems)

   Abstract Melt inclusions with large, positive Sr anomalies have been described in multiple tectonic settings, and the origins of this unusual geochemical feature are debated. Three origins have been proposed, all involving plagioclase as the source of the elevated Sr: (i) direct assimilation of plagioclase‐rich lithologies, (ii) recycled lower oceanic gabbro in the mantle source, and (iii) shallow‐level diffusive interaction between present day lower oceanic crust (i.e., plagioclase‐bearing lithologies) and the percolating melt. A “ghost plagioclase” signature (i.e., a large, positive Sr anomaly without associated high Al₂O₃) is present in melt inclusions from Mauna Loa. We present new⁸⁷Sr/⁸⁶Sr measurements of individual olivine‐hosted melt inclusions from three Hawaiian volcanoes, Mauna Loa, Loihi, and Koolau. The data set includes a Mauna Loa melt inclusion with the highest reported Sr anomaly (or highest (Sr/Ce)_N, which is 7.2) for Hawai'i. All melt inclusions have⁸⁷Sr/⁸⁶Sr values within the range reported previously for the lavas from each volcano. Critically, the⁸⁷Sr/⁸⁶Sr of the high (Sr/Ce)_Nmelt inclusion lies within the narrow range of⁸⁷Sr/⁸⁶Sr for Mauna Loa melts that lack high (Sr/Ce)_Nsignatures. Therefore, to explain the high (Sr/Ce)_Nratio of the ghost plagioclase signature using an ancient recycled gabbro, the gabbro‐infused mantle source would have had to evolve, by chance, to have the same⁸⁷Sr/⁸⁶Sr as the source of the Mauna Loa melts that lack a recycled gabbro (ghost plagioclase) signature. Alternatively, shallow‐level diffusive interactions between Mauna Loa plagioclase‐rich cumulates and a percolating mantle‐derived melt provides a simpler explanation for the presence of the high (Sr/Ce)_NMauna Loa melts. 

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3. A Four‐Coordinate Pr ⁴⁺ Imidophosphorane Complex

   https://doi.org/10.1002/anie.202409789  

   Boggiano, Andrew C; Chowdhury, Sabyasachi Roy; Roy, Michael D; Bernbeck, Maximilian G; Greer, Samuel M; Vlaisavljevich, Bess; La_Pierre, Henry S (September 2024, Angewandte Chemie International Edition)

   Abstract The imidophosphorane ligand, [NP^tBu₃]⁻(^tBu=tert‐butyl), enables isolation of a pseudo‐tetrahedral, tetravalent praseodymium complex, [Pr⁴⁺(NP^tBu₃)₄] (1‐Pr), which is characterized by a suite of physical characterization methods including single‐crystal X‐ray diffraction, electron paramagnetic resonance, and L₃‐edge X‐ray near‐edge spectroscopies. Variable‐temperature direct‐current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce³⁺analogue, driven by increased crystal field. The four‐coordinate environment around Pr⁴⁺in1‐Pr, which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin‐orbit coupling in a molecular tetravalent lanthanide within a pseudo‐tetrahedral coordination geometry. 

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4. Reconstructing Annual Δ ¹⁴ C During Miyake Events Using Deciduous and Evergreen Trees

   https://doi.org/10.1029/2024GB008423  

   Walker, M R; Shobe, C M; Andreu‐Hayles, L; Dey, L; Suran, B; Nachin, B; Hessl, A E (June 2025, Global Biogeochemical Cycles)

   Abstract Cosmic rays and solar energetic particles pose significant risks to satellites, space stations, and human space exploration. They also produce atmospheric radiocarbon (¹⁴C), which enters the carbon cycle and is recorded by paleoenvironmental proxies. Miyake events, rapid increases in atmospheric¹⁴C, first identified in annual tree rings and later confirmed through ice core¹⁰Be and³⁶Cl isotopes, are thought to result from extreme solar activity, are seven events identified over the last 14,300 years. However, uncertainty in annual¹⁴C measurements limits precise inferences about their timing and magnitude. This study examines uncertainties in¹⁴C during two Miyake events (774 CE and 993 CE) across trees with differing uptake, storage, and allocation of carbon. We hypothesize that tree species physiology affects tree‐ring Δ¹⁴C, with deciduous species recording lagged, attenuated tree‐ring Δ¹⁴C relative to evergreen species. Using Δ¹⁴C data from pine and larch in Mongolia and a larger multi‐species Northern Hemisphere data set, we employed a Bayesian framework to estimate the timing, duration, and magnitude of these two events. Our AMS results showed no differences in Δ¹⁴C between evergreen and deciduous species growing at similar sites during the 774 CE event. The 993 CE event was variable, but parameter estimates were consistent between species. Northern Hemisphere comparisons indicated that annual series of Δ¹⁴C from evergreen and deciduous conifers yielded relatively more precise modeled estimates of start date and duration relative to deciduous broadleaf species. Future studies should consider the role of species‐specific carbon allocation strategies and storage dynamics in determining the radiocarbon response to Miyake events. 

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5. Unexpected trends in the enhanced Ce ³⁺ surface concentration in ceria–zirconia catalyst materials

   https://doi.org/10.1039/D0TA02762F  

   Yuan, Weizi; Ma, Qing; Liang, Yangang; Sun, Chengjun; Narayanachari, K. V.; Bedzyk, Michael J.; Takeuchi, Ichiro; Haile, Sossina M. (May 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Despite the immense importance of ceria–zirconia solid solutions in heterogeneous catalysis, and the growing consensus that catalytic activity correlates with the concentration of reduced Ce 3+ species and accompanying oxygen vacancies, the extent of reduction at the surfaces of these materials, where catalysis occurs, is unknown. Using angle-resolved X-ray Absorption Near Edge Spectroscopy (XANES), we quantify under technologically relevant conditions the Ce 3+ concentration in the surface (2–3 nm) and bulk regions of ceria–zirconia films grown on single crystal yttria-stabilized zirconia, YSZ (001). In all circumstances, we observe substantial Ce 3+ enrichment at the surface relative to the bulk. Surprisingly, the degree of enhancement is highest in the absence of Zr. This behavior stands in direct contrast to that of the bulk in which the Ce 3+ concentration monotonically increases with increasing Zr content. These results suggest that while Zr enhances the oxygen storage capacity in ceria, undoped ceria may have higher surface catalytic activity. They further urge caution in the use of bulk properties as surrogate descriptors for surface characteristics and hence catalytic activity. 

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