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1. Igneous Rock Associations 29. The Nenana Magnetitite Lava Flow, Alaska Range, Alaska

   https://doi.org/10.12789/geocanj.2023.50.197  

   Reidel, Stephen P.; Ross, Marty E.; Kasbohm, Jennifer (July 2023, Geoscience Canada)

   Magnetitite deposits like El Laco (Chile) are rare and have controversial origins. An unusual magnetitite lava flow overlying a rhyolite unit occurs in the north-central Alaska Range and originally covered ~ 750 km2 of the Miocene Nenana basin. Dating of the rhyolite and relationships between the magnetitite and sedimentary rocks indicate that both are of Late Miocene age. The magnetitite flow is mainly magnetite with some post-eruptive alteration to hematite. Both the rhyolite flow and the magnetitite flow are vesicular, but the magnetitite flow also has small, millimetre-scale columnar jointing. The vesicular zones in the magnetitite flow grade into massive rock on the scale of a thin section, suggesting a degassing lava origin. Samples of the magnetitite flow contain between 12 and 26 wt.% SiO2 and between 45 and 75 wt.% FeO. Rare earth elements (REE) and trace elements from the magnetitite and rhyolite have similar patterns but with lesser abundance in the magnetitite. Both the rhyolite and the magnetitite have light-REE-enriched REE profiles with negative Eu anomalies. Electron microscopic analysis shows that most of the silica and trace element content of the magnetitite flow comes from very finely disseminated silicate minerals and glass in the magnetite. This suggests that the magnetitite was derived from a magma that had undergone unmixing into a silica-rich phase and an iron-rich phase prior to its eruption. Fractures and vesicles within the magnetitite flow contain minor rhyolitic glass and minerals suggesting that the rhyolite magma invaded columnar joints in the solidified magnetitite flow, and is a subvolcanic sill-like body at the studied locality. The magnetitite flow erupted prior to the emplacement of the rhyolite, which may be extrusive on a regional scale. The features of the Nenana magnetitite, and its geological relationships, are consistent with genetic models that invoke unmixing of magma into immiscible Fe-rich and Si-rich liquids during ascent. 

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2. Oceanic Zircon Records Extreme Fractional Crystallization of MORB to Rhyolite on the Alarcon Rise Mid-Ocean Ridge

   https://doi.org/10.1093/petrology/egac040  

   Portner, Ryan; Dreyer, Brian M; Clague, David A; Daczko, Nathan R; Castillo, Paterno R (June 2022, Journal of Petrology)

   Abstract The first known occurrence of rhyolite along the submarine segments of the mid-ocean ridge (MOR) system was discovered on Alarcon Rise, the northernmost segment of the East Pacific Rise (EPR), by the Monterey Bay Aquarium Research Institute in 2012. Zircon trace element and Hf and O isotope patterns indicate that the rhyolite formed by extreme crystal fractionation of primary mid-ocean ridge basalt (MORB) sourced from normal to enriched MOR mantle with little to no addition of continental lithosphere or hydrated oceanic crust. A large range in zircon ɛHf spanning 11 ɛ units is comparable to the range of whole rock ɛHf from the entire EPR. This variability is comparable to continental granitoids that develop over long periods of time from multiple sources. Zircon geochronology from Alarcon Rise suggests that at least 20 kyr was needed for rhyolite petrogenesis. Grain-scale textural discontinuities and trace element trends from zircon cores and rims are consistent with crystal fractionation from a MORB magma with possible perturbations associated with mixing or replenishment events. Comparison of whole rock and zircon oxygen isotopes with modeled fractionation and zircon-melt patterns suggests that, after they formed, rhyolite magmas entrained hydrated mafic crust from conduit walls during ascent and/or were hydrated by seawater in the vent during eruption. These data do not support a model where rhyolites formed directly from partial melts of hydrated oceanic crust or do they require assimilation of such crust during fractional crystallization, both models being commonly invoked for the formation of oceanic plagiogranites and dacites. A spatial association of highly evolved lavas (rhyolites) with an increased number of fault scarps on the northern Alarcon Rise might suggest that low magma flux for ~20 kyr facilitated extended magma residence necessary to generate rhyolite from MORB. 

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3. Photoluminescence detection of symmetry transformations in low-dimensional ferroelectric ABO ₃ perovskites

   https://doi.org/10.1039/D0TC01183E  

   Ofoegbuna, Tochukwu; Bajgiran, Khashayar R.; Kizilkaya, Orhan; Thomson, Stuart A.; Melvin, Adam T.; Dorman, James A. (August 2020, Journal of Materials Chemistry C)

   null (Ed.)

   Symmetry-dependent properties such as ferroelectricity are suppressed at room temperature in Pb-free ABO 3 perovskites due to antiferrodistortive dynamics (octahedral rotations/tilts), resulting in the preferential stabilization of centrosymmetric crystals. For this reason, defect engineering (Ca doping, oxygen vacancy, etc. ) has been leveraged to break the symmetry of these crystals by inducing symmetry/structural transitions to modify the local A/B-site environment. This work demonstrates the use of in situ / ex situ photoluminescence spectroscopy to systematically detect symmetry/structural transformations in prototypical ferroelectric ABO 3 perovskites. These baseline optical responses are compared to recently synthesized Ca x Sr 1−x NbO 3 (CSNO) nanocrystals, which undergoes similar ferroelectric/structural phase transitions. Furthermore, the resultant PL response is corroborated with X-ray diffraction (XRD) and absorption spectroscopy (XAS) measurements to confirm the structural changes. This ability to directly monitor the local site symmetry within ABO 3 perovskites via photoluminescence spectroscopy can be used to screen for temperature- and defect-induced ferroelectric transitions. 

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4. Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes

   https://doi.org/10.3390/molecules28186466  

   Garcia, Leslie; Koper, Makynna R.; Mondal, Somrita; Priddle, Joshua T.; Truong, William A.; Allbritton, Elisabeth M.; McAdoo, Ashtyn G.; Cannon-Smith, Desiray J.; Funwie, Neil L.; Hoang, Tuyet; et al (September 2023, Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes)

   Pellegrini, M; Saccani, C; Guzzini, A (Ed.)

   Twenty novel Mn, Fe, and Cu complexes of ethylene cross-bridged tetraazamacrocycles with potentially copolymerizable allyl and benzyl pendant arms were synthesized and characterized. Multiple X-ray crystal structures demonstrate the cis-folded pseudo-octahedral geometry forced by the rigidifying ethylene cross-bridge and show that two cis coordination cites are available for interaction with substrate and oxidant. The Cu complexes were used to determine kinetic stability under harsh acidic and high-temperature conditions, which revealed that the cyclam-based ligands provide superior stabilization with half-lives of many minutes or even hours in 5 M HCl at 50–90 °C. Cyclic voltammetry studies of the Fe and Mn complexes reveal reversible redox processes indicating stabilization of Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+ oxidation states, indicating the likelihood of catalytic oxidation for these complexes. Finally, dye-bleaching experiments with methylene blue, methyl orange, and rhodamine B demonstrate efficient catalytic decolorization and allow selection of the most successful monomeric catalysts for copolymerization to produce future heterogeneous water purification materials. 

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5. Crystal Mush Storage Constraints for the Puyehue-Cordon Caulle Volcanic Complex

   Heather Winslow, Philipp Ruprecht (January 2021, AGU Fall Meeting New Orleans, LA & Online Everywhere, 13-17 December 2021)

   Puyehue-Cordon Caulle (PCC) is an active volcanic complex located in the SVZ of the Andes that has had three major historic rhyodacitic eruptions with the most recent event in 2011-12. We provide petrologic and geochemical evidence that PCC is underlain by a crystal mush using recently identified basaltic mafic enclaves that highlights the involvement of distinct mafic magma components during the 2011-12 eruption. We suggest the mafic enclaves represent remnants of the crystal-rich mush that get entrained during eruption of the crystal-poor rhyodacite melt lens cap. This architecture requires the basaltic mush to produce rhyodacite through efficient fractionation. The dominant population of enclaves are equigranular, crystal-rich (45-55%), vesiculated (10-20%), and display interlocking grains between phases. Vesicles have complex shapes filling the irregular interlocking textures, while phenocrysts show stepwise normal zoning (uniform plagioclase cores, ~An90, overgrown with weakly zoned rims, ~An60). A second porphyritic population may represent mafic recharge into the system that bypasses the mush unperturbed. The porphyritic enclaves have spherical vesicles and tightly bound primitive mineral compositions (Fo80-86 vs Fo70-86 in the equigranular enclaves). Published geothermobarometry from the 2011-12 rhyodacite suggests shallow magma storage (5-7 km, 100-140 MPa, 895°C), which we compare against newly determined mineral-mineral trace-element partitioning based thermometry. Our thermometry indicates the equigranular enclaves were stored at ~900-1000°C at the time of eruption suggesting both a compositionally and thermally zoned magma system. We combine this temperature information with trace element data and mass balance calculations from various minerals phases and melt to substantiate our previous hypothesis that the basaltic enclaves can produce rhyodacite given their crystallinity. These estimates may support a spatially connected basaltic crystal-mush underlying a rhyodacite melt lens cap further proving highly efficient rhyolite formation at PCC. PCC’s enclaves present one of the largest compositional gaps on record globally. We compare them to other enclave-bearing systems and how PCC is an important end-member to understand enclaves as well as rhyolite formation. 

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