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1. Geochemical Constraints on the Origin of Primitive Potassic Lavas in the Eastern Virunga Volcanic Province

   https://doi.org/10.1029/2023GC010950  

   Pitcavage, E. ; Furman, T. ; Nelson, W. R. ; Graham, D. W. ; Shirey, S. ; Kulyanyingi, P. K. ; Barifaijo, E. ( June 2023 , Geochemistry, Geophysics, Geosystems)

   Young mafic lavas from the East African Western Rift record melting of subcontinental lithospheric mantle that was metasomatically modified by multiple tectonic events. We report new isotope data from monogenetic cinder cones near Bufumbira, Uganda, in the Virunga Volcanic Field:⁸⁷Sr/⁸⁶Sr = 0.7059–0.7079,ε_Nd = −6.5 to −1.3,ε_Hf = −6.3 to +0.9,²⁰⁸Pb/²⁰⁴Pb = 40.1–40.7,²⁰⁷Pb/²⁰⁴Pb = 15.68–15.75, and²⁰⁶Pb/²⁰⁴Pb = 19.27–19.45. Olivine phenocrysts from the Bufumbira lavas have³He/⁴He = 6.0–7.4R_A. The isotopic data, in conjunction with major and trace element systematics, indicate that primitive Bufumbira magmas are derived from two different metasomatized lithospheric source domains. Melts generated by lower degrees of melting record greater contributions from ∼1 to 2 Ga isotopically enriched garnet‐amphibole‐phlogopite pyroxenite veins within the lithosphere. As melting progresses, these vein melts become increasingly diluted by melts that originate near the lithosphere/asthenosphere boundary, shifting the isotopic compositions toward the common lithospheric mantle (CLM) proposed by Furman and Graham (1999,https://doi.org/10.1016/s0024-4937(99)00031-6). This ∼450–500 Ma source domain appears to underlie all Western Rift volcanic provinces and is characterized by⁸⁷Sr/⁸⁶Sr ∼ 0.705,ε_Nd∼ 0,ε_Hf∼ +1 to +3,²⁰⁶Pb/²⁰⁴Pb ∼ 19.0–19.2,²⁰⁸Pb/²⁰⁴Pb ∼ 39.7, and³He/⁴He ∼ 7R_A. Basal portions of the dense subcontinental lithospheric mantle may become gravitationally unstable and founder into underlying warmer asthenosphere, exposing surfaces where melting of locally heterogeneous veins produces small‐volume, alkaline mafic melts. Mafic lavas from all Western Rift volcanic provinces record mixing between the CLM and locally variable metasomatized source domains, suggesting this style of melt generation is fundamental to the development of magma‐poor rifts.

    

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2. 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)

   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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3. Seasonally Variable Aquifer Discharge and Cooler Climate in Bermuda During the Last Interglacial Revealed by Subannual Clumped Isotope Analysis

   https://doi.org/10.1029/2020PA004145  

   Zhang, Jade Z. ; Petersen, Sierra V. ; Winkelstern, Ian Z. ; Lohmann, Kyger C. ( May 2021 , Paleoceanography and Paleoclimatology)

   Faunal analog reconstructions suggest that Last Interglacial (MIS 5e) sea surface temperatures were cooler around Bermuda and in the Caribbean than modern climate. Here we describe new and revised clumped isotope measurements ofCittarium picafossil shells supporting previous findings of cooler than modern temperatures in Bermuda during the Last Interglacial. We resolve temperature and δ¹⁸O_wdifferences between two closely located and apparently coeval sites described in Winkelstern et al. (2017),https://doi.org/10.1002/2016pa003014through reprocessing raw isotopic data with the updated Brand/IUPAC parameters. New subannual‐resolution clumped isotope data reveal large variations in δ¹⁸O_wout of phase with seasonal temperature changes (i.e., lower δ¹⁸O_wvalues in winter). Supported by modern δ¹⁸O_wmeasurements identifying similar processes occurring today, we suggest past variations in coastal δ¹⁸O_wwere driven by seasonally variable freshwater discharge from a subterranean aquifer beneath the island. Taken together, our results emphasize the importance of δ¹⁸O_win controlling carbonate δ¹⁸O, and suggest that typical assumptions of constant δ¹⁸O_wshould be made cautiously in nearshore settings and can contribute to less accurate reconstructions of paleotemperature.

    

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4. MC‐ICP‐MS analyses of tin isotopes in Roman‐era bronze coins reveal temporal and spatial variation

   https://doi.org/10.1111/arcm.12459  

   Bower, N. W. ; Lundstrom, C. C. ; Hendin, D. B. ( January 2019 , Archaeometry)

   Tin's small mass fractionation and the lack of accepted reference standards have hindered Sn isotopy in archaeology and conservation science. Because of ore field variation and potential fractionation during ore reduction, attempts to determine artefacts’ ore sources have been limited. After norming the fractionations to NIST 3161a (Lot #070330), significant differences in Sn isotope mass fractionation in Judaean bronze ‘Biblical’ coins minted by different rulers during the first centuriesbceandcewere discovered. These variations and those inδ⁶⁵Cu and²⁰⁶Pb/²⁰⁴Pb are connected to historical events in the Levant.

    

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5. The effect of place on voting behavior: The case of the Arizona proposition to legalize recreational marijuana

   https://doi.org/10.1111/polp.12580  

   Mathews, Mason Clay ; Fotheringham, A Stewart ( February 2024 , Politics & Policy)

   In 2020, Arizonans approved Proposition 207, the Smart and Safe Arizona Act, which legalized recreational marijuana sales. Previous research has typically used non‐spatial survey data to understand marijuana legalization voting patterns. However, voting behavior can, in part, be shaped by geographic context, or place, which is unaccounted for in aspatial survey data. We use multiscale geographically weighted regression to analyze how place shaped Proposition 207 voting behavior, independently of demographic variations across space. We find significant spatial variability in the sensitivity of voting for Proposition 207 to changes in several of the predictor variables of opposition and support for recreational marijuana legalization. We argue that local statistical modeling approaches provide a more in‐depth understanding of ballot measure voting behavior than the current use of global models.

   Branton, Regina, and Ronald J. McGauvran. 2018. “Mary Jane Rocks the Vote: The Impact of Climate Context on Support for Cannabis Initiatives.”Politics & Policy46(2): 209–32.https://doi.org/10.1111/polp.12248.

   Brekken, Katheryn C., and Vanessa M. Fenley. 2020. “Part of the Narrative: Generic News Frames in the U.S. Recreational Marijuana Policy Subsystem.”Politics & Policy49(1): 6–32.https://doi.org/10.1111/polp.12388.

   Fisk, Jonathan M., Joseph A. Vonasek, and Elvis Davis. 2018. “‘Pot'reneurial Politics: The Budgetary Highs and Lows of Recreational Marijuana Policy Innovation.”Politics & Policy46(2): 189–208.https://doi.org/10.1111/polp.12246.

    

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