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1. Subaerial oxidative uranium mobilization at the culmination of the Great Oxidation Event

   https://doi.org/10.1073/pnas.2510289122  

   Bauer, Ann M; Li, Weiqiang; Rybacki, Kyle S; Roden, Eric E; Kump, Lee R; Johnson, Clark M (September 2025, Proceedings of the National Academy of Sciences)

   Redox-sensitive elements figure prominently in studies of the evolution of Earth’s surface redox state, including the first major rise in atmospheric O₂, the Paleoproterozoic Great Oxidation Event. Most Precambrian rocks endured multistage tectonothermal histories, however, adding ambiguity to interpretation of their chemistry. Here, we apply U-Th-Pb isotope geochronology to the highly oxidized ~2.06 Ga Kuetsjärvi Volcanic Formation, Pechenga Greenstone Belt, Russia, to constrain the age and extent of U oxidation. By contrasting the relative mobility of U and Th using Pb isotopes, we find that complete to near-complete oxidation and removal of U occurred shortly after eruption. We argue that this likely indicates relatively high atmospheric O₂, where oxidative weathering and alteration produced a global pulse of U to the oceans. Such a pulse could explain widespread shifts in the U-Th-Pb isotope character of mantle reservoirs at ~2 Ga, including a decrease in the²³²Th/²³⁸U ratio of the mid-ocean ridge basalt source and inception of the high-²³⁸U/²⁰⁴Pb (HIMU) source to ocean island basalts, underscoring the connections between the redox character of the Paleoproterozoic surface and deep Earth. Using²⁰⁷Pb-²⁰⁶Pb,²³⁸U-²⁰⁶Pb,²³⁵U-²⁰⁷Pb, and²³²Th-²⁰⁸Pb geochronology, ~2.06 Ga oxidative loss of U may be distinguished from reintroduction of U at ~1.8 Ga during regional metamorphism, as well as Pb loss during a Phanerozoic tectonothermal event. Our results therefore establish the complex history of redox-sensitive element behavior in the rocks, highlighting the fact that elemental abundances, by themselves, are unlikely to capture straightforward proxy information in rocks that have seen multistage geologic histories. 

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2. Timing of Dike and Sill Emplacement in the Inner Aureole of the Alta Stock, Utah Determined by Zircon and Monazite Petrochronology

   https://doi.org/10.1029/2024GC011946  

   Beno, C J; Stearns, M A; Bowman, J R; Bartley, J M; Fernandez, D P; Kylander‐Clark, A_R C (May 2025, Geochemistry, Geophysics, Geosystems)

   Abstract Detailed geochronology from two compositionally distinct generations of dikes and sills intruded into the Alta metamorphic aureole, north‐central Utah, complement previous geochronologic studies from the Alta stock, providing information on the timing of magmatism and the nature of emplacement. Uranium/thorium‐lead dates and chemistry were measured in zircon and monazite from these intrusions and associated reaction selvages in hornfels by split‐stream laser ablation techniques. Concordant zircon U‐Pb dates (n = 532) define a dispersed population of dates that range from ∼38 to 32 Ma. Monazite Th‐Pb dates (n = 888) from granodioritic compositions range from ∼40 to 32 Ma. Evaluation of²⁰⁸Pb/²³²Th and²⁰⁷Pb/²⁰⁶Pb‐corrected dates with respect to common Pb, U and Th/U values allows rigorous evaluation of the effects of excess²⁰⁶Pb in these young monazites, yielding concordant²⁰⁸Pb/²³²Th and²⁰⁷Pb/²⁰⁶Pb‐corrected dates in monazites from the granodiorite, consistent with zircon dates from the same thin sections. Leucogranite sills and dikes, which cross‐cut the older granodiorite, have younger monazite dates from ∼33 to 28 Ma. Elevated heavy rare earth element concentrations and trends of larger negative Eu anomalies in the youngest monazites suggest crystallization from an evolved melt. Integration of these new geochronology results and field relationships with prior results from the Alta stock indicate the granodiorite represents the oldest material emplaced in the Alta system. Leucogranite aplite/pegmatite dikes and sills in the inner Alta aureole were emplaced during the final stage of Alta stock construction by injection of evolved water‐rich magmas. 

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3. 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)

   Abstract 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. Related ArticlesBranton, 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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4. Data from: Influence of magmatism on the architecture of transpressional faults and shear zones in the deep crust of the Late Cretaceous Southern California batholith

   https://doi.org/10.5061/dryad.jh9w0vtn6  

   Klepeis, Keith; Schwartz, Joshua; Miranda, Elena; Baskin, Jillyan; Castro_Mendez, Anya; Mora-Klepeis, Gabriela (January 2026, Dryad)

   Structural analyses combined with U‐Pb zircon petrochronology show the influence of arc magmatism on the evolution of two transpressional shear zones in the deep root of the Late Cretaceous Southern California batholith.  The mid-crustal Black Belt and lower-crustal Cucamonga shear zones (eastern San Gabriel Mountains) formed at ~84 Ma shortly after a large mass of tonalite and granodiorite intruded the lower crust.  Both shear zones were active until at least ~74 Ma and probably until 72-70 Ma.  In the mid-crustal shear zone, rheological contrasts between mingling magmas localized deformation at dike margins.  The deformation began as hypersolidus flow in partially crystallized dikes and then transitioned to deformation below the solidus when alternations between viscous creep and brittle faulting produced interlayered pseudotachylyte, cataclasite, and mylonite. As the dikes solidified, strain hardening drove shear zone growth and created thin (10-30 m) high-strain zones and faults that are widely spaced across ~1 km. In contrast, the lower-crustal Cucamonga shear zone was magma-starved, lacks the variety of shear zone fabrics exhibited by its mid-crustal counterpart, and formed by the reactivation of a pre-existing fabric that records pure reverse displacements at 124-93 Ma.  The two shear zones created a partitioned style of intra-arc transpression where sinistral-reverse (mostly arc-parallel with some arc-oblique) displacements were accommodated on moderately dipping faults and shear zones and arc-normal shortening was accommodated by coeval folds.  This study shows how a magmatic surge influenced the architecture and style of Late Cretaceous transpression in the Southern California batholith, including the evolution of high-strain zones that record alternating episodes of brittle, ductile, and hypersolidus deformation.  The results illustrate how magmatism localizes strain on deep-crustal faults during orogenesis and oblique convergence. We conducted U-Pb analyses on 11 zircon-bearing samples to determine the timing of magmatism, metamorphism, and deformation in the Black Belt and Cucamonga shear zones. Some zircons exhibited interior core and rim domains that reflect a history of deformation and metamorphism at amphibolite- to granulite-facies conditions.  The methods used in this study closely follow those outlined in Kylander-Clark et al. (2013) and are described in detail by Schwartz et al. (2024b).  U-Pb ratios were collected at the University of California, Santa Barbara using a Nu Plasma multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) with a Photon Machines 193 ArF excimer laser with HelEx cell. Spot size and frequency were 35 µm and 4 Hz, respectively.  The primary standard (91500) was accessed every 10 analyses to correct for in-run fractionation of Pb/U and Pb isotopes. A secondary standard (Temora-2) was analyzed every ~10 analyses to assess data reproducibility. Uncertainties are reported as 2SE internal calculated from Iolite and IsoplotR (Paton et al., 2010; Vermeesch, 2018).  We assigned a 2% uncertainty to all dates for interlab comparisons to account for the reproducibility of standards. Zircon ages are reported using the ²⁰⁶Pb/²³⁸U date for analyses <1100 Ma, and the ²⁰⁷Pb/²⁰⁶Pb date for those >1100 Ma. For the former, discordance is calculated as the percent difference between the ²⁰⁷Pb/²³⁵U and ²⁰⁶Pb/2³⁸U dates. Corrections for minor amounts of common Pb in zircon were made on ²⁰⁶Pb/²³⁸U dates following the methods of Tera and Wasserburg (1972) using measured ²⁰⁷Pb/²⁰⁶Pb and ²³⁸U/²⁰⁶Pb ratios and an age-appropriate Pb isotopic composition of Stacey and Kramers (1975).  Zircons with large common Pb corrections (e.g., analyses interpreted as having ~20% or greater contribution from common Pb) were discarded. No corrections were made on ²⁰⁷Pb/²⁰⁶Pb dates due to large uncertainties in measured ²⁰⁴Pb. Cathodoluminescence images were obtained using a FEI Quanta scanning electron microscope before and after ablation to evaluate analyzed areas and compare them with growth textures. Where possible, we targeted all growth domains and report ²⁰⁷Pb/²⁰⁶Pb-corrected ²⁰⁶Pb/²³⁸U ages of texturally homogeneous populations. In a few cases where a laser spots overlapped multiple domains we report the data in tables but did not considered them in weighted mean calculations. Concordia plots and error-weighted average ages are shown in the accompanying journal article. Trace elements were measured simultaneously with U-Pb isotopes by LA-SF-ICPMS using Zr as the internal standard and nominal values of 43.14 % Zr. Trace element data were reduced using Iolite (Paton et al., 2010, 2011) and concentrations calculated relative to NIST-612 as a primary standard. BHVO-2G was analyzed as a secondary standard to assess reproducibility of the data. For zircon, model Ti-in-zircon temperatures were calculated using the Ferry and Watson (Ferry and Watson, 2007) calibration. Samples of granulite-facies rocks from the Cucamonga terrane contain rutile, allowing us to estimate the activity of TiO₂ to be one.  For samples that lack rutile we assume a value of 0.6 based on the presence of ilmenite. # Data from: Influence of magmatism on the architecture of transpressional faults and shear zones in the deep crust of the Late Cretaceous Southern California batholith [https://doi.org/10.5061/dryad.jh9w0vtn6](https://doi.org/10.5061/dryad.jh9w0vtn6) ## Description of the data and file structure All isotopic, geochemical, and trace element data were collected as part of a study to determine the timing of magmatism, metamorphism, and deformation in the Black Belt and Cucamonga shear zones in the southeastern San Gabriel Mountains in Southern California. Some zircons exhibited interior core and rim domains that reflect a history of deformation and metamorphism at amphibolite- to granulite-facies conditions. Where possible, we used zircon trace-element concentrations and ratios, particularly U (ppm), U/Th, Gd/Yb, and Dy/Yb, to distinguish metamorphic age populations. For more information on methods and an interpretation of the data, please see the publication in the journal *GSA Bulletin* by Klepeis et al. (2025). ### Files and variables #### File: Supplementary_Table_1_U-Pb_zircon_FINAL.xlsx **Description:** The table in the data sheet tab titled 'Table 1. U-Pb data unknowns' presents all U-Pb isotope data for the 11 samples analyzed plus the standards used. All standards are listed at the bottom of the table. The zircon standards include: Plesovice(Ples), which is used as a zircon U-Pb age standard; 91500, which is a primary zircon reference standard used for age normalization and reproducibility; Australian zircon suite (AusZ), which is a zircon age standard that is used as a secondary check on accuracy; GJ-1 zircon (GJ), which is a widely used zircon standard, the Malinau/Malim zircon suite (Mali) which is an additional age validation standard. Trace element standards include NIST 612 (N612), which is a synthetic silicate glass standard (see more information below), and BHVO, which is a natural basalt reference standard (see more information below). In the 'Table 1. U-Pb data unknowns' tab, n/a means not applicable. This refers to the lack of best ages and absolute error calculations for the standards N612 and BVHO. This information isn't applicable because these are non-zircon trace element standards, so no age is calculated. In contrast, the zircon standards (91500, AusZ, GJ, Mali, Plesovice) all have well-known ages, so best age and absolute error calculations are included. In the Table 1 data tab, n.d. means not detected. Only 1 average value and a standard deviation for the trace element analyses are provided for each sample in columns AP and AQ, respectively (the rest of the cells are blank). The tab titled 'NIST 612' shows data that used the widely used synthetic glass standard from the U.S. National Institute of Standards and Technology. The standard is commonly analyzed to calibrate trace-element concentrations during LA-ICP-MS work. The tab titled 'BHVO' reports data from a well-characterized natural basalt reference material (from Hawaii). This is used as a secondary standard to monitor analytical accuracy and precision. In the BHVO data tab, n.d. means not detected. Isotopic ratios and Apparent ages are not corrected for common lead. For the 206Pb/238U ages, common lead was corrected by inferring the initial Pb-composition from the Stacey and Kramers (1975) two stage isotope evolution model (Vermeesch, 2018). Analyses with greater than 10% uncertainty in 207Pb/206Pb age (1-sigma) or 5% uncertainty in 206Pb/238U age (1-sigma), 20% discordance, and/or 5% reverse discordance are excluded. Accepted ages were calculated by using 206Pb/238U ages for grains younger than 1100 Ma and 207Pb/206Pb ages for grains older than 1100 Ma. ##### Variables * U, U/Th, 238U/206U, 207Pb/206Pb, 207Pb/206Pb vs 238U/206Pb isotopic ratios, apparent ages and absolute errors. * Trace-element data for P, Ti, V, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta Abbreviations include: ppm is parts per million, abs is absolute, Ma is millions of years, abs err is absolute error, error corr is error correction. ## Code/software Uncertainties were calculated using Iolite and IsoplotR (Paton et al., 2010; Vermeesch, 2018) 

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5. Meridional Central Pacific Ocean Depth Section for Pb and Pb Isotopes (GEOTRACES GP15, 152°W, 56°N to 20°S) Including Shipboard Aerosols

   https://doi.org/10.1029/2024JC021674  

   Jiang, Shuo; Lanning, Nathan; Boyle, Edward; Fitzsimmons, Jessica; Ramezani, Jahandar; Wang, Avery G; Zhang, Jing (January 2025, Journal of Geophysical Research: Oceans)

   Goodkin, Nathalie (Ed.)

   Abstract Most oceanic lead (Pb) is from anthropogenic emissions into the atmosphere deposited into surface waters, mostly during the past two centuries. The space‐ and time‐dependent emission patterns of anthropogenic Pb (and its isotope ratios) constitute a global geochemical experiment providing information on advective, mixing, chemical, and particle flux processes redistributing Pb within the ocean. Pb shares aspects of its behavior with other elements, for example, atmospheric input, dust solubilization, biological uptake, and reversible exchange between dissolved and adsorbed Pb on sinking particles. The evolving distributions allow us to see signals hidden in steady‐state tracer distributions. The global anthropogenic Pb emission experiment serves as a tool to understand oceanic trace element dynamics. We obtained a high‐resolution (5° station spacing) depth transect of dissolved Pb concentrations and Pb isotopes from Alaska (55°N) to just north of Tahiti (20°S) near 152°W longitude. The sections reveal distinct sources of Pb (American, Australian, and Chinese), transport of Australian style Pb to the water mass formation region of Sub‐Antarctic Mode Water which is advected northward, columnar Pb isotope contours due to reversible particle exchange on sinking particles from high‐productivity particle veils, and a gradient of high northern deep water [Pb] to low southern deep water [Pb] that is created by reversible exchange release of Pb from sinking particles carrying predominantly northern hemisphere Pb.²⁰⁸Pb/²⁰⁶Pb versus²⁰⁶Pb/²⁰⁷Pb isotope relationships show that most oceanic Pb in the North Pacific is from Chinese and American sources, whereas Pb in the South Pacific is from Australian and American sources. 

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