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1. The 41 Ar(n,y) 42 Ar reaction

   https://doi.org/10.1051/epjconf/202328401037  

   Sahoo, R. N. ; Paul, M. ; Köster, U. ; Scott, R. ; Tessler, M. ; Zylstra, A. ; Avila, M. L. ; Dickerson, C. ; Jayatissa, H. ; Kohen, M.S. ; et al ( January 2023 , EPJ Web of Conferences)

   Mattoon, C.M. ; Vogt, R. ; Escher, J. ; Thompson, I. (Ed.)

   The cross-section of the thermal neutron capture⁴¹Ar(n,γ)⁴²Ar(t_1/2=32.9 y) reaction was measured by irradiating a⁴⁰Ar sample at the high-flux reactor of Institut Laue-Langevin (ILL) Grenoble, France. The signature of the two-neutron capture has been observed by measuring the growth curve and identifying the 1524.6 keV γ-lines of the shorter-lived⁴²K(12.4 h) β⁻daughter of⁴²Ar. Our preliminary value of the⁴¹Ar(n,γ)⁴²Ar thermal cross section is 240(80) mb at 25.3 meV. For the first time, direct counting of⁴²Ar was performed using the ultra-high sensitivity technique of noble gas accelerator mass spectrometry (NOGAMS) at Argonne National Laboratory, USA.

    

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2. DECIPHERING THE “FOOTPRINT” OF THE NEOACADIAN METAMORPHIC EVENT IN THE SOUTHERN APPALACHIANS: INSIGHTS FROM 40 AR/ 39 AR GEOCHRONOLOGY IN THE EASTERN BLUE RIDGE AND INNER PIEDMONT OF NORTH CAROLINA

   https://doi.org/10.1130/abs/2021SE-362173  

   Spencer, Brandon ; Thigpen, James ; Merschat, Arthur ; Powell, Nicholas E. ; McDonald, C.S. ( January 2021 , Abstracts Geological Society of America)

   The southern Appalachians preserve a composite thermal and deformational history that involves at least four orogenic pulses and spans >800 Myr from the middle Mesoproterozoic to the late Paleozoic. This complex history has made the discrete separation of metamorphic and deformational events persistently challenging, particularly for Paleozoic events. To address this, we report results from a new suite of amphibole 40Ar/39Ar data from the eastern Blue Ridge and Inner Piedmont (Tugaloo and Cat Square terranes) of western North Carolina to constrain the timing of cooling from thermal conditions greater than ~550 °C. Samples were collected along an orogen-normal transect from the Newton window, near the Central Piedmont suture, to the eastern Blue Ridge, west of the Grandfather Mountain window. Amphibole gneiss from the Spruce Pine area and Wilson Creek gneiss from the Grandfather Mountain window record dates of 380 and 496 Ma, respectively. Across the Brevard Fault zone, one sample from the western Inner Piedmont Tugaloo terrane yields a date of 377 Ma. Southeast of the Brindle Creek fault in the Cat Square terrane, three samples yield dates of 344-320 Ma while two samples from Tugaloo rocks of the Newton window yield dates of 335-330 Ma. Together, these dates suggest regional cooling of the Inner Piedmont progressed from northwest to southeast following the Neoacadian orogeny. The data also indicate either that high-grade (>550 °C) Alleghanian metamorphism may have only reset the amphibole40Ar/39Ar systematics in the most southeastern parts of the Inner Piedmont, near the Central Piedmont suture, or that these high-grade Neoacadian rocks were not exhumed from the mid-crust until the Alleghanian. Additionally, our new amphibole 40Ar/39Ar dates northwest of the Brevard Fault zone are not reset during Neoacadian orogenesis. Collectively, we interpret that high-grade metamorphism in this part of the southern Appalachians must have occurred prior to the Alleghanian, placing limits on the northwesternmost extent of mid- to high-grade Alleghanian metamorphism in this part of southern Appalachians. Additional data from the Sauratown Mountains window to the northeast and South Carolina and Georgia to the southwest may further constrain the spatial extent of the Neoacadian thermal event in the southern Appalachians. 

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3. Emplacement History of the Miocene Zebín Tuff Cone (Czech Republic) Revealed From Ground Geophysics, Anisotropy of Magnetic Susceptibility, Paleomagnetic, and 40 Ar/ 39 Ar Geochronology Data

   https://doi.org/10.1029/2017GC007324  

   Petronis, Michael ; Valenta, Jan ; Rapprich, Vladislav ; Lindline, Jennifer ; Heizler, Matthew ; van Wyk de Vries, Benjamin ; Shields, Sarah ; Balek, Jan ; Fojtíková, Lucia ; Tábořík, Petr ( October 2018 , Geochemistry, Geophysics, Geosystems)
4. 40 Ar/ 39 Ar Thermochronology for Submilligram Samples Using a Ta Platform Microfurnace, With Illustrations From the Bushveld Complex

   https://doi.org/10.1029/2020GC009182  

   Setera, Jacob B. ; Turrin, Brent D. ; Herzog, Gregory F. ; VanTongeren, Jill A. ; Delaney, Jeremy S. ; Swisher, III, Carl C. ( October 2020 , Geochemistry, Geophysics, Geosystems)

   We present a method for⁴⁰Ar/³⁹Ar step‐heating measurements on anhydrous K‐bearing minerals. Samples placed in dimples on Ta foil platforms are heated indirectly with a laser while temperatures are measured with a two‐color pyrometer. The system provides a simple, inexpensive, and reliable means for the heating of samples as small as a few to tens of micrograms. Results for plagioclase separates from the Rustenburg Layered Suite of the circa 2.06 Ga Bushveld Complex closely match previously published data.

    

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5. Preservation of ancient impact ages on the R chondrite parent body: 40 Ar/ 39 Ar age of hornblende‐bearing R chondrite LAP 04840

   https://doi.org/10.1111/maps.12692  

   Righter, K. ; Cosca, M. A. ; Morgan, L. E. ( August 2016 , Meteoritics & Planetary Science)

   The hornblende‐ and biotite‐bearing R chondriteLAP04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined⁴⁰Ar/³⁹Ar ages on hornblende‐rich separates of the meteorite, and obtained plateau ages of 4340(±40) to 4380(±30) Ma. These well‐defined plateau ages, coupled with evidence for postshock annealing, indicate this meteorite records an ancient shock event and subsequent annealing. The age of 4340–4380 Ma (or 4.34–4.38 Ga) for this and other previously dated R chondrites is much older than most impact events recorded by ordinary chondrites and points to an ancient event or events that predated the late heavy bombardment that is recorded in so many meteorites and lunar samples.

    

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