Cosmogenic 10 Be in pyroxene: laboratory progress, production rate systematics, and application of the 10 Be- 3 He nuclide pair in the Antarctic Dry Valleys

• Published in: Geochronology
• Main Authors: Balter-Kennedy, Allie, Schaefer, Joerg M., Schwartz, Roseanne, Lamp, Jennifer L., Penrose, Laura, Middleton, Jennifer, Hanley, Jean, Tibari, Bouchaïb, Blard, Pierre-Henri, Winckler, Gisela, Hidy, Alan J., Balco, Greg
• Other Authors: Lamont-Doherty Earth Observatory (LDEO), Columbia University New York, Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Lawrence Livermore National Laboratory (LLNL), Berkeley Geochronology Center (BGC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; Antarctic; The Antarctic; McMurdo Dry Valleys; Antarc*; Antarctica
• Online Access: https://insu.hal.science/insu-04198250; https://insu.hal.science/insu-04198250/document; https://insu.hal.science/insu-04198250/file/gchron-5-301-2023.pdf; https://doi.org/10.5194/gchron-5-301-2023

International audience Here, we present cosmogenic- 10 Be and cosmogenic- 3 He data from Ferrar dolerite pyroxenes in surficial rock samples and a bedrock core from the McMurdo Dry Valleys, Antarctica, with the goal of refining the laboratory methods for extracting beryllium from pyroxene, further estimating the 10 Be production rate in pyroxene and demonstrating the applicability of 10 Be- 3 He in mafic rock. The ability to routinely measure cosmogenic 10 Be in pyroxene will open new opportunities for quantifying exposure durations and Earth surface processes in mafic rocks. We describe scalable laboratory methods for isolating beryllium from pyroxene, which include a simple hydrofluoric acid leaching procedure for removing meteoric 10 Be and the addition of a pH 8 precipitation step to reduce the cation load prior to ion exchange chromatography. 10 Be measurements in pyroxene from the surface samples have apparent 3 He exposure ages of 1-6 Myr. We estimate a spallation production rate for 10 Be in pyroxene, referenced to 3 He, of 3.6 ± 0.2 atoms g -1 yr -1 . 10 Be and 3 He measurements in the bedrock core yield initial estimates for parameters associated with 10 Be and 3 He production by negative-muon capture (f 10 ∗ =0.00183 and f 3 ∗ fCfD=0.00337). Next, we demonstrate that the 10 Be- 3 He pair in pyroxene can be used to simultaneously resolve erosion rates and exposure ages, finding that the measured cosmogenic-nuclide concentrations in our surface samples are best explained by 2-8 Myr of exposure at erosion rates of 0-35 cm Myr -1 . Finally, given the low 10 Be in our laboratory blanks (average of 5.7 × 10 3 atoms), the reported measurement precision, and our estimated production rate, it should be possible to measure 2 g samples with 10 Be concentrations of 6 × 10 4 and 1.5 × 10 4 atoms g -1 with 5 % and 15 % uncertainty, respectively. With this level of precision, Last Glacial Maximum to Late Holocene surfaces can now be dated with 10 Be in pyroxene. Application of 10 Be in pyroxene, alone or in ...