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

Abstract

Abstract. Here, we present cosmogenic 10Be and 3He 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 10Be production rate in pyroxene, and demonstrating the applicability of the 10Be-3He in mafic rock. The ability to routinely measure cosmogenic 10Be 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 includes a simple hydrofluoric acid leaching procedure for removing meteoric 10Be, and the addition of a pH 8 precipitation step to reduce the cation load prior to ion exchange chromatography. 10Be measurements in pyroxene from the surface samples have apparent 3He exposure ages of 1–6 Ma. We estimate a spallation production rate for 10Be in pyroxene, referenced to 3He, of 3.6 ± 0.2 atoms g−1 yr−1. 10Be and 3He measurements in the bedrock core yield initial estimates for parameters associated with 10Be and 3He production by negative muon capture (f10* = 0.00183 and f3* fC fD = 0.00337). Next, we demonstrate that the 10Be-3He 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 Ma of exposure at erosion rates of 0–35 cm Myr−1. Finally, given the low 10Be in our laboratory blanks (average of 5.7 × 104 atoms), the reported measurement precision, and our estimated production rate, it should be possible to measure 2 g samples with 10Be concentrations of 6 × 104 atoms g−1 and 1.5 × 104 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 10Be in pyroxene. Application of 10Be in pyroxene, alone or in combination with 3He, will expand possibilities for investigating glacial histories and landscape change in mafic rock.

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

“…All analytical information associated with cosmogenic-nuclide measurements appear in the tables and Supplement. All MATLAB scripts used for model fitting and to generate the figures can be found at https://doi.org/10.5281/zenodo.8125448 (Balter-Kennedy and Balco, 2023).…”