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

Here, we present cosmogenic Be-10 and He-3 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 Be-10 production rate in pyroxene, and demonstrating the applicability of the Be-10-He-3 in mafic rock. The ability to routinely measure cosmogenic Be-10 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 Be-10, and the addition of a pH 8 precipitation step to reduce the cation load prior to ion exchange chromatography. Be-10 measurements in pyroxene from the surface samples have apparent He-3 exposure ages of 1-6 Ma. We estimate a spallation production rate for Be-10 in pyroxene, referenced to He-3, of 3.6 +/- 0.2 atoms g(-1) yr(-1). Be-10 and He-3 measurements in the bedrock core yield initial estimates for parameters associated with Be-10 and He-3 production by negative muon capture (f(10)(* )= 0.00183 and f(3)* f(C) f(D) = 0.00337). Next, we demonstrate that the Be-10-He-3 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 Be-10 in our laboratory blanks (average of 5.7 x 10(4) atoms), the reported measurement precision, and our estimated production rate, it should be possible to measure 2 g samples with Be-10 concentrations of 6 x 10(4) atoms g(-1) and 1.5 x 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 Be-10 in pyroxene. Application of Be-10 in pyroxene, alone or in combination with He-3, will expand possibilities for investigating glacial histories and landscape change in mafic rock.