Production rate of cosmogenic 21Ne in quartz estimated from 10Be, 26Al, and 21Ne concentrations in slowly eroding Antarctic bedrock surfaces

We estimated the production rate of Ne-21 in quartz using a set of samples from slowly eroding sandstone surfaces in the Antarctic Dry Valleys. Geologic evidence as well as cosmogenic Be-10 and Al-26 concentrations indicate that i) these sites have experienced millions of years of surface exposure at low erosion rates, and ii) steady erosion has been sustained long enough that surface Be-10 and Al-26 concentrations have reached equilibrium with the erosion rate. Under these conditions, surface cosmogenic Ne-21 concentrations should be a function only of the erosion rate and the Ne-21 production rate. As the erosion rate can be determined from Be-10 and Al-26 concentrations, this allows an estimate of the Ne-21 production rate. Estimating the reference Ne-21 production rate on this basis, with the assumption that all Ne-21 production is by neutron spallation, yields a poor fit to measured Ne-21 concentrations and a systematic residual that is correlated with the erosion rate of the sample site. The same steady-erosion assumption with a production model that includes production by deeply penetrating muons yields a good fit both to our measurements and to similar, independent, measurements from an Antarctic bedrock core. Both data sets together yield a total reference Ne-21 production rate of 18.3 +/- 0.4 atoms g(-1) a(-1), of which 0.66 +/- 0.10 atoms g(-1) a(-1) is due to muon interactions. (C) 2009 Elsevier B.V. All rights reserved.