Cosmogenic 3He and 21Ne production rates calibrated against 10Be in minerals from the Coso volcanic field

This study calibrates the production rate of cosmogenic He-3 in pyroxene, olivine, garnet, zircon and apatite as well as Ne-21 in quartz and pyroxene against the known production rate of Be-10 in quartz. The Devil's Kitchen rhyolite from the Coso volcanic field in southeastern California (elev. similar to 1300 m) was chosen for this study due to its young age (similar to 610 ka) and diverse mineral assemblage. Based on Be-10, our two rhyolite samples have apparent exposure ages of similar to 49 and 93 ka, indicating substantial erosion after eruption. Combining data from the two samples, we estimate sea level high latitude He-3 spallation production rates of 145 +/- 11, 141 +/- 16. and 144 +/- 30 at g(-1) a(-1) (2 sigma) for pyroxene, olivine and spessartine garnet respectively. For zircon and apatite, we estimate apparent He-3 spallation production rates of 114 +/- 8 and 149 +/- 28 at g(-1) a(-1) (2 sigma) respectively. The rates for zircon and apatite are reported as apparent production rates because we do not explicitly address the redistribution of spallation produced He-3 from adjacent minerals. These estimates quantitatively account for production of He-3 from both cosmogenic and radiogenic neutron reactions on Li-6 within the analyzed phases and also implanted from nuclear reactions in neighboring minerals: the high U, Th and Li content of this rhyolite provides a particularly rigorous test of this correction. We estimate Ne-21 production rates of 17.7 +/- 1.6 and 34.1 +/- 3.2 at g(-1) a(-1) (2 sigma) in quartz and pyroxene (Fe/Mg = 0.7 by mass) respectively. Although high U and Th contents create the potential for significant production of nucleogenic Ne-21, this component is small due to the young eruption age of the rhyolite. (C) 2009 Elsevier B.V. All Fights reserved.