Technical Note: Improved volume and derived value calculations for polished zircon

Abstract. Polishing mounted mineral crystals prior to bulk grain (U-Th)/He thermochronology analysis offers many advantages for characterizing and subsampling each grain via in situ methods to obtain the maximum geologically relevant information. However, polishing introduces complications for calculating grain volume, on which many derived (U-Th)/He data partially depend. Impacted data include isotope concentrations, effective uranium (a proxy for radiation damage), and alpha-ejection correction factors (F_T) which are used to correct (U-Th)/He dates. These derived data are integral to interpreting (U-Th)/He dates; without a way to accurately calculate these values for polished grains, the benefits of polishing and in situ measurements can be greatly reduced or negated. This reality has resulted in many studies forgoing polishing and thus missing potentially important data. To address this issue, this paper presents a set of equations encoded in an R script to calculate volume and derived values for polished zircon that can be easily integrated into existing workflows for bulk grain (U-Th)/He analysis.