The SPICE Project: Calibrated production rates of cosmogenic 3He and 21Ne in olivine and pyroxene from the 72 ka SP basalt flow, Arizona, USA

The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow that is preserved in the desert climate of northern Arizona, USA. The flow has an 40 Ar/ 39 Ar age of 72 +/- 4 ka (20) and has undergone negligible erosion and/or burial, making its surface an ideal site for direct calibration of cosmogenic nuclide production rates. Production rates for cosmogenic 3 He ( 3 He c ) and 21 Ne ( 21 Ne c ) have been determined from SP flow olivine and pyroxene in this study. The error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 3 He in olivine and pyroxene have identical values of 135 +/- 8 at/g/yr (2a x ; standard error) using time-independent Lal (1991)/Stone (2000) ( St ) scaling factors. These production rates decrease to identical values of 130 +/- 8 at/g/yr (2a x ; standard error) when 3 He measurements are standardized to the CRONUS-P pyroxene standard. The St- scaled, error-weighted mean, total reference production rates of 21 Ne in olivine and pyroxene are 48.4 +/- 2.9 at/g/yr and 26.5 +/- 1.7 at/g/yr (2a x ; standard error), respectively, increasing to 49.3 +/- 3.0 at/g/yr and 27.0 +/- 1.7 at/g/yr (2a x ; standard error), respectively, when standardized to the CREU-1 quartz standard. 3 He and 21 Ne production rates ( St ) overlap within 20 uncertainty with other St-scaled production rates in the literature. SLHL 3 He and 21 Ne production rates in SP flow olivine and pyroxene are nominally lower if time- dependent Lm and Sa scaling factors are used. Olivine and pyroxene both have identical, error-weighted mean SLHL production rates of 127 +/- 8 at/g/yr (2a x ; standard error) using Lm scaling factors and CRONUS-P standardized 3 He measurements. These production rates decrease to identical values of 110 +/- 7 at/g/yr (2a x ; standard error) for olivine and pyroxene when using Sa scaling factors. The Lm-scaled, error-weighted mean, total reference production rates of 21 Ne in olivine and pyroxene are 48.1 +/- 2.8 at/g/yr and 26.4 +/- 1.7 at/g/yr (2a x ; standard error), respectively, when standardized to the CREU-1 quartz standard. The error weighted mean, local 21 Ne/ 3 He production rate ratio in olivine is 0.358 +/- 0.009 (2a x ; standard error), which increases to 0.378 +/- 0.012 when using CREU-1 standardized 21 Ne production rates and CRONUS-P standardized 3 He production rates. The error weighted mean, local 21 Ne/ 3 He production rate ratio in pyroxene is 0.197 +/- 0.006, or 0.208 +/- 0.008 when 21 Ne and 3 He are standardized to CREU-1 and CRONUS-P, respectively. The updated, CREU-1 standardized 21 Ne c rate ( St ) in SPICE quartz is 16.5 +/- 1.1 at/g/yr. Production of 21 Ne in coexisting SPICE olivine (ol), pyroxene (px), and quartz (qz) (standardized to CREU-1; Fenton et al., 2019; this study) yields errorweighted mean, local production rate ratios of 3.00 +/- 0.13 (2a x ) and 1.64 +/- 0.08 (2a x ) for 21 Ne ol / 21 Ne qz and 21 Ne px / 21 Ne qz , respectively. This study suggests that production rates of 3 He and 21 Ne in SPICE olivine and pyroxene agree well with St- and Lm- scaled global mean production rates in the literature. It also indicates that CRONUS-P and CREU-1 standardizations yield production rates in even stronger agreement with these global mean rates.