The SPICE Project: The SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations
Final Report Abstract
This summary is based on preliminary findings from the SPICE Project. The results and conclusions presented here were still in review at the time of submission of the final report. Results and conclusions may, thus, be revised through the peer-review process. The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar age of 72±4 ka (2σ). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic Ne, 10Be, and 14C have been determined from SP-flow quartz. Production rate ratios for 21Ne/10Be, 21Ne/14C, and 14C/10Be are based on the local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2σ uncertainty) of 4.43 ± 0.31, 1.43± 0.10, and 2.86 ± 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 21Ne, 10Be, and 14C are 17.0±1.1, 3.84±0.24, and 11.2±0.4 at/g/yr (2σ), respectively, using time-independent Lal (1991)/Stone (2000) (St) scaling factors. St scaled spallogenic 10Be and 14C rates are 3.73±0.25 and 9.4±0.6 at/g/yr, respectively. These rates overlap within 2σ uncertainty with other St-scaled production rates in the literature, including the total reference SLHL 21Ne production rate of Niedermann (2000), which is revised in this paper to 16.8±2.9 at/g/yr (1σ; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SPICE SLHL production rates are lower if time-dependent scaling factors are used. Commonly used global, average SLHL 10Be and 14C production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field was weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. The SPICE study finds no measureable difference between St-scaled production rates of cosmogenic 21Ne and 10Be over the past 20 ka and St-scaled 21Ne and 10Be production rates over the past 72 ka. As such, the SPICE study suggests that 21Ne and 10Be production rates in quartz were not significantly greater during the period of decreased magnetic strength from 20 to 50 ka.
Publications
- 2016. The SPICE Project: Preliminary cosmogenic nuclide production rates in quartz calibrated at the ~70 ka SP lava flow, AZ, USA. Geological Society of America Abstracts with Programs. Vol. 48, No. 7
Fenton, C.R., Niedermann, S., Dunai, T., Binnie, S, Marerro, S.
- 2018. The SPICE Project: Preliminary cosmogenic 10Be, 14C, and 21Ne production rates in quartz from the 72 ka SP lava flow, AZ, USA. Goldschmidt Abstracts
Fenton, C.R., Niedermann, S., Dunai, T., Binnie, S.
- 2019. The SPICE Project: Production rates of cosmogenic 21Ne, 10Be, and 14C in quartz from the 72 ka SP basalt flow, Arizona, USA. Quaternary Geochronoloy, 54:101019
Fenton, C.R., Niedermann, S., Dunai, T., Binnie, S.
(See online at https://doi.org/10.1016/j.quageo.2019.101019)
