O01_09

A software framework for calculating compositionally dependent in situ ¹⁴C production rates

Koester A¹, Lifton N¹

¹Purdue University, West Lafayette, United States

In situ cosmogenic nuclides have revolutionized surficial process and Quaternary geologic studies, yet in situ cosmogenic ¹⁴C (in situ ¹⁴C) is unique among commonly measured nuclides in that its 5.7 ky half-life enables constraints on complex exposure/burial histories during the last ~25 ka. However, measurements are currently limited to common, but not ubiquitous, coarse-grained quartz-bearing rocks. The ability to extract in situ ¹⁴C from quartz-poor and fine-grained rocks would expand applications to a broader array of landscapes. As a first step toward this goal, a robust means of interpreting in situ ¹⁴C concentrations derived from rocks and minerals spanning wider compositional ranges is crucial. We have developed a MATLAB®-based software framework to quantify spallogenic production of in situ ¹⁴C from a wide range of silicate rock and mineral compositions, based on measured and modelled excitation functions. As expected from prior work, production from oxygen dominates the overall in situ ¹⁴C signal, accounting for >90% of production at sea-level and high latitudes. This work confirms that Si, Al, and Mg are important targets, but predicts greater production from Na than previously recognized. The compositionally dependent production rates predicted for rock and mineral compositions considered are typically lower than that for quartz, dropping as compositions become more mafic (particularly Fe-rich). Production rates predicted for quartz and albite are comparable, however, reflecting the significance of production from Na. This framework should thus be a useful tool in efforts to broaden the utility of in situ ¹⁴C, but would benefit from improved excitation functions.