Towards a more robust assessment of internal K-content for single-grain feldspar luminescence dating.

Accurate dose rate determination is essential in luminescence dating studies and when using feldspars, the internal K-content has to be considered. Until recently it was common practice to base the estimates for the internal content of 40K and 87Rb of feldspar extracts used for infra-red stimulated luminescence dating on literature values. However, in some regions of the world (e.g. Atacama, Java), feldspar extracts prepared for single-grain luminescence analyses exhibit a complex mineralogy affecting the reliable determination of the internal dose rate (e.g. Sontag-González et al., 2021). A proof of concept study on luminescence dating in the central Atacama Desert for example demonstrated that values suggested by literature overestimate the K-content of the luminescent feldspars (Zinelabedin et al., 2022).

Here we test and evaluate different methods to determine the K-content of feldspar grain separates and its impact on single grain luminescence dating. For a set of chemically and structurally different samples from various geological origins, we compare the labour-efficient determination of the K-concentration on 100 µg subsamples utilising a β-counter with two more time-consuming techniques (EDX, micro-XRF) measuring the K-content of the individual grains.

We test the validity of the time- and cost-efficient β-counter dose rate estimation procedure in comparison to more cost- and labour-intensive alternatives. We aim at establishing a methodological foundation for spatially-resolved and single-grain luminescence-based analysis of feldspar samples with the ultimate goal to investigate geomorphological processes on the μm-scale in the Atacama Desert.

References:

Sontag-González et al. 2021, QG 65, 101181.

Zinelabedin et al. 2022, QG 101341.