Cosmogenic 10Be in detrital quartz has been widely used to quantify spatially averaged erosion rates for entire catchments. Here we show how the technique can be expanded to quantify the relative weathering rates of different minerals in catchment soils. As a case in point, we consider magnetite and quartz, which should share the same relationship between 10Be production rate and depth during erosion to the surface. However, the minerals likely do not share the same susceptibility to chemical weathering. We expect quartz to be enriched relative to magnetite due to differential chemical erosion in soils. Quartz should therefore have a longer soil residence time than magnetite. Thus, 10Be should be more concentrated in quartz than magnetite, at a ratio that depends on both the 10Be production-rate ratio and the relative enrichment of the two minerals. Here we develop a theoretical basis for interpreting 10Be ratios in multiple minerals and show preliminary data from catchments in the Southern Sierra Critical Zone Observatory, where chemical erosion rates are well constrained by geochemical mass balance.
Rogers, H. E.; Riebe, C. S.; Granger, D. E. (2013): Cosmogenic 10Be in quartz and magnetite:Using the same nuclide in multiple minerals to quantify differential weathering. American Geophysical Union, Fall Meeting 2013, abstract #H51B-1188.
This Paper/Book acknowledges NSF CZO grant support.