Fractional changes in elemental mass (Ω) and relative variation curves: Unravelling elemental mass redistribution patterns within the regolith

• Ω is the modeled fractional change in original elemental mass.
• Relative variation curves model changes in Ω as weathering intensity increases.
• Results presented here follow closely to the predicted curves.
• Findings are supported by rigorous mass balance calculations.
• Relative variation diagrams have great visual impact and are easy to interpret.

Within the arid climate of southern California, USA, we uncovered through trenching a granodioritic-tonalitic corestone, a partially encircling fractured rind, and an overlying Ah2 horizon composed of sandy soil. Using the geometric mean of chemical data derived from an adjacent erosionally exhumed corestone as a proxy for unweathered bedrock, the compositional linear trend derived from weathering was calculated. Average weathering intensities (t-values) and 95% confidence intervals are as follows: uncovered corestone = 0.56 (± 0.13), inner fractured rind = 0.93 (± 0.08), outer fractured rind = 1.5 (± 0.05), and Ah2 = 1.7 (± 0.09).Ti was used as a reference frame for calculating Ω, the modeled fractional change in a given elements mass. Resulting relative variation curves plotted on 10 bivariate graphs, where the x-axis represents t-values and the y-axis is Ω, show that with the exception of P2O5, samples from each of the above textural groups, cluster and plot closely about the 10 relative variation curves. The clustering and ordering of samples analyzed from the uncovered corestone, inner rind, outer rind, and Ah2 horizon about the relative variation curves suggests that weathering of the section of regolith uncovered by trenching occurred in an orderly and sequential manner as the result of increasing pH and decreasing surface area for fluid/rock reactions. Mass balance calculations are consistent with the modeled relative variation curves, and the weathering of plagioclase to smectite and kaolinite, and biotite and chlorite to vermiculite.