A comparison of the Toorongo weathering profile, south Australia, and weathered regolith at Santa Margarita Ecological Reserve: Comparing...
A comparison of the Toorongo weathering profile, south Australia, and weathered regolith at Santa Margarita Ecological Reserve: Comparing weathering intensity factors derived from non-central principal component analysis
Compositional data derived from Cretaceous granodiorite at the Santa Margarita Ecological Reserve (SMER), southern California, are used to model a linear compositional weathering trend using non-central principal component analysis. Unlike the Chemical Index of Alteration (CIA) typically used to determine weathering intensity, non-central principal component analysis provides a translation invariant weathering intensity factor, thereby quantifying the degree of chemical weathering. This model yields a trend similar to the model of von Eynatten and colleagues of a compositional weathering trend adjusted to the Toorongo Granodiorite, south Australia. Both the SMER and Toorongo trends move away from the CN apex towards the A apex in A-CN-K ternary diagrams. Such trends are likely due to the removal of CaO and Na20 associated with the preferential weathering of plagioclase. Weathering intensity factors (t) of saprock at the SMER site range from 0.11-0.84 with a mean of 0.32 ±0.17 in contrast to the Toorongo site with a range of 0.03-3.94 and a mean of 1.29 ±0.76. This difference in weathering intensity of the Toorongo trend and the SMER trend is likely a result of climatic variations between the two localities. Principal component 1 (PCI) accounts for 90.9% of the total variability of data along the adjusted weathering trend of the SMER site.