Estimation of composition of uppermost continental crust and eroded material using a global geochemical dataset
Date:
Abstract
Constraining the modern composition of continental crust is a prerequisite to understanding crustal evolution over Earth’s history. The composition of material eroded from the continental crust is also of significant importance, as it influences how crustal composition changes over million-year timescales. However, estimations of crustal composition are debated. While the most direct data are the measured compositions of surficial samples, these samples are not evenly spatially distributed; that is, averaging all available data does not accurately represent crustal composition. Furthermore, while the composition of exposed crust influences the composition of eroded material, erosion rates are highly spatially variable. While the composition of eroded material is influenced by crustal composition, the two are not identical. Here we use a global geochemical dataset compiled from the EarthChem online geochemistry database to estimate the composition of the uppermost exposed continental crust and the associated eroded material. We use the Macrostrat geologic map database to find the lithology and age for a uniformly distributed set of points on the continental crust. To correct sampling bias in the EarthChem data, we algorithmically select an EarthChem sample for each point in our dataset based on temporal, spatial, and geochemical similarity. We estimate the composition of eroded material using both the composition of the continental crust at each point, and a logarithmic relationship between slope and erosion calibrated using erosion rates from cosmogenic isotopes. Our results fall within existing estimates of crustal composition based on the composition of cratons and orogenic belts, and demonstrate a new way to integrate lithologic and geochemical data.