Airborne gamma-ray spectrometry to quantify chemical erosion processes

摘要

Airborne gamma-ray spectrometry data (uranium,potassium and thorium contents) reveal geochemical heterogeneities within the monolithological Hyrome watershed (ca.150 km~2) in the Armorican massif (western France).Our observations and computations provide important constraints on the spatial distribution and the associated magnitudes of chemical erosion processes at the scale of a small watershed.Two distinct,partially preserved,weathering profiles exhibit a strong correlation between regolith evolution and airborne-derived K/Th ratios,suggesting that the variability is linked to supergene processes.Using both airborne data and laboratory measurements on rock samples,the total net export of potassium has been estimated at 422 +- 50 kg/m~2 and the chemical weathering rate of potassium at 17 +-2 kg/km~2/a.