REE and other trace elements in a granitic weathering profile from “Serre”, southern Italy

Abstract

REE, V, Cr, Ni, Rb, Sr, Y, Zr and Nb behaviour in a granitic weathering profile in southern Italy is studied. In the saprolites of the considered profile, depletion of V, Cr, Ni, Rb, Sr, Zr and Nb is observed. This is quite remarkable for Sr and Cr whereas REE and Y are enriched in the more altered portion of the profile and especially in its < 2- αm fraction. Such enrichment is associated with the LREE-HREE fractionation and the positive Ce anomaly. The former results from an increased solubility of HREE in a non-acid environment as well as from the removal of the HREE-rich phases from the residual component. The latter is related to the redox chemistry of Ce which, as CeO 2, is less soluble than the other REE. No analogy is observed between the behaviour of Ce and Fe, Mn and Cr. Saprolites also exhibit a negative Eu anomaly which is mostly inherited from the parental material. Finally, the influence of accessory minerals in the REE distribution of weathering products and in sediments calls for a careful evaluation of preferential settling phenomena of heavy minerals during transportation and deposition processes. This is especially true in the parent material-sediment relationships.