Geochemistry of redeposited and undisturbed ancient weathering zones in the Baikal Region

The distribution of major and trace elements was explored in the metamorphised weathering zones of the northern (Purpol Formation) and western (Anai and Angin formations) Baikal region. The alumina-rich schists of the Purpol and Anai formations intercalated with quartzites have a model age of 2.8–3.0 Ga and are redeposited products of the weathering of granitized basement inliers of the Siberian craton. Their trace element characteristics with high contents of Th, U, Nb, and REE and low Ta and Sr reflect the composition of predominant rocks in the Archean basement. Undisturbed weathering zones over the alkaline and calc-alkaline island-arc basalts of the Angin Formation are, in general, similar to modern laterites and redeposited residues with respect to the enrichment in hydrolyzate elements but are assigned to iron-rich laterites and distinguished by high contents of Fe, Ti, Nb, Ta, Zr, and Hf, which were inherited from their parent rocks. Their occurrence suggests subaerial eruptions of alkali basalts in the proximal part of the Angin-Talanchan island arc.