Chemical weathering in subtropical basalt-derived laterites: A mass balance interpretation (Misiones, NE Argentina).

CAMPODONICO, V.A.; PASQUINI, A.I.; LECOMTE K.L.; GARCÍA M.G.; DEPETRIS P.J.

Congreso; V Reunión Argentina de Geoquímica de la Superficie.; 2019

Subtropical laterites in Misiones province cover the Jurassic-Cretaceous Serra Geral basalts. Twohypotheses have been proposed to explain the origin of these laterites. The autochthonous theorystates that these deposits result from chemical weathering of the underlying tholeiitic basalts. However,during the last decade, an allochthonous ?tropical loess? model was proposed. A lateritic profile (~2 mthick, 26°9'58"S - 54°35'3"W) was analyzed in order to constrain the nature of weathering processesand the provenance of the lateritic layer. Different alteration indices showed the extreme leaching of thebasaltic bedrock. The index of lateritization (IOL = 35-50) and the accompanying SAF ternary plot(SiO2-Al2O3-Fe2O3), indicate an increasing weathering trend towards the profiles' top, reflecting themodest loss of SiO2 (relative to Al2O3 and Fe2O3) during kaolinitization. The geochemical approachused in this work clearly relates the analyzed laterites to the underlying tholeiitic basalts, supporting theautochthonous origin theory.