Behavior of major and trace elements (including REE) during Paleoproterozoic pedogenesis and diagenetic alteration of an Archean granite near Ville Marie, Quebec, Canada

摘要

This paper presents a complete set of chemical data from a pre-2.0-Ga weathering profile that formed on the Archean granite neat Ville Marie, Quebec. Examination of data from two sections of the paleosol indicates that Na, Ca, P, and Sr were lost from the paleosol, whereas Ti Nb, Th, Zr, Hf, and Ta remained immobile during chemical weathering and all subsequent alteration. Rare earth mobility during genesis of the Ville Marie paleosol closely follows the pattern of early stages of chemical weathering in modem profiles. Average concentration of REE in both profiles is 20-40% lower than what is found in the fresh granite, suggesting mobilization during pedogenesis. HREEs seem to be less mobilized than the LREEs. (La/Sm)(N) ratios gradually decrease toward the top of the paleosol but the values remain very close to that of the protolith. (Gd/Yb)(N) values remain unchanged in the weathering profile. (La/Yb)(N) values in the weathering profile are quite variable and generally lower than that of the protolith. Eu/Eu* and Ce/Ce* values are essentially the same as those of the protolith, but two samples from the uppermost part of the profile have developed positive cerium anomaly of approximate to0.3 relative to the protolith. Copyright (C) 2000 Elsevier Science Ltd. [References: 55]