Tracing ancient climates: the role of the weathering mantle in the Río de la Plata Craton's history

Abstract

This study provides the first detailed characterization of the weathering mantle on the Río de la Plata Craton (northwest Tandilia System, Argentina), probably exposed between ~ 2.000 (age of the crystalline basement) and > ~ 720 Ma (age suggested for the upper section of Villa Mónica Formation). Multi-scale analysis of five profiles, from outcrop and core, reveals up to four alteration levels—bedrock, lower saprolite, upper saprolite, and oxidized bed—defined by textural, mineralogical, and geochemical criteria. Profiles show progressive loss of igneous texture, alteration of primary minerals, and formation of sericite, illite, and hematite. Illite polytype data indicate a vertical shift from detrital 2 M to authigenic 1Md, the latter likely via smectite transformation from hydrolytic alteration of mafic minerals. Geochemically, SiO2 decreases upward, while Al2O3, TiO2, Fe2O3, Cr2O3, and MnO increase. Weathering indices peak in the upper saprolite, and REE patterns show a strong positive Ce3⁺ anomaly. Mineralogical and geochemical features indicate formation under a warm, humid, seasonal climate, consistent with low-latitude paleogeography. Variations in mantle thickness reflect differential weathering linked to paleorelief. Although exact timing is uncertain, the mantle predates sedimentary basin infill and offers the earliest detailed record of continental weathering in this craton prior to Rodinia’s breakup, providing a benchmark for global Precambrian paleoweathering studies.