Reviewing early chemical weathering in the Achala Batholith (Sierras Pampeanas, Cordoba, Argentina)

Appraising weathering intensity and rate in areas subjected to a weathering-limited regime-i.e. Achala batholith (Sierras Pampeanas de Cordoba, Argentina)-is complicated due to regolith scarcity and the absence of soil profiles. The A-type granite exhibits characteristic landforms patchily mantled with coarse-grained (i.e. grus) and poorly sorted regolith in topographic lows. Physical weathering is substantial; chemical weathering of granite and derived debris is incipient. Rainfall and scarce snowfall carry continental chemical signatures due to aerosols, largely supplied by extensive neighboring playas and arid/semiarid environments. Initial assessments of Achala's embryonic chemical weathering revealed that the chemical index of weathering (CIW) showed a significant difference between the granitic source and fine-grained regolith, triggered by mineral dissolution/hydrolysis. The delta O-18 and delta H-2 signatures of springs/streams are close to local rainfall, and show a significant deuterium excess (i.e. > 10 per mil). Stream chemistry suggested the contribution of plagioclase, and biotite, with calcite and gypsum (i.e. partly supplied as aerosols?), and likely pyrite oxidation adding to the dissolved pool. PHREEEQC inverse modeling applied in ephemeral/perennial springs, identified illite (similar to 32 mu mol kgw(-1)), Ca-montmorillonite (similar to 43 mu mol kg w(-1)), and sepiolite (similar to 22 mu mol kgw(-1)) as main transferred phases. First-order streams broadly concurred with previous findings, with gibbsite (similar to 23 mu mol kgw(-1)), chalcedony (similar to 87 mu mol kg w(-1)), and kaolinite (similar to 43 mu mol kgw(-1)) as frequent and more abundant crystalline phases. Modeling suggests that most dissolution and mineral formation occur within the realm of springs, with first-order streams largely expressing a reduced role in mole transferring.