Morphometric and hydrogeochemical weighting methodology to classify susceptibility to chemical weathering in the sub-basins of the Caplina River, Tacna, Peru

Abstract

A heuristic weighting methodology is formulated to classify the susceptibility to chemical weathering in the Caplina basin from two approaches: hydrogeochemical and geological morphometric. The main objective was to study the hydrological recharge of an arid basin with differential chemical weathering of geological formations in contact due to the salinization of water flow.

The parameters in the morphometric approach were analyzed in two proposed indices: (1) historical reload, from the parameters of shape and hypsometric curve; (2) runoff speed with low slopes (3-12 %), drainage density < 0.8 km^-1. According to their morphometry, the Caplina and Magollo sub-basins are more susceptible to chemical weathering in the Caplina basin.

For the validation of the methodology, the inventory of hydrochemical samples of the Peruvian Geological Service (Ingemmet) was used. The resulting classification of weights determined about 80 % of underground and surface sources in the basin are predominantly salinized in hydrogeological units of high and medium susceptibility to weathering. The final map generated at a scale of 1:500 000 identifies two hydrogeological units with high susceptibility to weathering: (1) fissured aquifers with hydrothermal alteration, in the Chachacumane, Chulluncane, Huilacollo, Volcánico Barroso formations, contributing calcium sulfate trends in 41.2 % of the total samples; (2) intrusive aquitards, in the Yarabamba and Challaviento formations, which influence the oxidation of sulfides in the hydrochemistry of 17.6 % of the samples. Likewise, aquitards of the volcanic origin of medium susceptibility to weathering are identified, with a considerable sodium contribution in 20.6 % of the study samples.