The hole of chemical denunudation on differential erosion processes in Quadril?tero Ferr?fero/MG.

O presente trabalho investiga a contribui??o da denuda??o geoqu?mica nos processos erosivos diferenciais do Quadril?tero Ferr?fero/MG, ?rea de relevante interesse geomorfol?gico por possuir, em seu modelado, importantes marcas desse tipo de processo. A fim de cumprir este objetivo foram utilizadas an?lises f?sico-qu?micas e qu?micas de ?guas superficiais coletadas em 18 (dezoito) pontos de monitoramento, localizados em quatro sub-bacias hidrogr?ficas que drenam a ?rea de estudo. A ?rea em quest?o possui clima tropical semi-?mido com esta??es seca (inverno) e ?mida (ver?o) bem delimitadas. A coleta das amostras de ?gua foi realizada nestes dois per?odos distintos. Os par?metros analisados foram: pH, s?lidos totais dissolvidos (TDS), s?lica, ferro, alum?nio, s?dio, c?lcio, magn?sio, mangan?s e pot?ssio. Os resultados demonstraram que a denuda??o geoqu?mica ? um dos fatores respons?veis pela eros?o diferencial, uma vez que ? poss?vel verificar a exist?ncia de tr?s comportamentos denudacionais geoqu?micos distintos: (i) elevadas taxas de denuda??o geoqu?mica nas ?reas moldadas sobre rochas carbon?ticas; (ii) taxas m?dias de denuda??o geoqu?mica nas ?reas modeladas sobre granitos, gnaisses, xistos e filitos e; (iii) baixas taxas de denuda??o geoqu?mica nas ?reas mais elevadas (quartzitos e itabiritos) em rela??o ?s depress?es adjacentes (xistos, filitos, granitos e gnaisses). Tal fato comprova para a ?rea investigada que as ?guas fluviais regionais s?o capazes de marcar a assinatura geoqu?mica dos litotipos que drenam. Foi poss?vel ainda concluir que, al?m dos litotipos, as ?reas das bacias hidrogr?ficas e as altitudes das mesmas em rela??o ao n?vel de base regional constituem fatores que tamb?m interferem na intensidade da denuda??o geoqu?mica.This work investigates the contribution of the chemical denudation to differential erosive processes in the Quadril?tero Ferr?fero (State of Minas Gerais, Brazil). This is an area of relevant geomorphologic interest because the record of this type of process is well-preserved in the landscape. Semi-humid tropical climatic conditions predominate in the area, with a well-defined dry season in winter and a humid season in summer. Superficial water samples were collected in both seasons at 18 monitoring points located in four hydrographic sub-basins. The parameters analyzed were: pH, total dissolved solids (TDS), silica, iron, aluminum, sodium, calcium, magnesium, manganese and potassium. The resulting data show that the geochemical denudation is one of the factors responsible for the differential erosion, once three distinct behaviors of geochemical denudation were identified: (i) high geochemical denudation rates in the areas developed on carbonatic rocks; (ii) medium geochemical denudation rates in the areas developed on granites, gneisses, schists and phyllites, and (iii) low geochemical denudation rates in the areas developed on quartzites and itabirites, which are topographically higher than the adjacent rocks (schists, phyllites, granites and gneisses). These results show that the regional fluvial waters are able to mark the geochemical signature of the rock types being drained. One can also conclude that, besides the rock types, the hydrographic basin and its altitude in relation to the regional base level are factors that interfere in the geochemical denudation intensity