Intemperismo de anortositos e formação de solos na região semiárida, Nordeste do Brasil

Abstract

Anorthosites are plutonic rocks distributed throughout all continents, consisting of calcium plagioclase and accessory minerals, of great and proven geological importance for mining, occupying extensive areas of geological complexes on which also agrarian activities occur in diverse climates. Several studies have been and are carried out to understand geological, petrological, petrographic, geochemical, mineral alterations for the understanding of hydrothermal and or crustal processes and for the understanding of planetary events of lunar anorthosites. There are very few studies on anorthosite weathering to understanding pedogenesis, physical, chemical, morphological, mineralogical and micromorphological properties of soils. In order to provide information on weathering and pedogenesis in semiarid climates, the present study was carried out in the semi-arid region of the Northeast of Brazil, in the Passira Metanorthositic Complex, in which two soil profiles were opened on anorthosites. Soils were analyzed physically, morphologically, chemically, mineralogically and micromorphologically. The results showed that in semi-arid environment the soils developed in situ on anortosites, labrodorite/andesin type are poorly developed (Cambisol), whose mineralogical assembly in sand and silt fractions is dominated by plagioclase that origin clays formed by kaolinite in well drained environmet and smectite and kaolinte in poor drained environment. They present low CEC, tendency of accumulation of sodium in subsurface, high bases saturation dominated by calcium under unbalance with potassium and magnesium.