Lateritas do Domínio Médio Coreaú - comportamento geoquímico de mantos lateríticos do Noroeste do Estado do Ceará

Abstract

In this paper an evaluation is made over the geochemistry signature of major elements in lateritic rocks on the counties of Granja, Martinópole and Parazinho, Northwest of Ceará State. Geologically, the area is located in Médio Coreaú Domain, characterized by the Granja Complex, which is the geological basement of the region, composed by gneiss, granulites and migmatites, and supracrustal sequences formed by quartizites and phyllites of Martinópole and Ubajara Group, and also cenozoic sediments of Barreiras Formation. Laterites are normally found in humid weather (seasonal or not), so it is more likely that the generation process of this lateritic beds were under ancient climatic conditions, totally different from the present. The laterites are associated with gneiss, quartzites and phyllites. The prevailing laterization process is the metal enrichment, especially iron. Iron content varies from 34.69 to 77.85% in the altered rock samples; this trend being more evident in gneiss, in which iron enrichment exceeds 75%. Al content increases 6 to 7% in altered rocks. Sm-Nd data showed that the ratios obtained in these laterites are similar to the protoliths and can be used to define autochthonous from allocththounus laterites and also confirm Sm and Nd mobility in the laterization process.