Gênese e inserção na paisagem das couraças ferruginosas (cangas) no Maciço da Pedra Rachada, Quadrilátero Ferrífero, MG

Abstract

The identification of alteration facies is an important tool for understanding the weathering products genesis. When associated with relief, they can provide relevant information about the landscape evolution. This study aimed to identify the physiological variations along the weathering mantle of itabirites in the Pedra Rachada massif, Quadrilátero Ferrífero, MG, comprising the genesis of the ferruginous duricrusts and its insertion in the local landscape. Samples were collected for macro and micromorphological characterization. Micro-chemical and XRD analysis were also carried out. The results indicated the presence of facies, from the bottom to the top, from the weakly altered itabirite (F1): placoidal (F2), fragmented placoidal (F3), disorganized fragmented placoidal (F4 and F5), structured ducricrust or canga (R1 to R4) and non-structured (stricto sensu) duricrust or canga (F6). The association of the facies allows us to consider a lateritic profi le composed of the saprolitic, structured and non-structured cangas zones. The weathering mantle formation occurred with a strong litho-structural infl uence, mainly the dip of the rock layers. These structures are fossilized by the structured canga, with the crest of the Serra falling in the same direction. However, the biogeochemical evolution for the non-structured canga was able to change the topography, making the flattened surface.