Magnetic phases of soils developed from igneous rocks in a climate gradient transept, Brazilian northern Amazonia

Author:

Silva Aduan L.1,Araújo Roberto C.1,Melo Valdinar F.1ORCID,Sergio Cássio S.1,Schaefer Carlos Ernesto G.R.2ORCID

Affiliation:

1. Federal University of Roraima, Boa Vista, Roraima69304-250, Brazil

2. Department of Soil, Federal University of Viçosa, Viçosa, Minas Gerais36570-900, Brazil

Abstract

Knowledge on magnetic phases and properties of magnetic minerals has wide applications in soils and in agriculture, by the possibility, and perspectives in application of rock magnetic methods in soil science and agriculture; however, their role in highly weathered soils is still unclear. We characterized the mineralogy of soils from Brazilian northern Amazonia, with emphasis on magnetic soils. Samples with varying weathering degrees were collected from four different localities, and their magnetic phases (MPs) were separated and subjected to the following analysis: X-ray fluorescence (XRF), X-ray diffractometry (XRD), and measurements of field and temperature magnetization. The chemical composition by XRF analyses revealed the predominance of Fe, Si, Ti, and Mn. The XRD analysis, using the Rietveld method, revealed the presence of hematite, goethite, maghemite, and magnetite as magnetic phases: The highest concentration of MPs was detected in an Fe-rich Typic Eutrudept (54% magnetite). Magnetization measurements of the magnetic phases showed the presence of magnetite, associated with hematite and goethite, with magnetization values and transition temperature characteristics of these minerals. The magnetization varied according to soil type, indicating different weathering processes. Soil magnetism varied as a function of parent igneous rocks, in the following order: diabase > basalt > granite. The results indicate that parent material and mineral weathering influence soil magnetism in a tropical climate.

Publisher

Canadian Science Publishing

Subject

Soil Science

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