Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by de Oliveira, M. T. G. Articles by Meunier, A. Search for Related Content GeoRef GeoRef Citation

THE TITANOMAGNETITE TO TITANOMAGHEMITE CONVERSION IN A WEATHERED BASALT PROFILE FROM SOUTHERN PARANÁ BASIN, BRAZIL

¹ Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, 91509-900 Porto Alegre, Brazil
² Instituto de Física, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonççalves, 9500, 91501-970, Porto Alegre, Brazil
³ Hydrasa UMR 6532 CNRS – University of Poitiers, 40, Avenue du Recteur Pineau, 86022 Poitiers Cedex, France

^* E-mail address of corresponding author: marisa.oliveira{at}ufrgs.br

This study of magnetic minerals in a weathering profile developed on plateau basalts of the subtropical southern Paraná Basin explores the evolution of titanomagnetite to titanomaghemite. Six samples studied by optical microscopy, X-ray diffraction (XRD), electron microprobe, Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) support the interpretations.

The profile studied has two major parts: an upper, porous red-clay Latosol, ~2–8 m deep, separated by a stone line from an underlying alterite which has two different facies – its argillaceous alterite consists of a clayey matrix with a well-developed fissure system whereas the underlying boulder alterite consists of rock cores surrounded by highly-porous cortexes of Al-goethite.

Optical microscopy showed the titanomagnetite-titanomaghemite changes in color and shape through the profile. The decrease in the lattice parameter a of the magnetic separates from the rock cores to the alterite facies was detected by XRD. Mössbauer spectroscopy identified non-stoichiometric magnetite in the rock cores and Ti-substituted maghemite in the argillaceous alterite. Chemical analysis of the titanomagnetite-titanomaghemite grains showed that the relative proportions of TiO₂ and Fe₂O₃ vary in the different weathering facies. By SEM and EDS we also detected the presence of minor components as Si, Al, Ca, K, Mg and Mn.

These results led to the interpretation that the titanomagnetites from the fresh Paraná basalts, located in the subtropical zone of Brazil, are unstable and gradually change to titanomaghemites. The evolution of these magnetic minerals is registered in the weathering facies related to climatic changes throughout geological time.

Key Words: Magnetic Minerals • Titanomaghemite • Titanomagnetite • Soils • Weathering

This article has been cited by other articles:

				M. Soubrand-Colin, H. Bril, C. Neel, A. Courtin-Nomade, and F. Martin WEATHERING OF BASALTIC ROCKS FROM THE FRENCH MASSIF CENTRAL: ORIGIN AND FATE OF Ni, Cr, Zn AND Cu Can Mineral, June 1, 2005; 43(3): 1077 - 1091. [Abstract] [Full Text] [PDF]