Mineralogical changes during thermal demagnetization of natural continental sandstones |
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| Authors: | C Prezzi R Somoza R C Mercader |
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| Institution: | (1) Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Geofísica D. Valencio, Departamento de Ciencias Geológicas, FCEyN, Universidad de Buenos Aires, Buenos Aires, Argentina;(2) Research Fellow of the Alexander von Humboldt Foundation, Institut für Geowissenschaften, Abteilung Geophysik, Christian Albrechts Universität, Otto Hahn Platz 1, 24118 Kiel, Germany;(3) Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Geofísica D. Valencio, Departamento de Ciencias Geológicas, FCEyN, Universidad de Buenos Aires, Buenos Aires, Argentina;(4) Consejo Nacional de Investigaciones Científicas y Técnicas, Departamento de Física, IFLP, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Mar del Plata, Argentina |
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| Abstract: | We study the mineralogical changes suffered by specimens of natural miocene red and green continental sandstones (from Pozuelos Formation and Tiomayo Formation) cropping out in the Argentine Puna that increase their bulk magnetic susceptibility and change color when thermally treated. We hypothesize that on heating siderite, which is present in small quantities as cement in the studied sandstones, would oxidize and decompose into maghemite and/or magnetite. Subsequent heating to higher temperatures sometimes would bring about the conversion of maghemite and/or magnetite to hematite. Mössbauer spectroscopy proved to be a very valuable tool for the determination of the presence of siderite in small amounts in the studied samples. The present results show that further work is needed in order to fully understand the mineralogical changes suffered by continental sandstones during heating. The characterization of such changes occurred during laboratory routines is relevant, since they can help to better understand natural processes. |
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| Keywords: | siderite cement transformation magnetite maghemite hematite |
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