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Oxidation processes and their effects on the magnetic remanence of Early Cretaceous subaerial basalts from Sierra Chica de Córdoba, Argentina

By
S. E. Geuna
S. E. Geuna
IGEBA (CONICET-UBA), Departamento de Cs. Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. 2, C1428EHA Buenos Aires, Argentina
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S. L. Lagorio
S. L. Lagorio
IGRM, Servicio Geológico Minero Argentino, Colectora Av. Gral. Paz 5445, edificio 25, Villa Martelli, Buenos Aires, Argentina
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H. Vizán
H. Vizán
IGEBA (CONICET-UBA), Departamento de Cs. Geológicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pab. 2, C1428EHA Buenos Aires, Argentina
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Published:
January 01, 2015

Abstract

We carried out magnetic analyses on a sequence of Cretaceous alkaline–transitional subaerial basalts of Córdoba Province, Argentina, which have high-Ti magnetite as the main opaque phase. Three different groups are identified based on the degree of high-temperature oxidation during the lava extrusion, combined with superimposed maghemitization and hematization. In the first group, titanomagnetites are optically homogeneous or exhibit coarse intergrowths with ilmenite. The magnetic susceptibility and its variation with temperature and magnetic field point to Ti-poorer compositions than those indicated by electron microprobe, which is interpreted as due to low-temperature oxidation with subsolvus microexsolution. The second group of basalts suffered moderate high-temperature oxidation, with crowded exsolved ilmenite laths within a Ti-poor magnetitess host, followed by maghemitization and hematite replacement. The third group shows a strongly advanced degree of low-temperature alteration, with the virtual disappearance of magnetite. Based on magnetic properties and field tests applied to the magnetic remanence, we interpret that maghemitization and hematization must have been responsible for the acquisition of a stable magnetic remanence, in the presence of hydrothermal fluids coeval with volcanism. The most advanced degree of alteration, typical of highly porous amygdaloidal lava flows and volcanic breccias, occurred later, probably due to weathering.

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Geological Society, London, Special Publications

The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes

M. H. Ort
M. H. Ort
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M. Porreca
M. Porreca
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J. W. Geissman
J. W. Geissman
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Geological Society of London
Volume
396
ISBN electronic:
9781862396722
Publication date:
January 01, 2015

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