Magnetic mineralogy of some granites from the French Massif Central: origin of their low-field susceptibility

作者: Olivier Jover , Pierre Rochette , Jean Pierre Lorand , Michel Maeder , Jean Luc Bouchez

DOI: 10.1016/0031-9201(89)90235-5

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摘要: Abstract With a view to better understanding of the origin low-field susceptibility in Variscan granitoids French Massif Central, for which extensive structural mapping using anisotropy magnetic (AMS) technique is currently applied, detailed study carriers has been undertaken. Origin studied high-field and low-temperature measurements cryogenic magnetometer, together with standard rock techniques. Additional determinations opaque phases have performed metallographic microscope, X-ray microdiffraction electron microprobe In almost all granite types, essentially carried by paramagnetic biotite crystals. Minor amounts ubiquitous oxides (ilmenite, rutile, ±(titano)haematite) do not contribute significantly susceptibility. This also case rare occurrences magnetite ( some granitoids, mainly cordierite-bearing anatexites, sulphides are found give large contribution. Magnetic mineralogy identifies mixture ferromagnetic pyrrhotite antiferromagnetic Fe9S10 hexagonal (hpo). The latter species identified as forming larger, unaltered grains. be smythite (Fe9S11), formed supergenic alteration monoclinic pyrrhotite, located along basal cleavage planes, microfractures grain boundaries hpo. study, constitutes first report properties rocks, indicates that derived from taken into account purposes studies AMS.

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