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

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

May 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989pepi...55...79j&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 55, Issue 1-2, p. 79-92.

Physics

29

Scientific paper

With a view to a better understanding of the origin of the low-field susceptibility in the Variscan granitoids of the French Massif Central, for which extensive structural mapping using the anisotropy of magnetic susceptibility (AMS) technique is currently applied, a detailed study of magnetic carriers has been undertaken. Origin of the susceptibility has been studied using high-field and low-temperature measurements in a cryogenic magnetometer, together with standard rock magnetic techniques. Additional determinations of the opaque phases have been performed with the metallographic microscope, X-ray microdiffraction and electron microprobe techniques.
In almost all the granite types, the magnetic susceptibility is essentially carried by the paramagnetic biotite crystals. Minor amounts of ubiquitous oxides (ilmenite, rutile, +/-(titano)haematite) do not contribute significantly to the susceptibility. This is also the case for rare occurrences of magnetite (< 10 ppm).
In some granitoids, mainly the cordierite-bearing anatexites, sulphides are found to give a large contribution. Magnetic mineralogy identifies a mixture of ferromagnetic pyrrhotite and antiferromagnetic Fe9S10 hexagonal pyrrhotite (hpo). The latter species is identified as forming the larger, unaltered pyrrhotite grains. The ferromagnetic pyrrhotite is identified to be mainly smythite (Fe9S11), a species formed by supergenic alteration of monoclinic pyrrhotite, located along the basal cleavage planes, the microfractures and the grain boundaries of the hpo. This study, which constitutes the first report of the magnetic properties of smythite in rocks, indicates that magnetic carriers derived from low-temperature alteration have to be taken into account for purposes of structural studies using AMS.

Affiliated with

Also associated with

No associations

Rating

Magnetic mineralogy of some granites from the French Massif Central: origin of their low-field susceptibility does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Magnetic mineralogy of some granites from the French Massif Central: origin of their low-field susceptibility, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic mineralogy of some granites from the French Massif Central: origin of their low-field susceptibility will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1875256