Magnetic fabric studies of high-grade metamorphic rocks from the Juiz de Fora Complex, Ribeira Belt, southeastern Brazil

Granulite from 66 sites along the Abem-Paraiba dextral shear zone were coll ected for magnetic analyses. The rocks were affected by the Braziliano orog eny, which was responsible for the present structural pattern. Magnetic fab rics were determined applying anisotropy of low-field magnetic susceptibili ty (AMS, all sites) and anisotropy of remanence magnetization (ARM, in 21 s ites). The ferromagnetic minerals are magnetite, titanohematite, and in som e samples, minor pyrrhotite. Hysteresis curves show that both para- and fer romagnetic minerals are the carriers of AMS. Thus AMS is due to the preferr ed crystallographic orientation of paramagnetic matrix minerals and titanoh ematite, to the shape anisotropy of magnetite grains, or to a combination o f all three. ARM was performed imposing both anhysteretic remanence (AAR) a nd isothermal remanence (AIRM). The AMS, AAR, and AIRM fabrics are coaxial and are tectonic in origin. Their parallelism indicates that both ferromagn etic and paramagnetic minerals recorded the same metamorphic event. A passi ve-marker model is suggested for ferromagnetic minerals at the outcrop scal e. The magnetic foliation is very close to the strike of the Alem Paraiba s hear zone, suggesting, that this generated the local rock fabrics during th e Braziliano orogeny.