TECTONIC VERSUS MINERALOGICAL CONTRIBUTION TO THE MAGNETIC FABRICS OFEPIMETAMORPHIC SLATY ROCKS - AN EXAMPLE FROM THE ARDENNES MASSIF (FRANCE-BELGIUM)

The discrimination of the respective contribution of strain and minera logy of the bulk Anisotropy of low field Magnetic Susceptibility (AMS) of rocks is addressed by a study of the Ardennes Variscan Thrust Belt . Unmetamorphosed to low-medium-grade rocks in the study area define a succession of magnetic parageneses: hematite + maghemite (?), hematit e + maghemite (?) + magnetite, magnetite + pyrrhotite. A direct contro l of the magnetic mineralogy on the magnitude of AMS axes is shown. In addition, in all cases, the interpretation of the directions of AMS a xes as kinematic indicators also applies to these rocks. We show a pro gressive change in shearing direction from the south of the Rocroi mas sif, where the nappe transport is N-directed; in the north, the vergen ce changes to northwestward.