SUBTLE STRETCHING LINEATION REVEALED BY MAGNETIC FABRIC OF CALLOVIAN OXFORDIAN BLACK SHALES (FRENCH ALPS)

The anisotropy of magnetic susceptibility (AMS) of Callovian-Oxfordian black shales from the Subalpine massifs of the French Alps has been measured. The magnetic susceptibility of these formations originates from ferromagnetic titanomagnetite and paramagnetic phyllosilicates (illite and chlorite). Although the magnetic fabric is complicated by the interaction of planar and linear structural elements and the presence of variable amounts of minerals, two types of lineation are preserved: a stretching lineation which exhibits counterclockwise rotation as a result of deformation from south to north and an intersection lineation parallel to the fold axis. This set of new structural data, together with semiquantitative analysis of AMS, is in agreement with the geodynamic evolution of the Western Alps.