MICROFRACTURING AND REGIONAL STRESS-FIELD - A STUDY OF THE PREFERRED ORIENTATIONS OF FLUID-INCLUSION PLANES IN A GRANITE FROM THE MASSIF-CENTRAL, FRANCE

A study of the deformation of a granitic massif indicates a relationship between palaeostress fields and the geometry of microfractures as defined by fluid-inclusion trails, that is, healed microfractures. A statistical study of the distribution of the trails leads to the following conclusions: trails exhibit several distinct preferred orientations on the scale of a grain, which may be observed in many samples; the orientations of the trails are similar to those of micro- and mesoscale fractures in the granite; and the dominant trail direction is parallel to the main direction of regional shortening. Thus, fluid-inclusion trails are mode I cracks which can be used as excellent markers of palaeostress fields.