New approach for the quantification of paleostress magnitudes: applicationto the Soultz vein system (Rhine graben, France)

Quartz veins often appear in pre-existing cracks and are the witnesses of p aleofluid flows. A new method of paleostress magnitude quantification is pr oposed in this paper based on the knowledge of: (i) the geometrical distrib ution of vein poles, (ii) empirical considerations of rupture criteria and (iii) the fluid pressure. Stress axis orientations, deduced from the geomet rical distribution of the vein poles, define angular relations allowing the reduced stress tensor and the Phi ratio characterization. Pf values, quant ified with fluid inclusion studies, and intrinsic curves drawn with empiric al relations depending on the rheologic properties of the pre-fractured roc k are combined to graphically fit the final Mohr circle. The resulting abso lute stress magnitudes take into account the fluid pressure influence. Appl ication of this method on the quartz vein system of Soultzsous-Forets (Rhin e graben, France) gives realistic magnitudes of the Oligocene extension and are similar to those found in previous study with other methods. (C) 2001 Elsevier Science B.V. All rights reserved.