3D geometric modelling of an external orogenic domain: a case history from the western Alps (massif de Morges, Pelvoux)

Abstract

Abstract Describing the 3D geometry of geological surfaces is a fundamental step to infer their structural history, especially when they have recorded successive deformation phases. This study aims at testing the contribution of 3D modelling to the understanding of orogenic domains. It focuses on the cover/basement contact of an External Crystalline Massif of the French Alps considered as a marker of the finite deformation at orogen scale. This contact is observable in outliers of Mesozoic cover in the test area located in the Massif de Morges (Pelvoux Massif). A 3D geometric model has been built from map and cross-section data derived from field structural and kinematic observations using STRIM software (Matra Datavision). 3D modelling ensures geometric consistency of geological interpretation. Moreover, the model has been unfolded to restore surfaces and to quantify shortening. Together with field analyses, those results show that two sub-perpendicular phases of deformation related to the Alpine cycle have occurred. The first and main one consisted of the NNE-SSW inversion of previous extensional paleo-faults that controlled the geometry of the Tethyan margin. The second one was an E-W compression of post-Early Oligocene age.