Structural Evolution of the Parmelan Anticline (Bornes Massif, France): Recording the Role of Structural Inheritance and Stress Field Changes on the Finite Deformation Pattern

Abstract

In many orogenic wedges, foreland basin systems are preferential sites for economical resource accumulation, typically hydrocarbons. Understanding how structural inheritance perturbs the evolution of folding-related deformation and impacts on subsurface fracture patterns bears first order economic and environmental implications, when also CO2 storage is considered. Studying properly selected field analogs of buried anticlines provides fundamental information on fracture patterns at the subseismic scale. The Parmelan anticline is a flat-topped box-fold located in the Bornes Massif (France) involving Lower Cretaceous platform carbonates (Urgonian Limestones). We studied this field analogue by combining structural analysis with syntectonic calcite vein petrography and geochemistry to unravel the progression of deformation and to obtain constraints on the regional stress field evolution. We documented (a) a network of pre-folding hinge-parallel and hinge-perpendicular extensional fault zones, (b) two deformation assemblages developed during pre-folding layer-parallel-shortening under different stress configurations including veins, bed-perpendicular stylolites and subsidiary reverse faults, (c) a limited occurrence of localized syn-folding deformation structures (i.e., hinge-parallel veins), and (d) an association of veins and stylolites oblique to the fold axial trend, formed in a post-folding stage. We propose that pre- and syn-orogenic inherited structures controlled first-order fold geometry and partial development of classical syn-folding deformation features. Moreover, our data reveal a complex stress history marked by permutations of the vertical principal stress axis from strike-slip to purely compressional stress regimes and vice versa, accompanied by a progressive counterclockwise rotation of the horizontal maximum stress axis.