Stylolite interfaces and surrounding matrix material: Nature and role of heterogeneities in roughness and microstructural development

Rough pressure solution interfaces, like stylolites, are one of the most evident features of localized slow deformation in rocks of the upper crust. There is a general consensus that the development of these rough structures is a result of localized, stress enhanced, dissolution of material along a fluid filled interface, but little is known on the initiation of this roughness. The aim of this article is to reveal the role of heterogeneities initially present in the host-rock on roughness initiation. This should give insights on whether stylolite roughness is generated by a stress-induced instability or by the presence of disorder in the material (i.e. quenched noise). We use a microstructural approach based on SEM/EBSD analysis combined with orientation contrast (OC) image analysis of stylolites in limestones. We found that the stylolite roughness is induced by heterogeneities in the host rock (clay particles and detrital quartz grains in our case). In addition, close to mature stylolite interfaces matrix modifications occur, which can be attributed to the compaction along the stylolite. The grain size decreases by 15–25% and a pre-existing shape- and lattice-preferred orientation (SPO, LPO) are significantly modified in the vicinity of the stylolite. The results presented here imply that localized pressure solution along stylolites is not necessarily restricted to the actual interface but influences the adjacent matrix. The heterogeneity data might serve as a quantitative basis for elaborate numerical models of localized compaction.