Stylolites are rough surfaces that form by localized stress-induced dissolution. Using a set of limestone rock samples collected at different depths from a vertical section in Cirque de Navacelles (France), we study the influence of the lithostatic stress on the stylolites morphology on the basis of a recent morphogenesis model. We measured the roughness of a series of bedding-parallel stylolites and show that their morphology exhibits a scaling invariance with two self-affine scaling regimes separated by a crossover-length (L) at the millimeter scale consistent with previous studies. The importance of the present contribution is to estimate the stylolite formation stress σ from the sample position in the stratigraphic series and compare it to the crossover-length L using the expected relationship: L ∼ σ −2 . We obtained a successful prediction of the crossover behavior and reasonable absolute stress magnitude estimates using relevant parameters: depth of stylolite formation between 300 to 600 m with corresponding normal stress in the range of 10-18 MPa. Accordingly, the stylolite morphology contains a signature of the stress field during formation and we thus suggest that stylolites could be used as paleo-stress gauges of deformation processes in the upper crust.
[1] Vertical stylolites are pressure solution features, which are considered to be caused by horizontal tectonic loading, with the largest principal compressive stress being (sub-) parallel to the Earth's surface. In the present study we analyze the roughness of such tectonic stylolites from two tectonic settings in southern Germany and northeastern Spain, aiming to investigate their scaling properties with respect to the stress during formation. High-resolution laser profilometry was carried out on opened stylolite surfaces of nine samples. These data sets were then analyzed using one-and two-dimensional Fourier power spectral approaches. We found that tectonic stylolites show two self-affine scaling regimes separated by a distinct crossover length (L), as known for bedding parallel stylolites. In addition, tectonic stylolites exhibit a clear in-plane scaling anisotropy that modifies L. Since the largest and smallest crossover lengths are oriented with the sample vertical and horizontal directions (i.e., s 2 and s 3 ) and L is a function of the stress field during formation as analytically predicted, we conclude that the scaling anisotropy of tectonic stylolites is possibly a function of the stress field. Knowledge of this crossoverlength anisotropy would enable the reconstruction of the full three-dimensional stress tensor if independent constraints of the depth of formation can be obtained.
International audienceIn this contribution we present numerical simulations of stylolite growth to decipher the effects of initial rock heterogeneity and stress on their morphology. We show that stylolite growth in a rock with a uniform grain size produces different patterns than stylolite growth in a rock with a bimodal grain size distribution. Strong pinning of large heterogeneities produce stylolite structures that are dominated by pronounced teeth, whereas a uniform grain size leads to spikes and a roughness that shows variable wavelengths. We compare the simulated stylolites with natural examples and show that the model can reproduce the real structures. In addition we show that strong pinning in the bimodal case can lead to a linear stylolite roughness growth in contrast to the non-linear growth of stylolites that develop from a uniform noise. In a set of 24 simulations we vary the main principle stress on the stylolite in order to test if our model can reproduce the analytically derived stress-scaling proposed by Schmittbuhl et al. (2004). We compare the calculated stresses with the applied stresses and show that the numerical model and the analytical solution are in good agreement. Our results strengthen the hypothesis that stylolites can be used as strain and stress gauges to estimate not only the orientation of paleo-stresses, but also their absolute values of formation stresses and amounts of compaction
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