Stylolites in limestone: Magnitude of contractional strain accommodated and scaling relationships

The amount of contractional strain accommodated by a set of stylolites is analyzed by comparing the amplitudes of stylolitic teeth and spikes to independent measures of thinning of the enclosing layer. The scaling relations between along-strike trace length (L) and the maximum (Dmax) and average (Davg) amplitudes of stylolitic topography are also investigated. The studied stylolites occur in a 212-mm thick limestone layer dragged into the damage zone of the Gubbio normal fault zone in central Italy. Layer thinning was assessed independently from the layer geometry, with a maximum value of ∼23% nearest the fault. A total of 28 mm of thinning are related to 24 stylolites whose lengths range from 6.4 to 146 mm with average amplitudes from 0.1 to 1.3 mm. The average and maximum amplitudes of stylolitic topography increase with stylolite length, with Davg = 0.0011L0.17, r2 = 0.57, implying propagation to greater lengths as contractional strains increase along them. The stylolites increase in number and amplitude into the most thinned area, correlating with increasing contractional strain accommodated by the layer. The average amplitude of stylolites visible in outcrop provides a measure of the minimum magnitude of contractional strain in the rock, although other mechanisms such as grain-scale dissolution appear necessary to account for the remaining layer thinning.