Evolution of compactive shear localization bands: geological data and numerical models

Description

Compactive shear bands with different ratio of compactive to shear inelastic deformation were recently studied in detail in different regions within the porous rocks. Among them are nicely exposed networks of conjugate cataclastic bands formed in a single tectonic event in the "Bassin du Sud-Est" (Provence, France) in Cretaceous sandstones. Microanalysis of the material within the bands shows that they underwent mainly thrust-sense shearing with a minor compactive component. The most striking feature of the evolution of these bands is their thickening at the flanks by incorporation of the intact host rock into the deformation bands and formation of new strands. This feature as well as the general band pattern was reproduced in 2-D finite-difference models where the hardening modulus h grew with inelastic deformation. This growth causes strengthening of the material within the initial bands (resulting from deformation bifurcation) and considerably slows down its inelastic deformation after it reaches a maximal value defined by all the constitutive parameters and most of all by the rate of increase in h. The strengthening above a certain level results in the band widening due to the accretion at its edges of material not yet deformed as it becomes involved in compactive shearing. The inelastic deformation is therefore the most rapid along the band flanks, while the thickening with time of the band core part mainly undergoes elastic unloading starting from some stage. The initial band spacing depends on the initial h value h0 and increases with h0 in accordance with predictions from bifurcation theory. During deformation, the spacing reduces due to the propagation of bands that largely saturate the model/layer, resulting in a band pattern that resembles the natural band networks. The increase of h imposed in the models appears therefore as both an important and realistic property that can also be derived from available experimental rock testing data. On the other hand, it is difficult to constrain with sufficient AGU Abstract Browser http://abstractsearch.agu.org/meetings/2011/FM/sections/T/sessions/T... 1 sur 3 05/01/2015 19:08 precision the evolution of h with deformation based only such data. Therefore the adjustment/calibration of the constitutive models based on the reproduction of natural deformation patterns in numerical simulations appears as an important tool.

Abstract

International audience

Additional details