Transient creep, aseismic damage and slow failure in Carrara marble deformed across the brittle‐ductile transition

Abstract

[1] Two triaxial compression experiments were performed on Carrara marble at high confining pressure, in creep conditions across the brittle-ductile transition. During cataclastic deformation, elastic wave velocity decrease demonstrated damage accumulation (microcracks). Keeping differential stress constant and reducing normal stress induced transient creep events (i.e., fast accelerations in strain) due to the sudden increase of microcrack growth. Tertiary creep and brittle failure followed as damage came close to criticality. Coalescence and rupture propagation were slow (60 -200 seconds with $150 MPa stress drops and millimetric slips) and radiated little energy in the e x p e r i m e n t a l f r e q u e n c y r a n g e ( 0 . 1 -1 M H z ). Microstructural analysis pointed out strong interactions between intra-crystalline plastic deformation (twinning and dislocation glide) and brittle deformation (microcracking) at the macroscopic level. Our observations highlight the dependence of acoustic efficiency on the material's rheology, at least in the ultrasonic frequency range, and the role played by pore fluid diffusion as an incubation process for delayed failure triggering. Citation: Schubnel,

Calcite and dolomite in intrusive carbonatites. I. Textural variations

“…This, in combination with the changing character of twin boundaries and optical extinction, points to dislocation creep as the principal mechanism of deformation in the ductile regime. As creep competes with cracking near the brittle-ductile transition at low T, dislocation pile-ups at grain boundaries and twin intersections yield micro-fractures (Schubnel et al 2006; Fig. 13d).…”

“…Under stress, the depth of brittle-ductile transition in these rocks will depend on the grain size, porosity, content and connectivity of non-carbonate material, availability of fluids, and temperature (De Bresser et al 2005;Paterson and Wong 2005;Renner et al 2007;and references therein), and can be as shallow as~1 km for a pure material (Fredrich et al 1989). A confining P of 0.5 kbar is typically cited for the reference Carrara marble (Schubnel et al 2006), which is closely similar to fine-grained anchimonomineralic (~98 % pure, with a mean grain size of 0.15 mm) calcite carbonatites. In a tectonically active environment, such as plate collision zones, carbonate rocks of any kind (including igneous) can thus be readily mobilized to undergo ductile deformation, stress-induced flow and emplacement into rigid fractured silicate wall rocks in the form of ex situ intrusions or Bextrusions^ (Roberts and Zwaan 2007;Chakhmouradian et al 2015a).…”

Evolution of the crack network in glass samples submitted to brittle creep conditions

“…Elastic wave velocities of cracked samples have been measured in the triaxial cell, before and during the creep experiments, with the 16 ultrasonic piezoelectric sensors (Birch 1960;Yin 1992;Schubnel et al 2006). These sensors were glued at different orientations to get the velocity in different orientations ).…”

Damage and rupture dynamics at the brittle-ductile transition: The case of gypsum

“…We will thus speak in terms of "streamed data" in the case of continuously recorded signals and "triggered data" in the other case. The main advantage of the streamed data is that it is possible to postprocess the full waveforms several times, and thus extract information that could be invisible on the triggered data (especially long-period waves [Thompson et al, 2005Schubnel et al, 2006Schubnel et al, , 2007Thompson et al, 2009]). This system is schematically summarized in Figure 3.…”