Simultaneous acoustic emissions monitoring and synchrotron X-ray diffraction at high pressure and temperature: Calibration and application to serpentinite dehydration

Abstract

International audienceWe have successfully developed an experimental setup that allows collecting in situ X-ray powder diffraction and simultaneously recording full waveform acoustic emissions (AE) at high pressure and temperature (PT) in a DIA multi-anvil device. This setup is a powerful tool for investigating rock embrittlement at high PT due to phase transitions and/or mineral reactions since both reaction progress (and kinetics) and AE triggering can be simultaneously monitored. The dehydration of natural serpentinite samples (antigorite-rich) under deviatoric stress has been investigated by this method since antigorite dehydration is believed to trigger intermediate depth earthquakes through dehydration embrittlement. We performed, beforehand, a series of tests on the cold compression of reference materials with contrasted mechanical behaviors (quartz beads and kaolinite powder). Due to grain crushing, cold compression of quartz gave rise to numerous AE events (several hundreds), which were located within the sample. Cold compression and heating of kaolinite, a ductile material, yielded no AEs, demonstrating that the pressure assembly is noiseless. Unexpectedly, antigorite-rich serpentinite samples produced no detectable AEs in the course of their dehydration under the differential stress imposed by alumina waveguides. The only AEs that were recorded occurred during cold compression. Sample microstructures indicate that conjugate faults inherited from the cold compression stage are activated during or after dehydration of the sample. The "aseismic" slip along these faults could be attributed to the presence of talc (or a talc-like phase) or of fine-grained materials (dehydration reaction products) in the fault gouge. Furthermore, AE triggering can also be influenced by hydraulic diffusivity and the differential stress level on the sample, two parameters that are not controlled in conventional multi-anvil experiments. Our results highlight the fact that coupling between dehydration reactions and seismicity might not be as straightforward as previously thought. In fact, fast reaction kinetics or high reaction extent may inhibit the nucleation of mechanical instabilities through rapid stress relaxation of the solid matrix

Dehydration‐induced damage and deformation in gypsum and implications for subduction zone processes

“…Localization of deformation and dynamic faulting was not observed during the dehydration test performed at constant differential stress, which is consistent with recent experiments on serpentinite [ Rutter et al , 2009; Chernak and Hirth , 2010; Gasc et al , 2011]. However, the substantial compaction (up to 10%) observed during the dehydration reaction indicates the high deformability of dehydrating rocks.…”

“…Two challenging problems encountered in addressing the possible importance of dehydration embrittlement in subduction are (1) the identification of dehydrating rocks within the subducting slab, for instance using seismic tomography, and (2) the understanding of the controlling factors promoting a macroscopic “embrittlement.” In particular, it is still unclear if dehydration reaction can induce strain localization and shear instabilities during deformation [ Hirose et al , 2006; Chernak and Hirth , 2010; Gasc et al , 2011]. …”

Seismic imaging of slab metamorphism and genesis of intermediate-depth intraslab earthquakes

“…They showed that unstable fault behavior did not develop in the specimens, but rather that slow slip events took place. Compression experiments of antigoriterich serpentinite by Gasc et al (2011), who used a newly developed experimental setup that allows simultaneous collection of in situ X-ray diffraction data and recording of the full waveforms of acoustic emissions with a multianvil device, showed that the serpentinite samples did not produce detectable acoustic waves over the course of their dehydration. Proctor and Hirth (2015) conducted deformation tests with a new experimental method to vary the pore fluid pressure.…”

Acoustic Emission and Damage Characteristics of Granite Subjected to High Temperature

“…In recent years, AE detection technology has been used in rock mechanics by many scholars [20][21][22][23][24][25][26][27]. For example, Ganne et al [20] studied the brittleness of rock before peak stress by the AE technique, and four stages of accumulated AE energy were given.…”

“…He et al [22] observed that there were much higher amplitude and lower frequency events near the bursting failure of rock samples, and the accumulated AE energy release increased rapidly from unloading state to rock failure. Gasc et al [23] studied rock structural transformation and mineral reaction under high temperatures and high pressures by X-ray diffraction and AE detection of serpentine. Chmel et al [24] studied AE energy release of granite under impact loading.…”