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<p>Previous studies of experimental and natural fault zones have shown that the formation of nanocrystals produced by thermal decomposition or deformation can lead to significant slip weakening and large earthquakes. Natural fault rocks contain various hydrous minerals that are easily decomposed by frictional heating and possibly form nanocrystals. High-velocity rotary-shear friction experiments on metapelites and amphibolites were performed at seismic slip rates of up to 1.3&#xa0;m/s and normal stresses of up to 16&#xa0;MPa to investigate the dehydration of hydrous minerals (biotite and hornblende) and formation of nanocrystals. Some of the experiments were stopped at various stages of slip behavior to examine the microstructural evolution of the simulated fault zones. During the final stage of steady-state friction, the fault zones comprise a principal slip zone (PSZ) filled with frictionally generated melt and damage zones (DZs) surrounding the PSZ. In the DZs, the color of hydrous minerals becomes darker toward the PSZ, with dark bands along cleavage planes in biotite of the metapelite, and in hornblende of the amphibolite. Transmitted electron microscopy analyses reveal that the dark bands consist of cavity- and nanocrystal-bearing layers along cleavage planes. The cavities and nanocrystals in the DZs were produced by the thermal decomposition of hydrous minerals due to frictional heating during seismic slip. The formation of nanocrystals and dehydration reactions in the DZs may contribute to the weakening of fault zones by facilitating lubrication and/or melting in the PSZ.</p>

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Dehydration microstructures of hornblende and biotite induced by frictional heating in high-velocity shearing experiments

  • 期刊论文

  • 发表日期：

    2025年5月5日

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  • Soolim Jung,
  • Sea Chae,
  • Jin-Han Ree,
  • Takehiro Hirose,
  • Jinwook Kim,
  • Hyeong Soo Kim

摘要

Previous studies of experimental and natural fault zones have shown that the formation of nanocrystals produced by thermal decomposition or deformation can lead to significant slip weakening and large earthquakes. Natural fault rocks contain various hydrous minerals that are easily decomposed by frictional heating and possibly form nanocrystals. High-velocity rotary-shear friction experiments on metapelites and amphibolites were performed at seismic slip rates of up to 1.3 m/s and normal stresses of up to 16 MPa to investigate the dehydration of hydrous minerals (biotite and hornblende) and formation of nanocrystals. Some of the experiments were stopped at various stages of slip behavior to examine the microstructural evolution of the simulated fault zones. During the final stage of steady-state friction, the fault zones comprise a principal slip zone (PSZ) filled with frictionally generated melt and damage zones (DZs) surrounding the PSZ. In the DZs, the color of hydrous minerals becomes darker toward the PSZ, with dark bands along cleavage planes in biotite of the metapelite, and in hornblende of the amphibolite. Transmitted electron microscopy analyses reveal that the dark bands consist of cavity- and nanocrystal-bearing layers along cleavage planes. The cavities and nanocrystals in the DZs were produced by the thermal decomposition of hydrous minerals due to frictional heating during seismic slip. The formation of nanocrystals and dehydration reactions in the DZs may contribute to the weakening of fault zones by facilitating lubrication and/or melting in the PSZ.