Experimental investigation of frictional melting of argillite at high slip rates: Implications for seismic slip in subduction‐accretion complexes
Experimental investigation of frictional melting of argillite at high slip rates: Implications for seismic slip in subduction‐accretion complexes
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DOI：
10.1029/2008jb006165
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发表时间：
2009-04
影响因子：
--
通讯作者：
K. Ujiie;A. Tsutsumi;Y. Fialko;H. Yamaguchi
中科院分区：
文献类型：
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作者：
K. Ujiie;A. Tsutsumi;Y. Fialko;H. Yamaguchi
[1]从出土的增生杂岩中发现的假玄武岩表明，俯冲地震期间沿富含伊利石的泥质岩源滑移带发生了摩擦熔融。在滑移率为1.13m/S、法向应力为2.67~13.33 Mpa的条件下，对泥岩进行了高速摩擦实验。实验表明，滑移减弱后滑移加强。滑移减弱与低粘度熔体斑块的形成和剪切有关。尽管由于熔体层的生长(增厚)导致剪切应变速率降低，但仍发生了随后的滑移强化，表明熔体层的粘度随滑移而增加。显微组织和化学分析表明，滑移强化过程中粘度的增加不是由于熔体层中固体颗粒和气泡体积分数的增加，而是主要由熔体层的脱水引起的。我们的实验结果表明，如果在地震滑动的时间尺度上发生实质性的熔体脱水，那么在俯冲-吸积杂岩的浅层，粘性制动是有效的。在俯冲-吸积杂岩中，熔融润滑可能发生在更深的地方，因为粘性剪切与法向应力的比率随着深度的增加而减小。在俯冲-吸积杂岩的孕震深度形成的泥质岩来源的天然拟玄武岩比实验生成的拟玄武岩更富含水，可能是几乎完全应力下降的证据。
[1] Discovery of pseudotachylytes from exhumed accretionary complexes indicates that frictional melting occurred along illite-rich, argillite-derived slip zones during subduction earthquakes. We conducted high-velocity friction experiments on argillite at a slip rate of 1.13 m/s and normal stresses of 2.67–13.33 MPa. Experiments show slip weakening followed by slip strengthening. Slip weakening is associated with the formation and shearing of low-viscosity melt patches. The subsequent slip strengthening occurred despite the reduction in shear strain rate due to the growth (thickening) of melt layer, suggesting that the viscosity of melt layer increased with slip. Microstructural and chemical analyses suggest that the viscosity increase during the slip strengthening is not due to an increase in the volume fraction of solid grains and bubbles in the melt layer but could be caused primarily by dehydration of the melt layer. Our experimental results suggest that viscous braking can be efficient at shallow depths of subduction-accretion complexes if substantial melt dehydration occurs on a timescale of seismic slip. Melt lubrication can possibly occur at greater depths within subduction-accretion complexes because the ratio of viscous shear to normal stress decreases with depth. Argillite-derived natural pseudotachylytes formed at seismogenic depths in subduction-accretion complexes are more hydrous than the experimentally generated pseudotachylytes and may be evidence of nearly complete stress drop.