Intermediate-depth earthquakes linked to localized heating in dunite and harzburgite
Intermediate-depth earthquakes linked to localized heating in dunite and harzburgite
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DOI：
10.1038/ngeo3011
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发表时间：
2017-08
影响因子：
18.3
通讯作者：
T. Ohuchi;X. Lei;H. Ohfuji;Y. Higo;Y. Tange;T. Sakai;K. Fujino;T. Irifune;T. Irifune
中科院分区：
文献类型：
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作者：
T. Ohuchi;X. Lei;H. Ohfuji;Y. Higo;Y. Tange;T. Sakai;K. Fujino;T. Irifune;T. Irifune
在俯冲板片中发生深度大于60公里的中深地震和深地震长期以来一直困扰着地球科学家。这些地震需要某种机制来加速断层在1.8GPa以上的高压下的运动。局部加热将有助于断层，但这种机制的实验证据已被限制在压力高达0.5 GPa。在这里，我们在1.0至2.6 GPa的压力和860至1,350 K的温度下对干燥的纯橄榄岩样品进行变形实验-接近于相对较浅的中深地震的条件。我们观察到纯橄榄岩的塑性变形，随后在约5 × 10−5s− 1或更高的加速应变速率下发生断层和声发射。我们发现，超细晶粒的断层泥层含有富铁的熔融膜，这是一个非常高峰温度约2,110 K沿着断层平面的指示。我们也观察到断层在湿方辉橄榄岩-脱水产物的antigorite-在自然应力水平为0.3至0.4千兆帕斯卡。因此，我们认为，如果背景应变率超过10 - 16 ~ 10 - 13 s-1范围内的阈值，则干俯冲板和湿俯冲板中的局部加热都可以诱发中深地震。
The occurrence of intermediate-depth and deep earthquakes at depths greater than 60 km in subducting slabs has long puzzled geoscientists. These earthquakes require some mechanism to accelerate the fault movement at high pressures above 1.8 GPa. Localized heating would contribute to faulting, but experimental evidence for this mechanism has been limited to pressures of up to 0.5 GPa. Here we conduct deformation experiments on dry dunite samples at pressures of 1.0 to 2.6 GPa and temperatures of 860 to 1,350 K—conditions close to those for relatively shallow intermediate-depth earthquakes. We observe plastic deformation of the dunite, followed by faulting and acoustic emissions at an accelerated strain rate of about 5 × 10−5s−1or higher. We find that ultrafine-grained gouge layers containing iron-rich melt films, which is indicative of a very high peak temperature of about 2,110 K along the fault planes. We also observe faulting in wet harzburgite—a dehydration product of antigorite—at natural stress levels of 0.3 to 0.4 gigapascals. We therefore suggest that intermediate-depth earthquakes can be induced by localized heating both in dry and wet subducting slabs, if the background strain rate exceeds a threshold value in the range from 10−16to 10−13s−1.