Laboratoire de Géologie, CNRS UMR 8538, Ecole Normale Supérieure, PSL Research University, 75005 Paris, France.
Unité Matériaux et Transformations - UMR 8207, CNRS, Univ. Lille, ENSCL, INRA, F-59000 Lille, France.
Nat Commun. 2017 May 15;8:15247. doi: 10.1038/ncomms15247.
Intermediate-depth earthquakes (30-300 km) have been extensively documented within subducting oceanic slabs, but their mechanics remains enigmatic. Here we decipher the mechanism of these earthquakes by performing deformation experiments on dehydrating serpentinized peridotites (synthetic antigorite-olivine aggregates, minerals representative of subduction zones lithologies) at upper mantle conditions. At a pressure of 1.1 gigapascals, dehydration of deforming samples containing only 5 vol% of antigorite suffices to trigger acoustic emissions, a laboratory-scale analogue of earthquakes. At 3.5 gigapascals, acoustic emissions are recorded from samples with up to 50 vol% of antigorite. Experimentally produced faults, observed post-mortem, are sealed by fluid-bearing micro-pseudotachylytes. Microstructural observations demonstrate that antigorite dehydration triggered dynamic shear failure of the olivine load-bearing network. These laboratory analogues of intermediate-depth earthquakes demonstrate that little dehydration is required to trigger embrittlement. We propose an alternative model to dehydration-embrittlement in which dehydration-driven stress transfer, rather than fluid overpressure, causes embrittlement.
中深度地震（30-300 公里）在俯冲海洋板块内得到了广泛的记录，但它们的力学机制仍然很神秘。在这里，我们通过在上地幔条件下对脱水蛇纹石化橄榄岩（俯冲带岩石的代表矿物）进行变形实验，来破译这些地震的机制。在 1.1 吉帕斯卡的压力下，仅含有 5%体积比的纤蛇纹石的变形样品的脱水足以引发声发射，这是地震的实验室规模模拟。在 3.5 吉帕斯卡时，含有高达 50%体积比的纤蛇纹石的样品也会记录到声发射。实验产生的断层，在事后观察到，被含流体的微假玄武岩密封。微观结构观察表明，纤蛇纹石脱水引发了橄榄石承载网络的动态剪切破坏。这些中深度地震的实验室模拟表明，只需少量脱水即可引发脆性。我们提出了一个替代脱水脆性的模型，其中脱水驱动的应力传递而不是流体超压导致脆性。
