Extreme hydrothermal conditions at an active plate-bounding fault
Extreme hydrothermal conditions at an active plate-bounding fault
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DOI：
10.1038/nature22355
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发表时间：
2017-05
期刊：
影响因子：
64.8
通讯作者：
R. Sutherland;John Townend;V. Toy;P. Upton;Jamie Coussens;M. Allen;L. Baratin;N. Barth;Leeza Becro
中科院分区：
文献类型：
--
作者：
R. Sutherland;John Townend;V. Toy;P. Upton;Jamie Coussens;M. Allen;L. Baratin;N. Barth;Leeza Becro
温度和流体压力条件控制着地质断层上的岩石变形和成矿作用，从而控制着地震的分布。典型的板内大陆地壳具有流体静压和近地表温度梯度，每公里31 ± 15摄氏度。在300-450摄氏度以上的温度下，通常在10-15公里以上的深度发现，石英和长石的晶体内可塑性通过无源蠕变释放应力，地震很少发生。水热条件控制矿物相的稳定性，因此与地震破裂周期的摩擦力学过程，但很少有温度和流体压力的数据，从活跃的板块边界断层。在这里，我们报告的结果，从钻孔到阿尔卑斯山断层，这是在其周期的应力积累，预计在未来几十年的8级地震破裂的上部。钻孔（深893米）显示，在断层上盘内，孔隙流体压力梯度超过流体静力水平9% ± 1%，平均地热梯度为每公里125 ± 55摄氏度。这些极端的热液条件是由快速的断层运动和地形驱动的流体运动造成的，断层运动从深处输送岩石和热量，地形驱动的流体运动将热量集中到山谷中。剪切加热可能发生在断层内，但不需要解释我们的观察结果。我们的数据和模型表明，高度异常的流体压力和温度梯度在孕震区的上部可以创建由断层滑动，岩石破裂和蚀变，和景观的发展在板块边界断层的过程之间的正反馈。
Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre,. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades,. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.