Coseismic magnetization of fault pseudotachylytes: 1. Thermal demagnetization experiments
Coseismic magnetization of fault pseudotachylytes: 1. Thermal demagnetization experiments
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DOI：
10.1002/2014jb011168
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发表时间：
2014-08
期刊：
影响因子：
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通讯作者：
E. Ferré;J. Geissman;F. Demory;J. Gattacceca;M. Zechmeister;M. Hill
中科院分区：
文献类型：
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作者：
E. Ferré;J. Geissman;F. Demory;J. Gattacceca;M. Zechmeister;M. Hill
断层假玄武玻璃是由同震摩擦熔融产生的硅酸盐液体淬火而形成的。在这里，我们表明，在天然的假玄武玻璃中，在摩擦熔体冷却过程中被阻挡的剩磁的主要载体是细粒磁铁矿。这证实了以前的研究摩擦熔化实验。化学计量的磁铁矿，在地震期间由铁镁硅酸盐分解产生，记录了地震滑动期间的环境磁场。我们发现，大多数故障pseudotachylytes暴露在圣罗莎山脉，南加州，一个典型的pseudotachylytes的地方，获得了他们的自然恢复磁化（NRM）后，冷却的摩擦熔体通过磁化阻断温度范围内的磁铁矿颗粒，这主要是一个热恢复磁化。大多数假玄武玻璃岩脉的典型NRM强度范围为1至60·10−4 Am 2/kg。然而，少数标本的磁化强度明显高于地球磁场，磁化方向在短距离内变化很大。其他磁化过程，可能与同震电流，可能涉及在孕震过程中，以控制NRM采集。
Fault pseudotachylytes form by quenching of silicate liquids produced through coseismic frictional melting. Here we show that in natural pseudotachylytes the main carrier of magnetic remanence blocked in during cooling of the frictional melt is fine‐grained magnetite. This confirms previous studies on friction melt experiments. Stoichiometric magnetite, produced during earthquakes by the breakdown of ferromagnesian silicates, records the ambient magnetic field during seismic slip. We find that most fault pseudotachylytes exposed in the Santa Rosa Mountains, southern California, a classic pseudotachylyte locality, acquired their natural remanent magnetization (NRM) upon cooling of the frictional melt through the range of magnetization blocking temperatures of the magnetite grains and this primarily constitutes a thermal remanent magnetization. NRM intensities typical of most pseudotachylyte veins range from 1 to 60·10−4 Am2/kg. A few specimens, however, contain magnetizations significantly higher than that caused by the Earth's field as well as magnetization directions that are highly variable over short distances. Other magnetization processes, possibly related to coseismic electric currents, may be involved during the seismogenic process to control NRM acquisition.