假玄武玻璃的研究进展与现状

在国外有关假玄武玻璃（pseudotachylite)的研究已经有百余年的历史,在野外产状、显微镜观察和实验模拟等方面积累了丰富的资料。而国内在这方面的研究甚少。近年来,随着人们对“活断层”研究的深入,所谓有“地震化石”之称的假玄武玻璃也日益为研究者们所重视。假玄武玻璃通常认为是与地震断层有关的高应变速率条件下的产物。假玄武玻璃的研究对了解地震时地下深处断层带的变形机制等多方面具有重要意义。尤其是通过模拟假玄武玻璃形成时的相似条件（主要是力学机制和化学机制）,可以了解假玄武玻璃形成时断层剪切带变形历史。为了使国内对这一研究领域感兴趣的学者了解假玄武玻璃的形成过程及其所反映的意义,本文从假玄武玻璃的地质特征及成因等几个方面进行了总结,以飧读者。

Advance and the Status quo of the Research on Pseudotachylites

Pseudotachylites have been recognized for over a century. However many problems concerning their formation remain in dispute. Pseudotachylites are traditionally interpreted as an indicator of high-velocity slip O10 cm/s) and hence the earthquake activity (Spray), the presence of pseudotachylites can not only be indicative of meteorite impacts, but also be used to infer the past deformation history and behavior of a fault zone or fault shear zone, especially the deformation mechanism of a fault zone in the deep crust while an earthquake occurs. In recent years, pseudotachylites, which are widely known as earthquake faulting fossils, have been paid great attention to by the researchers with the deepened researches on "active faults". Pseudotachylites can be discovered in different depths of the crust and can be divided into five types (under a microscope) according to micro-lites in the matrix. There are two contrasted kinds of pseudotachylites in the crust, one having been formed by frictional fusing of rocks in a fault zone and the other by extreme mylonitization of the rocks and injection of the finely pulverized material into fractures (Philpotts, 1964). The bulk compositions of pseudotachylites and their wall rocks show that they are generated chiefly by the preferential selective melting of minerals of the lowest melting points in the wall rocks. The latest experiment (Spray, 1995) shows that comminution is a prerequisite to frictional melting. Depending on the velocity-shear stress - displacement relations prevailing during the frictional slip, the rocks produced in seismogenic zones can be dominated by comminuted wall rocks or fragments-melt mixes (pseudotachylites).