假玄武玻璃年代学研究现状及其地震学指示意义

假玄武玻璃是一种呈暗色的微晶—隐晶质岩石,一般产于古地震断层滑动面,被认为是研究地震活动的＂化石岩＂。经过碎裂岩化或摩擦熔融,假玄武玻璃发育于从地表到岩石圈地幔的整个地震活动区,其年代学研究对于揭示某一地区古地震活动频次及发生规律有重要意义。假玄武玻璃的定年一般采用Rb-Sr、^40Ar-^39Ar、裂变径迹等三种方法,但Sr的扩散性质、假玄武玻璃内部结构和成分的不均一性及其形成高温快速过程中锆石的退火行为等诸多因素,制约了以上三种方法的应用。文中总结了三种方法,分析了其适用范围和局限性,探讨了假玄武玻璃定年研究中最适用的方法和需注意的事项。最后,阐述了假玄武玻璃研究的地震学指示意义。

Current Research on The Dating of Pseudotachylyte and Its Seismic Indication

Pseudotachylyte is an ultimate product of shearing in fault zones and formed with microlite-cryptocrystalline textures. It normally originates in the dislocation surface of ancient earthquakes and is treated as the "fossil rocks" in the paleo-seismic reasearch. Through comminution or friction melting, pseudotachylyte develops from the crustal surface to lithospheric mantle where earthquakes happen. Comprehensive chronological study on pseudotachylytes has great significances on our understanding of the frequency and rules of paleo-seismic events in certain areas. Currently, Rb-Sr, ~(40)Ar/~(39)Ar and fission track are the three methods often used on dating peseudotachylytes. However, many factors have limited their application in the pseudotachylytes' chronological study, such as the diffusion of Sr, the heterogeneities of peseudotachylytes in matrix structure and chemical composition, and the thermal annealing of zircon during the fast megathermal process of its formation, etc. This article summarizes and illustrates these three methods, analyzes their application range and limitations, proposes the proper method and relevant instructions on peseudotachylytes' chrolological study. By the end, this paper elaborates the significances of the pseudotachylyte research to seismology.