拉萨地块西段尼雄地区晚古生代地震事件及其地质意义

拉萨地块晚古生代处于伸展还是挤压背景一直以来存在较大的争议.在拉萨地块西段尼雄地区晚古生代地层中新发现了震积岩.拉嘎组一段震积岩单元位于含砾细砂岩冰水沉积中，可见震裂岩、震褶岩及塑性角砾岩等典型震积岩岩石类型，另见各种与震积岩相关的构造和沉积标志；拉嘎组二段震积岩单元位于潮坪沉积中，见液化卷曲变形及球-枕构造等；下拉组震积岩单元位于下段灰岩中，可见典型的粉（泥）晶灰岩脉和自碎屑角砾岩.下拉组和拉嘎组二段震积岩与燧石结核灰岩紧密共生，由此推测拉萨地块中部分晚古生代燧石结核灰岩可能与地震作用密切相关.结合区域资料，认为拉萨地块西段晚古生代地震事件与冈瓦纳大陆北缘裂陷盆地的发育有关，并为拉萨地块晚古生代演化新增了古地震活动资料. 

Late Paleozoic Earthquake Events in the Nixiong Area and Its Geological Significance,Western Lhasa Block

The tectonic background of Lhasa terrane located at the northern margin of Gondwana in the Late Paleozoic is still in dispute. Seismites have been newly discovered in the Late Paleozoic strata (Laga Formation and Xiala Formation) in Nixiong area in the western section of the Lhasa terrane. The seismite unit of the first member of Laga Formation is found in pebbled fine sandstone, which is ice-rafting deposit formed by the melting of sediment-laden ice blocks. In this unit, we have found massive seismites related sedimentary and structure features. Furthermore, typical seismite rock types, including seismic corrugated rock, shattering rock, and plastic breccia are recognized. The authors have also found soft sediment deformation structures related to earthquake in the tidal-flat sedimentary in the second member of Laga Formation, such as convolute bedding, sand ball-pillow structure. Chert limestone with micrite veins, located at the bottom of Xiala Formation, is another seismite horizon. Based on the paragenetic relationship between chert limestones and seismite horizons of the Angjie Formation and the Xiala Formation, it can be inferred that partial chert limestones in the Late Paleozoic in Lhasa terrane may be closely related to the earthquake. Combined with the regional data, it is concluded that a series of seismic events in the Late Paleozoic recorded the rifting process at the northern margin of Gondwana, and proved a new seismic activity for Late Paleozoic basin evolution of the Lhasa terrane.