滇西新构造运动时期陆内伸展作用

A STUDY OF CONTINENTAL EXTENSION DURING NEOTECTONIC MOVEMENT IN WEST YUNNAN

上新世一第四纪为滇西的新构造运动时期,代表了本区喜马拉雅造山期后的伸展作用时间,除形成区域性的角度不整合外,还形成了一系列小规模的转换拉张盆地,并产生大规模玄武岩浆喷发。洱源—遮放地震深度-速度剖面的P波速度,显示本区岩石圈具4层结构,即上部壳层、韧性壳层、下部固态壳层和地幔岩石圈。各层对比表明,地幔隆起导致热隆伸展作用及热流上涌,并在壳幔界面产生局部混熔,下部壳层发生区域深变质作用;韧性壳层产生强烈纯剪流动,上部壳层则以脆性—脆韧性走滑断层及层圈式滑脱被动地调整;地壳均衡作用不断地调整地幔隆起与地壳厚度的关系。

By analysis the information of tectonic, structure motion and tectonic stress field, the au- thors find that the time of neotectonic is from Early Pliocene to Quaternary, and this time is no difference to the continental extension after Himalayan orogenic epoch in west yunnan. During extension, regional angular unconformity and a series of transform-pull basins had formed, companied with a large scale of magma eruption. The P-wave which is showed in the velocity- depth medel of seismic refraction profile from Eryuan to Zhefang indicates that the lithosphere includes four Iayers. i. e. upper crust layer. ductile crust layer, solid lower crust and mantle lithosphere. The comparison of defomnation and nature characteristics among layers show that rising of mantle produce thermal flowing up and extension by thermal rising, also produce mixed melting of crust-mantle substance in some part of the boundary between mantle and crust. The reglonal deep metamorphism formed in solid Iower crust. At the same time, strong strain and pure shear fluid happened in ductile crust layer and brittle to brittle-ductile strike- slip fault and layered delludation fault formed in upper layer. The isostatic action continued to adjust the relations between rising of mantle and thickness of crust.