松辽盆地北部徐家围子断陷营城组大型破火山口的发现  

Discovery of a giant caldera in the Yingcheng Formation in the Xujiaweizi fault depression, northern Songliao basin

作　　者：贺电[1] 李江海[1] 刘守偈[1] 韩亮[1] 

机构地区：[1]教育部造山带与地壳演化重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《中国地质》2008年第3期463-471,共9页Geology in China

基　　金：国家重点基础研究发展计划(973)项目(2006CB403502)资助

摘　　要：破火山口的形成是火山物质喷发量最大、破坏力最强的一种火山作用现象,因此,探寻破火山口存在的证据是明晰松辽盆地北部徐家围子断陷下白垩统营城组火山喷发规律和叠置关系的关键。徐家围子断陷营城组地层中徐东破火山口呈一个长轴约17km,短轴约10km的椭圆形、塌陷深度近3km的大型破火山口,其天窗式塌陷是下方岩浆房的不对称形态或岩浆房的不对称抽空导致。徐东破火山口内被厚层流纹质凝灰岩和熔岩填充,剖面上显示一对发育完整的正、逆断层,指示徐东破火山口经历了完整的沉降、塌陷、火山喷发过程。徐东破火山口形成于大陆裂谷背景下,是岩石圈减薄,大规模岩浆作用的产物。受区域NNW向构造格架控制,形成破火山口南北延伸的椭圆形态。The formation of a caldera is the most catastrophic volcanic phenomenon leading to the most voluminous pyroclastic eruptions. Therefore, to explore the evidence for the existence of a caldera is the key to the understanding of the characteristics and superimposition relationship of volcanic eruptions in the Lower Cretaceous Yingcheng Formation in the Xujiaweizi fault depression, northern Songliao basin. The Xudong caldera, filled with thick rhyolitic tuff and lava, is a large caldera, ellipse in form with an area of 17 km×10 km and a maximum subsidence depth of 3 km. Its trapdoor subsidence was caused by its underlying asymmetrical magma chamber or asymmetrical deflation of the magma chamber. In section, there is a pair of completely developed normal and reverse faults, indicating that the Xudong caldera experienced a complete process of sinking subsidcnce, and syn-subsidence volcanic eruption. The caldera is the product of lithosphere thinning and substantial magmatism in a continental rift setting. The N-S-elongated ellipse shape of the caldera was formed under the control of the NNW-trending structures.

关 键 词：徐家围子断陷 破火山口 天窗式塌陷 流纹质凝灰岩 

分 类 号：P588.14[天文地球—岩石学]