北京沿河城地区东岭台组酸性火山碎屑流的碎屑分形特征及其成因  

Fractal characteristics and their geneses of pyroclasts from silicic pyroclastic flows of Donglingtai Formation in the Yanhecheng area,Beijing

作　　者：刘永顺[1] 冯肖兵 聂保锋[1] 彭年[1] 孙善平[2] 

机构地区：[1]首都师范大学资源环境与旅游学院,北京100048 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2014年第12期3671-3680,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40872062;40472039);北京市教委科技计划项目(08530568199);北京市自然科学基金项目(1082006)联合资助

摘　　要：火山碎屑岩中的碎屑颗粒形态、分布和显微结构保存着岩浆房内岩浆的结晶状态、火山爆炸过程中的岩浆气泡化和碎裂作用以及火山碎屑堆积和变形过程的大量物理信息。为揭示北京西山沿河城地区东岭台组酸性火山碎屑流形成的物理过程,本文以东岭台组第三岩性段的酸性熔结火山碎屑岩的火山地质、岩相学研究为基础,应用分形理论和方法对酸性熔结火山碎屑岩中的碎屑形态的分形特征开展了定量研究。不同类型碎屑的表面和边界盒维数的数值范围大小具有一致性。玻屑变幅较大,石英晶屑和岩屑变幅较小,这说明碎屑的塑性和流变性对碎屑形态多样性的影响较大。在几类碎屑中,熔蚀石英的边界盒维数和周长-面积法获得的分形维数最大,说明熔蚀作用对石英斑晶边界形态复杂性的影响超过了其它机制对火山碎屑形态复杂性的影响。东岭台组酸性火山碎屑岩中的熔蚀石英、石英碎屑、长石碎屑、玻屑和岩屑的分形特征有明显差异,反映了火山喷发过程中围岩和岩浆性质、物理化学条件以及火山作用机制的差异。火山碎屑形态的分形特征和幂率规律,证明火山爆炸过程是一种自组织临界条件下发生的。The form and distribution of pyroclasts and their microscopic textures in the pyroclastic rocks preserve a large amount of physical information on the crystallization situation in magma chamber, the vesiculation and fragmentation in the volcanic explosion, and the deposit and deformation of pyroclasts. The silicic welded pyroclastic rocks of Donglingtai Formation in the Yanhecheng area, Western Hills of Beijing, derived from the deposits and diageneses from silicic pyroclastic flows. In order to reveal the physical processes of pyroclastic flow on the basis of the researches of geology and petrography of silicic welded pyroclastic recks from the third Member of Donglingtai Formation, by the application of fractal theories and methods, we studied the fractal characteristics and their geneses on the complex shapes of single pyroclast and plenty of pyroclasts under the thin sections of the silicic welded pyroclastic recks. The range of surface and edge box-counting fractal dimensions of pyroclasts from silicic welded pyroclastic rocks is consistent, and the values of vitric fragments have the wider range in comparison with the narrower one of quartz crystal fragments and lithic fragments, which shows that the ductility and theology of fragments has a great effect on the diversity of fragment form. Among the various kinds of fragments, the edge box-counting fraetal dimensions and the box-counting fractal dimensions with the double log method of area and periphery of resolved quartzes are the largest, which shows that the effect of resorpsion on the edge of quartz phenocrysts exceeds one of other mechanisms on the form complexity of pyroclastic fragments. The fractal characteristics of resolved quartzes, quartz crystal fragments, feldspar crystal fragments, lithic fragments and vitric fragments in the silicic welded pyroclastic rocks of Donglingtai Formation are obviously different, as reflects the different textures of surrounding rocks and properties of magma, the changes of physical and chemical condition and the d

关 键 词：东岭台组 火山碎屑流 岩相结构 分形特征 北京西山 

分 类 号：P317[天文地球—固体地球物理学]