天池火山三期浮岩气孔结构局域化特征与喷发动力学初探

Preliminary research on the localization characteristics of vesicular structures of pumices and eruption dynamics in the three stages of Tianchi Volcano eruption

本文在长白山天池火山野外地质工作基础上,对天池火山黄色浮岩(50000年前大喷发)、灰白色浮岩(千年大喷发)和黑色浮岩(八卦庙期喷发)等三期空降浮岩开展了扫描电子显微镜高精度结构分析以及浮岩气孔结构的局域化定量研究。三期浮岩洛伦茨分析表明:黄色浮岩和黑色浮岩气孔均一化程度基本一致,而灰白色浮岩均一化程度更高,反映了千年大喷发在岩浆演化程度和喷发动力学行为上的特殊性,推测可能与幔源岩浆注入地壳岩浆房的动力过程有关。气孔大小幂律分布以及气孔形态分形特征的复杂性分析表明,50000年前大喷发的浮岩幂指数和分形维数最高,揭示了其自组织临界态程度最高,对外界环境触发最为敏感,而另外两期浮岩幂指数和分形维数呈现出标准的幂律衰减,据此我们推测三期喷发可能均处在天池火山系统逐渐稳态恢复的大周期中。

Based on the field geological survey of Tianchi Volcano in the area of Changbai Mountains,the high precision structure analyses of scanning electron microscopy and quantitative localization of vesicular structures were carried out for the three stages of pumices,i.e.yellow pumice(50 000 years BP eruption),gray-white pumice(Millennium eruption)and black pumice(Baguamiao stage eruption).Lorentz analyses of three stages of pumices show that the homogenization degrees of vesicles of yellow pumice and black pumice are very similar,and lower than the one of gray-white pumice,which reflects the particularity of magma evolution and dynamic behavior of Millennium eruption.It is speculated that this may be related to the dynamic process of mantle-derived magma injection into crustal magma chamber.The power law distribution of vesicle size and the complexity of fractal characteristics of vesicle morphology reveal that the power exponent and the fractal dimension of pumice erupted 50 000 years ago are the highest,which implies that it has the highest degree of self-organized criticality and is the most sensitive to the triggering of external environment change.The power exponent and the fractal dimension of pumices in the other two stages display the standard power law attenuation.Accordingly,we suppose that the three stages of eruption may be in the large period of gradual steady-state recovery of Tianchi Volcano system.