长白山天池火山气象站期碱流岩辉石环带混沌吸引子的发现及意义  

Discovery and implications of the chaotic attractor from zoned pyroxene in Qixiangzhan comenditic lava,Tianchi volcano,NE China

作　　者：郭文峰[1,2] 刘永顺[2] 吴才来[1] 魏海泉[3] 聂保锋[2] 彭年[2] 陈正全[3] 雷敏[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]首都师范大学资源环境与旅游学院,北京100048 [3]中国地震局地质研究所,北京100029

出　　处：《科学通报》2017年第30期3470-3478,共9页Chinese Science Bulletin

基　　金：国家自然科学基金(41602342;40872062;41372342;41302266;41002121);北京市自然科学基金(1082006);公益性行业科研专项(201211095-4)资助

摘　　要：火山岩中矿物的成分环带中蕴含着其生长过程中岩浆成分和温压等物理状态的变化信息,对研究岩浆演化和火山喷发动力过程非常重要.长白山天池火山气象站期碱流岩辉石具有明显的环带结构,其成因尚未讨论.本文通过了辉石环带的电子探针分析,发现MgO和Na_2O等元素的相对含量呈剧烈的振荡形态.同时,利用非线性时间序列分析的方法,对MgO元素沿辉石环带成分进行了相空间重构的探索性研究.结果发现,辉石环带成分时间序列的相空间吸引子为混沌吸引子.这说明辉石斑晶在生长时所处的系统具有高的自由度和高度的复杂性,其结晶和生长时周围岩浆的成分是高度非稳态和不平衡的.我们认为是岩浆房补给混合和热对流作用过程导致辉石所处的岩浆成分在高MgO、低MgO之间激烈振荡变化,形成了辉石环带成分的剧烈振荡.而这些补给-混合-对流的过程可能最终导致岩浆房超压而发生溢流喷发.Mineral compositional analysis is a powerful tool for identifying both volcanic and petrogenetic processes. This property is observed because spatial variations in the composition of magmatic minerals record chemical and physical changes in the magma from which they crystallized. Thus, these variations can also be used to decipher the history of a magmatic system and its triggering mechanism prior to eruption. The Tianchi volcano, located in the Changbaishan volcanic region, is one of the most active and dangerous volcanoes in East Asia; however, the eruptional mechanism of most recent eruptions are not well-resolved, especially the comenditic lava flow in the Qixiangzhan stage, Tianchi volcano. We focused on the zoned patterns in pyroxene phenocrysts of the comenditic lava to decipher the magma process and triggering mechanism of this silicic lava eruption. We analyzed major and minor element concentrations by point measurement and line-scan across a zoned pyroxene grain using the electron probe micro-analyzer （EPMA） equipped with the energy-dispersive （ED） spectrum. We also extracted a compositional time series by considering the variation of zone thickness across oscillatory zoning and reconstructed the phase space of the compositional time series using the optimal time delay method. First, we calculated the optimal time delay of phase space reconstruction obtained from the first minimum method of mutual information, and we later determined the embedded dimension. Using two parameters （i.e., time delay and embedded dimension）, we subsequently reconstructed the phase space. We also present the Poincare section of the reconstructed system. The results of EPMA point measurement （Table 1 and Figure 4） showed that the zoned pyroxenes have higher MgO （2 wt%-2.12 wt%） and lower Na2O （1.26 wt%-1.39 wt%） in the core compared with the rim （MgO, 1.22 wt%-1.54 wt%; Na20, 1.71 wt%-1.92 wt%）. The results of the line-scan of EPMA-ED showed that the normalized concentration of each minor element �

关 键 词：天池火山 碱流岩 辉石环带 非线性时间序列分析 混沌吸引子 岩浆混合 

分 类 号：P317[天文地球—固体地球物理学] P588.14[天文地球—地球物理学]