长白山天池火山造锥阶段岩浆演化及其喷发的动力学过程--来自熔体包裹体的证据

The eruption history of the Changbaishan Tianchi volcano included three stages. At the beginning of the early Pleistocene, the Tianchi volcano started the trachybasaltic activity of the shield-forming stage, and then the trachybasaltic magma changed to the trachytic and trachyandesiti magmas at the end of the early Pleistocene; the cone-forming stage of trachyte occurred in the middle Pleistocene, and the trachyte magma changed to the pantelleritic magma at the late Pleistocene.The cone-forming period include four stages,which produce trachyte and pantellerite. There were many studies for the shield-forming stage and pantelleritic magma eruption stage on the evolutionary history of the volcanic and magma, but relatively less studies for the cone-forming stage on the origin and evolution of magma, and the dynamics of magma eruption process. On the basis of previous studies, using the stepwise opening procedure of LA-ICP-MS technique and laser Raman spectroscopy we analyze the host rock and melt inclusions from Baekdu. We will get their chemical composition and the initial information of volatile content, and then discuss the trend of magma evolution. Further, the compositions of the rock-forming minerals are determined by the electron microprobe. Using the information, we calculate temperature and pressure of magma, at the same time calculate physical and chemical conditions when magma erupts. They include viscosity, density and melt structure. In the end, we combine all the parameters and date to discuss the dynamic processes of the Tianchi volcanic activity.

长白山天池火山经历了早更新世早期的粗面玄武岩造盾，中更新世的粗面岩造锥和全新世碱流质岩浆爆发三个阶段。在造锥的不同阶段产生了不同类型的喷发产物，含粗面岩、碱流岩以及浮岩，而不同类型的喷发产物及其矿物中熔体包裹体的成分及其挥发分可以提供重要的动力学信息。目前对该阶段火山岩岩浆起源、演化与岩浆喷发的动力学过程的关系研究相对较少。在前人研究的基础上，本项目采用原位LA-ICP-MS技术的分步剥蚀法和激光拉曼光谱对天池火山造锥阶段的白头山四期火山岩中熔体包裹体进行测试分析，获得其化学组分以及挥发分含量的最原始的信息，讨论岩浆的演化趋势；并利用电子探针技术对白头山四期岩石样品中主要造岩矿物进行成分测定，采用新的温压计进行温压计算，获得岩浆形成时的物理化学条件（粘度、密度、熔体结构），探讨天池火山造锥阶段岩浆演化与动力学过程的关系。