从剖面上晶屑含量变化探讨火山灰流凝灰岩火山爆发的机制

处于重力稳定状态的岩浆房要产生喷发作用，其可能的躯动力有两种：其一是开放体系岩浆房的下部岩浆脉冲补给使岩浆房体积膨胀，产生可克服上覆围岩强度的超压；其二是封闭岩浆房中的结晶作用，导致挥发组分出溶、体积膨胀而产生克服上覆围岩强度的超压。本文通过对江西广丰地区中生代火山灰流相凝灰岩研究认为，这两种可能的火山喷发机制可通过剖面上晶屑含量与岩石地球化学成分的对应变化关系来识别，前者为晶屑含量呈递增的喷发韵律，而化学成分无明显变化，后者则晶屑含量呈快速递减的喷发韵律，化学成分变化较大。这两种机制的识别，对于预测现代活火山喷发周期，分析古火山活动阶段有重要的意义。

THE MECHANISM OF VOLCANO ERUPTION OF PYROCLASTIC FLOW TUFF ACCORDING TO THE RESEARCH OF THE CHANGES OF PYROGENIC MINERAL CONTENTS IN FIELD SECTION

Tow dynamic force would result volcano eruption from a gravity stabilized magma chamber, which are the magma pulse and magma crystallization. At a opened magma system, new magma added to chamber by magma pulse would result a over-pressure which is strong enough to overcome the tensile streagth of wall rocks. In a closed magma chamber, the increase of the crystallinity would result Volatile exsolution and the volume expansion of magma chamber, which also forms a over-pressure. Based on the study of the pyroclastic flow tuff from Guangfong district of Jiangxi province, it is suggest that tow mechanism can be recognized by the changes of pyrogenic minerals content and composition of the tuff at field section. When tuff eruption is resulted from the magma pulse, the tuff will decrease the pyrogenic mineral content, and change largely their abundance of chemical elements. The case is contrary when the eruptions are resulted from the increase of crystallinity. These conclusions are important to analysis of the eruption rhythm of present active volcano and evolution stage of ancient volcano.