琼北射气岩浆喷发力学机制探讨  

DYNAMIC MECHANISM OF PHREATOMAGMATIC ERUPTION IN NORTHERN HAINAN ISLAND

作　　者：孙谦[1] 樊祺诚[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《地震地质》2005年第1期63-72,共10页Seismology and Geology

基　　金：国家自然科学基金(40402010);中国地质大学"岩石圈构造;深部过程及探测技术开放实验室课题(2003006)共同资助。

摘　　要：　琼北第四纪火山区分布着为数众多、大小不一的射气岩浆喷发成因的低平火山口。上升的岩浆遇到地下水会发生射气岩浆喷发,形成地表出露的低平火山口,并伴随出现基浪堆积物。根据低平火山口的半径、爆炸发生时上覆地层的厚度、岩浆与地下水接触面的半径等参数,运用弹性力学基本原理建立了简单的喷发模型,初步模拟爆破冲击力与上述各参数之间的关系和变化规律,并计算出上覆地层中任一点的应力状态,初次探讨了射气岩浆喷发的力学机制。Maars of various scales produced by phreatomagmatic eruption are widely distributed in the Quaternary volcanic region of the Northern Hainan Island. The Pleistocene volcanic activity in Northern Hainan Island was characterized by the alternating of effluent magma eruption and phreatomagmatic eruption. In fact, phreatomagmatic eruption was concentrated in Middle Pleistocene to Upper Pleistocene, resulting in a lot of maars of various sizes, such as Longfeng-Longji, Shuangchiling, and Yanghua maars etc. In this area, different maars have different scale. The radius of maar is variable from several ten meters to above 1km. When ascending basaltic magma meets with ground water, violent explosion would occur, i.e. phreatomagmatic eruption. This kind of volcanic eruption may result in maars exposed on the earth's surface, and gives rise to the formation of base-surge. As to the base-surge, it has long been treated as sedimentary tuff by mistake. Usually, base-surge is distributed around maar, different from the distribution of sedimentary tuff. The base-surge is characterized by large-scale and low-angle cross-bedding, slaty-bedding, current-bedding and distal facies accretionary lapilli. In order to explain the dynamic mechanism of phreatomagmatic eruption thoroughly, we propose a simple mathematic model in this paper in the light of the elasticity theory. In addition, according to several parameters, such as the radius of maars, thickness of overlying formation when explosion occurred, and the radius of contact plane between the magma and groundwater, we have simulated the relation between the explosive wallop and these parameters, as well as its variation rule. Furthermore, we calculate the stress state at any point in the overlying formation. Some conclusion can be drawn as follows: the larger the radius of maar, the larger the explosive wallop needed for the formation of maar is; provided that the radius of maar and depth of explosive point are limited, then the larger the area of contact surface between magm

关 键 词：射气岩浆喷发 琼北 火山口 力学机制 上覆地层 火山区 第四纪 接触面 应力状态 地下水 

分 类 号：P317[天文地球—固体地球物理学] P631.4[天文地球—地球物理学]