Analysis on the underground rock stress state under compositing tectonic force and gravity

针对大别一带超高压变质作用的形成深度存在两种观点:其一是形成深度可用静流体公式h=p/(ρg)算出,并得出变质作用形成于90 km或更深处;其二是超高压是重力、构造力和其他力合成的,并不只是重力的作用,从而该变质作用可以在地壳内形成.地下的岩石处于固态,而静止流体公式不适用于固体.事实上,围压不仅来自重力,而且也来自构造力和其他力,所以合理的求深度算法应该是从总压力中减去构造力获得纯重力才可用来计算深度.还简要解释了诸如剪应力、差应力、构造力等概念.There are two viewpoints on the formation depth under the effect of ultrahigh pressure metamorphism in Dabie area:(1) The formation depth can be calculated by the hydrostatic equation h =p/(pg),which concludes that the metamorphism was formed under the depth of 90 km or more;(2) The ultrahigh pressure was composed of gravity,tectonic and other forces instead of gravity forces alone,and the metamorphism can be formed in the Earth'curst.The underground rocks are all in solid state and the hydrostatic equation is not applicable to solid body.In fact,the confining pressure was not only formed by gravity force,other forces including tectonic force also play a part.So the correct way of calculating formation depth is to subtract the tectonic force from the total pressure force and use the remaining force,i.e.unmixed gravity force,to calculate the depth.Certain concepts such as shear stress,differential stress,tectonic force and gravity force are briefly explained in this paper.国土资源部科技发展计划项目“地壳深部压力与超高压岩石形成研究”; 国家计委科技找矿项目; 国家科委基础司特别支持项目中国科学引文数据库(CSCD)216-222