中温榴辉岩中柯石英和金刚石形成的一种地震成因模型

AN EARTHQUAKE MODEL FOR FORMATION OF COESITE AND DIAMOND IN MEDIUMTEMPERATURE ECLOGITES

中温榴辉岩中超高压相矿物柯石英和金刚石的发现引起了地质学界的广泛关注，这不仅来自其本身的岩石学意义，而且也来源于对板块构造的过程和造山带的演化提出了限制条件。因此进一步研究这两种矿物可能的成因十分必要，为此本文提出柯石英和金刚石形成的一种新的模型─地震有关的成因模型．本文的论述将主要来自目前我们对大别一苏鲁地区含柯石英金刚石榴辉岩的了解。

Though the ultrahigh pressure for formation of coesite and diamond was widespreadly attributed to lithostatic pressure so far in medium temperature eclogites,the author in this paper disagrees with this kind of idea and proposes that origin of coesite and diamond was probably related to local stress concentration in earthquake process.The idea propsed in this paper bases on the consideration and facts as follows:First,of ultrahigh pressure represented by coesite and diamond were lithostatic,this would lead to the conclusion that the continental crust would had subducted into mantle-because the metamorphism of eclogites is compatible with their gneissic country rocks during continent-continent collision.It's evidently questionable because of the less density of continental rocks than mantles; Second coesite and diamond occur as micro-graded inclusion in garnet,omphacite,kynite and epidote,meanwhile,there are other minerals as inclusion, for example,amphibole,paragonite et al.Amphibole was unstable in stable area of coesite and diamond according to some experimental information.This means that the pressure of estimation from coesite and diamond don't match with.other mineral assamblage;Third the nucleation and growth of coesite and diamond is very fast,even transient,based on findings of coesite and diamond in meteor crater,so it's possible that ultrahigh pressure recorded by coesite and diamond in medium temperature eclogites be transient,the author thinks the earthquake is a mover that leads to forming the transient ultrahigh pressure.Eclogites occur as blocks in gneiss,this proves that eclogite has more strength than gneiss.When an earthquake rupture passes through the area contained eclogite body,eclogite will become the barrier on the rupture surface and the stress concentration will be produced around eclogite body with fault moving in earthquak process.The magnitude order of the stress concentration is significant for formation of coesite and diamond according to some simple estimation in the paper,especially in eclogitic metamorphic condition.The author dis cusses the orogenic earthquakes based on Himalayas situation and points out that earthquake's responsibility for origin of coesite and diamond is probably important.