AN EARTHQUAKE MODEL FOR FORMATION OF COESITE AND DIAMOND IN MEDIUMTEMPERATURE ECLOGITES
中温榴辉岩中柯石英和金刚石形成的一种地震成因模型

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.