胶南造山带中高压、超高压变质矿

HIGH-PRESSURE AND ALTRAHIGH-PRESSURE

胶南造山带榴辉岩中的高压、超高压变质矿物主要有绿辉石、镁铝榴石、柯石英、金刚石、金红石等。柯石英、金刚石均呈微晶状包裹于石榴子石、绿辉石中。柯石英多已转化为石英聚晶，并使包裹它的矿物产生放射状胀裂纹；金刚石呈近等轴八面体等，其形成压力达３．５ＧＰａ以上。榴辉岩围岩中的高压、超高压变质矿物主要有辉石类（透辉石、霓石、暗硬玉）、钠钙质钠质角闪石（钠闪石、镁钠闪石）、多硅白云母（３Ｔ型）、钠长石、绿帘石等。高压、超高压变质矿物的广泛出现指示区内存在两期高压变质作用：早期为超高压榴辉岩相变质作用；晚期为高压绿片岩相榴辉岩相变质作用。华北板块与扬子板块的多次碰撞是区内高压、超高压变质作用产生的主要原因。

? The high and altrahigh-pressure metamorphic minerals in the eclogites of Jiaonan tectonic belt were mainly composed of omphacite,pyrope,coesite,diamond and rutile,etc.The coesite and diamond are included in the garnet and omphacite as a microlic.The coesite mainly changed quartz glomerocryst which made its including minerals creat radial cracks;and the diamond with an equant octahedron formed at >3.5GPa.The high and altrahigh-pressure metamorphic minerals in eclogite country rocks are mainly composed of pyroxene (diopside,aegirine,dark jadeite),sadium-calcium to sadium amphibolite(riebeckite and magnesioriebeckite),lepidomorphite(3T type),albite and epidote.These metamorphic minerals indicate that two stages of high-pressure metamorphism occurred here.The early stage is altrahigh-pressure eclogite facies metamorphism;and the late one is high-pressure greenschist facies to eclogite facies metamorphism.The high and altrahigh-pressure metamorphism are mainly caused by collisions between Huabei and Yangtz plates.