华中陆壳高压变质带类白片岩的岩石矿物特征

PETROLOGY AND MINERALOGY OF QUASI—WHITESCHISTS IN THE HIGH—PRESSURE METAMORPHIC BELT OF THE CONTINENTAI CRUST IN CENTNAL CHINA

华中陆壳高_压变质带以蓝片岩-榴辉岩-类白片岩三位一体为特征。类白片岩为一套富含高铝质矿物的岩石类型,分布在中元古界。主要岩石类型为刚玉蓝晶石岩、蓝晶石钠云母片岩,蓝晶石自云石英片岩和蓝晶石黄玉石英岩。变质矿物有蓝晶石、蓝刚玉、黄玉。钠云母、硬绿泥石和白云母等。类白片岩形成的温压条件为P=2000MPa,T=850—900℃,为高压条件下变质的泥质岩石。该类岩石与西德岩石学家Schreyer(1973)命名的典塑白片岩(蓝晶石+滑石)在矿物组合上略有不同,但其地质意义却很一致,都代表高压变质的泥质岩石,可作为地壳物质俯冲到地幔深度的指示剂,故称为类白片岩。

The high-pressure metamorphic belt of the continental crust in central China consists of blueschist, ecologite and quasi-whiteschist. Quasi-whiteschist is a rock type which contains abundant high-Al minerals. It occurs in the middle Proterozoic. Metamorphic minerals include kyanite, corundum, topaz, paragonite, chloritoid and muscovite. The conditions of formation are P=2000 MPa and T=850—900℃. It is metapelitic rocks formed under high-pressure conditions. Typical mineral associations are Ky+Tz+Q, Ky+Co and Ky+Pa+Mus.The associations are slightly different from typical whiteschist (Ky+Tc) termed by Schreyer, but their geological signifioance is similar. Ther are both metapelitic rocks formed under the high-pressure conditions and regarded as an indicator suggesting that crustal materials have been subducted to the mantle depths. Therefore the Al-rich rocks in central China is named quasi-whiteschists.