华北麻粒岩相岩石的主要特征及今后研究中值得注意的几个问题

THE MAIN CHARACTERISTICS OF GRANULITES IN NORTH CHINA AND THE ORIENTATION OF FURTHER RESEARCH ON THEM

华北前寒武纪麻粒岩与国外同类组合相比有特殊性,如(1)具面状分布的特点;(2)麻粒岩类型缺少斜长岩-淡色辉长岩组合以及下部堆晶相辉长岩组合,灰色片麻岩比例少,并普遍受到钾质交代;(3)多为不亏损型麻粒岩,未发现熔融残留型麻粒岩;(4)变质压力为低—中压过渡型,堇青石在变质沉积岩中普遍存在;(5)华北克拉通经历了多期麻粒岩相变质作用。这些特征对于深入研究华北麻粒岩的成因、下部地壳的性质以及克拉通的形成和演化都是必须加以考虑的。

The granulites in North China are geologically different from other areas of the world: 1 ) Granuiites in North China extensively occur as a metamorphic-crystalline basement. 2 ) Anorthosites and cumulates of layered gabbro bodies are few. The dominant orthogneisses are granitic other than grey gneisses suffered reworking and migmatization. 3) Most granulites are of undepleted type. Any melting-residual type of granulites has not been reported so far. 4 ) Metamorphic pressure of granulites is lower-middle, and cordierites are widely occurred in metasedimentary granulites. 5 ) The North China craton has suffered multi-metamorphism of granulite facies. It implies that the granu]ites in North China craton have a unstable and multimobilizated early evolutional history. These characteristics of granulites lead us to consider a new approach to the properties and construction of the lower crust, petrogeneses of various granulites and evolution of North China craton.