苏北海州群细碧角斑岩系的成因

    THE PETROGENESIS OF THE SPILITE-KERATOPHYRESEQUENCE OF THE HAIZHOU GROUP IN NORTHERN JIANGSU

    • 摘要: 海州群的变质火山岩地层,以石英角斑岩为主,细碧岩次之,角斑岩类稀少,属于细碧岩—石英角斑岩组合类型,且以普遍含钾偏高为特点。根据该岩系的岩相、岩石化学、稀土元素含量情况分析,它是元古代晚期在张性条件作用下产生陆内裂谷一海州裂陷槽,并形成海底火山喷发活动的产物。其中细碧岩和石英角斑岩分别来源于上地幔碱性玄武岩和硅铝地壳偏碱性流纹岩浆,所以具有双峰模式的组合特点。海州群沉积之后,曾多次发生区域性中一高压绿片岩相变质作用,分布上可划分为兰闪石绿片岩相、低绿片岩相、高绿片宕相等三个变质带,显示了递增变质的规律性变化。

       

      Abstract: The matavolcanic rock sequence of the Hiazhou Group in northern Jiangsu,consistingmainly of quartz keratophyre with subordinate spilite and rare keratophyres,belongs to aspilite-quartz keratophyre association type and is characterized by a generally higherK content.On the basis of analyses of the petrography,petrochemistry and REE contents ,it is material ofsubmarine eruption in the Haizhou rift trough an intracontinental rift formed under inter-mediate conditions during the Late Proterozoic. Spilite and quartz keratophyre were derivedfrom alkali basaItic magma of the upper mantle and subalkaline rhyoritic magma of the sialiccrust respectively,so show the features of a bin1odal model. After the deposition of the HaizhouGroup, regional medium-and high-pressure greenschist facies metamorphism occurred severaltimes. Three metamorphic facies zones may be distinguished :the glaucophane greenschist facieszone ,Iow greenschist facies zone and high greenschist facies zone,showing a progressive meta-morphism.

       

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