丹凤群的岩石组合特征及其构造意义

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CHARACTERISTICS OF PETROLOGICAL ASSEMBLAGE IN THE DANFENG GROUP AND ITS TECTONIC SIGNIFICANCE

摘要: 本文通过岩石组合和岩石地球化学特征,研究东秦岭丹凤群火山岩的大地构造环境。丹凤群由火山熔岩、火山碎屑岩和变质砂岩组成。火山熔岩是以玄武岩、安山岩为主的玄武岩—安山岩—英安岩—流纹岩组合,根据Peacok指数把它归入钙碱质火山岩系;其稀土总量含量高,轻稀土富集,Ce明显亏损,具大陆壳性质,属岛弧型火山岩。处在火山岛弧构造环境的丹凤群分布区,是刘岭群不成熟杂砂岩的物源区。

Abstract: On the basis of the characteristics of petrological assemblage and pe-trogeochemistry, the tectonic environment of volcanic recks in the Danfeng Group, east Qinling is studied. The Danfeng Group consists of volcanic lavas, pyroclastic rocks and metamorphic sandstones. Volcanic lava dominated by basalt and andesite is composed of basalt-andesite-dacite-rhyolite assemblage, which is classified as calc-alkalic volcanic rock series according to Peacok index, and has a hightotal amount of rare earth elements enriched in light rare earth. The loss of Ce is obvious.This assemblage should belong to the volcanic rocks of island arc type. It is distributed in an envircnment of volcanic island-arc tectonism over the area of the Danfeng Group which is the source area of immuture apogrites in the Liuling Group.

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