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

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.