北秦岭黑河丹凤群岛弧火山岩建造的发现及其构造意义

陕西省周至县黑河丹凤群有大规模安山岩浆活动的证据，地球化学研究表明这些安山岩形成于典型的岛弧环境，如：轻稀土富集；在痕量元素原始地幔标准化丰度模型图上，所有样品均具有明显的Ｎｂ、Ｔｉ和Ｐ负异常；在Ｂａ－Ｎｂ－Ｔｈ－Ｌａ图解上，所有样品均落在岛弧区等。由此可以推断黑河丹凤群有一套安山岩为主的岛弧火山岩建造。这一发现为证明北秦岭古生代岛弧构造环境提供了重要的证据，为进一步揭示秦岭造山带的构造格架和演化历史提供了信息。

THE DISCOVERY OF ISLAND ARC ANDESITE FROM DANFENG GROUP HEIHE,NORTH QINLING AREA AND ITS TECTONIC SIGNIFICANCE

Andesite was found from Danfeng Group in Heihe,North Qinling area on a wide scale.Geochemical characteristics of the andesite,for example,high LREE abundance and evident negative anomaly of Nb,Ti and P,which is obviously the result of subduction,suggest that the andesite was formed in a typical island are tectonic environment.In the Ba-Nb-Th-La diagrams,all the samples analyzed fall into IAB area.This discovery is an important evidence that supports the existence of an ancient island are in North Qinling area.It also gives some useful information about the tectonic pattern and the evolution history of Qinling Orogenic Belt.