南秦岭勉县─略阳结合带蛇绿岩与岛弧火山岩地球化学及其大地构造意义

GEOCHEMISTRY OF THE OPHIOLITE AND ISLAND ARC VOLCANIC ROCK IN THE MIANXIAN-LUEYANG SUTURE ZONE, SOUTHERN QINLING AND THEIR TECTONIC SIGNIFICANCES

南秦岭勉县-略阳结合带中超基性岩类主要为方辉橄榄岩和纯橄榄岩，稀土特征为轻稀土亏损，铕富集型；辉绿岩均为轻稀土富集型。变质火山岩可区分为两种组合：一为轻稀土亏损的洋脊拉斑玄武岩，其Ti／V．Th／Ta、Th／Yb、Ta／Yb表明其为MORB型玄武岩，代表本区消失了的洋壳岩石，指示本区晚古生代一早中生代期间的一个古洋盆。另一类为岛弧火山岩组合，除岛弧拉斑玄武岩外，甚至还有大量中、酸性岛弧火山岩，它们并非洋壳的物质组成，而是大陆弧岩浆活动的产物。这表明勉略洋盆在晚古生代-早中生代期间曾经经历过一个较完整的有限洋盆的发生、发展与消亡过程，这期间秦岭已成为一独立的岩石圈微板块，其南缘具有活动大陆边缘的构造属性，秦岭并非华北与扬子陆块之间的简单碰撞产物。

The ultlabasic rocks in the Mianxian-Lueyang ophiolitic melange include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The diabase dike swarm show LREE enrichment but slightly slightly Eu anomaly. Metamorphosed volcanic rocks can be divided intO two groups in terms of their REE geochemistry and trace element ratios of Ti / V, Th / Ta, Th / Yb and Ta /Yb. One is the MORB-type basalt with LREE depletion, representing the fragments of oceanic crust The other is the island-are volcanic rocks including tholeiitic and cafe-alkaline associations. They were formed in the continental margin.