镇安县云镇小磨岭岛弧火山岩地球化学及其大地构造意义

分布于陕西省镇安云镇小磨岭糖坊沟一带的中性火山熔岩，为钾玄质高镁质安山岩，稀土总量较低，微量元素中高场强元素(Nb、Ta、Ti)相对亏损和大离子亲石元素(CS、Rb、K等)相对富集，均反映具岛弧火山岩特征，与原划的耀岭河火山岩有明显的区别。反映元古代中、晚期，随松树沟洋盆的形成与演化，原始古秦岭地块南部(南秦岭)由初期的裂谷构造环境，已逐渐转化为新元古代南秦岭活动陆缘构造环境，图区已进入板块构造体制的演化阶段。

GEOCHEMISTRY AND TECTONIC SIGNIFICANCE OF THE XIAOMOLING ISLAND ARC VOLCANIC ROCKS

The intermediate volcanic lava, distributed in Xiaomoling area of Zhen'an county, Shaanxi, is characterized by potash and high magnesium andesite, lower content of the total amount of rare earth elements, comparative losing of medium high field strong elements (Nb, Ta and Ti) in microelements and comparative enrichment of large ion lithophile elements (Cs, Rb and K), reflecting its island arc volcanic features different from the original Yaolinghe volcanic rocks. It also indicates the formation and evolution of the Songshugou ocean basin in the middle late period of Proterozoic era and the rift structural environment of the Qinlin paleo massif (the southern Qinling) changed into active epicontinental structural environment of the southern Qinlin in the neo Proterozoic era gradually. The mapping area has developed into the stage of plate structural evolution.