论赣东北地区中生代火山岩的特征及其演化规律

本文在研究德兴银山及其邻区信江盆地火山岩的基础上,探讨了赣东北地区中生代火山岩的特征、成因和演化。赣东北地区中生代火山岩是酸性和中酸性的,属钙碱性岩系,其中在岩浆分异的晚阶段所形成的富钾的偏碱性岩是十分特征的。赣东北地区中生代火山活动十分强烈。从北西往南东方向,火山岩的年龄从164百万年到131百万年,锶同位素初始比值(87Sr/86Sr)。从0.704变化到0.713;同时,火山岩的Rb/Sr比值,Eu亏损,K_2O含量以及亲石元素丰度也逐渐增加。考虑到本区双桥山群变质基底的特征,笔者认为有关的岩浆是在部分上地慢分熔产物的参与下,由变质基底部分熔融形成的。

THE CHARACTERISTICS AND EVOLUTION OF THE MESOZOIC VOLCANIC ROCKS IN NORTHEASTERN JIANGXI

The characteristics, origin, and evolution of the Mesozoic volcanic rocks in Northeastern Jiangxi were discussed based on the study of the Mesozoic volcanic rocks in Yinshan and Sinjiang region. These rocks are acidic and intermediate acidic,and belong to a calc-alkalic rock series. They are characterized by potash-rich subalkalic rocks at the late stage of the magmatic diffenciation. The strong volcanic activity ranges from 164 to 131 m.y.from the northwest to the southeast of the working area, and the initial ratio of strontium changes synchronously from 0.704 to 0.713. At the same time, the Rb/Sr ratio, Eu depleion, K_2O content and the lithophile element abundance increase gradually. Considering the features of the Shuangqiaoshan Group as the metamor phic basement of the working area, the authors suggest that the magma was formed from the partial melting of the metamorphic basement with some of upper mantle differential fusion products.