藏北火山岩的微量元素特征——关于弧后盆地演化的地球化学证据

Trace element characteristics of the volcanics in the northern Xizang(Tibet)

用仪器中子活化法测定了藏北火山岩微量元素丰度,结果证明藏北蛇绿岩是形成在一个规模不大,存在时间不长的弧后盆地环境内。根据火山岩的层位关系,岩浆来源和微量元素特征把该盆地的地质演化概括为扩张阶段、封闭阶段和造山后阶段。这种认识与区域地质资料相一致。

Abundances of trace and rare earth elements from a representative volcanics in the northern Xizang have been measured by instrumental neutron activation analysis. The results indicate that the ophiolitic complex was formed in a small back-arc basin. On the basis of the stratigraphy, magmatic source and geochemical characteristics of volcanics, the evolution process of the northern Xizang back-arc basin may be summarized into three continual periods as following: the expanding, the clossing and post-orogenic periods. Distinct volcanism was occurred in each periods. This hypothesis is consistent with regional geologic data.