摘要
中国华北克拉通及邻区的早前寒武纪不存在碱性玄武岩。全球范围内碱性玄武岩的形成也存在时限性，它们在中新生代以来相对大量的出现。碱性玄武岩可划分为钾质碱性玄武岩和钠质碱性玄武岩两大类，后者还可作进一步划分。它们在同位素组成和元素组成上存在相互过渡的变化，这与地幔源区外来加入物质的种类和比例不同有关。高压和低程度熔融是所有碱性玄武岩形成的必要条件。研究表明，碱性玄武岩形成具时限性主要与地球热状态从热向冷的历史演化有关。碱性玄武岩的形成需要地幔俯冲作用，可达到相当深度的地幔俯冲作用只是到了太古宙以后才发生，并在中新生代以来达到高潮。
The alkaline basalts do not occur in the early precambrian in the North China Craton and itsneighbouring area. The restriction in their forming-time is also a world-scale phenomenon. Theyare predominanlly formed after the Mesozoic. There are two types of the alkaline basalts , namelythe potassic and the sodic. The later can be further divided into normal and abnormal ones. Theirisotopic and element compositions change gradually each other , prabably caused by the variation ofthe types and proportion of the material adding into the mantle source regions. High presure and lowdegree of melting appear to be the necessary requirements for the formation of the alkaline basalts.It is suggested that the restriction in the form ing-time of the alkaline basalts is mainly related to thehistory state evolution of the Earth from hot to cold. supposed to be needed for the formation Of al-kaline basalts ,the mantle subduction could atlain sufficient depth only after the Archaean ,andmight great depth post Mesozoic .
关键词
碱性玄武岩
同位素
元素地球化学
玄武岩
time limit of the formation of alkaline basalts isotopic and element geochemistryhistory state evolution of the Earth from hot to cold
