闽中地区绿片岩的微量元素地球化学及其形成的构造背景

闽中地区前寒武纪龙北溪组绿片岩沿政和－大埔断裂带分布。常量元素研究表明,绿片岩的原岩为苦橄玄武岩和玄武岩。研究区内前寒武纪变质酸性火山岩常与这些基性火山岩伴生,具有“双峰式”大陆裂谷火山岩特征。本区绿片岩的微量元素地球化学特征不同于洋中脊玄武岩（MORB）及火山弧玄武岩（VAB）,具有较高浓度的大离子半径亲岩不同于洋中脊玄武岩（MORB）及火山弧玄武岩（VAB）,具有较高浓度的大离子半径亲岩元素(LILE),如K、Rb、Ba、Zr直至Ti;REE球性陨石标准模式圈为富LREE类型。δEu无异常到弱异常。利用Ti－Zr－Y,Nb－Zr－Y图判别,绿片岩为板内拉斑玄武岩(WPT)。因此,绿片岩原岩为大陆拉斑玄武岩,其形成的构造背景为大陆裂谷。这一结果对进一步研究政和一大埔断裂带性质以及华南地区构造演化具有重要意义。

TRACE ELEMENT GEOCHEMISTRY AND TECTONIC SETTING OF GREENSCHISTS IN THE CENTRAL PART OF FUJIAN PROVINCE

The Precambrian greenschists of the Longbeiqi Group in the central part of Fujian province are distributed along the Zhenghe-Daipu fult belt. Major chemical compositions of the greenschists indicate that they were originated from picrite basalt and basalt. The Precambrian metamorphic acidic volcanics are generally associated with the basic ones,and demonstrate a "biomode" feature of the continental rift volcanic rocks. The geochemical characteristics of trace elements of the greenschists are different from MORB and VAB in higher contents of LILE, such as K,Rb, Ba, Zr and Ti; The chondrite-normalized REE patterns are enriched in LREE with a small Eu anomaly. Based on the Ti-Zr-Y and Ti-Zr-Nb diagrams, the greenschist is identified as within plate tholeiite (WPT). Consequently, the greenschists in the central Fujian province are considered to be derived from the continental tholeiite formed in a continental rift tectonic setting. Our results may have important siginificance for further studies of Zhenghe-Daipu fault belt, as well as the tectonic evolution of South East China.