武夷山新元古代蛇绿混杂岩岩石地球化学特征

Rock geochemical characteristics of the Neoproterozoic Wuyishan ophiolite mélange

岩石地球化学研究表明,华南造山带东段武夷山新元古代蛇绿混杂岩中的玄武岩和安山岩可以分为两种类型:一种为拉斑玄武岩类,TiO2含量为2.26%～2.59%(平均2.43%),轻稀土元素比重稀土元素富集,(La)N/(Yb)N=6.4～9.4(平均7.8),相对富集Nb、Ta和Ti,微量元素特征类似于洋岛玄武岩;另一种岩石属于钙碱系列,TiO2含量为0.69%～0.93%(平均0.83%),表现为轻稀土元素富集,(La)N/(Yb)N=4.2～12.6(平均8.4),略显Eu负异常,并以低Nb、Ta、Ti等元素为特征,富集Ba、Rb、Th、K等大离子亲石元素,具有岛弧玄武岩的特征,属于俯冲作用的产物。蛇绿混杂岩中这两类岩石共生,记录了扬子地块和华夏地块之间古大洋消减闭合和弧-弧碰撞拼贴的历史。

Abstract：According to a rock geochemical study, basalt and andesite in the Neoproterozoic Wuyishan ophiolite mélange in the South China orogenic belt may be divided into two types： one is tholeiite, which is characterized by TiO2=2.26%-2.59% （average 2.43）, LREE being richer than HREE, （La）N/（Yb）N=6.4-9.4 （average 7.8）, relative enrichment in Nb, Ta and Ti and the trace element characteristics being similar to those of OIB; and the other is of calc-alkaline type, which is characterized by TIO2=0.69%-0.93% （average 0.83%）, LREE enrichment, （La）N/（Yb）N= 4.2-12.6 （average 8.4）, weak negative Eu anomaly, lower Nb, Ta and Ti contents and enrichment in LILE such as Ba, Rb, Th and K, shows the characteristics of IAB and is the product of subduction. The two types of rock coexist in the ophiolite mélange and record the history of the subduction and closing of a paleo-ocean between the Yangtze block and Cathaysia block and arc-arc collision and amalgamation.