新疆托里蛇绿岩中两种不同玄武岩的地球化学特征及成因

托里蛇绿岩中分布着高Ti玄武岩与低Ti玄武岩,在地球化学特征上存在明显的差异;表明二者之间不存在过渡关系,有着不同的形成条件。它们分别代表岛弧拉张不同阶段之产物,本文讨论了玄武岩的地球化学特征,从而揭示了蛇绿岩形成于弧后盆地的微扩张环境。

GEOCHEMICAL CHARACTERISTICS AND ORIGIN OF TWO KINDS OF BASALTS IN THE TUOLI OPHIOLITE,XINJIANG

Basalts developed widely in the Tuoli ophiolite may be divided into high-Ti and low-Ti types according to the difference in their geochemi-cal characters. They occur in isolated flows or in association with ultramafin rocks to form ophiolitic melange.The high-Ti basalt, being calc-alkalic, is rich in large-ion elements and LREE, such as, Zr, Sr, Nb, P, TiO2 and K2O, etc, Whereas, the low-Ti basalt, being tholeiite, contents lesser large-ion elements and LREE. The geochemistry of basalts and petrochemical statistical analysis clealy denote that there seems to be no transition between the two types. The high-Ti basalt is similar to caic-alkalic basalt of island arc, formed in the early stage of back -are basin or rift and is probably the product of low partial melting of upple mantle. The low-Ti basalt is similar to ocean ridge basalt, formed in the advanced rift stage of back-are basin and is the product of high partial melting of upple mantle.The geochemical characteristics at basalts indicate that the Tuoli ophio-iite was formed under micro-rift environment in back-arc basin.