西准噶尔科克萨依OIB型玄武岩地球化学特征及意义

摘要

The Ophiolite of Kekesayi district in western Jungger of XinJiang,is a melange belt formed of serpentinite, pillow basalt,andesite-basaltic tuff lava,gabbro(diabase dyke) and siliceous rock.We have done a detailed geochemical study on the pillow basalt from the association. It turned out that the basalt is characterised by the low magnesium(Mg#=0.27~0.33)and high titanium(1.31%~2.43%);the REE pattern shows the enrichment of LREE(La/Yb)N=9.22~13.01 and unobvious Eu anomaly(δEu=0.95~1.15);Rb and Sr show a little negative anomaly.Comparing to the oceanic island basalt,the high field-strength elements(Nb,Ta,Zr,Hf,Ti,P) show unobvious anomaly.The trace elements and REE distribu-tion patterns are similar to those of the oceanic island basalt(OIB),which indicates they have the characteristics of the typical oceanic island basalt.The comprehensive study suggests that the basalt in the Kekesayi is formed in the oceanic island(seamount) environment within the oceanic plate.This provides a new basis for the hot point activity in oceanic plate of western junggar kekesayi region.%新疆西准噶尔地区的科克萨依蛇绿岩带，为一套由蛇纹岩、枕状玄武岩及安山玄武质凝灰熔岩、辉长岩（辉绿岩墙）、硅质岩构成的混杂岩带。选择组合中的枕状玄武岩进行地球化学研究，结果表明，玄武岩以低镁（Mg#=0.27~0.33）、高钛（1.31%~2.43%）为特征；稀土分布有 LREE 富集（La/Yb）N=9.22~13.01，无明显 Eu 异常（δEu=0.95~1.15）；Rb，Sr略显负异常，高场强元素（Nb，Ta，Zr，Hf，Ti，P）相对OIB型玄武岩无明显异常。稀土元素及微量元素分布模式与洋岛玄武岩基本一致，具典型洋岛（海山）型玄武岩特征。综合研究认为，科克萨依玄武岩形成于大洋板内洋岛（海山）环境。