盈江县超上地区橄榄辉石岩脉地球化学特征、岩石成因及其构造环境

Geochemistry, Petrogenesis and Tectonic Setting of Olivine Pyroxenite Dyke in the Chaoshang Region, Yingjiang, Yunnan

盈江县超上地区橄榄辉石岩脉的全岩地球化学特征表明:岩脉具有高Al、低Ti、贫P2O5和低碱的特点,属于低钾拉斑系列。另外具有与橄榄岩平衡的原生岩浆相一致的Mg#值为(70.89~72.18)、略微的Eu正异常(δEu=1.16~1.40),轻稀土元素富集,重稀土元素相对平缓;微量元素蛛网图上岩脉富集大离子亲石元素U、Th、Pb等,强烈亏损高场强元素Nb、Ta、Hf、P、Ti等。通过综合分析,认为岩脉岩浆源区为被俯冲板片流体改造过的亏损地幔,由其形成的母岩浆在演化过程中遭受了不同程度的下地壳物质的同化混染作用和有限的结晶分异作用,并可能经历了辉石的堆晶作用。结合区域资料,认为盈江县超上橄榄辉石岩脉形成于岛弧环境,超上地区可能在侏罗纪时期经历了中特提斯洋的俯冲消减。

The whole-rock geochemistry of the olivine pyroxenite dyke in the Chaoshang Region, Yingjiang, Yunnan shows that the dyke is characterized by high Al, low Ti, poor P2O5 and low alkali, and belongs to low K tholeiite series. In addition, it is characterized by Mg # values consistent with peridotite equilibrium primary magma of 70.89~72.18, δEu values of 1.16~1.4, enrichment in LREE, enrichment in large-ion lithophile elements such as U, Th, Pb, strong depletion in high field strength elements such as Nb, Ta, Hf, P, Ti. These indicate that the primitive magma was derived from the depleted mantle reformed by subducting plate and suffered different degrees of assimilation and contamination of lower crust material and cumulation of pyroxene and limited crystallization differentiation. And this olivine pyroxenite dyke was emplaced in an island arc setting during the Jurassic.