幔源岩浆岩源区成分判别原理及峨眉山玄武岩地幔源区性质

THE PRINCIPLES FOR DISCRIMINATION OF THE SOURCE COMPOSITION OF MANTLE-DERIVED IGNEOUS ROCKS AND THE NATURE OF THE MANTLE SOURCE REGION OF THE EMEISHAN BASALT

提出了用微量元素丰度关系探索幔源岩浆岩源区成分特征的原理、推论和方法。认为:并非所有亲岩浆(不相容)元素都是幔源成分的良好指示剂;两个强亲岩浆元素的比值,或两个亲岩浆性相同的元素的比值,不受岩浆形成方式和演化程度的影响,而保持岩浆形成前地幔源区成分特点;这些特点与不同的幔壳结构和动力学有关。峨眉山玄武岩系的幔源成分类似于南大西洋拉开时形成的孪生洋脊玄武岩和巴西陆缘玄武岩,它们可能具有类似的源区和构造环境。

This paper discusses the discrimination principles, deductions and methods for probing into the features of the source composition of mantle-derived magma. The magmatopile (incompatible) trace elements are not all optimal tracers for mantle source composition. The raios of two strong magmatopile elements (D<1) or the ratios of two trace elements with the same D value are not controlled by the formation model and evolution degree of a magma, but maintain the characteristics of their composition in mantle source region prior to the magma formation. The ratios are related to different mantle-crust structures and dynamics. The mantle source composition of the Emeishan basalt series is similar to that of the South Atlantic Rio Grande Rise-Walvis Ridge basahs and Brazil continental-margin basahs. This may indicate that those basalt series might have similar source regions and tectonic environments.