湖南若水地区钾镁煌斑岩

THE LAMPROITE IN RUOSHUi DISTRICT, HUNAN PROVINCE

我们首次在湖南发现了钾镁煌斑岩。这套岩石由于遭受强烈风化和蚀变,与典型的西澳钾镁煌斑岩相比,其K_2O和MgO含量明显偏低,Al_2O_3含量偏高。REE含量、金云母成分及以金云母作为主要载体的元素(如Rb、Ba、Ti、Sc、Zn、Ga和Nb等)都与西澳的钾镁煌斑岩基本一致,此外高度富集LREE和U,Th、Nb、Ta、Zr等不相容元素,并有高的δ^(18)O‰值,表明形成这套岩石的上地幔源区受到了软流圈的交代作用。

We first found the lamproite in Hunan Province. Its K_2O and MgO contents are obviously lower than those in lamproite from West Australia. The study of chemical compositions of the rocks, the geochemical nature of Rb and Ba, mineral chemistry and distribution of trace elements in the rock and its minerals show that lower K_2O and MgO and higher Al_2O_3 contents resulted from weathering, or that the magma which formed this lamproite had high Al_2O_3 content. Their REE content, compositions of phlogopite and its characteristic trace elements are consistent with those in West Australia. Moreover, the lamproite from Ruoshui district is greatly rich in LREE, U, Th, Nb,Ta,Zr and so on and has higher δ^(18) O‰ values. It indicares a metasomatic reaction having taken place in the upper mantle from which this rock was formed.