长白山区图们江流域新生代火山岩的岩石化学研究

Petrochemistry of Cenozoic volcanic rocks in the Tureen river field,Changbai mountain region.

图们江流域新生代火山岩以溢流式喷发为特征,其主要岩石类型以拉斑玄武岩为主,含少量玄武质粗安岩、碱性玄武岩、玄武质安山岩和粗面玄武岩。根据图们江流域火山岩的Mg~#(Mg~#=100Mg^(2+)/(Mg^(2+)+Fe^(2+)))值多数≤60,Ni含量＜100μg/g和主、微量元素地球化学特征综合表明,形成火山岩的岩浆不是原始岩浆,它们是原始岩浆在上地幔经历了橄榄石、辉石分离结晶作用后形成的以拉斑玄武岩为主,包括碱性玄武岩和粗面玄武岩等演化岩浆,结晶分异作用是岩浆演化过程的主要控制因素。拉斑玄武质岩浆在上升过程中发生了不同程度的壳源物质同化混染作用,发生在上地壳遭受较大程度混染的岩浆K_2O含量明显偏高(＞2．6%),形成玄武质粗安岩。

The Cenozoic volcanic rocks in Tumen river field are located on eastern of Tianchi volcanic crater, Changbai Mountain area, in Jilin province, northeast of China. All of volcanic products are basaltic rocks, which erupted by flooding way. Main type of these basaltic rocks are tholeiite, included some differential rocks, such as basaltic trachy-andesite, alkaline basalt, basaltic andesite and trachy-basalt. According to the basaltic rocks have low Mg#（ most of them ≤60, Ni 〈 100μg/g）, with its major and minor elements data, we concluded that all the magmas which come into being volcanic rocks in Tumen river field are not parental magmas, but are derived magmas by way of olivine and pyroxene differentiation in the upper mantle. After different degree of differentiation, different types of derived magmas include tholeiitic basaltic magmas, alkaline basaltic magmas and trachy-basaltic magmas are formed. The differentiation is the most key action lead to come into being different types of volcanic rocks. Such as tholeiite, alkaline basalt and trachy-basalt. While the process of magmas ascending, different degree of contamination occur in different sites. The main spots of contamination are located in upper crust, the rocks which are situated in east of Tumen river field, relatively received much more degree of contamination than its western part, in this cause, the eastern parts of rocks have high K2O（ 〉 2. 6% ） and come into being basaltic trachy-andesite.