塔源地区吉祥沟岩组的地球化学特征及构造意义

Geochemical characteristics and tectonic significance behind Jixianggou rock formation in Tayuan area

为获得大兴安岭北部早古生代构造演化信息,利用研究区内1∶50000区域地质矿产调查成果,采用岩石学、岩石地球化学等方法,探讨吉祥沟岩组变沉积岩地球化学特征及源区构造背景。研究结果表明:变沉积岩中w(SiO_(2))为56.04%~77.78%、w(Al_(2)O_(3))为11.30%~21.80%,均高于上地壳丰度,Ba、Th、Co平均质量分数分别为678.0×10^(-6)、14.7×10^(-6)、11.6×10^(-6),与上地壳丰度一致;轻重稀土元素分异明显,轻稀土富集、重稀土亏损,δEu为0.43~0.89,具有明显的负异常;成分变异指数多大于1,化学蚀变指数为53.47~78.64,反映了源区物质成分为来源于上地壳的长英质火成岩及沉积岩,物源区处于寒冷—温暖、半干旱气候条件,具中—低风化程度;变沉积岩的地球化学特征显示岩石形成于活动大陆边缘—大陆岛弧环境。

This paper aims to obtain information about early Paleozoic tectonic evolution in northern Daxinganling.The study involves investigating the geochemistry characteristics and tectonic setting in the source region of meta-sedimentary rocks in Jixianggou rock formation using Petrology and geochemistry methods based on mineral resources survey within the study area 1∶50000 geological region.The study results show that in meta-sedimentary rocks,w(SiO_(2))is 56.04%-77.78%and w(Al_(2)O_(3))is 11.30%-21.80%,which are higher than the abundance of upper crust;the average mass fractions of Ba,Th and Co are 678.0×10^(-6),14.7×10^(-6) and 11.6×10^(-6),which are consistent with the abundance of the upper crust.The different distribution patterns exist with LREE enrichment,HREE deficiency,the obvious negative anomaly appears along withδEu 0.43-0.89;the indexs of compositional variation are more than 1 and the chemical index of alteration is 53.47-78.64,show that the material composition in the source area is felsic igneous rocks and sedimentary rocks from the upper crust,the source area located in cold,warm and semi-arid climate condition performs moderate and low weathering degree;and therefore,the meta-sedimentary rocks are formed in active continental margin and continental arc environment,which is the geochemical characteristics of meta-sedimentary rocks.