摘要
准噶尔盆地基底火山岩主要岩石类型为玄武岩和安山岩 ,并有部分英安岩和流纹岩。火山岩的微量元素地幔标准化模式显示LREE弱富集 ,(La/Yb) N 变化于 1.9～ 5 .2 3之间 ,高场强元素Nb、Ta相对于大离子亲石元素的亏损较明显 ,具俯冲带火山岩的典型特征。Nd -Sr同位素分析表明 ,3个火山岩区的火山岩 εNd(0 )均为正值 ,(87Sr/ 86 Sr) i 较低 ,说明它们主要来源于亏损地幔。Sm -Nd同位素单阶段模式年龄集中在 4 0 0～ 70 0Ma之间 ,反映俯冲沉积物的形成时代不早于 70 0Ma。玄武质火山岩微量元素和同位素研究表明 3个火山岩岩区应分属不同的岛弧增生体系 ,原始地幔物质通过岛弧火山作用加入到地壳中 ,推测准噶尔盆地的基底由分属于周边的哈萨克斯坦、塔里木和西伯利亚板块的年轻岛弧增生地体拼合而成 ,前寒武纪地壳演化历史并不明显。
The volcanic rocks in Junggar Basin are mainly basaltic and andesitic rocks, and subordinately dacite and rhyolite. Most of the rocks exhibit slight enrichment of LREE and somewhat low HFSE abundances relative to the LIFE. Such features are commonly regarded as characteristics of subduction_related magmatism. The rocks in the three regions have positive εNd(0) and relatively low ( 87 Sr/ 86 Sr) i, suggesting that the basement volcanic rocks were generated in the depleted mantle wedge that had been enriched in incompatible elements by subduction without old continental contamination. In addition, Nd single_stage model ages vary from 400 Ma to 700 Ma. The single_stage model age indicates that the subducted sedimentary rocks are younger than 700 Ma. The isotopic and trace element geochemical characteristics of basaltic volcanic rocks imply that these regions should belong to different arc accretionary systems. On such a basis, it can be inferred that the basement volcanics formed in the environment of arc accretion and the juvenile materials added to the crust through the arc volcanism, which constituted the most important mechanism at that time, and that the basement of Junggar Basin was presumably assembled by the three different arc accretion terrains which belonged to Middle Asian Kazakstan, Tarim, and Siberia Plate respectively.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2002年第1期1-10,共10页
Acta Petrologica et Mineralogica
基金
新疆石油管理局基础研究项目(4 9873 0 0 9)
