大兴安岭北段漠河地区塔木兰沟组火山岩地球化学特征

Geochemistry of Tamulangou Formation Volcanic Rocks in Mohe,North Da Hinggan Mountains

大兴安岭北段漠河地区分布有大面积的晚中生代火山岩，塔木兰沟组是其中喷发较早的一期。塔木兰沟组是一套中基性火山岩。包括熔岩和火山碎屑岩，研究其成因对于理解大兴安岭北段的构造演化具有重要意义。对塔木兰沟组火山岩样品进行了系统的主量元素和微量元素地球化学分析。结果表明：样品大部分呈碱性，SiO。的质量分数为52.7％-57．8％。为中基性岩石，岩石类型为玄武质粗面安山岩和粗面安山岩；相容的过渡族金属元素如Cr、Co、Ni等含量低。微量元素比值如Nb／La、Ba／Nb、Nb/U、Ce／Pb等及稀土元素总量的变化范围大。具有右倾的轻稀土元素富集的稀土元素分布模式。岩石成因分析表明，富集的大陆岩石圈地幔先经历了部分熔融，然后熔浆受到了轻度的地壳物质的混染以及一定程度的分离结晶作用，最终形成了塔木兰沟组火山岩。

There are large areas of late Mesozoic volcanic rocks in Mohe, north Da Hinggan Mountains. Among these volcanic rocks, the Tamulangou Formation erupted earlier than other formations. The Tamulangou Formation is a set of basic to intermediate volcanic rocks, including lavas and pyroclastic rocks. The study of petrogenesis of the Tamulangou Formation may provide a very important insight for the tectonic evolution of north Da Hinggan Mountains. A systematic geochemical analysis of major and trace elements was carried out with samples from the Tamulangou Formation. It is shown that most samples are alkaline basic to intermediate rocks with SiO2 contents of 52.7%-57.8%. These rocks are basaltic trachy andesites and trachy andesites. Compatible transitional elements such as Cr, Co and Ni are low in contents. Trace element ratios such as Nb/La, Ba/Nb, Nb/U and Ce/Pb and the total rare earth elements contents of these samples vary in a large range, with a right-oblique rare earth element distribution mode. The petrogenesis study indicates that the partial melting of the enriched continental lithospheric mantle plus a slight crustal contamination and a certain degree of fractional crystallization are responsible for the formation of the Tamulangou Formation volcanic rocks.