摘要
通过锆石定年和剖面研究,将大兴安岭西南段锡林浩特地区原上侏罗统满克头鄂博组火山岩重新厘定为下白垩统梅勒图组。火山岩分为上、下两段,下部主要为粗面安山岩及少量粗面岩;上部为粗面岩和流纹岩,上部粗面岩的锆石U-Pb年龄为118.1±1.3Ma,限定其形成时代为早白垩世晚期。该组火山岩富碱、富钾、铝含量高但变化范围大、Fe_2O3/FeO值高(>0.5),富轻稀土元素和大离子亲石元素(Rb、Ba、Th、Pb等),贫高场强元素(Nb、Ta、P等),在AFM图上表现出明显的贫铁演化趋势,在SiO_2-K_2O图上表现出倒钩型演化趋势,具有明显的钾玄岩特征。研究表明,研究区梅勒图组中酸性火山岩具同源岩浆演化的特征,岩浆源自交代的富集地幔,是伸展构造背景下的产物,与太平洋板块的俯冲后撤有关。
According to the research on zircon dating and cross section, the authors redefined Late Jurassic Manketou Formation as Early Cretaceous Meletu Formation in the southwestern segment of the Da Xinggan Mountains. Volcanic rocks are divided into two kinds of lithology, the lower segment is mainly trachy-andesite with minor trachyte, whereas the upper is trachyte and rhyolite. The zircon U-Pb age of trachyte is 118.1 ± 1.3Ma, suggesting that its formation age is Early Cretaceous. Rocks have rich alkali, rich potassium, and high aluminum whose value varies in a wide range, high Fe2O3/FeO ratios （〉0.5）, and relatively rich light rare earth elements and LILE （such as Rb, Ba, Th and Pb） but poor high field strength elements （such as Nb, Ta, and P）. Rocks have obvious iron-depletion evolution trend in the AFM diagram and＂Barbed＂evolution trend in the SiO 2-K2O diagram, with conspicuous characteristics of shoshonites. Studies show that the intermediate acidic volcanic rocks of the Meletu Formation in the study area have magmatic evolution characteristics of the same source region. Magma originated from enrichment of mantle metasomatism and was formed in a stretching tectonic background and related to the retreat of subduction of the Pacific Plate.
出处
《地质通报》
CAS
CSCD
北大核心
2016年第6期919-931,共13页
Geological Bulletin of China
基金
中国地质调查局项目(编号:12120114042801)
关键词
大兴安岭西南段
早白垩世晚期
梅勒图组
伸展环境
交代富集地幔
southwestern segment of the Da Hinggan Mountains
late Early Cretaceous
Meletu Formation
extensional environ-ment
metasomatic enriched mantle
