• 责任者：Li Shichao (College of Earth Sciences ; Jilin University ; Changchun 130061 ; China) ; Xu Zhongyuan
• 刊名：Geological Bulletin of China
• 出版年：2013
• 卷期：32(2/3)
• 关键词：火山岩 ; volcanic rocks ; 铀—铅计时 ; U-Pb dating ; 大兴安岭 ; Greater Hinggan Mountains
• 页码：p.399-407
• 图表：illus., 3 tables, 27 refs.
• 分类号：0801
• issnNo：ISSN1671-2552
• isbnNo：CN11-4648/P

In this study, LA-ICP-MS zircon U-Pb dating results and geochemical data were obtained from the volcanic rocks in Manitu Formation of Chaihe area lying in southwest Zhalantun City of central Da Hinggan Mountains. Zircon U-Pb dating results show that they were formed in early Cretaceous（135Ma）. The volcanic rocks belonging chemically to the shoshonite series have SiO2 59.5%--70.8% and are enriched in alkali and potassium, with Rittman index from 3.2 to 4.7（σ=3.2-4.7）. In addition, they are characterized by low total rare earth elements （∑REE=112×10^-6-172×10^-6）, significant fractionations of REE（La/Yb）N=6.5-9.2）, moderate negative Eu anomalies （BEu=0.54-0.77）, enrichment of large ion lithophile elements （LILEs, such as Ba and K） and light rare earth elements （LREEs） and depletion of high field strength elements （HFSEs, such as Nb, Ti and P）. The values of such iron family elements as Cr, Co and Ni are all low （Cr=6.55×10^-6, Cr=6.97×10^-6, Ni=4.35×10^-6 on average）. Recent researches show that the volcanic rocks might have been formed in an extensional setting after the closure of the Mongol-Okhotsk Ocean. Considering the regional resources, the authors have reached the conclusion that the volcanic rocks in Manim Formation of central Da Hinggan Mountains region were formed in two structural environments. Total REE amounts are relatively low（ ∑REE = 112 × 10^-6-172× 10^-6, fractionation between LREE and HREE （La/Yb）N=6.5-9.2） is obvious, and there exist moderate negative Eu anomalies （δEu=0.54-0.77）. They are enriched in high LILE （e.g., Ba, K） and LREE, and depleted in HFSE （e.g., Nb, Ti, P） and iron family elements such as Cr, Co and Ni（Cr=6.55×10^-6, Cr=6.97×10^-6, Ni=4.35×10^-6 on average）. The research above shows that the tectonic background of Manitu Formation volcanics in the study area are formed on the lithospheric extensional structure after the closure orogeny of Mongolia-Ehucike, which is similar to the north section of the Great Xing＇an Ramge but different from the south section generated in the compression and uplifr.