摘要
对位于华北克拉通北缘内蒙古赤峰北部解放营子地区的原志留纪八当山流纹质凝灰岩进行锆石LA-ICP-MS U-Pb定年,结果表明,其形成时代为403.7Ma±1.3Ma,属于早泥盆世。岩石化学分析揭示火山岩SiO2含量介于76.90%-78.74%之间,K2O和Na2O含量分别为1.68%-4.01%和2.23%-5.02%,属于亚碱性系列火山岩。岩石Al2O3含量较高,介于12.11%-12.86%之间,CaO含量偏低,为0.13%-0.74%,铝饱和指数(A/CNK)介于1.07-1.52之间,出现过铝质岩石的特征。Hf同位素分析结果表明,锆石εHf(t)均为负值,介于-22.0--16.4之间,两阶段模式年龄(TDM2)介于2423-2770Ma之间,表明该火山岩起源于华北克拉通古老地壳物质的部分熔融。结合区域地质资料分析,八当山火山岩的形成可能与白乃庙岛弧与华北克拉通北缘在早古生代末的碰撞作用有关。
Zircon LA-ICP-MS U-Pb dating of the Badangshan rhyolitic tuff from Jiefangyingzi area in northern Chifeng City of Inner Mongolia was carried out in this paper. The study area is located on the northern margin of the North China craton tectonically. The dating result reveals that the volcanic rocks were formed in early Devonian （403.7Ma±1.3Ma） rather than in Silurian as previously thought. The volcanic rocks are characterized by high SiO2 （76.90%-78.74%） and Al2O3 （12.11%-12.86%）, low CaO （0.13-0.74） and variable K20 （1.68%-4.01%） and Na20 （2.23%-5.02%）, with the aluminum saturation index （A/CNK） being 1.07-1.52. Chemically, they belong to calc-alkaline series and peralurrfinous volcanic rocks. Zircon εHf（t） values are negative （-22.0--16.4） and two stage model ages （TDM2） are from 2423Ma to 2770Ma, indicating that the volcanic rocks originated from partial melting of the ancient crustal materials of the North China craton. A synthetic study of the geochemical characteristics of the Badangshan volcanic rocks and the regional geological data reveals that the volcanic rocks were formed in the setting of late Early l^aleozoic collision between the Bainaimiao island arc and the northern margin of the North China craton.
出处
《地质通报》
CAS
CSCD
北大核心
2013年第2期267-278,共12页
Geological Bulletin of China
基金
中国地质调查局项目<兴蒙造山带基本构造格局综合调查和研究>(编号:1212011085476)
<中国主要陆块晚前寒武纪以来裂解重组过程的再造及其对成矿作用的制约>(编号:1212011121064)
国家自然科学基金项目<大兴安岭南段二叠纪火山岩形成的构造环境>(批准号:41102029)
关键词
华北克拉通北缘
八当山火山岩
泥盆纪
地球化学特征
锆石HF同位素
northern margin of North China craton
Badangshan volcanic rocks
Devonian
geochemical characteristics
zircon Hf isotope
