大兴安岭北段八大关地区早侏罗世流纹岩锆石U-Pb定年与岩石成因

发布时间：2018-03-14 05:49

本文选题：早侏罗世　切入点：流纹岩　出处：《中国地质》2017年02期 　论文类型：期刊论文

【摘要】：大兴安岭北段八大关地区首次发现早侏罗世火山岩,该类岩石主要由流纹岩组成,含少量英安岩和流纹质凝灰岩,LA-ICPMS锆石U-Pb定年结果显示其形成于185~190 Ma,岩石地球化学研究表明,流纹岩具有高硅富碱,贫镁钙和高FeO~T/MgO比值的特征,属于高钾钙碱性系列;稀土总量不高(ΣREE=103.80×10~(-6)~194.31×10~(-6)),轻重稀土分馏较明显((La/Yb)N=7.12~10.22),中等负Eu异常(δEu=0.34~0.74),微量元素以富集Rb、Ba、Th、U、K和LREE,强烈亏损Sr、P、Ti,相对亏损Nb、Ta为特征,显示地壳来源,结合较低的Ga/Al比值,该区流纹岩具有I型花岗岩特点,在(Y+Nb)-Rb和(Yb+Ta)-Rb判别图解上显示其形成于活动大陆边缘环境。综合研究表明,八大关地区早侏罗世之前为活动陆缘环境,蒙古—鄂霍茨克大洋板块向额尔古纳地块之下俯冲。
[Abstract]:The early Jurassic volcanic rocks were first found in Badaguan area of northern Daxinganling Mountains. These rocks are mainly composed of rhyolite, and contain a small amount of dolomite and fluvial tuff. The results of U-Pb dating of zircon from LA-ICPMS indicate that they were formed at 1859 ~ 190 Ma. Rhyolite is characterized by high silicon and alkali, poor magnesium and calcium and high FeO~T/MgO ratio, which belongs to high potassium calc-alkaline series. The total amount of rare earth elements is not high (危 REE=103.80 脳 10 ~ (10) ~ (1)) ~ (6) ~ 1 脳 10 ~ (-1) ~ (10) ~ (6) C ~ (-1), the fractionation of light and light rare earths is more obvious than that of Lap / Yb ~ (1) N ~ (7.12) ~ (10) ~ (22) N ~ (2 +), medium negative EU anomalies (未 EU ~ (0.34) ~ (0.34) ~ (0.74)), trace elements are enriched in RbBX, BaThUK and LREE, strongly depleted SrP#en0#, relatively depleted NB ~ (+) Ta, indicating crustal origin, combined with low Ga/Al ratio. The rhyolite in this area is characterized by I-type granite, which was formed in the active continental margin environment on the discriminant diagrams of Y Nb)-Rb and Yb Ta)-Rb. A comprehensive study shows that the Badaguan area was an active continental margin environment prior to the early Jurassic. The Mongolian-Okhotsk oceanic plate subducts under the Erguna block.
【作者单位】：吉林大学地球科学学院;核工业二四0研究所;
【基金】：国家自然科学基金(41472051) 中国地质调查局地质调查项目(12120113053700)资助~~
【分类号】：P588.141;P597.3

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