大兴安岭绿林林场一带兴华渡口岩群原岩恢复及大地构造环境探讨

PROTOLITH RECONSTRUCTION AND GEOTECTONIC ENVIRONMENTAL RESEARCH OF XINGHUADUKOU ROCK GROUP IN LVLIN FORESTRY CENTER,DAXING'ANLING

兴华渡口岩群作为额尔古纳地块的基底,其变质年龄、原岩类型及大地构造背景一直是地质学家关注的热点。以大兴安岭北段绿林林场一带兴华渡口岩群作为研究对象,利用锆石U-Pb同位素测年限定了原岩的变质时代,结合岩相学与地球化学综合分析方法开展原岩恢复,并进一步讨论了其形成的大地构造背景。研究认为兴华渡口岩群主要由斜长角闪岩类、浅粒岩类、变粒岩类和石英岩类组成;斜长角闪岩类原岩为基性火山岩,浅粒岩类原岩为英安质凝灰岩,石英岩和变粒岩原岩为泥质粉砂岩;斜长角闪岩类亏损非活动性微量元素Ta、Nd、P,大地构造环境属岛弧环境;浅粒岩类主要亏损Ta、Nd、P、Sr、Ti等元素,形成于大陆边缘造山带环境。绿林林场一带兴华渡口岩群的变质年龄下限为774.1±3.8 Ma。

Xinghuadukou Rock Group, as the basement of Ergun massif, its metamorphic age, protolith types and geotectonic setting has always been a hot spot for geologists. With Xinghuadukou Rock Group in lvlin forestry center, north part of Daxing′anling, as the research object, zircons U-Pb isotopic dating was used to define the metamorphic age of protolith. Protolith reconstruction was carried out combining with the comprehensive analysis methods of petrography and geochemistry, and its geotectonic setting was further discussed. The resarch suggests that Xinghuadukou Rock Group is mainly composed of amphibolite, leptite, granulite and quartzite. The protolith of these four kinds respectively are basic volcanic rock, dacite tuff, pelitic siltstone and pelitic siltstone. Amphibolite is lack of non-active trace elements Ta、Nd、P, and it belongs to the island-arc geotectonic environment. Leptite mainly lacks Ta、Nd、P、Sr、Ti and other elements, and it is formed in the orogenic belt environment of continental margin. The lower limit of metamorphic age of Xinghuadukou Rock Group in Lvlin forestry center is 774.1±3.8 Ma.