摘要
白银都西群主要由斜长角闪岩、变粒岩、长英片岩和条带状混合岩组成,是白银都西-白乃庙地体的重要组成部分,主要分布在内蒙古白乃庙铜(金)矿床东北白银都西一带。长期以来,由于缺乏可信的同位素年龄数据,该套岩层的归属,构造性质和形成机理尚不清楚。笔者首次对白银都西群斜长角闪岩的Nd和Sr同位素组成进行了测定,所获Sm-Nd同位素等时年龄为1394±46Ma(23),Nd初始比值为0.511 243±8(23)和εNd(T)=+7.9±2.1(23)。^(87)Sr/^(86)Sr和^(87)Rb/^(86)Sr比值分别为0.705 79—0.709 12和0.17—0.34,两者之间不存在任何相关关系。结合野外地质证据和岩相学特征,我们认为:白银都西群基性火山活动发生在中元古代,成岩物质来自亏损地幔源,成岩以后构造变动和变质热液活动致使Rb-Sr同位素体系受到严重干扰破坏。
Sm-Nd and Rb-Sr isotope data for amphibolite of the Bayanduxi Group, Inner Mongolia, China, are presented in the paper. Five whole-rock samples of the amphibolite, which intruded into metasediments, give a Sm-Nd isochron age of 1394±46 Ma(2σ) and εNd(T) value of ε7.9±2.1(2σ). This age may represent the time of intrusion of mafic magma, which was derived from a depleted mantle. Therefore, the Baiyinduxi Group has been existing since 1 400 Ma ago. No correlation exists between 87Rb/86Sr and 87Sr/86Sr ratios of the amphibolite. This may indicate that the Rb-Sr isdtope system was strongly disturbed. This is consistent with field and petrographic evidence that the amphibolite has undergone meta-morphism and tectonism to some extent.
出处
《地质论评》
CAS
CSCD
北大核心
1994年第5期476-481,共6页
Geological Review
基金
国家青年自然科学基金 (编号49000040)
内蒙古地质矿产局联合资助项目
关键词
火山岩
钕
锶
同位素
变质火山岩
Nd and Sr isotope study, metavolcanic rock, Bayanduxi Group
