摘要
内蒙古西北部的宝音图群由角闪岩相的变质地层组成。该群中斜长角闪片岩的Sm-Nd全岩等时线年龄为2485±128Ma,可代表宝音图群的形成年龄。等时线的ε_(Nd)(t)值为2.73±2.81,说明岩浆来源于亏损的地幔源区。相同样品的Rb-Sr全岩等时线年龄为623±36Ma,显然反映后期Rb-Sr体系重新均一化的强烈影响,因此该年龄被解释为变质年龄。上述结果表明宝音图群形成于古元古代早期,应属华北板块北缘已知的最古老岩石地层单位,并保留了新元古代末期构造—变质事件的记录。这些认识有助于查明华北板块北缘元古宙构造演化的历史。
The Baoyintu Group in the Wulatehouqi, northwestern Inner Mongolia consists of amphibo-lite-facies metamorphic rocks. It is divided into five members: (1) quartzites, mica quartz-schists, staurolite kyanite-schists intercalated with marbles and plagioclase amphibole-schists; (2) dolomitic marbles intercalated with quartzites and mica quartz-schists; (3) staurolite, garnet mica-schists, amphibole biotite-schists intercalated with plagioclase amphibole-schists, marbles and quartizites; (4) mica quartz-schists, marbles and leptynites;(5) interbedded quartizites and marbles intercalated with actinolite schists. Five whole-rock samples collected within the plagioclase amphibolite-schists from Member 1 were analyzed with the Sm-Nd and Rb-Sr analyses. The Sm- Nd whole rock analytical data for the five samples define an isochron of 2485 ±128 Ma, with δNd(t) = 2. 73 ±2. 81. The Sm-Nd data suggest that the Baoyintu Group should be the known oldest rock unit belonging to a Proterozoic active belt within the northern continental margin of the North China plate. The δNd(t) value reveals that there might be a depleted mantle source. An Rb-Sr whole-rock isochron age of 623±36 Ma is yielded from four of the five samples, which provides evidence for the metamorphic event which occurred during the end of the Neoprotero-zoic. The Isr value for the Rb-Sr isochron is 0. 7135 ± 0. 0001, which suggests that the metamorphic fluid was related to partial melting of the continental crust.
出处
《地质论评》
CAS
CSCD
北大核心
2000年第1期86-90,共5页
Geological Review
基金
教育部留学回国人员科研启动基金
博士点基金 (编号97000151)
