摘要
18个乌拉山群片麻岩和麻粒岩样品的REE含量分析显示,乌拉山群岩石形成于古大陆边缘岛弧环境。碎屑沉积岩和火山碎屑沉积岩的沉积物来自邻近的火山岛弧。其中,138号标本(石英二长片麻岩)的ΣREE=62.3ppm,(La/Yb)_N=87.5,δEu=3.26,代表了太古代高级区的特征岩类。麻粒岩的ΣREE较低,显示在麻粒岩相变质过程中有REE的亏损。
The high-grade metamorphic rocks of Archean Wulashan group outcrops east-wes-ternly in Mt. Daqingshan area, Inner Mongolia and comprises the Archean granulite belt in Mt. Daqingshan which is the west section of the Archean granulite facies metamorphic belt of North China craton. Wulashan group includes such rock types as magnetite-pyroxene granulite, pyroxene-biotite-hornblende-plagioclase granulite, ortho and clino-pyroxene-K-feldspar-plagioclase granulite, garnet-biotite-plagioclase gneiss, felsic gneiss, hornblende-plagioclase gneiss, pyroxene-hornblende-(garnet)-biotite gneiss, hornblendite and marbles. Granulites are mainly located at the lower part of Wulashan group sequences at the south side of Mt. Daqingshan. 18 samples of Wulashan group rocks have been analysed for REE geochemistry. The results show that original protolith types of Wulashan group metamorphic rocks are detrital sedimentary rocks, volcanic detrital sediments and basalts, those were formed in volcanic island arc environment at active continental margin. The detrital sedimentary materials came mainly from the volcanic island arc nearby. REE geochemical characters of some Wulashan group rocks are similar with that of tholeiitic basalts, while others are similar to those of alkali basalts. This might indicate that the petrogenetic environment of Wulashan group rocks is like one kind of active-continental margin and the thickness of Archean crustal is thick enough at that time. Sample No. 138, quartz-plagioclase-K-feldspar-gneiss, shows special characters of REE geochemistry, 2 REE = 62.3ppm, (La/Yb)N = 87.5, <5Eu = 3.26. This sample may represent one kind of typical rocks of Archean high-grade metamorphic terrane. The 2 REE of granulites of Wulashan group are very low. Two granulites samples' 2REE are 48.5 ppm and 44.9 ppm respectively, which means that granulite facies metamorphism of Wulashan group caused obvious migration of rare earth elements totally while the basic relationship of REE in original rocks did not change as a whole.
出处
《北京大学学报（自然科学版）》
CAS
CSCD
北大核心
1991年第2期210-219,共10页
Acta Scientiarum Naturalium Universitatis Pekinensis
基金
国家自然科学基金
关键词
稀土
地球化学
成岩环境
太古代
REE geochemiaty
Petrogenetic environment
Archean
Granulite
Wulashan group
