阜平群下部太古代变质岩石的REE、Rb-Sr和Sm-Nd年龄及其意义  

ARCHAEAN METAMORPHIC ROCKS FROM THE LOWER FUPING GROUP IN THE MT. TAIHANG REGION, NORTH CHINA: REE GEOCHEMISTRY, Rb-Sr AND Sm-Nd AGES AND IMPLICATIONS

作　　者：张宗清[1] 伍家善[1] 叶笑江 

机构地区：[1]地质矿产部地质研究所,北京100037

出　　处：《地球化学》1991年第2期118-127,共10页Geochimica

摘　　要：对采自阜平群下部16个变质岩石样品进行了Sm-Nd年龄测定,部分样品还进行了Rb-Sr年龄测定和REE分析。Sm-Nd同位素结果形成两条等时线。一条等时线具有年龄为:2790±171(2σ)Ma,I_(Nd)=0.50917±16(2σ),ε_(Nd)(t)=±1.6;另一条等时线,t=1949±84(2σ)Ma,I_(Nd)=0.50986±5(2σ),ε_(Nd)(t)=-5.0±1.0。Rb-Sr同位素数据分散,参考等时线年龄为2070Ma。The Fuping Group, being situated in the Mt. Taihang region between Hebei and Shanxi provinces, consists mostly of granulites, gneisses and some marbles, with a total thickness exceeding 10000m. It is an important part of the North China basement block and also one of the most typical terrains for the Archaean study in China.16 samples of granulite and gneiss from the lower Fuping Group were dated by the Sm-Nd and Rb-Sr methods. The REE of some samples were analyzed. Two isochrons were obtained on the basis of the Sm-Nd data. The first one involving 13 samples gives an age of 2790±17l(2σ) Ma, with INd = 0.50917±16(2σ) and εNd (t) = 2.9± 1.6. This age is in good agreement with a zircon U-Pb discordia age of 2800-150 +230 Ma reported by Liu et al. (1984). The model ages tDM for all the samples are within the range of 2.66-2.92Ga except for 4 samples with tDM = 3.00 Ga. The REE and isotope data show that metamorphic rocks of the lower Fuping Group were derived from partial melting of the depleted upper mantle and remelting of basic rocks, and then emplaced at about 2790Ma. The other involving 3 acid gneiss samples gives an isochron age of 1949 ± 84(2σ)Ma, with INd = 0.50986±5(2σ) and εNd(t) = -5.0±1.0. This age is in good agreement with the reported K-Ar, 39Ar-40Ar and some zircon U-Pb discordia ages (1800-2000Ma), and also with the reference isochron age 2070Ma calculated from the whole-rock Rb-Sr data in this paper. This indicates clearly that the rocks of the Fuping Group underwent an intensive metamorphism and local remelting at about 1949 Ma corresponding to the Luliang movement in China.The εNd and ages of Archaean metamorphic rocks from the different parts of the North China Archaean basement block reported in recent years imply a high depletion of LIL and LREE in the Archaean upper mantle in North China.

关 键 词：阜平群 地球化学 变质岩石 RB-SR 

分 类 号：P588.3[天文地球—岩石学]