贺兰山群变质岩的地球化学特征

GEOCHEMICAL CHARACTERISTICS OF THE HELANSHAN GROUP METAMORPHIC ROCKS

贺兰山变质岩是一套晚太古宙的孔兹岩系，与典型的太古代沉积岩相比，这套变质岩的SiO2、K2O、P2O5、Rb、Zr、Hf、Nb，尤其是K、Rb偏高，而MgO、FeO、Ni、Cr、Cu、Co、V、Sc、Na、Ti、Sr等偏低。在稀土元素方面，有ΣREE高，轻、重稀土分异强，Eu负异常的显著特征。这些特征表明，华北地台西部在晚太古宙就已存在丰富的花岗质源区，比东部有更高的演化，可能是他台基底的陆核。

The Helanshan Group metamorphic rocks belong to the Late Archean khondalite series. In contrast with the same rock type of the Archean,these metamorphic rocks are high in SiO2,K2O,P2O,,Rb,Zr, Hf and Nb,especially in K2O and Rb and low in MgO,FeO,CaO,Na2O, TiO2, Ni,Cr,Cu,Co, V, Sc and Sr, especially in Ni,Cr,Cu, MgO and CaO. High ΣREE, high ΣLREE/ ΣHREE ratio and remarkable Eu negative anomaly show that the meta-pelites differ obviously in REE from common Archean pelites. The geochemical characteristics 1mply that the erosional area of the west ern part of the North China platform had heen of granitic crust during the Late Archean,and that the crust ln the weatern part had more highly evolved than in the eastern part at that time.