山西中条山地区北峪奥长花岗岩的同位素年龄和同位素地球化学特征

GEOCHRONOLOGY AND ISOTOPIC GEOCHEMISTRY OF BEIYU TRONDHJEMITES FROM ZHONGTIAO MOUNTAINS,SHANXI PROVINCE

追索北峪奥长花岗岩与围岩（早元古代绛县群变富钾流纹岩）接触关系，发现北峪奥长花岗岩已侵入于围岩地层中，表明其为早元古代岩浆型侵人体。使用全岩Ｒｂ－Ｓｒ等时线方法测定北峪奥长花岗岩时代，获得的年龄为２１０７±５９Ｍａ（２），由此推断北峪岩体成岩时代为２１００Ｍａ，代表了本区绛县运动岩浆深成事件年龄。其８７Ｓｒ／８６Ｓｒ初始比值为０．７０２３，呈现出幄源花岗岩的特点，但结合其铝过饱和特点以及具高的Ｏ全岩比例，推测其主要来源于下地壳麻粒岩相变质的沉积岩，但可能存在地幔物质添加或已遭受地幔交代作用的改造。

Beiyu trondhjemites is mainly composed of homogenous trondhjemites and tredhjemiticgneisses with a large amount of enclaves of fine-graind biotite leptites., biotite schistes, scapolite biotite schistes and metamorphic Potash(K) -rich rhyolites. According to the previously dominantopinions, Beiyu trondhjemites is referred to the migmatite of shushui Complex in Archean or themigmatite(or magma body) in Zhongtiao Movement.Beiyu trondhjemites have been intrused into the adjoining Proterozoic K-rich rhyolites ofJiangxian Group from the geological mapping, which give a relative younger age for the Beiyutrondhjemites. Selecting seven whole rock samples for the Rb-Sr isochron dating, the age of 2107±59 Ma(2) has been obtained, which should date the crystallization age of the trondhjemites.considering the geological setting of the Zhongtiao Mountains, Beiyu trondhjemites is a intrusivebody during the Jiangxian Movement.Beiyu trondhjemites with tow 87Sr/86Sr initial value may give an evidence that trondhjemitederived from mantle, but the characetr of low 87Sr/86Sr value also can due to the source rocksthat had been sufferred by the granulite factes metamorphism. This is conformed by the depletionof Rb, K, U, Th and low Rb/Sr ratioes. Combining the peraluminous S-type and high 18OwR(9.75-11.70‰), Beiyu trodhjemite favor an origin involving partial melting of metamorphicsedimentary protoliths.KeyWords: Beiyu Trondhjemites, Rb-Sr isochron, S-type granite, Jiangxian Movement,Proterozoic