中条山北峪奥长花岗岩地质学及其地质年代学

Geology and geochronology of the Beiyu trondhjemitic granite in Zhongtiaoshan

北峪奥长花岗岩 (体 )位于中条裂谷的西部 ,和霏细斑岩及辉长岩组成侵入杂岩体 ,呈南北向展布。区内中条群因受多期挤压作用 ,构成剥离断层和叠加褶皱的干扰图形 ,貌似“短轴背斜”的构造背景。北峪奥长花岗岩与相邻的铜矿峪变花岗斑岩均为S型花岗岩 ,属裂谷早期拉张阶段产物 ,但岩性并不雷同。从岩石学、地球化学分析 ,北峪奥长花岗岩的源岩为下地壳麻粒岩相沉积物经分熔作用的结果 ,形成于大陆环境。据同位素数据分析 ,侵入杂岩体的辉长岩和靡细斑岩应在 2 70 0Ma左右 ;北峪奥长花岗岩是在 2 30 0Ma以前侵位 ,略早于铜矿峪变花岗斑岩。

The Beiyu trondhjemite,together with felsite porphyry and gabbro,forms an intrusive complex extending S-N in the western part of the Zhongtiao rift.The metamorphic rocks surrounding the complex exhibit a dome-like structure interfered by detachment faults and subordinate folds.Both the Beiyu trondhjemite and the adjacent Tongkuangyu meta-granite porphyry belong to the S-type and were formed during the early extensional phase of the Zhongtiao rift,but they are different not only in lithology but also in petrogenesis.Based on petrological and geochemical data,the Beiyu trondhjemitec granite was produced by partial melting of the sediments that had undergone granulite-facies metamorphism in the lower crust in a continental environment.Isotope dating indicates that the intrusive complex was emplaced some 2 700 Ma ago while the Beiyu granite is most likely to have been emplaced about 2 300 Ma and is thus a little earlier than the Tongkuangyu granite porphyry.