中祁连东段湟源群的年代学新证据及其地质意义

New chronological evidence of the age of Huangyuan Group in the eastern segment of Mid-Qilian massif and its geological significance

根据新近获得的中祁连地块东段湟源群中变质火山岩(910±6.7)Ma和侵位于湟源群中的响河尔花岗岩(917±12)Ma的单颗粒锆石UPb年龄,结合区域地质背景分析认为:(1)湟源群时代不是古元古代,而是中晚元古代,上限在900Ma左右;(2)响河尔花岗岩是晋宁期花岗岩而非中条期花岗岩;(3)湟源群及侵位于其中的晋宁期花岗岩代表了中祁连晋宁旋回结晶基底,并非中条旋回结晶基底。湟源群时代的重新厘定使得已经建立的中祁连地块东段前寒武纪地层格架和中祁连地块性质。

Recently, the U Pb isotope dating of single grain zircon from metavolcanic rock of Huangyuan Group yields an age of (910±6.7)Ma,and that from Xiangheer granite,which intrude into Huangyuan Group,yields an age of (917±12) Ma.In conbination with regional geological setting, it was considered that: (1) Huangyuan Group was formed not in Lower Proterozoic Subera, but in Middle Upper Proterozoic Subera, with upper age limit of about 900Ma; (2) Xiangheer granite was formed in Jinningian, rather than in Zhongtiaoian; and (3)both Huangyuan Group and the Jinningian granites which intrude into the former represent the crystalline basement of Jinningian cycle, not that of Zhongtiao cycle. The correction of the age of Huangyuan Group makes it necessary to further reexamine and study the previously established stratigraphic framework in east segment of Mid Qilian massif and its relationship with North China Plate and Yangtze Plate.