中祁连西段前寒武纪地层时代新认识:肃北地区石板墩铁矿的碎屑锆石U-Pb年代学  

NEW INSIGHTS INTO THE PRECAMBRIAN STRATA IN THE WESTERN CENTRAL QILIAN BLOCK: DETRITAL ZIRCON U-PB GEOCHRONOLOGY OF THE SHIBANDUN IRON MINE, SUBEI AREA

作　　者：孙郎 杨传 孙智新 孙玮辰 苗兰云 潘兵 陈波[1,2] 殷宗军 赵方臣[1,2,3] 李国祥[1,2] 朱茂炎 SUN Lang;YANG Chuan;SUN Zhi Xin;SUN Wei Chen;MIAO Lan Yun;PAN Bing;CHEN Bo;YIN Zong Jun;ZHAO Fang Chen;LI Guo Xiang;ZHU Mao Yan(State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academyof Sciences,Nanjing210008;Center for Excellence in Life and Paleoenvironment,Chinese Academy of Sciences,Nanjing 210008;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049;University of Science and Technology of China,Hefei 230026)

机构地区：[1]中国科学院南京地质古生物研究所,现代古生物学和地层学国家重点实验室,江苏南京210008 [2]中国科学院生物演化与环境卓越创新中心,江苏南京210008 [3]中国科学院大学地球与行星科学院,北京100049 [4]中国科学技术大学,安徽合肥230026

出　　处：《地层学杂志》2022年第3期215-229,共15页Journal of Stratigraphy

基　　金：第二次青藏科考研究国家专项(2019QZKK0706);中国科学院战略性先导科技专项(XDB26000000);国家自然科学基金(41921002)共同资助。

摘　　要：祁连造山带内发育有多套富铁沉积地层和具有经济开采价值的铁矿,包括肃南著名的镜铁山铁矿和肃北石板墩铁矿。其中,石板墩铁矿发育于中祁连地块西段龚岔群哈什哈尔组中,哈什哈尔组的时代一直被认为是新元古代青白口纪,但是缺少可靠的年代地层学和同位素年代学证据支撑,阻碍了祁连造山带内铁矿时代的对比和对成矿机制的认识。本文首次在哈什哈尔组下部碎屑岩中获得569±2 Ma的最大沉积年龄,表明含石板墩铁矿的哈什哈尔组的形成时代晚于569±2 Ma,可能属于新元古代晚期埃迪卡拉纪地层。同时,新的年代学证据还表明,该地区龚岔群之上多若诺尔群中可能的冰碛杂砾岩地层与中祁连地块邻区埃迪卡拉纪末期普遍发育的冰川沉积地层相当。本文首次明确了中祁连地块内埃迪卡拉纪地层的存在,表明中祁连西段前寒武纪地层时代需要重新系统修订,从而为认识该地区的构造演化史提供年代地层框架。There are several suites of the iron-rich strata and iron deposits of economic importance developed in the Qilian Orogen, including the Jingtieshan iron mine in Sunan County and the Shibandun iron mine in Subei County. The Shibandun iron mine developed in the Hashhar Formation, Gongcha Group in western Central Qilian Block, and its age was considered as the Qingbaikouian(Tonian) Period although without reliable chronostratigraphic and isotope geochronological evidence. The unreliability of the ages hinders the stratigraphic correlation of the iron deposits in the Qilian Orogen and the understanding of the metallogenic mechanism. In this paper, the maximum depositional age of 569± 2 Ma was obtained from the clastic rock in the lower part of the Hashhar Formation for the first time, indicating that the depositional age of the Hashhar Formation is younger than 569 ± 2 Ma, being late Ediacaran in age. Meanwhile, the new geochronological evidence also indicates that the strata with occurrence of diamictite, which may be tillite, in the Doronor Group, lying above the Gongcha Group, could be correlated with the late Ediacaran tillites developed widely in other regions adjacent to the Central Qilian Block. The new geochronological evidence in this paper confirms the existence of Ediacaran strata in the Central Qilian Block for the first time, and indicates that the ages of the Precambrian strata in the western Central Qilian Block need to be systematically revised in order to provide a chronostratigraphic basis for the understanding of the tectonic evolution history of the Qilian Orogen.

关 键 词：祁连造山带 石板墩铁矿 龚岔群 哈什哈尔组 碎屑锆石 U-PB年代学 

分 类 号：P534.1[天文地球—古生物学与地层学]