兴蒙造山带南缘早古生代增生造山带内前寒武纪地层的识别及其地质意义  

Identification of Precambrian Strata in Early Paleozoic Accretion Zone on Southern Margin of Xing-Meng Orogenic Belt and Its geological Significance

作　　者：杨泽黎 胡晓佳 王树庆 王文龙 赵利刚 段霄龙 田健 程银行 Yang Zeli;Hu Xiaojia;Wang Shuqin;Wang Wenlong;Zhao Ligang;Duan Xiaolong;Tian Jian;Cheng Yinhang(Tianjin Center of China Geological Survey,Tianjin 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170

出　　处：《地球科学》2021年第8期2786-2803,共18页Earth Science

基　　金：中国地质调查局项目(No.DD20190038);国家自然科学基金项目(No.41872068)。

摘　　要：兴蒙造山带南缘早古生代增生造山带内是否存在陆壳一直缺少直接证据,制约了对增生带结构及演化的认识.在达茂旗东北部兴蒙造山带南缘增生带内识别出一套原地的变质地层,野外观察及锆石U-Pb年代学、Hf同位素地球化学研究表明,该套地层形成时代为中元古代晚期,可能代表了增生造山带内的古老地壳.地层的碎屑锆石峰值年龄集中于~1.8 Ga,并具有~3.0 Ga、~2.8 Ga、~2.5 Ga、~1.6 Ga等次级峰值,与华北北缘白云鄂博、化德、狼山群等地层碎屑锆石年龄组成一致;表明其应为华北陆块的一部分,物源则主要来自于华北克拉通内部不同时代地质体的剥蚀.该套地层的识别及其与华北陆块的亲缘性表明,早古生代兴蒙造山带南缘增生带内存在陆壳,构造环境上应为古亚洲洋向华北克拉通俯冲形成的活动陆缘;同时,其与车根达来构造带的关系显示后者并非蛇绿岩,更可能为弧后伸展引起的超基性岩对陆壳的侵入形成.There has been a lack of direct evidence for the existence of continental crust in the Early Paleozoic accretion zone on the southern margin of Xing-Meng Orogenic Belt(XMOB), which restricts the understanding on the structure and evolution of the orogen. This study identified Late Mesoproterozoic metamorphic strata in the Chegendalai area, Northeast Damaoqi, which belongs to the southern margin of XMOB. Field investigation, zircon geochronology and Hf isotopic geochemistry indicate that this set of strata represents the continental crust in the accretion zone. The detrital zircon ages of the strata are mainly concentrated at ~1.8 Ga, and with minor peaks such as ~3.0 Ga, ~2.8 Ga, ~2.5 Ga, and ~1.6 Ga. This age distribution is consistent with the Bayan Obo Group, Huade Group and Langshan Group in the north margin of North China, implying the continental crust in accretion zone should be part of the North China Block, and its material provenance is also mainly from the northern margin of North China Craton. The identification of the Mesoproterozoic strata and its affinity with North China Block indicate that the southern margin of XMOB belongs to active continental margin in Early Paleozoic. In addition, the relationship between the strata and Chegendalai tectonic belts shows that the latter is not an ophiolite, but is more likely to be generated by the intrusion of ultrabasic rocks resulted from back-arc extension.

关 键 词：早古生代 兴蒙造山带南缘 前寒武纪地层 碎屑锆石 华北克拉通 地质年代学 

分 类 号：P588.21[天文地球—岩石学]