Paleozoic sedimentary record of the Xing-Meng Orogenic Belt, Inner Mongolia: Implications for the provenances and tectonic evolution of the Central Asian Orogenic Belt  

作　　者：LI DaPeng CHEN YueLong WANG Zhong LIN Yu ZHOU Jian 

机构地区：[1]School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China [2]State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan 430000,China [3]Geological Survey Institute of Inner Mongolia,Hohhot 010000,China [4]Institute of Geophysical and Geochemical Exploration,Langfang 102849,China

出　　处：《Chinese Science Bulletin》2012年第7期776-785,共10页

基　　金：supported by the National Natural Science Foundation of China (40973010);the Fundamental Research Funds for the Central Universities (2011YYL012);the Department of Land and Resources, Inner Mongolia Autonomous Region (05-6-YS2)

摘　　要：The Xing-Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt, which marks the boundary between the North China and Siberian blocks. Key information on the collision between these two blocks and the evolution of this orogenic belt at the end of the Paleozoic are preserved in the widely distributed Paleozoic sedimentary sequences. Petrographic studies of the clastic sedimentary rocks from the Ordovician to the Permian in this region have shown that the rocks are mainly greywackes and arkosic sandstones characterized by low maturity, poor sorting and a large number of lithic fragments. Provenances of Paleozoic sandstones are mainly newly accreted crustal materials. Nd model ages range from the Neoproterozoic to the Late Mesoproterozoic. These ages are very different from those of the North China Block, but the change of εNd(t) (from the initial εNd value) is similar to that of igneous rocks in the Xing-Meng Orogen. This result indicates that provenances of these Paleozoic sedimentary rocks mainly arise from the Xing-Meng Orogen itself. These clastic sedimentary rocks mainly consist of inputs of juvenile accreted crustal materials and limited recycled old crusts. Their provenance is controlled by the following three end members: a felsic basement, a partially melted mafic, and a mafic end member. From the point view of lithology, these three end members must have mixed in a ratio of 53:41:5 to form the average composition of the clastic sedimentary rocks. The depositional environment began to change from an arc to an orogen during the Permian, and therefore the collision was complete before the Triassic. This interpretation is consistent with the argument that the final collision time was at the end of the Permian or beginning of the Triassic.The Xing-Meng Orogenic Belt is the eastern extension of the Central Asian Orogenic Belt, which marks the boundary between the North China and Siberian blocks. Key information on the collision between these two blocks and the evolution of this orogen- ic belt at the end of the Paleozoic are preserved in the widely distributed Paleozoic sedimentary sequences. Petrographic studies of the clastic sedimentary rocks from the Ordovician to the Permian in this region have shown that the rocks are mainly greywackes and arkosic sandstones characterized by low maturity, poor sorting and a large number of lithic fragments. Provenances of Paleo- zoic sandstones are mainly newly accreted crustal materials. Nd model ages range from the Neoproterozoic to the Late Mesopro- terozoic. These ages are very different from those of the North China Block, but the change of eNd（t） （from the initial eNd value） is similar to that of igneous rocks in the Xing-Meng Orogen. This result indicates that provenances of these Paleozoic sedimentary rocks mainly arise from the Xing-Meng Orogen itself. These clastic sedimentary rocks mainly consist of inputs of juvenile ac- creted crustal materials and limited recycled old crusts. Their provenance is controlled by the following three end members： a felsic basement, a partially melted mafic, and a mafic end member. From the point view of lithology, these three end members must have mixed in a ratio of 53 ： 41 ： 5 to form the average composition of the clastic sedimentary rocks. The depositional envi- ronment began to change from an arc to an orogen during the Permian, and therefore the collision was complete before the Trias- sic. This interpretation is consistent with the argument that the final collision time was at the end of the Permian or beginning of the Triassic.

关 键 词：中亚造山带 古生代 构造演化 沉积记录 种源 内蒙古 碎屑沉积岩 ND模式年龄 

分 类 号：P618.2[天文地球—矿床学] P534.4[天文地球—地质学]