Chronology And Significance Of Bayan Obo Group In Siziwangqi,Inner Mongolia

North China Craton(NCC) comprises several microcontinents, and its basement finally formed at 1.85 Ga. After 1.8Ga, its covering layer started to deposit, accompanied by the development of the several important rifts within the North China craton, such as Xiong’er Aulacogen, Yanliao rift, Langshan- Bayan Obo rift in chronological order. Bayan Obo group deposited at the Bayan Obo rift, there are two controversial deposition Age:Based on isotopic age finds its formed in Proterozoic; Paleontological evidence also showed that formed in the early Paleozoic. In this paper, the research area lacks Paleontology, But grows integral sequence and structure of the Bayan Obo Group, Therefore, pick out two samples from the bottom of the Bayan Obo Dulahala group and Jianchan Group, one sample from the Central of the Bayan Obo Bilute group, then use LAICP-MS to determine the detrital zircons U-Pb ages, the results show: the ages of Dulahala group are between 1809 Ma ~ 2666 Ma, the youngest age is 1809 ± 36Ma; the ages of Jianshan Group are between 1810 Ma ~ 2762 Ma, the youngest age is 1810 ± 38Ma; the ages of Bilute group are between 1583 Ma ~ 2573 Ma, the youngest age is 1583 ± 61 Ma, all represent the deposit limit. Wang zifeng(2015, Master’s thesis) Measured the top of Bayan Obo group—— Baiyinbaolage group’s youngest detrital zircon ages is 1183 Ma, Therefore, the deposition age of the Bayan Obo group should be Mesoproterozoic. Through statisticing both top and bottom Dulaha group’s gravel, and comparising magmatic zircons ages with Bayan Obo rift, Yinshan Block and North China Craton basement, to discuss Dulahala group,Jian group and Bilute group’s material source: the source of Dulahala group is relatively close, from the early rapid accumulation under tensional rift background, the material came from internal and periphery of the rift provided a source of material;Jianshan group’s material source mainly came from the NCC, secondly,came from dulahala group; Bilute group’s material source came from NCC and Yinshan Block, and material source before 1800 Ma came from NCC, additional, There are gabbro of 1670 Ma and kimberlite of 1560 Ma invaded into Dulahala group, then guess the underlying strata of Bilute group undergone overall uplift, resulting in intrusive rocks exposed and erosion, provide provenance to Bilute group. Yanliao rift has the same tectonic setting with Bayan Obo rift but there ages are different, The stratigraphic section at Yanliao area has long been used as a standard stratigraphic section of the NCC at Mesoproterozoic, Thus the two rifts’ stratigraphic sequence and magmatic events can be compared, Combining with the latest edition of "China Stratigraphic Guide"(2014 edition), redefine their stratigraphic ages. By comparing magmatic events, also found the cracking of Columbia supercontinent and the occurrence of these magmatic events coincide in time, combining the overall uplift event of underlying strata of Bilute group, Prove NCC responded to the Columbia supercontinent’s cleavage.