The Mesoproterozoic rifting in the North China Craton: A case study for magmatism and sedimentation of the Zhaertai-Bayan Obo-Huade rift zone

The Mesoproterozoic rift zones in the North China Craton include the Xiong'er,Yanliao and Zhaertai-Bayan Obo-Huade rift zones from south to north. The Xiong'er Group is featured by the major volcanism at 1780 ~ 1750 Ma,above which the Wufoshan,Ruyang and Guandaokou groups were formed in a passive continental margin. The Yanliao rift zone includes the Changcheng,Jixian and Qingbaikou systems. The Tuanshanzi and Dahongyu formations of the Changcheng system have volcanic rocks at ca. 1640 Ma and1626 ~ 1622 Ma,respectively. The tuffs in the Gaoyuzhuang,Wumishan and Tieling formations of the Jixian system were formed at1560 Ma,1485Ma and 1437 Ma respectively,whereas the Xiamaling tuffs in the unnamed system have ages of 1366 ~ 1380 Ma. In the Zhaertai-Bayan Obo-Huade rift zone,the Shujigou basalts and Agulugou felsic volcanics of the Zhaertai Group have ages of 1743 Ma and~ 810 Ma,respectively. The Jianshan Formation of the Bayan Obo Group has mafic volcanics of 1728 Ma and the Bilute tuffs of the Huade Group formed at 1515 Ma. Besides the volcanisms in the rift zones,the Mesoproterozoic magmatism include three episodes of mafic dyke swarms( ca. 1780 Ma Taihang-Luliang dyke swarm,ca. 1730 Ma Miyun dyke swarm and ca. 1620 Ma Taishan dyke swarm)and 1. 76 ~ 1. 65 Ga anorogenic magmatism( anorthosite-rapakivi granite-A-type granite). In the Middle Mesoproterozoic,mafic sills( dykes),A-type granites and carbonate dykes develop in the northern margin of the North China Craton. The bimodal magmatism suggests that the northern margin of North China Craton has experienced rifting in the Middle Mesoproterozoic,which are related with final breakup of the Columbia Supercontinent and formation of the giant Bayan Obo REE-Nb-Fe deposit. The two rift zones in the northern North China Craton have similar stratigraphic sequences and formation ages. The Middle Mesoproterozoic anorogenic magmatism can be compared with those in other cratons and suggests that the North China Craton is involved in the final breakup of the Columbia Supercontinent. Paleomagnetic data indicate that the Siberia,Laurentia,Baltica,Amazion and North China cratons are connected together in the Columbia Supercontinent,and the rift-related magmatic rocks in the northern margin suggest that it connected with another craton. However,whether the Xiong'er volcanics in the southern margin of the North China Craton formed in a continental rift or active continental margin is important about whether it was connected with another craton or faced an ocean,which need further studies.