Sedimentary Characteristics And Tectonic Paleogeographic Significance Of Penglai Group And Wufoshan Group In The Southern Margin Of North China Craton

The Meso-Neoproterozoic strata in the southern margin of the North China Craton are well developed,especially the early Neoproterozoic strata,which can reflect the evolution of North China Craton in the period of assemblage of Rodinia supercontinent.In this thesis,sedimentology and isotopic geochronology of the Wufoshan Group in Songshan area and Penglai Group in the North Shandong Province area on the southern margin of the NCC are studied.The stratigraphic correlation of the southern margin of the NCC is further revised and the tectonic setting of the southern margin of the NCC in early Neoproterozoic is restored1.Detrital zircon U-Pb dating of the Fuzikuang Formation of the Penglai Group shows two main peaks ages are 1600 Ma and 1200 Ma respectively,and the youngest zircon age is 1094±39Ma.The age of the Penglai Group is limited to 1.0-0.92 Ga by combining regional stratigraphic correlation and intrusive basic dike age.By comparing the detrital zircon age spectrum characteristics and the youngest zircon age of the Penglai Group in North Shandong Province and the Wufoshan Group in western Henan,it is considered that the Penglai Group has the same age as the Luotuopan and Heyao Formations in the Wufoshan Group,while the Maanshan and Puyu Formation in the lower part of Wufoshan Group are older.2.The Luotuopan Formation is mainly braided river sedimentary system,and the main body belongs to braided river and braided river-delta front subfacies.The rose diagram of 119 sets of cross-bedding in 4 measuring points shows that the main paleocurrent(sediment diffusion direction)of the Luotuopan Formation sandstone points to the north,indicating that there was a tectonic uplift area as provenance in the south of the study area.3.Many large sand dikes developed in the Wufoshan Group have been discovered and systematically studied.The sand of the Luotuopan Formation has been poured into the structural fracture of the Puyu Formation before diagenesis.Based on the geometric characteristics of sand veins,sandstone structure and the cataclastic characteristics of the Puyu Formation mudstone in structural fractures,it is determined that when the sand veins are developed,the Puyu Formation has been diagenetic and formed cataclastic rocks associated with structural fractures,while the Luotuopan Formation is in the state of non-diagenesis.Therefore,there is no integrated contact between the Puyu Formation and the overlying Luotuopan Formation.4.In the dolomite series of the third member of the Heyao Formation,there are soft sedimentary deformation structures induced by earthquakes,such as bulbous pillow structure,water plastic fold,fluid conglomerate,liquefaction vein and dish structure,which indicate that the Heyao Formation was deposited in an active geodynamic environment.5.Based on the above new achievements,combined with the regional tectonic research and previous detrital zircon age spectrum,basic dyke swarms and paleomagnetic data,it is speculated that the Luotuopan and Heyao Formation in the upper part of the Wufoshan Group developed in the sedimentary basin related to the Grenvillian orogeny,which is directly related to the arc continent collision between the NCC and the late Precambrian magmatic arc in Qinling.The collision between the North Qinling and the NCC formed a peripheral foreland basin in the southern margin of the NCC,which is a part of the Grenville orogen.