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Magnetostratigraphic Study of Lower Cretaceous at mas-microsoft-com:office:smarttags" />Chengde Basin, Yanshan Area and Its Restriction on North China Craton Destruction
详细信息   
摘要
mary name="EnDivSummary">Lithosphere thinning,mantle property transforming and extensional tectonic activity are important performances of the North China Craton destruction.The timing of North China Craton destruction has been continuous paid attention to.There have already been plenty of research from Geology,Geophysics and Geochemistry.However,the exact destruction age of North China Craton is still controversial.In this paper,we try to put forward geomagnetic evidence of the peaking destruction age of North China Craton.Yanshan orogen is located at the northern edge of North China Craton and affected significantly by its destruction.Chengde Basin is located at the middle section of Yanshan orogen,which makes it an ideal area for studying the basin record of North China Craton destruction.Specific geomagnetic study is carried out at the area.The rock-magnetic results indicate that magnetic minerals of volcanics are complex,including magnetite,maghemite and hematite while sedimentary magnetic minerals are mainly magnetite,possibly including small amount of maghemite and hematite.The complexity of volcanic magnetic minerals may be closely related to the deep dynamic process of crustal deformation,magmatic activity,mantle upwelling and lower crustal remelting accompanying with the peak age of North China Craton.An age of 129~128 Ma is obtained from the radiometric dating result(private communication with B.Schoene).Magnetostratigraphic result shows three polarity sections: the lower normal section(N2),the middle reversal section(R1) and the upper normal section(N1).Comparing with the Geologic Time Scale 2004 and combining the radiometric dating result,it is believed that the N2 section is related to M3n,R1 related to M1r and N1 related to M1n.Therefore,it is concluded that Chengde Basin starts to sedimentate at about 128 Ma,which is a strong constraint on the peaking age of North China Craton destruction.Synthesizing the Geologic,Geophysical and Geochemical results,a peak destruction age of 128~125 Ma is obtained,which is supported by the appearance age of a great quantity of extensional tectonics(135~115 Ma) and peak transition(from N—S contraction to NWW—SEE extension led by subduction of Paleo-Pacific Plate and closure of Mongolia-Okhotsk Sea in late Mesozoic) age of dynamic mechanism at North China Craton(128~125 Ma).It is inferred based on existed research that North China Craton destruction is the primary element leading to formation of the great quantity of rift basins in late Mesozoic at Yanshan area.One of the shallow responses accompanying with the peak age of North China Craton destruction is regional extensional activity and formation of rift basin.It is characterized by the appearance of metamorphic core complexes at the northern rim of the North China Craton,which may be related to magmatic activity caused by detachment of lower crust.The deep dynamic is due to instability of mantle convection system at the eastern part of the North China Craton arose from physical and chemical processes such as subduction and dehydration of the Pacific Plate.

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